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  • American Institute of Physics (AIP)  (9,740)
  • American Geophysical Union  (4,241)
  • 2010-2014
  • 1995-1999  (13,981)
  • 1997  (13,981)
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Publisher
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  • 2010-2014
  • 1995-1999  (13,981)
Year
  • 101
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    Electronic Resource
    Saturation of stimulated Brillouin scatter by self-consistent flow profile modification in laser hot spots (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 437-446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scattering instabilities, such as stimulated Brillouin scatter (SBS) and stimulated Raman scatter (SRS), transfer momentum to the plasma which leads to flow inhomogeneities in laser hot spots that may significantly reduce the level of SBS. Simple estimates and simulations shown that the magnitude of flow fluctuations can reach Mach numbers of order unity in a time scale of hundreds of picoseconds. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872102
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  • 102
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    Stability thresholds for ballooning modes driven by high β internal kinks (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4192-4194 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear destabilization of pressure driven (ballooning) modes by internal kink modes during sawtooth cycles was found in the Tokamak Fusion Test Reactor (TFTR) [Park et al., Phys. Rev. Lett. 75, 1763 (1995)]. It is shown by a numerical parameter study, including aspect ratio and magnetic shear profile effects, that in ideal magneto-hydrodynamics (MHD), this nonlinear destabilization occurs in plasma equilibria close to marginal stability to linear sub-harmonics of the internal kink with toroidal mode number n≥3. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872610
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  • 103
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    Transverse electron susceptibility and the electromagnetic wave absorption in weakly collisional plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4205-4209 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of plasma response to electromagnetic perturbations has been developed based on the full solution to the Fokker–Planck equation in high Z plasmas without electron–electron collisions. For the first time the transverse electron susceptibility has been calculated for the entire range of frequencies and wave numbers including the quantitative description of the weakly collisional regime where the wave frequency is comparable to the electron–ion collision frequency and the wave number is comparable to the inverse electron mean free path. The results have been compared to approximate expressions for the electron conductivity based on the Drude model showing discrepancy by a factor of few in regions where the spatial dispersion is important. The theory is applied to the calculation of laser light absorption in solid density plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872581
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  • 104
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    Ion transport in a partially ionized impure edge plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4218-4226 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetic theory of transport in an impure, partially ionized, edge plasma is developed. It is found that the thermal force between bulk ions and impurities is enhanced by the presence of neutral atoms, but the dynamical friction is not affected by the neutrals. When the neutral viscosity is large, an additional force on the impurities also arises. This force is parallel to the magnetic field, and is proportional to the shear of the parallel plasma velocity and the perpendicular ion density and temperature gradients. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872583
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  • 105
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    Nonlinear dynamics of a charged dust grain in a plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4210-4217 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For an arbitrary monotonic charging function, the dynamics of a dust grain is dissipative and energy is a Liapunov function. In an arbitrary external potential two types of equilibria exist. The first type, with uncharged grain, is always unstable. The second type of equilibrium, admitting states of both positive and negative charge, can be marginally stable; stability depends on the local potential. Under spatially uniform (constant or time-dependent) potentials, motion is free while the charge adapts to the potential. For a spatially oscillating potential, the phase space is that of the simple pendulum with one additional degree of freedom, the charge. Dissipation in the charging process forbids periodic behavior and ensures the existence of attractors: A grain is at stable equilibrium only when charged positively and trapped in a potential well, or when charged negatively on top of a hill. The small oscillations near a stable equilibrium decay weakly, and the grain charge oscillates at twice the oscillation frequency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872582
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  • 106
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    Effects of ion and electron drifts on large amplitude solitary waves in a relativistic plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4232-4235 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of ion and electron drifts on the existence of arbitrary amplitude solitary waves is studied using Sagdeev's pseudopotential method. It is found that if the electron drift velocity u0 is finite, solitary waves may exist for relatively large values of v0/c, where v0 is the ion drift velocity and c is the velocity of light. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872585
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  • 107
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    Numerical simulation of a negative ion plasma expansion into vacuum (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4240-4253 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The expansion into vacuum of a one-dimensional, collisionless, negative ion plasma is investigated in the framework of the Vlasov–Poisson model. The basic equations are written in a "new time space" by use of a rescaling transformation and, subsequently, solved numerically through a fully Eulerian code. As in the case of a two species plasma, the time-asymptotic regime is found to be self-similar with the temperature decreasing as t−2. The numerical results exhibit clearly the physically expected effects produced by the variation of parameters such as initial temperatures, mass ratios and charge of the negative ions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872587
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  • 108
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    Near-forward stimulated Brillouin scattering (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4227-4231 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatiotemporal evolution of near-forward stimulated Brillouin scattering (SBS) is studied in detail. For large scattering angles SBS grows and saturates as a three-wave instability. For small scattering angles SBS begins to grow as a three-wave instability, then continues to grow and saturates as a four-wave instability. Expressions for the saturation time and steady-state gain exponent of SBS are derived for large and small scattering angles. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872584
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  • 109
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    A new mathematical approach for shock-wave solution in a dusty plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4236-4239 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of nonlinear Burger equation in a plasma contaminated with heavy dust grains has been revisited. As discussed earlier [C. B. Dwivedi and B. P. Pandey, Phys. Plasmas 2, 9 (1995)], the Burger equation originates due to dust charge fluctuation dynamics. A new alternate mathematical approach based on a simple traveling wave formalism has been applied to find out the solution of the derived Burger equation, and the method recovers the known shock-wave solution. This technique, although having its own limitation, predicts successfully the salient features of the weak shock-wave structure in a dusty plasma with dust charge fluctuation dynamics. It is emphasized that this approach of the traveling wave formalism is being applied for the first time to solve the nonlinear wave equation in plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872586
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  • 110
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    Plasma screening effects on eikonal phase for electron-ion elastic collisions in weakly coupled plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4254-4257 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Eikonal approximation is applied to investigate elastic electron-ion collisions in weakly coupled plasmas. Plasma screening effects on eikonal phase are investigated for eikonal differential elastic scattering cross sections. The electron-ion interaction potential in weakly coupled plasmas has been obtained by the introduction of the longitudinal plasma dielectric function. The semiclassical straight-line trajectory method is applied to the path of the projectile electron in order to investigate the variation of the eikonal phase as a function of the impact parameter and the plasma parameters. In the first-order eikonal approximation, the dynamic plasma screening effect is identical to the static screening effect obtained by the Debye–Hückel potential. The eikonal differential elastic cross section substantially decreases with an increase in the projectile energy and increases as the plasma screening effect decreases through the Debye length. The plasma screening effects are more significant for large impact parameters. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872588
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  • 111
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    Effect of the flow continuum on magnetohydrodynamic stability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3744-3748 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The flow resonance is concealed when the linearized equation of motion in magnetohydrodynamics is written in terms of the Lagrangian displacement vector. Its contribution to the dispersion equation of a rotating cylindrical plasma column, surrounded by a thin resistive wall, is clarified by a simple model calculation, relevant for axisymmetric modes, in the Eulerian representation. Under certain assumptions the flow resonance is shown to damp the resistive wall mode, with the damping proportional to the square of the gradient of vorticity at the resonant surface. It is shown that a flow resonance can stabilize a slightly elliptical plasma, surrounded by a thin resistive wall, against axisymmetric modes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872498
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  • 112
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    The shear Alfvén continuum in an asymmetric magnetohydrodynamic equilibrium (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3770-3782 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Alfvén continuum of an asymmetric plasma configuration that is an exact solution of the equilibrium equations of ideal magnetohydrodynamics is treated. The equilibrium is parallel to an infinite straight magnetic axis about which the magnetic lines of force form closed magnetic surfaces. Properties of the governing continuum equation for small plasma beta are explored, and the associated spectrum is determined. The continuum has a localized component characterized by modes that decay to zero along magnetic field lines, and a non-localized component characterized by modes that approach non-zero constants at the plasma ends. The localized component is restricted to real frequencies, while the non-localized component covers the entire complex frequency plane. The non-localized modes can be joined generally with those on neighboring field lines to form modes that smoothly cover the entire magnetic surface. The localized modes do not occur in symmetric plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872502
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  • 113
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    A variational approach to parametric instabilities in inhomogeneous plasmas I: Two model problems (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3788-3802 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A variational formalism is introduced in the theory of three-wave parametric instabilities in inhomogeneous plasmas. This minimum pump strength principle (MPSP) is then applied to two model problems, the first being the Rosenbluth model equations [Phys. Rev. Lett. 29, 565 (1972)]. By choosing appropriate trial functions, the MPSP is used to solve for the complex eigenfrequency of the most unstable mode. The wave vector mismatch is assumed to be of the form κ(x)=κ(n)(0)xn/n!, where n is any positive integer. The results are compared to numerical solutions of the same eigenvalue problem. The second problem is the Liu, Rosenbluth, and White Raman sidescattering model [Phys. Fluids 17, 1211 (1974)], which is treated for any positive-integer power law density profile. The choice of trial functions, the role of symmetry, and various useful approximations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872504
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  • 114
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    A variational approach to parametric instabilities in inhomogeneous plasmas III: Two-plasmon decay (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3827-3844 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theory of the two-plasmon decay instability is recast in the form of a variational principle for the pump strength or intensity of the incident laser. This allows the calculation of growth rates, frequency shifts, and threshold conditions for two-plasmon decay modes that occur in integer power law density profiles, including the effects of oblique incidence of the laser and both S and P polarizations. The transition between parabolic profiles occurring at the peak of an exploding foil target and linear profiles on its flanks is treated as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872506
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  • 115
