Cyclotron wave instabilities in axisymmetric mirror-trapped plasmas with anisotropic temperature

Abstract

Dispersion relations have been derived for field-aligned cyclotron waves in the two-dimensional axisymmetric mirror-trapped plasma models with anisotropic temperature. The transverse dielectric characteristics are evaluated by solving the Vlasov equations for charged particles in the zero-order of magnetization parameters taking into account the cyclotron and bounce resonances for the straight mirror traps, inner part of the Earth's magnetosphere and laboratory magnetic dipole plasmas. The steady-state Maxwellian and bi-Maxwellian distribution functions of plasma particles are considered.

Cyclotron Electromagnetic Instabilities in a Laboratory Dipole Magnetospheric Plasma with bi-Kappa Distributions

“…In the limit of a very large power-index κ → ∞ the dielectric characteristics (28) and (29) and dispersion relations (37) reproduce the corresponding expressions obtained in Ref. [24] for biMaxwellian distributions. It should be mentioned that for isotropic temperatures (T || = T ⊥ = T ) expressions (28)-(36) simplify, and provide the corresponding expressions for the dielectric susceptibility elements in a LDM plasma with isotropic Kappa distributions.…”

“…These expressions are markedly different from those obtained in LDM plasmas with bi-Maxwellian distributions [24], and which can be recovered in the limit κ → ∞. The electromagnetic ion-cyclotron and electroncyclotron waves in LDM plasmas with anisotropic temperature are limited to frequency ranges below the minimal cyclotron frequencies of ions, Reω < Ω co,i , and electrons, Reω < |Ω co,e |, respectively.…”

“…The 2D steady-state magnetic field is modeled by a laboratory dipole approximation [23,24] accounting for a finite radius of the current-ring creating the magnetic dipole. A 2D axisymmetric LDM plasma, schematically shown in Fig.…”

“…In this case the dispersion and stability properties need to be described in the frame of a 2D kinetic wave theory implying a specific dielectric tensor. Moreover, the wave-particle interactions should take into account that in a LDM plasma there are two entirely different groups of the so-called trapped and untrapped particles [23,24]. In the inner Earth's magnetosphere only trapped particles can exist bouncing along the geomagnetic field lines.…”

“…These waves have been characterized in Ref. [24] for an idealized LDM plasma with anisotropic bi-Maxwellian particles, while here we generalize the approach by assuming both the electron and ion (proton) populations well described by bi-Kappa distributions in velocity space. The generalized Kappa power-laws are more appropriate to reproduce the velocity distributions with enhanced high-energy tails, which are frequently reported by the in-situ measurements in space plasmas, i.e., the solar wind and planetary magnetospheres [25,26].…”