STUDY OF ION HEATING AND COOLING IN A NITROGEN PLASMA BY LASER-INDUCED FLUORESCENCE

Laser-induced fluorescence from a low-pressure, magnetized, radio-frequency-generated plasma was observed for the first negative (1N) system of N2+ (B2SIGMA(u)+ -X2SIGMA(g)+). A tunable dye laser was used to excite the 1N system in the (0-0) and (0-1) transitions; individual rotational lines in the R branch were seen up to N=30, with the spin-slit doublets resolved for N>16. Rotational ion temperature derived from the distribution of lines in the R branch is compared against translational temperature found from the linewidth. The heating of the plasma ions during the discharge and their cooling in the afterglow is observed by both rotational and translational temperatures. Results show that, for the present apparatus, the translational temperature is higher than the rotational temperature by a factor of approximately 10.