EFFECTS OF RAPIDLY DECAYING PLASMAS ON LANGMUIR PROBE MEASUREMENTS

Sheath motion, displacement current, and probe edge effects on tempora l Langmuir probe (LP) ion saturation current measurements are investig ated for a pulsed laser produced plasma during the period 100 ns-->100 0 ns after the turn on of the laser pulse. The plasma has a large volu me (hundreds of cm(3)) and a high initial plasma density (n(e)>10(13) cm(-3)). The sheath motion and edge effects are found to be very impor tant, but the displacement current is found to be very small. We prese nt both a quantitative correction for the effects of rapidly decaying plasmas on LP ion saturation current measurements and a validity condi tion for this method. The results are compared with the densities pred icted from electron saturation currents, and the former are less than or equal to 30% lower than the latter. The corrected probe measurement s are utilized to determine the plasma recombination coefficient. It i s found to be in good a,agreement with the results obtained by Stalder and Eckstrom [J. Appl. Phys. 72, 3917 (1992)] who utilized a microwav e method. (C) 1998 American Institute of Physics.