Measurements of spatial structures of different discharge modes in a helicon source

Abstract

This paper reports on two-dimensional measurements of plasma parameters and magnetic eigenmode profiles in capacitive, inductive and helicon wave sustained discharge modes of a helicon source with high spatial resolution. It is demonstrated that plasma densities ranging over four orders of magnitude can be achieved. The plasma profiles of the capacitive and inductive discharges are completely consistent with the accepted discharge models. The magnetic eigenmode structure in the helicon mode shows great differences in the mode number and axial wavelength compared to the capacitively coupled discharge. In particular, multiple reflections of the obliquely propagating helicon wave fronts at the plasma boundaries are observed in the helicon wave sustained plasma. Moreover, the consistent connection of plasma parameters with discharge parameters via the helicon wave dispersion is demonstrated with varying magnetic field and for various discharge power levels.