Spectral and spatial characterization of a radio frequency power absorption in high pressure helicon plasmas

A power absorption in helicon plasma excited by double m=0 antenna is considered at high argon pressures, when the electron collision frequency exceeds the driving frequency. The influence of various factors is examined, including the plasma density and nonuniformity, magnetic field, gas pressure, and antenna spectrum. The wave dispersion curves and absorbed power spectra are comparatively examined to find out the scaling laws. The spatial distribution of the deposited power is characterized both qualitatively and quantitatively by considering the absorption profiles and fractions of the total power absorbed in the under antenna and edge regions of the plasma column. Dependencies of the plasma load resistance on various parameters and magnetic field profiles are examined and compared with experimental results. Computations are performed using two alternative models, either taking into account or neglecting the excitation of quasi-electrostatic Trivelpiece–Gould (TG) waves. Results on the plasma resistance are found to be close in both models provided collisional damping of helicons is not so low as to give rise to the cavity resonances. Inclusion of the TG waves yields magnetic field profiles which are substantially localized near the antenna, and absorption profiles strongly peaking in the peripheral plasma, underneath the antenna. With neglect of the TG waves, the magnetic fields and absorption profiles are found to be much more extended in both axial and radial directions from the antenna. Theory accounting for the TG waves gives a better fit over a broad range of parameters to the measured data, especially regarding the magnetic field profiles.