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  • American Chemical Society  (22,385)
  • American Institute of Physics (AIP)  (9,740)
  • American Meteorological Society
  • 1995-1999  (33,472)
  • 1997  (33,472)
Collection
Publisher
Years
  • 1995-1999  (33,472)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Exact order reduction method in mode conversion problems (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3129-3140 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exact order reduction method solves the fourth-order system of equations from the Vlasov equations that describe mode conversion by breaking the solution into two steps. The first step is to find the numerical solutions of a pair of second-order equations for the fast waves and slow waves, respectively, which are easily obtained. The second step uses an associated integral equation to obtain the coupling between the fast and slow waves. Potential difficulties due to singularities in the kernel of the integral equations near the axis are resolved by altering the integration path. This allows accurate estimates for mode conversion efficiencies in realistic geometries as the integral equation is solved only in a narrow region near resonance, while the global fast wave solution of the reduced second-order equation covers the entire cross section. The method makes virtually no approximations except that it keeps only the lowest nontrivial order terms in the Larmor radius expansion. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872452
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  • 2
    Electronic Resource
    Electronic Resource
    Turbulization of nonlinear Langmuir oscillations in a cold plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3200-3203 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that the electric field of Langmuir oscillations in a cold plasma contains a component, independent of time, setting ions in motion. Using Lagrange variables, one-dimensional dynamics of plasma in respect to the interaction between electron oscillations and ion movement is investigated. As a consequence of this interaction, the crossing of electron trajectories occurs even at small amplitudes at time tc, i.e., one-dimensional turbulence appears in the system. The expression for tc is derived. In time tc ion displacements as well as ion energy are found to depend only on the electron–ion mass relationship. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872460
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  • 3
    Electronic Resource
    Electronic Resource
    The bootstrap current in a tokamak with electron cyclotron heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3211-3216 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bootstrap current in a non-Maxwellian tokamak plasma with electron cyclotron heating is calculated. The calculation is exact in the limit of highly charged ions, where pitch-angle scattering dominates over quasilinear diffusion, and shows that the current is entirely determined by the pressure of the trapped electrons. If the ion charge is finite, the current is shown to consist of two terms: one driven by collisions, and one driven by the heating and losses. The former is calculated approximately by using a model collision operator, and is found to be determined by the distribution of trapped electrons alone; the latter is discussed qualitatively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872462
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  • 4
    Electronic Resource
    Electronic Resource
    Anomalous width variations for ion acoustic rarefactive solitary waves in a warm ion plasma with two electron temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3204-3210 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalous width–amplitude variations were observed in large amplitude rarefactive solitary waves which show increasing width with increasing amplitude, contrasting the usual reciprocal relation between the square of the width and the amplitude, beyond a certain value of the plasma parameters [S. S. Ghosh, K. K. Ghosh, and A. N. Sekar Iyengar, Phys. Plasmas, 3, 3939 (1996)]. For the limiting maximum amplitude, the "increasing width" solitary wave tends to a double layer-like solution. The overall variation was found to depend crucially on the specific parameter space. From a detailed investigation of the above behavior, a plausible physical explanation has been presented for such increases in the width. It is found that the ions' initial kinetic energies and the cold electron concentration within the perturbed region play a significant role in determining the observed width–amplitude variation. This contradicts the investigation of Sayal, Yadav, and Sharma [Phys. Scr. 47, 576 (1993)]. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872461
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  • 5
    Electronic Resource
    Electronic Resource
    Aspect ratio scaling of toroidal plasma equilibria and the tokamak bootstrap effect (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3254-3261 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The aspect ratio scaling of toroidal plasma equilibria is examined using a parametrization of an exact Solov'ev solution to the Grad–Shafranov equation in Boozer coordinates. The equilibrium analysis suggests that simultaneous enhancements in magnetohydrodynamic (MHD) stability and the bootstrap effect are possible in tight aspect ratio (A→1) tokamaks. The fundamental physical mechanism causing the enhancements is shown to be the natural increase of the MHD safety factor q in tight aspect ratio toroidal geometries. The results of the scaling model suggest that the lowest bootstrap current fractions are obtained in tokamaks with aspect ratios A(approximate)3. It is also shown that a tight aspect ratio bootstrapped tokamak can be a weakly paramagnetic device. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872410
