Examination of argon metastable atom velocity distribution function close to a conducting wall

Abstract

The spatial evolution of the 1s5 metastable argon atom velocity distribution function is recorded in the sheath and pre-sheath regions of a metallic wall using laser induced fluorescence (LIF) spectroscopy. Metastable argon atom temperature and fluid velocity are computed from measured data. Owing to the loss of metastable argon atom after a collision with the surface, the atom temperature seemingly decreases and the velocity increases when approaching the wall. These artifacts are carefully examined and explained in terms of changes in the metastable argon atom distribution function. In addition, the atom nonelastic reflection coefficient is computed from the ratio of outward to inward atom flux to the surface. This study indicates less than 1% of metastable atoms survive a collision with the metallic wall.