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    A variational approach to parametric instabilities in inhomogeneous plasmas II: Stimulated Raman scattering (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3803-3826 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theory of temporally unstable modes or bound states associated with stimulated Raman scattering in inhomogeneous plasmas is recast in the form of a variational principle for the pump strength or intensity of the incident laser. This Minimum Pump Strength–Variational Principle (MPS–VP) formalism allows the unification of disparate results on growth rates, frequency shifts, and threshold conditions, which in the past relied on specific and restrictive assumptions on the density profile, scattering geometry, temperature, and damping rates. The variational approach leads to generalizations of these results in a uniform manner. Various levels of sophistication in the choice of trial and dual functions are explored. Simplifications and short cuts that will be used throughout this series of papers are tested here, and their regions of validity explored. The principle new result of some practical interest is the growth rate of Raman sidescattering occurring anywhere at the peak or on the flanks of a parabolic density profile such as can be found in an exploding foil experiment. This new calculation includes any density at or below quarter-critical, at any temperature, and at low or high damping rate limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872505
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  • 116
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    A variational approach to parametric instabilities in inhomogeneous plasmas IV: The mixed polarization high-frequency instability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3845-3862 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theories of the two plasmon decay (TPD) instability and stimulated Raman scattering (SRS) are unified and presented using a variational formulation. The mixed polarization high-frequency instability is the resulting generalization which has SRS and TPD as special cases. The most unstable mode's properties are derived and shown as a function of perpendicular wave number. For vanishing wave number we recover the Raman backscattering result and for wave numbers a few times larger than the square root of the homogeneous plasma growth rate normalized to the pump frequency, the two plasmon decay instability modes are recovered. This transition is accompanied by a change of polarization from a purely electromagnetic transversely polarized wave in the case of Raman to a strictly electrostatic or longitudinally polarized wave in the case of TPD, and admixtures in between. Experimental signatures of these modes are given and a method is proposed by which the density scale length and electron temperature would be simultaneously inferred from the width and height of the spectral signature corresponding to these hybrid modes in an ideal experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872507
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  • 117
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    Plasma emission by a nonlinear beam instability in a weakly magnetized plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3863-3881 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent series of publications, a new theory of electromagnetic radiation with emission frequency close to the plasma frequency and/or its harmonic (i.e., the plasma emission) was presented. In this theory, the emission of radiation takes place as a result of excitation of long wavelength modes by a nonlinear beam-plasma instability, which are converted to radiative electromagnetic waves by a nonlinear mode conversion process. Unlike standard theories, the new theory predicts high radiation growth rate. In all the previous efforts on this theory, however, effects due to the presence of constant background magnetic field were ignored. The purpose of this article is to generalize the new theory to the case of weakly magnetized plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872508
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  • 118
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    Long-range correlations in dusty plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3882-3894 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The correlations in dusty plasmas in the gaseous state is considered. It is shown that the long-ranged correlations of dust particles, contrary to usual matter, start to form in a weakly correlated state, leading finally to the formation of dust crystals and dust liquids with not strong but intermediate strength correlations. The physical mechanism leading to long-ranged correlations is the dust attraction due to shadow effects of the plasma particle fluxes. An analytic theory for the long-ranged dust density correlation function is developed and the numerical results for a broad range of dust densities and plasma temperatures are presented. The long-ranged correlations induced by dust for electron densities, ion densities, and dust charges are also investigated, and the results for electron density correlations are presented in a way that permits measurement of the long-ranged correlation function in laser and radio-wave scattering experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872509
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  • 119
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    The realizable Markovian closure and realizable test-field model. II. Application to anisotropic drift-wave dynamics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3895-3909 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The test-field model is shown to be potentially nonrealizable in the presence of linear waves such as those frequently encountered in models of plasma and geophysical turbulence. A new statistical closure, the realizable test-field model (RTFM), is proposed as a remedy. Both the damping rate and frequency are renormalized to account for nonlinear damping and frequency shifts. Like the realizable Markovian closure (RMC), the RTFM is based on a modified fluctuation-dissipation ansatz. Numerical solutions of the RTFM, RMC, and direct-interaction approximation for the Hasegawa–Mima equation are presented; rough agreement with direct numerical solution is found. The number of retained Fourier modes is dramatically reduced with an anisotropic generalization of a recently developed wave-number partitioning scheme. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872510
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  • 120
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    Bäcklund transformations and Painlevé analysis: Exact soliton solutions for strongly rarefied relativistic cold plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3910-3922 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relativistic nonlinear self-consistent equations for a strongly rarefied plasma with stationary ions is considered. The resulting system of equations is reduced to a single sinh-Gordon equation. Using the Bäcklund transformations technique and Painlevé analysis, a set of exact soliton solutions is obtained for stationary and nonstationary equations that describes the charge density equilibrium configuration. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872511
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  • 121
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    Corrugation instability of radiative shock waves in a relativistically hot plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3923-3927 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The corrugation instability of magnetic shock waves in a relativistically hot plasma with photon gas has been investigated. Conditions under which spontaneous amplification of surface corrugations on the discontinuity occurs are obtained. The corrugation instability may cause the condensation of the plasma number density, as well as the magnetic field behind the shock wave. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872512
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  • 122
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    Effects of orbit squeezing on transport fluxes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3928-3932 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When the ratio μ1i/μ1e is of the order of unity, electron transport fluxes such as bootstrap current can be affected by the ion orbit squeezing. Here, μ1e is the electron viscous coefficient, and μ1i is the ion viscous coefficient with the effects of ion orbit squeezing included. The condition μ1i/μ1e∼1 can be satisfied for plasmas, such as those in enhanced reversed shear (ERS) mode, with ion temperature greater than electron temperature and orbit squeezing factor S(very-much-greater-than)1. Transport fluxes for both standard squeezed banana orbits and for squeezed orbits close to the magnetic axis are calculated for a large aspect ratio tokamak. It is found that ion heat flux and bootstrap current are reduced in ERS-like plasmas. Furthermore, the bootstrap current density does not vanish on the magnetic axis for a parabolic pressure profile in minor radius r due to the finite value of the fraction of trapped particles. This makes it possible to operate tokamaks in steady state. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872513
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    Simulation of the nonlinear dynamics of grid sheath oscillations in double plasma devices (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3933-3942 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The oscillation of ion bunches around a strongly negative grid in a double plasma device is studied with one–dimensional particle–in–cell simulation. The system exhibits feedback amplified virtual anode oscillations in the target chamber. The undriven system is shown to perform relaxation processes which can be described by the van der Pol equation for high nonlinearity. The periodically driven system exhibits nonlinear phenomena like mode locking and periodic pulling, which are in quantitative agreement with theoretical predictions for the driven van der Pol oscillator. For large driver amplitudes period doubling and weak chaos are found. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872514
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  • 124
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    Stationary symmetric magnetohydrodynamic flows (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3544-3564 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of translation symmetric stationary magnetohydrodynamic (MHD) flow is analyzed with respect to the different permitted flow regimes. A minimal set of equilibrium functions is constructed facilitating the complete explicit solution in the case of self-similar flow. It is found that limiting line and Alfvén singularities leads to a division in four distinct velocity regimes which cannot be connected by continuous flows. Instead, the three types of MHD shocks appear, enabling the system to pass from the high to the low speed regimes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872251
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  • 125
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    Nonlinear magnetohydrodynamic detonation: Part I (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3565-3580 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sudden release of magnetic free energy, as occurs in spectacular solar flare events, tokamak disruptions, and enigmatic magnetospheric substorms, has long defied any acceptable theoretical explanation. Usual attempts at explaining these explosive events invoke magnetic reconnection and/or ideal magnetohydrodynamic (MHD) instability. However, neither of these two mechanisms can explain the fast time scales without nonlinear destabilization. Recently, Cowley et al. [Phys. Plasmas 3, 1848 (1996)] have demonstrated a new mechanism for nonlinear explosive MHD destabilization of a line tied Rayleigh–Taylor model. In this paper, this picture is generalized to arbitrary magnetic field geometries. As an intermediate step, the ballooning equation in a general equilibrium is derived including the effects of magnetic field curvature, shear, and gravity. This equation determines the linear stability of the plasma configuration and the behavior of the plasma displacement along the magnetic field line. The nonlinear equation which determines the time and spatial dependence, transverse to the equilibrium magnetic field, of the plasma displacement is obtained in fifth order of the expansion. The equations show that explosive behavior is a natural and generic property of ballooning instabilities close to the linear stability boundary. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872252
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    Collisional δf method (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3591-3598 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general method for including various collisional effects, such as the drag and diffusion of test particles due to background plasmas, the effect of particle source and sink, and the like-particle Coloumb collisions, is presented. The marker density g is generally unknown along the particle trajectory, and its evaluation depends on the way particles are initially loaded and new particles are injected into the simulation. The method is demonstrated for the problem of the nonlinear evolution of the toroidicity induced Alfvén eigenmode, driven by energetic α particles. The saturation amplitude is found to scale with the collision rate in a way as predicted by theory.© 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872254
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    Determination of microturbulence enhanced electron collisionality in magnetized coaxial accelerator channels by direct magnetic field measurement (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3581-3590 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A miniature magnetic probe array, consisting of 10 spatially separated coils, has been used to obtain profile information on the time varying magnetic field within the 2.54 cm wide flow channel of the coaxial plasma source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)]. The magnetic field data have been used, together with a resistive, Hall magnetohydrodynamic (MHD) model of applied field distortion by the flowing plasma, to obtain estimates of the microturbulent enhancement to electron collisionality within the CPS-1 flow channel. These measurements provide direct experimental evidence of anomalous electron collisionality, a previously predicted effect in these devices. The anomaly parameter, a=νan/νcl, determined both from the distortion of contours of constant magnetic flux, and from local Bθ and Bz measurements scales with the classical electron magnetization parameter (Ωcl=ωce/νecl), indicating that collisionality plays a strong role in determining the level of anomalous transport in the plasma. When this anomaly parameter scaling is cast in terms of the ratio νecl/ωlh, it is found that the resistivity enhancement scales with νecl/ωlh, and becomes significant at νecl/ωlh≤1, suggesting that a lower hybrid drift instability may be the responsible mechanism for enhanced transport. © 1997 American Institute of Physics.
