A microwave discharge source operating at pressures of several atmospheres

The design of a microwave source in which a discharge is initiated by an electromagnetic surface wave at 2.45 GHz is described. A stable discharge was supported at a gas pressure p0 exceeding the atmospheric pressure in He, N2, and in H2-Ar, H2-He, and O2-He mixtures in a 2-mm inner diameter quartz tube with a 0.15-mm diameter nozzle at a 50- to 115-W microwave power. A degree of dissociation of up to 80% was reached for pure H2 at p0 = 6 Torr and a 6% mixture of H2 and He at p0 = 50 Torr. When p0 increases to 19 Torr for H2 and to 300 Torr for the mixture, the hydrogen-atom beam intensity, in spite of a decrease in the degree of dissociation, increases due to narrowing of the beam particle velocity distribution.