LANGMUIR PROBE DETERMINATION OF CHARGED-PARTICLE NUMBER DENSITY IN A FLOWING AFTERGLOW PLASMA

Experimental study of the electron and ion density determined by Langm uir probe is presented. The probe data have been obtained on FALP appa ratus for electron (and ion) number densities ranging from 10(12) m(-3 ) to 10(16) m(-3), at electron temperatures equal to room temperature and also roughly ten times higher and at neutral pressures from 60 Pa to 150 Pa. The number densities of electrons for all measured probe da ta have been deduced from the electron current to the probe at the spa ce potential and also by means of OML method from the electron current measured for positive probe with respect to the space potential. In t he paper it is shown that in the flowing afterglow plasma the values o f the electron density determined according both methods are in a good agreement and it is possible to take them as the reference number den sity for comparison with apparent ion densities obtained from the ion current. The number densities obtained from the ion currents in the io n accelerating region (negative probe with respect to the space potent ial) according to different applicable probe theories have been compar ed with reference value. It is found that the best agreement between t he number densities evaluated from the electron current and from the i on current gives the theory of ion collection by TICHY et al. [16], wh ich takes into account the collisions of ions with neutrals in the spa ce charge sheath around the probe provided that the conditions corresp ond to the OML regime.