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    The evidence for nonlocal transport in the Texas Experimental Tokamak (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3599-3613 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron temperature response of a tokamak to rapid edge cooling has characteristics difficult to reconcile with local transport analysis. The initial observations in the Texas Experimental Tokamak [K. W. Gentle, Nucl. Tech. Fusion 1, 479 (1981)] have been extended to a wider range of plasma and perturbation parameters, including auxiliary heating, and the associated turbulence changes have been measured across the plasma radius. The fast edge temperature drops and core temperature increases are quantified by more extensive analysis. A perturbation complementary to edge cooling, edge heating by a fast current ramp, evokes a completely complementary plasma response. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872255
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    Local test of parallel electrical resistivity in the Tokamak Fusion Test Reactor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3614-3619 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local, time-resolved measurements have been made of the response of the internal magnetic-field distribution to large changes in the total plasma current. Measurements were made by the motional Stark effect (MSE) polarimeter on the Tokamak Fusion Test Reactor (TFTR). [R. J. Hawryluk et al., Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987) Vol. I, p. 51.] A direct test of the classical and neoclassical resistivity models was made by comparing the predicted field evolution using either model to that measured. It was found that the neoclassical resistivity model was a better predictor of the local magnetic-field temporal evolution than was the classical model. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872256
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    Ion temperature and plasma flows in improved confinement mode in the H-1 heliac (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3629-3634 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low and improved confinement modes in the H-1 heliac [M. G. Shats et al., Phys. Rev. Lett. 77, 4190 (1996)] are studied experimentally in rf-sustained (〈100 kW, 7 MHz) argon discharges at low magnetic fields (〈0.15 T). Surprisingly high ion temperature, measured using a retarding field energy analyzer, is found which increases across the transition to improved confinement mode from 40 to 80 eV, while the electron density increases by about 50%. Both toroidal and poloidal plasma flow velocities do not change across the transition. The increase in a radial electric field in high mode is balanced on average by a corresponding increase in the ion pressure gradient. © 1997 American Institute of Physics.
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    Magnetic fluctuation driven cross-field particle transport in the reversed-field pinch (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3620-3628 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrostatic and electromagnetic fluctuations generally cause cross-field particle transport in confined plasmas. Thus core localized turbulence must be kept at low levels for sufficient energy confinement in magnetic fusion plasmas. Reversed-field pinch (RFP) equilibria can, theoretically, be completely stable to ideal and resistive (tearing) magnetohydrodynamic (MHD) modes at zero beta. Unstable resistive interchange modes are, however, always present at experimentally relevant values of the poloidal beta βθ. An analytical quasilinear, ambipolar diffusion model is here used to model associated particle transport. The results indicate that core density fluctuations should not exceed a level of about 1% for plasmas of fusion interest. Parameters of experimentally relevant stationary states of the RFP were adjusted to minimize growth rates, using a fully resistive linearized MHD stability code. Density gradient effects are included through employing a parabolic density profile. The scaling of particle diffusion [D(r)∝λ2n0.5T/aB, where λ is the mode width] is such that the effects of particle transport are milder in present day RFP experiments than in future reactor-relevant plasmas. © 1997 American Institute of Physics.
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    Normal curvature, local magnetic shear and parallel current density in tokamaks and torsatrons (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 153-161 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reversed magnetic shear is associated with large negative surface averaged parallel current densities that increase in magnitude towards the plasma edge and guarantee stability at large β in tokamaks. The surface averaged parallel current density is smaller and decreases in magnitude radially in conventional shear tokamaks. This results in much lower magnetohydrodynamic (MHD) stable β. The parallel current density in torsatrons is dominated by the Pfirsch–Schlüter currents, the global shear contributes negligibly to the local shear and the β limits are comparable to that of a conventional tokamak. A simplistic evaluation of the local sign of the driving terms in the energy principle does not provide a useful guide to even qualitatively describe the MHD stability of a device. Ballooning instabilities concentrate in regions where the curvature is most destabilizing. Their localization does not appear to depend on the sign of the interaction between the parallel current density and the local magnetic shear contribution to the driving term. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872126
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    Gyrokinetic simulation of isotope effects in tokamak plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 169-173 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional (3-D) global gyrokinetic particle code in toroidal geometry has been used for investigating the transport properties of ion temperature gradient (ITG) drift instabilities in tokamak plasmas. Using the isotopes of hydrogen (H+), deuterium (D+) and tritium (T+), it is found that, under otherwise identical conditions, there exists a trend for favorable isotope scaling for the ion thermal diffusivity, i.e., χi decreases with mass. Such a trend, which exists both at the saturation of the instability and also at the fully nonlinear stage, can be understood from the resulting wave number and frequency spectra. © 1997 American Institute of Physics.
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    Effects of applied rotating magnetic perturbations on ion drift orbits in the Compact Auburn Torsatron (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 162-168 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion drift surfaces in the presence of applied rotating magnetic perturbations in the Compact Auburn Torsatron (CAT) [Fusion Technol. 18, 281 (1990)] have been studied. A compact, monoenergetic ion gun was used to launch a continuous beam of 6Li+ ions in the vacuum magnetic fields of the CAT. The ions are detected on a paddle probe that is swept though a poloidal cross section of the torsatron. The applied magnetic perturbation was produced using helical magnetic perturbation coils capable of generating rotating magnetic islands. Using a fixed energy ion beam the effects of constant frequency perturbations on ion drift orbits were studied as a function of the direction of rotation, amplitude, and frequency of the perturbation. A drift Hamiltonian model was developed to simulate ion trajectories in the presence of constant frequency rotating islands. The results of this experiment agree well with the predictions of the Hamiltonian model. Preliminary results of ion orbit modification by swept-frequency, rotating magnetic perturbations are also presented. © 1997 American Institute of Physics.
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    An interface current balance formulation of neutral atom transport theory in plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 179-189 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An interface current balance (ICB) method for neutral particle transport is presented and specialized to the calculation of neutral atom transport in background plasmas. A multigroup extension of the ICB methodology is presented which enables the direct calculation of neutral atom energy distributions and energy and momentum transport, as well as particle transport. Extension of the ICB methodology to multidimensions recovers the transmission/escape probability method. © 1997 American Institute of Physics.
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    High efficiency cavity design of a 170 GHz gyrotron for fusion applications (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 209-216 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The design of high power, continuous wave (cw), 170 GHz gyrotron cavities is considered. The anticipated degradation of efficiency with beam velocity spread places a premium on the optimization of efficiency. For parameters of interest achievement of high efficiency requires utilization of a high quality cavity. Two options are considered: a barrel cavity and a long simple tapered cavity operating at low voltage. The cavities are examined for their sensitivity to velocity spread, their mode competition, and their maximum Ohmic power dissipation. © 1997 American Institute of Physics.
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    Separatrix reconnection and periodic orbit annihilation in the Harper map (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 245-253 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Structure of the periodic accelerator orbits of the Harper map is investigated in detail from the viewpoint of underlying scenario of chaos in the area preserving nontwist map. Since the twist function of the Harper map is free from the polynomial local approximation, it admits rigorous treatment for the entire range of phase variable. The results obtained in the present analysis describes generic novel phenomena, which are outside of the applicability of the Kolmogorov-Arnol'd-Moser theory. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.166225
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    Parameter renormalization of maps based on potential function (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 278-289 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic way for deriving the parameter renormalization group equation for one-dimensional maps is presented and the critical behavior of periodic doubling is investigated. Introducing a formal potential function in one-parameter cases, it is shown that accumulation points correspond to local potential maxima and universal constants are easily determined. The estimates of accumulation points and universal constants match the known values asymptotically when the order of potential grows large. The potential function shows scaling in the parameter space with the universal convergent rate at the accumulation point similar to the Feigenbaum universal function. For two-parameter cases, a parameter reduction transformation is found to be useful to determine some important fixed points. A locally defined potential function is introduced and its scaling property is discussed. © 1997 American Institute of Physics.
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    Maintenance of chaos in a computational model of a thermal pulse combustor (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 605-613 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of a thermal pulse combustor model are examined. It is found that, as a parameter related to the fuel flow rate is varied, the combustor will undergo a transition from periodic pulsing to chaotic pulsing to a chaotic transient leading to flameout. Results from the numerical model are compared to those obtained from a laboratory-scale thermal pulse combustor. Finally the technique of maintenance (or anticontrol) of chaos is successfully applied to the model, with the result that the operation of the combustor can be continued well into the flameout regime. © 1997 American Institute of Physics.
