He metastable density in a double layer formed by a diameter discontinuityin a positive column - art. no. 036403

The population density profile of triplet metastable He (2 S-3(1)) is measu red in the multiple space-charge (double) layer formed at an abrupt transit ion of the tube diameter in a positive column discharge. The double layer i s formed at the transition from a 2.6 cm diameter to a 0.6 cm diameter tube in a static pressure discharge. The line integrated He 2 S-3(1) population density profile in the double-layer region is determined by diode-laser ab sorption. The triplet metastable density profiles are measured with dischar ge currents of 1, 2, and 5 mA at 1 Torr pressure for both polarity conditio ns: (a) when the cathode end of the discharge is in the large diameter tube and (b) when the anode end of the discharge is in the large diameter tube. The diode-laser absorption profiles show enhanced production of triplet me tastable He 2 S-3(1) in the double-layer region as compared to the unpertur bed positive column (0.6 cm. diameter) with the magnitude being strongly de pendent on the discharge polarity.