Transport of neutral atomic hydrogen in a supersonic plasma jet.

Abstract

ABSTRACT: In a supersonically expanding plasma jet created by a cascaded arc from an Ar‐H2 mixture, spatially resolved densities, temperatures, and velocities of ground state atomic hydrogen are obtained by applying two‐photon excitation laser induced fluorescence. The axial velocity profile of H indicates a strong coupling between Ar and H atoms and it can be fully described in terms of a supersonic expansion model. However, whereas H atoms temperature profiles along the jet centerline clearly reveal the presence of a normal shock front, the atomic hydrogen density profiles do not. From the absence of a density jump across the normal shock front, it is conclude that the atomic hydrogen flux in the axial direction is not conserved. There are several indications that the coupling between H and Ar atoms is lost in the course of the expansion and that hydrogen atoms can escape the supersonic domain by a scattering process due to their large mean free path.