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    On a simple recursive control algorithm automated and applied to an electrochemical experiment (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 653-663 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We review a simple recursive proportional feedback (RPF) control strategy for stabilizing unstable periodic orbits found in chaotic attractors. The method is generally applicable to high-dimensional systems and stabilizes periodic orbits even if they are completely unstable, i.e., have no stable manifolds. The goal of the control scheme is the fixed point itself rather than a stable manifold and the controlled system reaches the fixed point in d+1 steps, where d is the dimension of the state space of the Poincaré map. We provide a geometrical interpretation of the control method based on an extended phase space. Controllability conditions or special symmetries that limit the possibility of using a single control parameter to control multiply unstable periodic orbits are discussed. An automated adaptive learning algorithm is described for the application of the control method to an experimental system with no previous knowledge about its dynamics. The automated control system is used to stabilize a period-one orbit in an experimental system involving electrodissolution of copper. © 1997 American Institute of Physics.
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    Generalized entropies of chaotic maps and flows: A unified approach (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 694-700 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A thermodynamic study of nonlinear dynamical systems, based on the orbits' return times to the elements of a generating partition, is proposed. Its grand canonical nature makes it suitable for application to both maps and flows, including autonomous ones. When specialized to the evaluation of the generalized entropies Kq, this technique reproduces a well-known formula for the metric entropy K1 and clarifies the relationship between a flow and the associated Poincaré maps, beyond the straightforward case of periodically forced nonautonomous systems. Numerical estimates of the topological and metric entropy are presented for the Lorenz and Rössler systems. The analysis has been carried out exclusively by embedding scalar time series, ignoring any further knowledge about the systems, in order to illustrate its usefulness for experimental signals as well. Approximations to the generating partitions have been constructed by locating the unstable periodic orbits of the systems up to order 9. The results agree with independent estimates obtained from suitable averages of the local expansion rates along the unstable manifolds. © 1997 American Institute of Physics.
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    Ring wave solutions of a n+1-dimensional Sine–Gordon model (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 765-768 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamical properties of the ring wave solutions of the model ψtt−∇n2ψ+sin ψ+ε sin (ψ/2)+αψt=0 (0≤ε(very-much-less-than)1,0≤α(very-much-less-than)1) are studied analytically and numerically for spatial dimension (n=2,3). The model is obtained as a continuum approximation of a multidimensional Frenkel–Kontorowa lattice. We will show that in the case ε〉0, α=0 (or α〉0) the return effect of the ring wave does not occur only for well defined values of ε. It will be shown numerically that the dissipative perturbation αψt (α〉0) stabilizes both the velocity and the wave profile of the ring wave when the return effect does not occur. © 1997 American Institute of Physics.
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    An experimental spatio-temporal state transition of coupled magneto-elastic system (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 810-816 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the vibration and the traveling wave in a coupled magneto-elastic beam system are discussed experimentally. The vibration excited by the periodical forcing at the beam system propagates to another as a wave through the coupling elastic beams. Each magneto-elastic beam shows the variety of vibrations caused by the nonlinearity of the potential well and the wave propagation with time delay. The temporal vibration of the magneto-elastic beam is explained with relations to the spatial state transition based on the experimental results. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.166281
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    The convergence of chaotic integrals (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 361-367 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We review the convergence of chaotic integrals computed by Monte Carlo simulation, the trace method, dynamical zeta function, and Fredholm determinant on a simple one-dimensional example: the parabola repeller. There is a dramatic difference in convergence between these approaches. The convergence of the Monte Carlo method follows an inverse power law, whereas the trace method and dynamical zeta function converge exponentially, and the Fredholm determinant converges faster than any exponential. © 1997 American Institute of Physics.
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    Master-slave synchronization and the Lorenz equations (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 392-394 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since the seminal remark by Pecora and Carroll [Phys. Rev. Lett. 64, 821 (1990)] that one can synchronize chaotic systems, the main example in the related literature has been the Lorenz equations. Yet this literature contains a mixture of true and false, and of justified and unsubstantiated claims about the synchronization properties of the Lorenz equations. In this note we clarify some of the confusion. © 1997 American Institute of Physics.
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    Scalar observations from a class of high-dimensional chaotic systems: Limitations of the time delay embedding (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 423-429 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time delay embedding for the reconstruction of a state space from scalar data introduces strong folding of the smooth manifold in which a chaotic attractor is embedded, which is absent in some more natural state space. In order to observe the deterministic nature of data, the typical length scale related to this folding has to be resolved. Above this length scale the data appear to be random. For a particular model class we prove these statements and we derive analytically the dependence of this length scale on the complexity of the system. We show that the number of scalar observations required to observe determinism increases exponentially in the product of the system's entropy and dimension. © 1997 American Institute of Physics.
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    Cellular pattern formation in circular domains (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 463-475 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of stationary and nonstationary cellular patterns observed in premixed flames on a circular, porous plug burner is presented. A phenomenological model is introduced, that exhibits patterns similar to the experimental states. The primary modes of the model are combinations of Fourier–Bessel functions, whose radial parts have neighboring zeros. This observation explains several features of patterns, such as the existence of concentric rings of cells and the weak coupling between rings. Properties of rotating rings of cells, including the existence of modulated rotations and heteroclinic cycles can be deduced using mode coupling. For nonstationary patterns, the modal decomposition of experimental data can be carried out using the Karhunen–Loéve (KL) analysis. Experimental states are used to demonstrate the possibility of using KL analysis to differentiate between uniform and nonuniform rotations. The methodology can be extended to study more complicated nonstationary patterns. In particular, it is shown how the complexity of "hopping states" can be unraveled through the analysis. © 1997 American Institute of Physics.
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    Branching equation of Andronov-Hopf bifurcation under group symmetry conditions (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 229-238 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In branching theory of solutions of nonlinear equations group analysis methods [Ovsyannikov, Group Analysis of Differential Equations (Nauka, Moscow, 1978); Lectures on the Theory of Group Properties of Differential Equations (Novosibirsk University, Novosibirsk, 1966)] give the general approach for the construction of the complete form of branching equation and its subsequent investigation. These methods are applied here to the general situation of Andronov-Hopf bifurcation when there are some multiple semisimple eigenvalues on imaginary axis. © 1997 American Institute of Physics.
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    Average exit time for volume-preserving maps (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 139-147 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a volume-preserving map, we show that the exit time averaged over the entry set of a region is given by the ratio of the measure of the accessible subset of the region to that of the entry set. This result is primarily of interest to show two things: First, it gives a simple bound on the algebraic decay exponent of the survival probability. Second, it gives a tool for computing the measure of the accessible set. We use this to compute the measure of the bounded orbits for the Hénon quadratic map. © 1997 American Institute of Physics.
