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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3195-3223 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of E×B-drifting plasma clouds is investigated with the aid of a computational technique denoted here as "dielectric-in-cell." Many of the familiar phenomena associated with clouds of collisionless plasma are seen and explained and less-well-known phenomena associated with convection patterns, with the stripping of cloud material, and with the evolution of plasma clouds composed of differing ion species are investigated. The effects of spatially uniform diffusion are studied with the dielectric-in-cell technique and with another computational technique denoted as "N-body dielectric;" the suppression of convection, the suppression of structure growth, the increase in material stripping, and the evolution of cloud anisotropy are examined. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1892-1907 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When a sufficiently dense plasma stream moves across a magnetic field, the stream will form polarization charge layers and will E×B drift across the field. One charge layer is composed of electrons and the other is composed of ions. The phenomena associated with the expansion of these polarization charge layers along the magnetic field away from the stream is investigated by means of analytic theory and is confirmed by two-dimensional electrostatic particle-in-cell computer simulations. At very early times, the expansion of the electron charge layer is described by single-particle motion in a dipolelike electric field. Eventually, the electron expansion is halted by the net positive charge left behind at the stream. Then an ambipolar expansion of the electron and ion charge layers forms, with the expansion velocity set by the stream voltage rather than by plasma temperatures. Steady decreases in the cross-field-propagation velocities of the streams are observed, owing to the steady losses of charge from the stream edges.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1114-1127 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pumping of plasmas by sawtooth-waveform magnetic induction variations is studied theoretically and by means of computer simulations. A sawtooth is a cyclic waveform that is characterized by a slow increase in the magnetic induction followed by a rapid drop in the induction. Two types of sawtooth pumping are analyzed, and the types classified as to whether or not the first adiabatic invariants of the plasma particles are conserved during the rapid drops in the magnetic induction. When the invariants are conserved, the sawtooth waveforms are found to be less efficient than square waves for pumping plasmas. When the adiabatic invariants are not conserved, the pumping efficiency is found to be a slight improvement over square waves. Both types of pumping are applied to a hypothetical tokamak plasma and it is concluded that neither type of sawtooth pumping is practical for heating magnetically confined fusion plasmas.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 700-702 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When induced by pitch-angle scattering, waves of the middle branch of the extraordinary mode will give up their energy to a plasma by magnetically pumping electrons. The damping decrement for small-amplitude extraordinary waves is calculated and the decrement for finite-amplitude waves is estimated. Because heating a plasma makes it a better absorber of extraordinary waves, such waves can produce localized hot cavities in plasmas. The evolution of electron distribution functions f(v) is examined and it is found that magnetic-pumping-mediated absorption leads to f∝v−3 tails.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 857-862 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electrostatic linear analysis is performed for a finite-width electron or ion beam streaming along a strong magnetic field in the presence of a homogeneous background plasma. The linear fluid equations have been solved as a boundary value problem for planar and cylindrical beam shapes, and the dispersion which results as an eigenvalue problem is solved numerically without approximation as a function of the electron beam width. The solution gives unstable modes for any beam width and the dispersion relation shows different branches. There is a branch in both configurations that represents the most unstable mode, and the wavelength of this unstable mode for the cylindrical beam is larger than the corresponding wavelength for the most unstable mode of the slab-shaped beam.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2518-2526 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When injected across an ambient magnetic field, a stream of collisionless plasma polarizes, and the resulting polarization electric field may allow the stream to penetrate the magnetic field. The polarization charge spreads from the stream sides along the magnetic-field lines and any ambient plasma that is magnetically connected to the stream will be picked up to form Alfvén wings of co-moving plasma. As the stream and wing plasmas move across the magnetic field, their outer edges are continually stripped off. Because of these processes, the stream must expend charge, momentum, and kinetic energy in order to continue its cross-field motion. These expenditures derive from five requirements of charge from the stream: charge is required (1) to polarize the stream plasma, (2) to replace the charge stripped from the stream's edges as it propagates, (3) to set up the Alfvén wings on the stream, (4) to replace the charge stripped from the sides of the wings as they propagate, and (5) to supply any conduction currents in the ambient plasma. By using idealized stream configurations, approximate limits on the propagation distance are obtained.