[en] Plasma is characterized by electrical quasineutrality and the collective behavior. There exists a longitudinal low-frequency wave called an ion-acoustic wave in a plasma. One problem in the experimental study of ion-acoustic waves has been that sometimes they are observed to be reflected from discharge tube walls, and sometimes to be absorbed. Theoretical computation reveals that a velocity gradient produced by a density gradient plays a significant role in the reflection. The velocity gradient produces the subsonic-supersonic transition and long wavelength waves are reflected before reaching the transition while short wavelength waves penetrate over the transition and are absorbed in the supersonic flow plasma

No abstract available

[en] The nonlinear evolution of one-dimensional electron-ion two-stream instability in a field-free plasma is studied both analytically and numerically (computer simulation). The instability is dominated by the fastest growing mode and its harmonics, provided that the initial fluctuation level is sufficiently small. A nonlinear dispersion relation is derived and solved numerically, taking into account; (a) the frequency and growth rate modulation, (b) the electric field up to epsilon/sub k/⁴, and (c) the renormalized particle distribution functions. The model can successfully explain the results of a computer simulation, particularly the presence of an algebraic growth stage following the breakdown of the exponential linear growth, the appearance of harmonics, and the final saturation level. The minimum conductivity found scales as (M/m)⁰⁶¹ω/sub p/e, where M/m is the ion/electron mass ratio

No abstract available

No abstract available

[en] Statistics of charged particles in turbulent electric fields has been studied numerically, and compared with quasilinear and resonance broadening diffusion processes. Particle trajectories are followed by solving the equation of motion for an ensemble of particles where the turbulent electrostatic fields having amplitude sigma are assumed to have gaussian spectrum k/sub j/ = (j-1)Δk, j = 1,2,3,..., with spectrum width deltak and random phases /theta//sub j/. We recover the results obtained by Doveil and Gresillon (1982), namely the quasilinear theory predicts the correct particle diffusion in velocity space in weak turbulent fields and both quasilinear and resonance broadening theory fail to predict the correct diffusion coefficients in strong turbulent electric fields. Our extended calculation reveals the following: The velocity variance <Δv²>, defined by <(v-v/sub o/)²> where v/sub o/ is the initial velocity, exhibits two different linear stages in time: the initial linear rise is followed by the second slow (but still linear) rise characterized by a longer duration and shorter correlation time. The diffusion coefficient estimated from the initial linear rise of <Δv²> substantially differs from those predicted by either quasilinear or resonance broadening theory even at modest field amplitudes. The observed friction coefficient is in good agreement with the prediction of quasilinear theory only for weak turbulence fields. For stronger turbulence fields, the acceleration of some particles to high energy is observed

[en] Wave-particle interaction in plasma turbulence is studied from the viewpoint of quantum electrodynamics. The waves in a plasma turbulence are considered as a collection of quasiparticles. These quasi particles interact with particles of the plasma and the interactions are described in terms of Dirac interaction Hamiltonian. A modified Fermi golden rule is used to describe the rate of change of the particle distribution function. A radiative, collective, resonant and nonresonant effects are discussed. (author)

[en] Analytic formulation is presented for the absolute stability of drift waves when the density gradient is nonuniform. Drift waves can be absolutely unstable if the nonuniformity is strong enough, and under certain conditions the Drall-Rosenbluth stability criterion remains effective. (author)

[en] It is shown that the conventional mode differential equation for low frequency electrostatic waves in a tokamak does not contain full ion dynamics. Both electrons and ions contribute to the ballooning term, which is subject to finite ion Larmor radius effects. Also, both fluid ion approximation and kinetic ion model yield the same correction. Reexamined are the density gradient universal mode and ion temperature gradient instability employing the lowest order Pearlstein-Berk type radial eigenfunctions. No unstable, bounded, energy outgoing eigenfunctions have been found. In particular, a large ion temperature gradient (eta/sub i/) tends to further stabilize the temperature gradient driven mode

[en] Charged particles in random electric fields are known to diffuse over phase velocity resonant layer in velocity space, while charge particles placed in a sheared magnetic field diffuse over the mode rational surfaces due to ExB random fluctuations. The authors study in detail the transition of particle diffusion in turbulent fields from quasilinear (constant diffusion rate) to nonlinear regime (time depend rate) by test particle numerical experiments. They observe that particle diffusion rate is substantially deviated from the quasilinear value and depends on time when the amplitude of random field becomes larger. Such a transition from quasilinear to nonlinear diffusion is observed without particle loss from the resonance region. Time dependence diffusion coefficient may be explained by the effect of retarded friction caused by turbulent fluctuations