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  • 6
    Electronic Resource
    Electronic Resource
    Resistive pressure gradient-driven turbulence at stellarator plasma edge (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3282-3292 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution calculations of resistive pressure gradient-driven turbulence for the plasma edge parameters of the Advanced Toroidal Facility (ATF) [J. F. Lyon et al., Fusion Technol. 10, 179 (1986)] electron cyclotron heated discharges give fluctuation levels, consistent with the experimental measurements. This turbulence model is also used to simulate the transition from the low confinement to the high confinement mode. The transition is triggered through the poloidal flow amplification induced by the Reynolds stress. After the transition, the confinement improvement is relatively low (30%–40%), even for unrealistically low poloidal viscosity. In the high confinement mode, the characteristic radial scale length of the poloidal flow in the three-dimensional calculations (separation between the lowest-n resonant surfaces) is different from the single helicity results (radial correlation length of the fluctuations). The simple criterion based on the ratio of shearing rate to the linear growth rate does not quantitatively account for the fluctuation reduction. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872469
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  • 7
    Electronic Resource
    Electronic Resource
    Extended neoclassical transport theory for incompressible tokamak plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3320-3322 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conventional neoclassical transport theory is extended to include the effects of orbit squeezing, and to allow the effective poloidal Mach number UpM=[(V(parallel)/vt)+(VEB/vtBp)] of the order of unity for incompressible tokamak plasmas. Here, V(parallel) is the parallel mass flow, vt is the ion thermal speed, VE is the poloidal E×B drift speed, B is the magnetic field strength, and Bp is the poloidal magnetic field strength. It is found that ion thermal conductivity is reduced from its conventional neoclassical value in both banana and plateau regimes if UpM〉1 and S〉1. Here, S=[1+cI2Φ′′/(Ω0B0)] is the orbit squeezing factor with c the speed of light, I=RBt, R the major radius, Φ the electrostatic potential, B0 the magnetic field strength on the axis, Ω0=eB0/Mc, M the ion mass, e the ion charge, Φ′′=d2Φ/dψ2, and ψ the poloidal flux function. However, there is an irreducible minimum for the ion thermal conductivity in the banana-plateau regime set by the conventional Pfirsch–Schlüter transport. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872472
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  • 8
    Electronic Resource
    Electronic Resource
    Studies of instability and transport in sheared-slab plasmas with very weak magnetic shear (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3334-3340 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using kinetic theory, for tokamak plasmas with very weak (positive or negative) magnetic shear (VWS). The gradient of magnetic shear as well as the effects of parallel and perpendicular velocity shear (v(parallel)′ and vE′) are included in the defining equations. Two eigenmodes: the double (D) and the global (G) are found to coexist. Parametric dependence of these instabilities, and of the corresponding quasilinear transport is systematically analyzed. It is shown that, in VWS plasmas, a parallel velocity shear (PVS) may stabilize or destabilize the modes, depending on the individual as well as the relative signs of PVS and of the gradient of magnetic shear. The quasilinear transport induced by the instabilities may be significantly reduced with PVS in VWS plasmas. The vE′ values required to completely suppress the instabilities are much lower in VWS plasmas than they are in normal plasmas. Possible correlations with tokamak experiments are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872474
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of a wiggler on two-stream instability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3380-3381 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a plasma-filled free electron laser two-stream instability is a serious consideration. The growth rate of the instability could be significantly reduced by coupling it to the electromagnetic modes/quasimodes through the wiggler. The effect is important near wiggler plasma resonance, where plasma frequency equals the product of wiggler wave number and beam velocity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872478
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  • 10
    Electronic Resource
    Electronic Resource
    A high-efficiency free-electron laser-peniotron hybrid with a longitudinal wiggler magnetic field (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3390-3393 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated emission from the interaction of a cold, relativistic beam of electrons gyrating in a combined solenoidal and longitudinally polarized periodic wiggler magnetic field is considered as a source of high-efficiency and short-wavelength radiation. The analysis of electron motion in such a combined field shows the motion covers rich Fourier components. The first Fourier component, with the cyclotron frequency of ωc+kwv(parallel), has relatively large transverse velocity compared with the velocity of the motion. The study of the interaction of this Fourier component with the peniotron electromagnetic mode indicates that a high efficiency of 36% is obtained. Its working mechanism is explained and the influence of the wiggler field on the saturation efficiency is analyzed. The electron bunching in the transverse plane and the evolution of the efficiency with the interaction distance is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872480
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