Scaling laws for atomic and molecular hydrogen in a multicusp ion source

Abstract

We have determined scaling laws for the densities of atomic and molecular hydrogen in a discharge. For diagnosis we use a multiphoton-ionization technique. Both atoms and molecules are detected in their electronic ground state. The lowest three vibrational levels of the molecules, with vibrational quantum numbers v''=0, 1, and 2, are investigated separately. From the scaling laws for the v''=1 and 2 populations, we obtain experimental evidence that they are produced by low-energy-electron collisions with unexcited molecules, and are destroyed predominantly by collisions with other discharge-produced particles, presumably atoms and/or thermal electrons. Scaling laws concerning the atomic density are found to be compatible with production mainly via primary electron excitations of electronic ground-state molecules and destruction dominated by wall collisions.