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3245-3260 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a quiescent collisionless plasma the motion of charged particles within a magnetosonic wave is reversible, but in the presence of electromagnetic plasma waves that pitch-angle scatter the particles, this is no longer true, and the plasma may be magnetically pumped by the magnetosonic wave, extracting energy from the wave. The particles that are energized are in resonance with the catalyst electromagnetic waves but gain their energy from the magnetosonic wave. To study this mechanism, three types of numerical simulations are used. In the first type, the magnetic pumping of an element of plasma is numerically simulated in detail by following the magnetosonic-wave-driven convection of the particle distribution through pitch-angle/momentum space and by computationally solving a pitch-angle diffusion equation for the distribution-function evolution under the action of the electromagnetic fluctuations. It is found that the magnetosonic-wave energy is transferred predominantly to high-energy particles. In the second type of simulation, the absorption of magnetosonic waves by a semi-infinite plasma and the resulting plasma heating and expansion are followed. It is found that magnetosonic waves produce a hot surface layer on the plasma that is ablated by the wave energy. In the third type of simulation, a Fokker–Planck equation for the magnetic-pumping process is numerically solved. It is found that this momentum-diffusion description is a satisfactory representation of magnetic pumping by small-amplitude magnetosonic waves.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1074-1100 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent interaction between solid objects and the unmagnetized plasmas in which they are immersed is investigated. To this end over 1900 high-resolution, one-dimensional particle-in-cell simulations of the plasmas surrounding cylindrical and planar objects are statistically analyzed. Numerical shot noise produces an electron-plasma-frequency ringing in the simulations, the amplitude of which is related to the plasma temperature and to the numerical system temperature. Whenever the potential of an object is rapidly biased, the surrounding plasma rings with a large amplitude at the electron-plasma frequency. During this ringing, a depletion layer forms around the object on ion-acoustic time scales. Positively charged objects discharge via plasma currents in about τpe /4 and negatively charged objects discharge in about τpi . Owing to charge separations in the plasmas, for the first few ion-plasma periods after a perturbation, the potential of an object is not directly related to the charge on it. The electron-plasma-frequency ringing drives large-amplitude Langmuir waves, which energize electrons and drive cavitation in the plasma. The fluxes of electrons reaching the objects are bursty at ωpe, and the energies of the ions striking the object slowly and systematically vary with time.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 540-550 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the study of relativistic plasma double layers is described through the solution of the one-dimensional, unmagnetized, steady-state Poisson–Vlasov equations and by means of one-dimensional, unmagnetized, particle-in-cell simulations. The thickness versus potential-drop scaling law is extended to relativistic potential drops and relativistic plasma temperatures. The transition in the scaling law for "strong'' double layers suggested by analytical two-beam models by Carlqvist [Astrophys. Space Sci. 87, 21 (1982)] is confirmed, and causality problems of standard double-layer simulation techniques applied to relativistic plasma systems are discussed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2660-2674 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of charged particles near X-type magnetic neutral lines is investigated. The magnetic field is taken to be hyperbolic and time stationary, with a uniform electric field perpendicular to the magnetic field. The general properties of the orbits of noninteracting particles in that field geometry are examined. Approximate analytic solutions to the orbit equations are derived by considering a magnetic-insulation picture where there is a hole in the magnetic insulation around the neutral line. Scaling laws for the dependence of the energy gain on strengths of the magnetic and electric fields are derived. The kinetic-energy distribution function for accelerated particles is derived for particles flowing past the neutral line. These analytic derivations are supported by computer simulations, in which the relativistic equations of motion for single test particles are numerically solved and the orbits and kinetic-energy gains of the particles are obtained. A number of simulations were performed and one parameter at a time was varied. Applications of the results to magnetic-neutral-line regions in space physics and astrophysics are possible.
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