Influence of electron temperature anisotropy onwave mode propagation and power deposition characteristics in helicon plasma

As the core issue in helicon discharge, the physical mechanism behind the high ionization rate phenomenonis still not fully understood. Based on the warm plasma dielectric tensor model which contains both the particledrift velocity and temperature anisotropy effect, by employing the general dispersion relation of electromagneticwaves propagating in magnetized and uniform plasma with typical helicon discharge parameter conditions, wavemode propagation characteristic and collisional, cyclotron and Landua damping induced wave power depositionproperties of azimuthally symmetric mode are theoretically investigated. Systematic analysis shows thefollowing findings. 1) Under typical helicon plasma parameter conditions, i.e. wave frequency w/(2 pi)=13.56MHz, ion temperature is one tenth of the electron temperature, and for a given magnetic field B0 (or wave frequency w),there exists a critical wave frequency wcr (or magnetic field B0,cr), above which (or below B0,cr) the damping ofthe n = 1, 2, 3 cyclotron harmonics begins to increase sharply. 2) For the electron temperature isotropic case,the attenuation constants of different harmonics start to increase significantly and monotonically at differentthresholds of magnetic field, while the phase constant abruptly increases monotonically from the beginning ofthe parameter interval. On the other hand, for the electron temperature anisotropic case, both the phaseconstant and attenuation constant have peaking phenomenon, i.e. the attenuation constant begins to increasesharply at a certain value of B0 and meanwhile the phase constant presents a maximum value near the samevalue of magnetic field, thus the phase constant starts to keep constant at a certain value of B0 and meanwhilethe attenuation constant has a maximum value near this same value of magnetic field. 3) For the wave powerdeposition properties, under electron temperature anisotropy conditions, power deposition due to collisionaldamping of Trivelpiece-Gould (TG) wave plays a dominant role in a low field (B0= 48 Gs) (1 Gs = 10-4 T); byconsidering the electron finite Larmor radius (FLR) effect, the power deposition of TG wave presents amaximum value at a certain point of parallel electron temperature Te,//; with the decrease of Te,perpendicular to/Te,//, themaximum value of power deposition increases gradually. All these findings are very important in furtherrevealing the physical mechanism behind the high ionization rate in helicon plasma