Electromagnetic ion cyclotron instability driven by ion energy anisotropy in high-beta plasmas

Abstract

Low frequency (ω≈ωci=eiB0/mic) transverse electromagnetic perturbations propagating parallel to a confining magnetic field B0êz are shown to exhibit instability in the presence of ion energy anisotropy with Ti⊥≳Ti∥. The characteristic maximum growth rate for Ti⊥≫Ti∥ is γM≈(βi⊥/2)1/2ωci, where βi⊥=8πniTi⊥/B20, and the wavelengths corresponding to instability are of order c/ωpi, where ωpi is the ion plasma frequency. Within the context of a quasi-linear model, it is shown that the characteristic time scale for energy isotropization through nonlinear response of the ions to the instability is several γ−1M. Since γ−1M≪τii (the ion-ion binary collision time) in typical high-density pinch experiments, this instablity appears to provide a viable collective mechanism for ion energy isotropization during the implosion or post-implosion phases of these experiments. It is also shown that the instability persists in the limit of weakly magnetized ions (‖ω+iγ‖≫‖ωci‖, k2zr2Li≫1) and strongly magnetized electrons (‖ω+iγ‖≪‖ωce‖, k2zr2Le≪1) provided βi⊥≫1. The instability also has applications to astrophysical plasmas with Ti⊥≳Ti∥ as well as laboratory plasmas heated by neutral-particle injection perpendicular to B0.

Present status of mirror stability theory

“…x 0 e , we find (5) 7 (6) This.scaling law correlBtes with observed simulation results when various input paramete.rs. are varied.…”

Kinetic instabilities in the solar wind driven by temperature anisotropies

“…In this regard, the simplest nonlinear theory, i.e., quasilinear kinetic theory, is a suitable choice for studying the nonlinear evolution of the plasma system subject to instabilities. Quasilinear theory of the anisotropy-driven instabilities of the type pioneered by Davidson and Ogden (1975) was first extended to include the mirror and ioncyclotron instabilities by the present author (Yoon 1992). The present review will extensively rely on such a formalism to include other unstable modes along the same line of theoretical approach as taken in Davidson and Ogden (1975) and Yoon (1992).…”

“…Quasilinear theory of the anisotropy-driven instabilities of the type pioneered by Davidson and Ogden (1975) was first extended to include the mirror and ioncyclotron instabilities by the present author (Yoon 1992). The present review will extensively rely on such a formalism to include other unstable modes along the same line of theoretical approach as taken in Davidson and Ogden (1975) and Yoon (1992). Thus far, such an effort has been quite successful, except that the quasilinear moment theory for the so-called oblique firehose instability has not been done, so this review will have to leave it out.…”

“…The Vlasov theory of linear waves and quasilinear kinetic theory depend on the particle distribution function, but in general, it is not so straightforward to incorporate the information associated with the kinetic-scale particle distribution function directly into the equations governing large-scale velocity space integrated quantities. To facilitate the coupling between large-and small-scale quantities and physics, we will adopt and extensively utilize the method pioneered by Davidson and Ogden (1975), in which velocity moments are taken over the particle kinetic equation under the assumption of bi-Maxwellian distribution function. Such a method may be termed the quasilinear ''moment'' theory, or macroscopic quasilinear theory.…”

Application of multivariate Maxwellian mixture model to plasma velocity distribution function

“…We examine the electromagnetic dispersion relation in a homogeneous plasma described in the previous literature [e.g., Gary, 1991 which is also found to be most unstable for parallel propagation. The mode can be considered to be excited by the electromagnetic ion/ion cyclotron (EMIIC) instability [Gary, 1991] or the electromagnetic ion cyclotron (EMIC) instability [Davidson and Ogden, 1975].…”