Radially localized electron heating in helicon plasmas by X-wave microwave injection

Abstract

Here, we report on modifications to the electron energy distribution function during X-mode microwave injection in argon and helium helicon plasmas. No electron heating is observed in argon helicon plasmas. Significant electron heating, ΔTe∼1 eV, is observed in helium plasmas. The heating is spatially localized to the upper hybrid resonance layer. Previously absent helium ion emission lines, from states over 50 eV above the helium ion ground state, are observed with the injection of X-mode microwaves.