Impact of electron temperature anisotropy on power deposition characteristic of helicon wave

Abstract

As a core phenomenon in helicon discharge, the plasma temperature anisotropy may play a crucial role in helicon wave power deposition. Under radially inhomogeneous plasma circumstances, by employing the warm plasma dielectric tensor model and considering the finite Larmor radius (FLR) effect and plasma temperature anisotropy effect, for the typical helicon discharge parameter conditions, the helicon wave and Trivelpiece-Gould (TG) wave mode coupling characteristic and impact of electron temperature anisotropy on the helicon wave power deposition induced by collisional and Landau damping mechanism are theoretically investigated. Detailed analysis shows that, for typical helicon plasma electron temperature <i>T</i>_<i>e</i> =3 eV and low magnetic field <i>B</i>₀ =48 G, the electron FLR effect should be considered, while the ion FLR effect can be ignored due to its large inertia effect; compared to the | <i>n</i> |<2 cyclotron harmonics, the contribution of the| <i>n</i> |>1 harmonics in the calculation of plasma dielectric tensor elements can be ignored due to low magnetic field conditions. For the propagation constant, detailed investigation indicates that the phase constant has a maximum value at a certain radial position, near the same position mode coupling between helicon wave and TG wave happens. Fully analysis suggests that the power deposition of the <i>m</i>=1 helicon mode peaked in certain radial position and increased gradually with the increase of the axial electron temperature, besides, compared to the Landau damping, the collisional damping plays a dominant role in the power deposition under current parameter conditions; importantly, the electron temperature anisotropy imposed significant impact on the power deposition characteristic, both the increase and decrease of electron temperature anisotropy factor (χ=<i>T</i>_<i>e,⊥</i>/T_<i>e,z</i>) can lead to drastic changes in the power deposition intensity. All these conclusions are crucial for us to understand the discharge mechanism of helicon plasma.