Characterization of a microwave generated plasma with varying fractional ionization on magnetic surfaces*

Understanding the transition region between fully ionized and neutral dominated plasma is important to the study of the magnetosphere/ionosphere as well as the solar corona/chromosphere transition regions of the earth and sun. We are exploring the use of the magnetic surfaces of a stellarator confinement device, the Compact Toroidal Hybrid, to contain plasmas with widely varying fractional ionization with the goal of studying those naturally occurring transitions. These plasmas are heated using ECRH at two fundamental cyclotron frequencies of 17.65GHz and 18GHz with up to 10kW of power. A radially scannable triple probe and optical diagnostics are used to characterize plasma parameters.  Results from a systematic study of varying ECRH input power and neutral gas fill pressure to access a range of plasma fractional ionization levels and electron temperatures will be presented.