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    Self-similarity and renormalization in chaotic dynamics (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 1-1 
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    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166235
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    On a general concept of multifractality: Multifractal spectra for dimensions, entropies, and Lyapunov exponents. Multifractal rigidity (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 27-38 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We introduce the mathematical concept of multifractality and describe various multifractal spectra for dynamical systems, including spectra for dimensions and spectra for entropies. We support the study by providing some physical motivation and describing several nontrivial examples. Among them are subshifts of finite type and one-dimensional Markov maps. An essential part of the article is devoted to the concept of multifractal rigidity. In particular, we use the multifractal spectra to obtain a "physical'' classification of dynamical systems. For a class of Markov maps, we show that, if the multifractal spectra for dimensions of two maps coincide, then the maps are differentiably equivalent. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166232
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    Theory of pulse–particle interaction in one dimension (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3101-3112 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interaction of charged particles with various types of one-dimensional pulses is investigated systematically. Gaussian pulses of arbitrary velocity and polarization, both electrostatic and electromagnetic, are considered. The pulses range from ordinary wave packets to impulses. Analytic expressions are obtained for velocities of charged particles interacting with those traveling pulses, and are compared with numerical counterparts. Dependence of the interaction on pulse size, initial particle velocity, and external magnetic field is investigated. For many nonrelativistic pulses traveling along an external magnetic field, the interaction can be divided into two types, i.e., transit-time acceleration and reflection in the wave frame. In the absence of the magnetic field, transit-time acceleration is significant only for impulses with sizes of less than one wavelength. On the other hand, with a magnetic field (transit-time) cyclotron acceleration becomes possible for pulses of sizes greater than one wavelength. With larger amplitudes the wave-frame reflection becomes increasingly important, typically occurring at the pulse head or tail. However, it tends to be suppressed by external magnetic fields. Compact expressions are obtained for final velocities of the particles for the two types of interaction. Both types of acceleration mechanism may be important in dissipating relatively large-amplitude waves. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872449
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    Asynchronous cycling as a convergence acceleration method in particle simulation of direct current glow discharges (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3152-3162 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of multiple time scales in modeling plasmas by dynamical particle simulation methods, such as the particle-in-cell (PIC) method, is well known. One important cause is the large ratio of the ion and electron mass. Ways to overcome this problem are the implicit PIC, or simply, the use of a reduced ion–electron mass ratio. However, these methods are not acceptable in modeling dc glow discharges by the PIC-Monte Carlo hybrid simulation technique. Therefore, a new method called asynchronous cycling was developed, which manipulates the synchronization of the electron and ion simulation cycles. It allows a 50 times faster convergence due to direct reduction of the different time scales for situations in which the changes of macroscopic quantities are slower than the ion movement. This is demonstrated by the modeling of a complete one-dimensional dc glow discharge including cathode fall, plasma bulk, and anode fall. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872454
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    Expansion of the relativistic Fokker-Planck equation including non-linear terms and a non-Maxwellian background (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2464-2481 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relativistic Fokker-Planck collision term in Braams and Karney [Phys. Fluids B 1, 1355 (1989)] is expanded using Cartesian tensors (equivalent to associated Legendre spherical harmonics) retaining all non-linear terms and an arbitrary zeroth order distribution background. Expressions are given for collision terms between all harmonics and the background distribution in terms of the j and y functions in Braams and Karney. The results reduce to Braams and Karney for the first order harmonic term with a Maxwellian background and to those given by Shkarofsky [Can. J. Phys. 41, 1753 (1963)] in the non-relativistic limit. Expressions for the energy and momentum transfer associated with relativistic Coulomb collisions are given. The fast two dimensional Fokker-Planck solver in Shoucri and Shkarofsky [Comput. Phys. Commun. 82, 287 (1994)] has been extended to include the second order harmonic term. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872227
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    Observation of the Langmuir decay instability driven by stimulated Raman scattering (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3012-3020 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering was used to measure the Langmuir wave spectrum driven by stimulated Raman scattering. The Thomson scattering signals measured in the experiment showed Langmuir waves with components both parallel and antiparallel to the incident laser's wave vector, k0. The parallel component was attributed to stimulated Raman scattering. However, the Langmuir waves with components antiparallel to k0, which cannot be explained by stimulated Raman scattering, were attributed to the Langmuir decay instability (LDI). The relative amplitude of the two Langmuir wave features and their angular width supported the conclusion that the Langmuir waves traveling antiparallel to the incident laser's wave vector were driven by the Langmuir decay instability. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872436
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    Two-dimensional effects in a tunnel ionized plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3040-3042 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An intense short pulse laser of finite spot size propagating through a gas produces plasma via tunnel ionization on a femtosecond time scale. The radial profile of plasma density is strongly peaked on the axis and has a defocusing property. As electron density grows with time, the trailing part of the laser pulse suffers stronger divergence than the leading front, causing severe temporal distortion of the pulse. A self-consistent paraxial ray theory of electron density evolution and defocusing of the laser reveals that a square (in time) laser pulse, after propagating one Rayleigh length, has an order of magnitude difference in the axial intensity at the front and the tail of the pulse. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872438
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    Radiative transfer in anisotropic, weakly inhomogeneous media with internal sources (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3070-3076 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport of radiation in anisotropic, weakly inhomogeneous and spatially dispersive media with internal sources is considered on the basis of the relevant geometric optics far-field as a function of position and frequency. The second rank radiation intensity tensor is obtained directly from the autocorrelation of the electric far-field in terms of a second rank emissivity tensor and accounts for coherent as well as incoherent emission, along with the effects of generalized Faraday rotation. The case of Cerenkov radiation is considered in detail. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872562
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    International Thermonuclear Experimental Reactor: Physics issues, capabilities and physics program plans : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2642-2652 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Present status and understanding of the principal plasma-performance determining physics issues that affect the physics design and operational capabilities of the International Thermonuclear Experimental Reactor (ITER) [ITER EDA Agreement and Protocol 2 (International Atomic Energy Agency, Vienna, 1994)] are presented. Emphasis is placed on the five major physics-basis issues—energy confinement, beta limit, density limit, impurity dilution and radiation loss, and the feasibility of obtaining partial-detached divertor operation—that directly affect projections of ITER fusion power and burn duration performance. A summary of these projections is presented and the effect of uncertainties in the physics-basis issues is examined. ITER capabilities for experimental flexibility and plasma-performance optimization are also described, and how these capabilities may enter into the ITER physics program plan is discussed.
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    URL: http://dx.doi.org/10.1063/1.872406
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    Interaction of two neighboring laser beams taking into account the effects of plasma hydrodynamics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2670-2680 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction between two neighboring laser beams focused in a hot underdense homogeneous plasma is investigated using the non-paraxial wave coupling code KOLIBRI [S. Hüller et al., Phys. Scr. T63, 151 (1996)] in two and three spatial dimensions. Both the plasma hydrodynamic evolution and the stimulated Brillouin scattering (SBS) aspects are studied in the case of strongly damped ion sound waves. The hydrodynamic effects consist in ponderomotively driven density perturbations located between the beams which may, in turn, influence strongly the light propagation through the plasma. The two beams are found to merge whenever the distance between them is smaller than or of the order of their diameter. Concerning the SBS aspect, it is found that due to interference effects between the beams, the spatial amplification of the backscattered light is asymmetric with respect to the laser axis. SBS can also enforce the hydrodynamic effects and the beam merging. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872352
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    Quasilinear evolution of the weakly relativistic electron cyclotron maser instability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2697-2706 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a quasilinear analysis of the relativistic electron cyclotron maser instability in which the self-consistent set of equations governing the evolution of the particle distribution function and the energy spectra of unstable waves is numerically solved for parameters typical of the Earth's auroral zone plasma, taking into account both resonant and non-resonant diffusions. The results obtained show that only 0.1%∼0.2% of the particle energy is converted into wave energy by the loss cone instability, and also show that the saturation amplitude for the extraordinary mode increases in proportion to the ratio between electron cyclotron frequency and electron plasma frequency, in agreement with previous results obtained with numerical simulations. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872139
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    Effects of non-Maxwellian (super-Gaussian) electron velocity distribution on the spectrum of Thomson scattering (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2736-2740 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic form factor for Thomson scattering with a non-Maxwellian (super-Gaussian) electron velocity distribution is analytically and numerically studied for the first time. Both the ion and electron features of the spectra for α〉1 are found to be affected strongly. For the ion feature, the use of the usual theoretical spectra with the assumption of a Maxwellian distribution for fitting the measured Thomson scattering spectra may have resulted in some errors in calculating the plasma parameters in high-Z plasmas irradiated with high intensity light. However, it is impossible to use the ion feature of the measured spectra alone to deduce the form of the electron distribution. For the electron feature, the spectral shape (in particular the peak amplitude) changes sensitively with the distribution index. It would be possible to detect the super-Gaussian distribution by simultaneously measuring the ion and electron features of the spectra. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872141
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    Two-dimensional plasma flow past a laser beam (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2376-2396 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical results are presented for laser beam deflection rate due to plasma flow when the ponderomotive force (PMF) is static and given. Explicit expressions are obtained in various parameter regimes including that of weak PMF for the case of a coherent (diffraction limited) beam and a beam whose fluctuations are spatially homogeneous, as in the case of a model random phase plate beam. When the Landau damping coefficient, γ0, is negligible and the beam is either coherent and cylindrically symmetric, or random with isotropic fluctuations, the deflection rate is obtained as a closed form function of plasma flow Mach number, M. For finite damping, results are expressed in terms of a universal, one dimensional integral parameterized by M and γ0. For arbitrary PMF and M small, the problem is identified with one in the theory of random dielectric media. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872219
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    Stochastic particle transport in a magnetic island due to electrostatic drift waves (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2365-2375 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of poloidally mode coupled, ballooning type electrostatic drift waves on a magnetic island has been studied both analytically and numerically. It has been shown quantitatively that particle orbits become stochastic and their behavior can be a possible candidate for the radial plasma transport across a magnetic island of a tokamak. The transport is significant in that it takes place even when the flux surface is not destroyed. The mechanism of the stochasticity generation is understood as an overlapping of secondary islands caused by resonance between periodic particle motions in the magnetic island and Fourier modes of E×B drift due to the electrostatic drift waves. The diffusion process perpendicular to magnetic surface has been analyzed by approximating the distribution to the Gaussian type. In addition, local diffusion process in the vicinity of Kolmogorov, Arnold, and Moser surfaces has been discussed. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872218
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    Quasilinear theory of collisionless electron heating in radio frequency gas discharges (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2413-2421 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: On the basis of quasilinear kinetic theory, the electron heating of rf discharges is treated for characteristic scale lengths of the heating field much shorter than the electron mean free path. The analysis considers plasmas bounded by walls providing specular reflection. The expressions for the coefficients of electron diffusion in energy space are obtained and analyzed for inductively and capacitively coupled plasmas. Accounting for the oscillatory spatial structure of the penetrating electric field in the regime of anomalous skin effect leads to a decrease of the diffusion coefficient for high, and an increase for low, energy electrons. It is shown that the presence of a second boundary in the case of collisionless plasma slabs results in a similar effect. The formation of energy distribution functions in various regimes of collisionless heating is discussed. The diffusion coefficients are presented taking into account ambipolar electric fields. © 1997 American Institute of Physics.
