Density enhancement near lower hybrid resonance layer in m=0 helicon wave plasmas

Radial density profiles are measured with various frequencies, powers, pres sures, and gas masses in m = 0 helicon wave plasmas. The radial density pro files show clear mode changes for the E mode (capacitive coupling), the H m ode (inductive coupling), and the W mode (wave coupling) as the rf (radio f requency) power increases. The radial density profile hardly changes as the frequency varies in the E and the H modes but changes substantially in the W mode; it changes from a central peak profile to a hollow density profile near the lower hybrid resonance frequency. The change of radial density pr ofile near the lower hybrid resonance frequency occurs only at pressures be low 20 mTorr, and the resonance effects become very weak at higher pressure s. The change of the radial density profile may be explained by the density enhancement near the lower hybrid resonance layer. The experiments with va rious magnetic fields and gas masses show a close correlation between the l ower hybrid frequencies and the density profile changes. (C) 2001 American Institute of Physics. [DOI: 10.1063/1.1332987].