Electron Landau damping in a laboratory dipole magnetic field plasma

Abstract

Transverse and longitudinal dielectric permittivity elements are derived for radio frequency waves in a laboratory dipole magnetic field plasma (LDMFP) accounting for the finite ring current radius. The main feature of LDMFP is the fact that, in contrast to planetary magnetospheric plasmas, the untrapped (circulating) particles can exist/circulate (together with the trapped particles) along the equilibrium magnetic field lines. To estimate the wave power absorbed in LDMFP the perturbed electric field and current density components are decomposed in a Fourier series over the poloidal angle. The wave absorption is expressed by the summation of contributions of all harmonics of the perturbed electric field and both the diagonal and non-diagonal dielectric permittivity elements. In this paper, we analyze numerically the separate contributions of the trapped and untrapped electrons to the imaginary part of the longitudinal permittivity elements in LDMFP with an equilibrium (Maxwellian) distribution functions of plasma particles in velocity space. This information is necessary to estimate the collisionless wave dissipation by electron Landau damping. The computations are carried out in a wide range of the wave frequencies.