Joseph H. Orens

Theory and Simulation of Turbulent Heating by the Modified Two-Stream Instability.

Results of an analytical and numerical study of the nonresonant, modified plasma two‐stream instability, which is driven by relative streaming of electrons and ions across a magnetic field B0 are presented. The instability has characteristic frequency and growth rate comparable to the lower‐hybrid frequency. The linear theory is discussed both in the electrostatic and fully electromagnetic cases, and a detailed numerical study of the dependence of the unstable roots of the dispersion relation for a wide range of plasma parameters is presented. The nonlinear theory includes discussions of (1) quasilinear theory, (2) trapping, which is responsible for nonlinear stabilization, (3) a derivation of a fully nonlinear scaling law which shows how results scale with electron‐ion mass ratio, and (4) the effect of cross‐field vortex‐like motion caused by turbulence induced E × B drifts. One‐and two‐dimensional computer simulations with dense k‐space spectra are presented in support of this theory. The simulations sh...

Theory and Simulation of the Beam Cyclotron Instability

A detailed theory in conjunction with the results of computer simulation experiments is presented for the beam cyclotron instability. The main results are (1) After a period of exponential quasilinear development, turbulent wave‐particle interactions cause cross‐field diffusion of the electrons which smears out the electron gyroresonances. This occurs at a level of turbulence which scales as Σκ(| Eκ |2/4πN0Te)∼(Ωe/ωe)2(Ωe/kve), where Ωe and ωe are the electron cyclotron and plasma frequencies, and results in a transition to ordinary ion sound modes that would occur in an unmagnetized plasma. The magnetic field serves to reduce the effects of electron trapping. (2) This level of turbulence appears to have virtually no effect on long wavelength fluid modes. (3) At this level the instability stabilizes if ordinary ion sound is stable due to ion Landau damping. For cold ions it continues to develop at the slower ion acoustic growth rate until the fields become strong enough to trap the ions. After the fields ...

Two-Dimensional Study of Electron-Ion Streaming Instabilities.

A two‐dimensional study is presented, based on computer simulation, of strong electron‐ion streaming instabilities induced by counterstreaming ion beams, for initially cold electrons (ve ≪ vd). Wave growth initially agrees well with linear theory. Higher harmonics appear later, in good agreement with mode coupling theory. The wave spectrum, initially very broad perpendicular to the streaming direction, narrows as the electrons heat and the waves saturate, in accordance with quasilinear theory. Electron heating is explained by nonresonant quasilinear diffusion at early times, and by resonant turbulent diffusion at later times. In contrast to previous one‐dimensional studies, it is found that electron heating continues well after wave saturation and after ve > vd. However, the heating rate at late times is somewhat reduced by partial plateau formation in the electron velocity distribution. Coherent electron trapping is not seen, as it is in the one‐dimensional situation, but coherent ion trapping does occur...

Low‐frequency parametric instabilities of magnetized plasmas with two ion species

A theoretical and computer simulation treatment is presented of the response of magnetized plasmas with two ion species to low‐frequency, electric fields oscillating at ω0 near the lower‐hybrid frequency ωlh that shows the existence of parametric instabilities. A new decay instability involving the Buchsbaum two ion resonance occurs for ω0>ωlh, and a purely growing instability occurs for ω0<ωlh. The analysis is valid even when the masses of the ion components are comparable and applies, for example, to deuterium‐tritium plasmas. Computer simulation experiments demonstrate the potential importance of these instabilities as ion heating mechanisms.

Anomalous Resistance due to Cross‐Field Electron‐Ion Streaming Instabilities

New computer simulations show that the nonlinear stage of the beam cyclotron instability is stabilized if Ti/Te≳υd/υe, similar to ion sound, as has been predicted theoretically. In this case, the instability makes no significant contribution to anomalous resistance, for the conditions of typical laboratory resistive shocks. In the opposite case, a theoretical study of the later development shows that after the onset of ion trapping, both wave energy and electron temperature grow linearly with time, and the anomalous electron‐ion collision frequency becomes constant at ∼0.02 times the electron plasma frequency. These conclusions are supported by simulation studies.

On the theory of the beam cyclotron instability in plasmas

Abstract Important new aspects of the linear theory of the beam cyclotron instability in a magnetized plasma are discussed.

Theory and simulation of collisional damping of longitudinal waves in a two‐dimensional plasma

The collisional damping of plasma oscillations is studied by numerical simulation techniques. The results agree with the theoretical calculation of collisional damping in a two‐dimensional plasma, resolving discrepancies which had previously existed between analytic and simulation approaches to this problem.