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    Numerical measurement of turbulent responses in drift-Alfvén turbulence (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2443-2453 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A drift-Alfvén magnetoturbulence model that augments reduced magnetohydrodynamics with evolution of electron density under parallel compression and fluid advection has been studied numerically. In the Alfvénic regime, measurement of spectral transfer rates, frequency spectra, energy partitions, and the ensemble-averaged turbulent response reveals both Alfvénic and hydrodynamic characteristics. The rms turbulent frequency is Alfvénic, the energies are equipartitioned, and there is a fast, Alfvén-time scale relaxation in the turbulent response. The mean frequency is hydrodynamic, with diamagnetic and eddy straining signatures, and there is an eddy straining decorrelation appearing as a distinct, long time scale branch in the turbulent response. The decay rates and relative fluctuation strengths associated with fast and slow time scale decorrelation are in good agreement with theoretical predictions that posit a Kolmogorov spectrum in the Alfvénic regime. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872225
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    Energy principles for linear dissipative systems with application to resistive MHD stability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3141-3151 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A formalism for the construction of energy principles for dissipative systems is presented. It is shown that dissipative systems satisfy a conservation law for the bilinear Hamiltonian provided the Lagrangian is time invariant. The energy on the other hand, differs from the Hamiltonian by being quadratic and by having a negative definite time derivative (positive power dissipation). The energy is a Lyapunov functional whose definiteness yields necessary and sufficient stability criteria. The stability problem of resistive magnetohydrodynamic (MHD) is addressed: the energy principle for ideal MHD is generalized and the stability criterion by Tasso [Phys. Lett. 147, 28 (1990)] is shown to be necessary in addition to sufficient for real growth rates. An energy principle is found for the inner layer equations that yields the resistive stability criterion DR〈0 in the incompressible limit, whereas the tearing mode criterion Δ′〈0 is shown to result from the conservation law of the bilinear concomitant in the resistive layer. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872453
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    Dust-acoustic solitary waves and double layers in dusty plasma consisting of cold dust particles and two-temperature isothermal ions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3167-3172 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is found that a dusty plasma with inertial dust fluid and two-temperature isothermal ions admits both compressive and rarefactive solitary waves, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature ions). In this paper, Korteweg-de Vries equation (KdV-type equations) with cubic and fourth-order nonlinearity at the critical density of low-temperature isothermal ions are derived to discuss properties of dust-acoustic solitary waves. In the vicinity of critical density of low-temperature ions, KdV-type equation with mixed nonlinearity is discussed. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that rarefactive dust-acoustic solitons exist when 1〈M〈M1c and compressive dust acoustic solitons exist when 1〈M〈M2c. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872456
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    Chaotic behavior and strange attractor in time-dependent solutions of the magnetohydrodynamic equations for the Faraday disc (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3173-3176 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chaos and a strange attractor were found in time-dependent solutions of the full magnetohydrodynamic equations for a Faraday disc in an applied magnetic "seed" field. These were treated by the Galerkin method, truncated at five modes. The seed field is amplified several hundredfold. There are also aperiodic "partial pole reversals." © 1997 American Institute of Physics.
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    Nonlinear density expulsion and electron heating in the nonadiabatic regime, and application to Ion Bernstein Wave heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3187-3193 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the limit where a strong parallel electric field has short parallel scale lengths, the parallel electron motion becomes nonadiabatic and highly nonlinear, and the usual ponderomotive treatment of the slow time scale behavior of electrons is invalid. Here, a new nonadiabatic model for describing the resulting heating and expulsion of electrons from regions of a strong electric field is developed. The model shows that a typical electron is heated to a value characterized by the "quiver" velocity in the applied field. A nonlinear density expulsion still occurs in this nonadiabatic strong rf field limit, but exhibits an algebraic dependence on the wave amplitude in contrast to the exponential dependence that occurs in conventional ponderomotive theory. Results are applied to electrons in the edge plasma, near a high-power Ion Bernstein Wave heating antenna. © 1997 American Institute of Physics.
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    Free electron laser in a partially filled waveguide (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2727-2735 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear theory for a free electron laser with a one-dimensional helical wiggler and axial magnetic field in the collective regime is presented. The configuration consists of a cylindrical waveguide with arbitrary ratio of electron beam radius a to waveguide inner radius R. Parametric decay of the wiggler pump wave, in the beam frame, into a space-charge wave and an electric–magnetic (EH) waveguide mode is analyzed in three dimensions. A nonlinear wave equation for the three-wave interaction is derived and employed to obtain a formula for the spatial growth rate of the excited eigenmodes. It was found that the relativistic treatment of the electron oscillations in the wiggler field destroys the cyclotron resonance which appears in the nonrelativistic case. Nevertheless, appreciable amplification was found. Numerical analysis is conducted to study the growth rate, radiation wavelength, and required relativistic factor as functions of axial magnetic field B0 and radius ratio a/R. The suitable value for a/R was found to be around 0.65 for our choice of parameters. © 1997 American Institute of Physics.
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    Fluid models for kinetic effects on coherent nonlinear Alfvén waves. II. Numerical solutions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1257-1285 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of various kinetic effects (e.g., Landau damping, diffusive and collisional dissipation, and finite Larmor radius terms) on the nonlinear evolution of finite amplitude Alfvénic wave trains in a finite-β environment is systematically investigated using a novel, kinetic nonlinear Schrödinger (KNLS) equation. The dynamics of Alfvén waves is sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. Numerical solution for the case with Landau damping reveals the formation of dissipative structures, which are quasi-stationary, S-polarized directional (and rotational) discontinuities which self-organize from parallel propagating, linearly polarized waves. Parallel propagating circularly polarized packets evolve to a few circularly polarized Alfvén harmonics on large scales. Stationary arc-polarized rotational discontinuities form from obliquely propagating waves. Collisional dissipation, even if weak, introduces enhanced wave damping when β is very close to unity. Cyclotron motion effects on resonant particle interactions introduce cyclotron resonance into the nonlinear Alfvén wave dynamics. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872356
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    Generalized ballooning and sheath instabilities in the scrape-off layer of divertor tokamaks (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1330-1341 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of the scrape-off layer to high toroidal mode number ballooning-type instabilities is considered. The equilibrium includes a simple model of the X-point geometry, and parallel (as well as cross-field) equilibrium variations of temperature, density, and potential. The latter are computed numerically from the Braginskii form for Ohm's law. The stability analysis includes the effects of curvature, resistivity, parallel variation of the E×B drift frequency, and sheath boundary conditions at the divertor plate. Importantly, the equilibrium model assures consistency among the possible instability drives; i.e., the pressure weighting of the curvature, the plasma potential (E×B drift), and the conditions at the divertor plate are coupled by the equilibrium model. Numerical solutions indicate two modes: (i) the curvature-driven mode with growth rate enhanced by the sheaths; and (ii) the E×B shear mode driven by equilibrium variations in the region between the X point and the plate. The latter mode is shown to be partly driven by the X-point geometry. The effect of finite Larmor radius, resistivity, and electron inertia on these modes is investigated. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872309
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    Two-dimensional time-dependent solution of Stix's equation for the distribution function of minority ions during ion cyclotron resonant heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2052-2061 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent flux-surface-averaged Fokker–Planck equation for the distribution function of minority ions during ion cyclotron resonant heating introduced by Stix in a classic paper [T. H. Stix, Nucl. Fusion 15, 737 (1975)] is solved keeping two dimensions (2-D) in velocity space (speed and pitch-angle). An analysis of the applicability of the method of expansion of the distribution function f in Legendre polynomials of the pitch-angle, a method suggested by Stix and subsequently used by others, is given. A full numerical 2-D solution is also calculated. It is shown that the convergence of the Legendre polynomial expansion is very slow and non-uniform with respect to both particle energy and pitch-angle, making the method impractical when f is required at energies much higher than the background plasma thermal energy. However, the iterative sequences for the moments of f are found to converge very fast. In particular, a good approximation to the pitch-angle average of the distribution function is obtained already with two terms kept in the expansion, for a wide range of heating parameters. The validity of Stix's analytical one-dimensional approximations is analysed in detail. © 1997 American Institute of Physics.
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    Stability of ideal and resistive modes in cylindrical plasmas with resistive walls and plasma rotation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2081-2089 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stabilization of cylindrical plasmas by resistive walls combined with plasma rotation is analyzed. Perturbations with a single mode rational surface q=m/n in a finitely conducting plasma are treated by the "resistive kink" dispersion relation of Coppi et al. [Sov. J. Plasma Phys. 2, 533 (1976)]. The possibilities for stabilization of ideal and resistive instabilities are explored systematically in different regions of parameter space. The study confirms that an ideal instability can be stabilized by a close-fitting wall and a rotation velocity on the order of resistive growth rates [J. M. Finn, Phys. Plasmas 2, 3782 (1995)]. However, the region in parameter space where such stabilization occurs is very small and appears to be difficult to exploit in experiments. The overall conclusion from the cylindrical plasma model is that resistive modes can readily be wall stabilized, whereas complete wall stabilization is hard to achieve for plasmas that are ideally unstable with the wall at infinity. © 1997 American Institute of Physics.
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    Relativistic theory of classical collisional transport in a weakly coupled plasma: Solution of Fokker–Planck equation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2101-2105 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A generalized Fokker–Planck equation is developed in the pattern of a well-known collision operator [Beliaev and Budker, Sov. Phys. Dokl. 1, 218 (1957)] and solved for a relativistic singly charged electron–ion plasma under the impact of crossed electric and magnetic fields. Using the differential form of the collision operator and the modified Rosenbluth potentials appropriate for the relativistic plasma various cross-field transport coefficients are derived analytically in the limit of nonrelativistic, moderately relativistic and ultrarelativistic temperatures. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872396
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    Nonlinear reduced Braginskii equations with ion thermal dynamics in toroidal plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2134-2138 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Starting from the Braginskii fluid equations, a set of nonlinear reduced equations are derived which describe the low frequency dynamics of electron and ion energy and density in a toroidal plasma. The equations have an energy integral. The equations are appropriate for studying the relation between electron and ion thermal transport and particle transport in low temperature plasma near the edge of plasma confinement devices. © 1997 American Institute of Physics.
