Characterization of a Waveguide ECR Plasma Source

The design and preliminary testing of a waveguide electron cyclotron resonance (ECR) heated plasma source is presented in this paper. The design utilizes resonant absorption of traveling microwaves to heat the discharge, avoiding any lifetime constraints on the device due to barium depletion or ion bombardment in more conventional devices. Results from magnetostatic calculations are presented, which are used to design the magnetic field geometry with samarium cobalt permanent magnets. The results from microwave solver simulations used to finalize the waveguide design are presented. The source, which operates in the circular TE11 mode, produces a discharge through either ECR or upper hybrid heating, depending on the magnet geometry. Preliminary tests show that the self-starting source is capable of delivering 226 mA of current at an absorbed power level of 80 W and argon flow rate of 2.6 sccm. The strong magnetic field perpendicular to the desired direction of plasma flow confines the plasma quite well. However, it appears to be the limiting factor on the amount of extractable current along with the plasma density at the extraction electrode. Langmuir probe traces at the location of the extraction electrode suggest that the plasma density is highly peaked at low flow rates, while the electron temperature is nearly independent of flow rate over the gas flow range investigated.