Impact of electron temperature anisotropy on wave mode propagation and power deposition characteristics in helicon plasma

As the core issue in helicon discharge, the physical mechanism behind the high ionization rate phenomenon is still not fully understood. Based on the warm plasma dielectric tensor model which contains both the particle drift velocity and temperature anisotropy effect, by employing the general dispersion relation of electromagnetic waves propagating in magnetized and uniform plasma with typical helicon discharge parameter conditions, wave mode propagation characteristic and collisional, cyclotron and Landua damping induced wave power deposition properties of azimuthally symmetric mode were theoretically investigated. Systematic analysis shows that, under typical helicon plasma parameter conditions, i.e., wave frequency ω/2π=13.56 MHz, ion temperature is one tenth of the electron temperature, for given magnetic field B0 (or wave frequency ω), there exists a critical wave frequency ωcr (or magnetic field B0,cr ), above which (or below B0,cr) the damping of the n=1,2,3 cyclotron harmonics begins to increase sharply; for the electron temperature isotropic case, the attenuation constant of different harmonics starts to increase significantly and monotonically at different threshold of magnetic field, while the phase constant abruptly increases monotonically from the beginning of the parameter interval, on the other hand, for the electron temperature anisotropic case, both the phase constant and attenuation constant have peak phenomenon, i.e., the attenuation constant begins to increase sharply at a certain value of B0 and meanwhile the phase constant appears a maximum value near the same value of magnetic field, the phase constant starts to keep constant at a certain value of B0 and meanwhile the attenuation constant has a maximum value near this same value of magnetic field; for the wave power deposition properties, under electron temperature anisotropy conditions, power deposition due to collisional damping of Trivelpiece-Gould (TG) wave plays a dominant role in low field (B0=48 Gs), and by considering the electron finite Larmor radius (FLR) effect, the power deposition of TG wave appears a maximum value at a certain point of parallel electron temperature Te, // , and with the decrease of Te,⊥/Te, //, the maximum value of power deposition increases gradually. All these conclusions are very important for us to further reveal the physical mechanism of high ionization rate in helicon plasma.