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    Flush mounted Langmuir probes in an oblique magnetic field (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2151-2160 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Due to the high heat flux to the target plates of present day divertor tokamaks, the use of thermally robust flush mounted Langmuir probes becomes more and more important. The surface normal of the probe defines a direction in space which is generally neither parallel nor perpendicular to the magnetic field, and the angle between these two vectors plays an important role for the physics in front of the probe. An analytic description of the sheath physics in front of a target plate is presented, and a model for the analysis of the I–V characteristics of such probes is derived therefrom. The model includes, on the one hand, considerably more physics than previous descriptions, and is, on the other hand, much simpler and more practical than numerical solutions and simulations. Subsequently the application of this model to triple probes is discussed. It will become evident that flush mounted probes can be used as reliably as domed probes to determine the plasma parameters in front of the target plates. © 1997 American Institute of Physics.
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    Passive particle dynamics in a flow exhibiting transition to turbulence (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2864-2870 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of a passive particle in a flow that exhibits bifurcations in the transition to a turbulent regime is investigated. The flow considered is a variant of the Charney–Hasegawa–Mima equation. The scalar particle dynamics is considered for different regimes of the main flow. A regime of anomalous diffusion (hypodiffusion) is observed when the field has few harmonics whereas normal diffusion occurs in the strange attractor regime. The analysis of the singular orbit reveals the presence of traps and flights that control the transport. ©1997 American Institute of Physics.
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    Formation of wave-front pattern accompanied by current-driven electrostatic ion-cyclotron instabilities (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2886-2892 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Formation of a wave-front pattern accompanied by an electrostatic ion-cyclotron instability driven by electrons drifting along a magnetic field is investigated by two-and-half dimensional particle simulations. A clear spatial wave-front pattern appears as the ion cyclotron wave grows due to the instability. When the electron stream is uniform in the system, an obliquely intersected stripe wave-front pattern is formed. When the stream has a bell-shaped pattern across the magnetic field, a V-shaped stripe wave-front pattern appears. The wave fronts have small angles with the magnetic field lines and propagate from the high-stream region to the low-stream region. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872613
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    Plasma transport near the separatrix of a magnetic island (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2920-2927 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The simplest nontrivial model of transport across a magnetic island chain in the presence of collisionless streaming along the magnetic field is solved by a Wiener–Hopf procedure. The solution found is valid provided the boundary layer about the island separatrix is narrow compared to the island width. The result demonstrates that when this assumption is satisfied the flattened profile region is reduced by the boundary layer width. The calculation is similar to the recent work by Fitzpatrick [Phys. Plasmas 2, 825 (1995)] but is carried out in the collisionless, rather than the collisional, limit of parallel transport, and determines the plasma parameters on the separatrix self-consistently. © 1997 American Institute of Physics.
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    On the stabilization of neoclassical magnetohydrodynamic tearing modes using localized current drive or heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2940-2946 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effectiveness of using localized current drive or heating to suppress the formation and growth of neoclassical magnetohydrodynamic (MHD) tearing modes is addressed. The most efficient way to use an auxiliary current source is to cause current to flow in the same direction as the equilibrium bootstrap current and phase the current relative to the magnetic island such that the current is deposited on the O-point of the island. Theoretical estimates for the amount of required current to suppress the formation of a large magnetic island is of order a few percent of the equilibrium current. If the suppression is successful, the magnetic island will saturate at a width of order the radial localization width of the current source. Localized heating at the O-point of the magnetic island can also produce stabilizing effects relative to magnetic island growth. The effects of the driven current or heating can be illustrated by using a phase diagram of the island growth. © 1997 American Institute of Physics.
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    Nonsingular canonical coordinates for the drift Hamiltonian in a magnetic field with a separatrix (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2962-2966 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic coordinates are singular on a separatrix. A method is given for transforming to nonsingular coordinates that are closely related to magnetic coordinates and can be used in the canonical coordinates of the Hamiltonian for particle drifts. The case of a magnetic separatrix with a single X point is emphasized and approximate expressions are given for the functions that appear in the drift Hamiltonian. © 1997 American Institute of Physics.
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    Structures, wavelet and intermittency in tokamak edge turbulence (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2982-2988 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The wavelet bicoherence technique is used to examine floating potential fluctuations in ADITYA tokamak edge plasma, which have shown vortex-like coherent structures on statistical basis [Proceedings of the 15th International Conference on Plasma Physics and Controlled Nuclear Fusion, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, p. 583]. On a single discharge basis, the data exhibit intermittent episodes of quadratic interaction in which low and high frequency components are coupled. The broadband nonlinear phase coupling is used as a diagnostic signature of localized coherent structure. It is observed that the wavelet bicoherence is high in the presence of sparse structures and small when the structures are closely packed. The turbulent edge plasma has regions of packed Gaussian structures and sparse non-Gaussian structures. © 1997 American Institute of Physics.
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    Steady-state magnetohydrodynamic plasma flow past conducting sphere (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3031-3039 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytic solution to the problem of strongly magnetized plasma flow past a smooth, conducting sphere is considered. The magnetic field is taken to be uniform at very large distances and the sphere is assumed to be unmagnetized. In addition, the flow speed is assumed to be subsonic and super-Alfvénic. It is shown that a steady state solution is possible only if the frozen-in condition can be relaxed near the surface of the sphere. By inclusion of a small resistivity, the presence of two, nested boundary layers near the surface is demonstrated. The magnetic field is shown to drape about the sphere with a scale size of the order of the square root of the resistivity. © 1997 American Institute of Physics.
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    Particle simulations of divergent and convergent radial electron flows in cylindrical Pierce diodes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3049-3063 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A special class of Pierce diodes, that consists of a pair of grounded coaxial cylindrical electrodes, with electrons streaming radially between them, is studied. The full set of roots of the dispersion relation of the Pierce instability is obtained by solving the dispersion relation numerically. The nonlinear behaviour of the system is then investigated using particle simulation. It is shown that the behaviour of cylindrical systems depends on two nondimensional parameters. Linear and nonlinear properties are different for convergent and divergent configurations. Several remarkable differences between cylindrical and planar Pierce diodes are reported. © 1997 American Institute of Physics.
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    Comment on "Onsager symmetry for inhomogeneous magnetized plasmas" [Phys. Plasmas 3, 4325 (1996)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3091-3093 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effective dielectric tensor for inhomogeneous magnetized plasmas was previously derived using a modified local mode approximation. We give a brief account of this derivation from a paper by Caldela Filho et al. (1989) to restate their priority. (AIP) © 1997 American Institute of Physics.
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    Analysis of magneto-plasma dynamic transients in a combustion gas magnetohydrodynamic generator (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3082-3090 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present work a model for the two-dimensional time dependent description of the magneto-fluid dynamics in the channel of an MHD (magnetohydrodynamic) generator is described. The numerical code obtained from it can be used for the analysis of the MHD channel operation, during the design procedure and for numerical experiments. The model is based on a time dependent two-dimensional description of the fluid dynamics iteratively coupled to a steady state two-dimensional description of the electrodynamics. In the plasma flow considered the magnetic field diffusion dominates over the magnetic field convection. A semi-implicit finite difference pressure scheme has been utilized for the solution of the fluid dynamic problem. The turbulence behavior is taken into account. The electrodynamics is described by a second order elliptic partial differential equation, obtained from the Maxwell equations and generalized Ohm's law, and solved by means of an exponential fitting finite difference method. The model has been validated by the comparison of its results with experimental data. Two regime conditions and a transient caused by the interruption of the seeding injection, have been analyzed. © 1997 American Institute of Physics.
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    Crossed-field secondary emission electron source (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2319-2321 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel crossed-field secondary-emission (CFSE) electron source that is capable of producing high-current tubular electron beams is described. This new electron source is based on the mechanism of secondary-emission multiplication of electron current in a magnetron-like device having smooth cylindrical electrodes. The input electron current may be as low as a few mA. The multiplication process starts at the negative slope of an applied voltage pulse. After initiation, the current is extracted from the diode region with no regard to the voltage pulse shape and as a consequence, the CFSE electron source can operate in a long pulse mode. At the diode voltage of ∼40 kV for a diode gap of ∼6 mm, the output current reaches a value of more than 100 A.
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    A model for particle acceleration in lower hybrid collapse (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2357-2364 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for particle acceleration during the nonlinear collapse of lower hybrid waves is described. Using the Musher-Sturman wave equation to describe the effects of nonlinear processes and a velocity diffusion equation for the particle velocity distribution, the model self-consistently describes the exchange of energy between the fields and the particles in the local plasma. Two-dimensional solutions are presented for the modulational instability of a plane wave and the collapse of a cylindrical wave packet. These calculations were motivated by sounding rocket observations in the vicinity of auroral arcs in the Earth's ionosphere, which have revealed the existence of large-amplitude lower-hybrid wave packets associated with ions accelerated to energies of 100 eV. The scaling of the sizes of these wave packets is consistent with the theory of lower-hybrid collapse and the observed lower-hybrid field amplitudes are adequate to accelerate the ionospheric ions to the observed energies.
