Stabilization of the microwave plasma facility (MPF) by a microwave isolator

The authors recently added a microwave isolator and a new tuner to the UTK Microwave Plasma Facility (MPF), an approximately 200 liter steady-state, uniform plasma generated by 2 kW of 2.45 GHz microwave power. Plasma ion implantation is accomplished by pulsed biasing of the sample to negative potentials greater than 15 kV, which accelerates ions and implants them to depths which provide beneficial effects for wear and corrosion resistance. The uniform steady state plasma, before the addition of the microwave isolator, had an electron number density of about 6 x 1016 electrons/m3 and an electron kinetic temperature of 16 eV. This plasma was nonresonant, in that it did not rely on the absorption at the ECR resonance in the containment volume to generate the plasma. The plasma was difficult to stabilize since the reflected power reacted with the magnetron source, changing its characteristics. The microwave isolator has successfully decoupled the reflected power from the load, thus facilitating the process of tuning the plasma. Additional tuning stubs in the microwave circuit have further enhanced the ease of tuning the plasma and minimizing the amount of reflected power. In this paper they report on the improvement in operation of the MPF; the improved ease of tuning; the stabilized profiles of electron number density of the plasma both in the axial and radial direction; and the effect of the isolator on the electron number density and kinetic temperature. They also will present photographs of the plasma during plasma ion implantation