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    Theory of fast ion transport induced by sawtooth oscillations: Overview and new results (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2544-2554 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The work contains both an overview of recent theories and new results on the influence of sawtooth oscillations on the superthermal ions in a tokamak plasma. In particular, new results of numerical simulations of the sawtooth-crash-induced redistribution of fast ions are presented. The results are based on the approach suggested by the authors earlier [Nucl. Fusion 36, 159 (1996)]. Peculiarities of the particle motion during the crash are revealed. Dependence of the behavior of fast ions on their parameters, as well as on tokamak parameters and features of sawteeth, is analyzed. Based on this analysis, a simple picture showing the different effects of sawtooth oscillations on various groups of particles is suggested. © 1997 American Institute of Physics.
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    Improvement of the highly energetic passing particle confinement in torsatrons and heliotrons (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2584-2596 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The configurational effects on the confinement of highly energetic passing particles, especially the helical-field ripple effects, are considered in torsatrons and heliotrons from the viewpoint of increasing the efficiency of tangential neutral beam injection (NBI) heating of plasma. The drift resonances of passing particles (ιΩφ=ΩD, where ι is the rotational transform, Ωφ is the particle toroidal transit frequency, and ΩD is the particle drift frequency) are investigated. It is discovered that the resonant passing particles oscillate poloidally through the variation of the field-line curvature. The passing particles with the energies located in the vicinity of the resonance separatrix are revealed to be as dangerous for confinement, as superbananas are. The existence of the highly poloidally localized resonant particles with lower radial deviations than the corresponding values for the nonresonant particles was found. The particles with the energies close to the state of the high poloidal localization are proposed as the most preferable beam particles for the tangential NBI heating of plasma. © 1997 American Institute of Physics.
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    Velocity and magnetic field structures in a magnetohydrodynamic dynamo : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1569-1575 
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    Topics: Physics
    Notes: Computer simulation of the magnetohydrodynamic dynamo in a rotating spherical shell geometry is performed. The convection velocity and the magnetic field structures are investigated in detail when the magnetic field is exponentially growing. It is found that the magnetic energy is strongly localized in space. The energy is generated when toroidal field lines are stretched by the fluid flows in columnar convection cells. © 1997 American Institute of Physics.
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    Measurements of laser-plasma instability relevant to ignition hohlraums : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1849-1856 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The potential for laser-plasma instability is a serious concern for indirect-drive inertial confinement fusion (ICF), where laser beams illuminate the interior of a cavity (called a hohlraum) to produce x-rays for imploding a fusion capsule symmetrically. The speckled nature of laser beams used in ICF is an important factor in laser-plasma instability processes. For example, models which calculate the spatial growth of convective instability by properly accounting for the laser speckles successfully predict the observed onsets of backscattering due to stimulated Brillouin and Raman scattering instabilities (SBS and SRS). Assuming pump depletion as the only saturation mechanism in these models results in very large predicted levels of SBS and SRS backscattering from the long-scale plasmas expected in ignition hohlraums. However, in the long-scale plasmas studied in the Nova and Trident lasers [E. M. Campbell, Rev. Sci. Instrum. 57, 2101 (1986) and N. K. Moncur et al., Appl. Opt. 34, 4274 (1995)], SRS and SBS are observed to saturate much below the levels expected from pump depletion. While the mechanism of SBS saturation is not understood at present, the observations of SRS saturation are qualitatively understood. © 1997 American Institute of Physics.
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    Laboratory studies of field-aligned density striations and their relationship to auroral processes : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1881-1888 
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    Topics: Physics
    Notes: Magnetic field-aligned structures in current, density, and temperature are common features of the auroral ionospheric plasma. These structures both generate and transform low frequency waves in the plasma. The results of laboratory studies of two processes involving magnetic field-aligned density depletions (striations) that play a role in auroral plasma dynamics are presented. The first process involves the spontaneous generation of density and magnetic fluctuations at the striation edge. The nature of the fluctuations depends upon the electron plasma beta. At high beta (greater than the electron to ion mass ratio, m/M) the drift Alfvén wave is excited. At lower beta the density and magnetic field fluctuations separate and the shear Alfvén wave dominates. This process creates an environment conducive to electron acceleration along the magnetic field when the striation size is on the order of the electron skin depth because the shear Alfvén wave then has a substantial field-aligned electric field. The second process is the direct conversion of electromagnetic whistler waves to electrostatic lower hybrid waves at the striation edge. This process provides a mechanism for concentrating lower hybrid wave energy in the vicinity of striations where it may play a role in electron and ion heating. © 1997 American Institute of Physics.
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    High-power operation of a 170 GHz megawatt gyrotron : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1907-1914 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent gyrotron oscillator experiments have achieved record powers at 170 GHz. Single mode emission with a peak output power of 1.5 MW and an efficiency of 35% has been measured. The experiment is based on a resonant TE28,8,1 cylindrical cavity situated in a 6.7 T magnetic field. Microwaves are generated in the cavity by an 83 kV annular electron beam produced by a triode-type magnetron injection gun that is capable of currents up to 50 A. Megawatt power levels with efficiencies between 30%–36% have been measured over a wide range of operating parameters for the TE28,8,1 mode. Similar results were also achieved in the neighboring TE27,8,1 mode at 166.6 GHz, and the TE29,8,1 mode at 173.5 GHz. The high output power is the result of a carefully designed electron gun with low perpendicular velocity spread (6%–10%) and a novel cavity with an output iris that is less prone to mode competition. These results are in good agreement with nonlinear multimode simulations. © 1997 American Institute of Physics.
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    Conventional solar flare theory re-examined : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1929-1935 
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    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Major objections are raised to the fundamental paradigm underlying conventional solar flare theory, viz., that the required free energy can be stored in situ at the requisite density in the corona in nonpotential magnetic fields by the action of photospheric convective motion, that it can be released rapidly through magnetic reconnection by a triggering event, and that a significant fraction of this energy is converted to x rays. An alternative explanation that avoids these difficulties requires that magnetic energy in the form of strongly sheared flux tubes be stored subphotospherically prior to the flare. It is the emergence of this subphotospherically stored magnetic shear energy into the photosphere and above, and its rapid conversion through internal magnetic reconnection to other forms that constitutes an actual flare. © 1997 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.872572
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    Three-dimensional magnetic reconnection in the solar corona : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1945-1952 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In two dimensions the notions of magnetic topology and null-point bifurcations are straightforward. In addition, the nature of magnetic reconnection is fairly well understood and can be described by a new generation of fast reconnection mechanisms known as almost-uniform reconnection and nonuniform reconnection. However, in complex three-dimensional (3-D) magnetic fields, such as exist in the solar corona, these phenomena are only just beginning to be explored and are considerably more complex. The structural properties of the magnetic field created in turn by two, three and more magnetic sources at the photosphere have been recently studied. Passing through each 3-D magnetic null there is an isolated spine field line and a flux surface known as a fan. The fans form separatrix surfaces that separate the volume into topologically distinct regions, and the fan of one null can terminate at the spine of another null, while the spine terminates either at a source or at infinity. The skeleton of complex 3-D fields in the corona, therefore, comprises the magnetic-null points and a network of spine curves and separatrix fan surfaces. Magnetic reconnection can occur in these fields by a variety of mechanisms, including spine reconnection, fan reconnection, separator reconnection, and quasiseparatrix layer reconnection. These types of reconnection and the bifurcations of null points are described and found to be much richer than in the relatively simple two-dimensional fields. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872571
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    Measurements of direct drive laser imprint in thin foils by radiography using an x-ray laser backlighter : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1985-1993 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. An x-ray laser is used as an extreme ultraviolet backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and by spectral dispersion for both 0.35 and 0.53 μm irradiation, and by induced spatial incoherence for 0.53 μm irradiation. Measurements of the imprinted modulation due to a single optical mode generated by two beam interference, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process are demonstrated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872340
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    Supernova hydrodynamics experiments on the Nova laser : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1994-2003 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In studying complex astrophysical phenomena such as supernovae, one does not have the luxury of setting up clean, well-controlled experiments in the universe to test the physics of current models and theories. Consequently, creating a surrogate environment to serve as an experimental astrophysics testbed would be highly beneficial. The existence of highly sophisticated, modern research lasers, developed largely as a result of the world-wide effort in inertial confinement fusion, opens a new potential for creating just such an experimental testbed utilizing well-controlled, well-diagnosed laser-produced plasmas. Two areas of physics critical to an understanding of supernovae are discussed that are amenable to supporting research on large lasers: (1) compressible nonlinear hydrodynamic mixing and (2) radiative shock hydrodynamics. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872341
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    Two-fluid theory of collisionless magnetic reconnection (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1002-1009 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical studies of collisionless reconnection in the framework of two-fluid theory are presented. In the high-β case (β(approximately-greater-than)1) reconnection is controlled by the whistler mode, leading to decoupling of ions from electrons on scales 〈c/ωpi. Though reconnection requires electron inertia, the reconnection rate is independent thereof, controlled only by ion inertia. Reconnection is hence much faster than in the absence of the Hall term. In the opposite limit of small β the strong axial field suppresses the whistler mode. Hence ions have to follow the electrons in the narrow reconnection layer δ∼c/ωpe, forming a macroscopic current sheet which strongly reduces the reconnection rate. Theoretical scaling laws are confirmed by numerical simulations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872211
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