ARGON-HYDROGEN PLASMA-JET INVESTIGATED BY ACTIVE AND PASSIVE SPECTROSCOPIC MEANS

A supersonically expanding argon cascaded arc plasma, with different a mounts of hydrogen added (0, 0.7, and 1.4 vol % H-2), was studied usin g Thomson-Rayleigh scattering and optical emission spectroscopy. With hydrogen added, the electron density profile as a function of the dist ance from the onset of the expansion shows a large extra ionization lo ss (compared to the pure argon case), especially after the stationary shock front. This anomalous loss of ionization is attributed to molecu lar processes, such as associative charge transfer between Ar+ and H-2 , and dissociative recombination of the resulting ArH+ molecular ion. Spatially resolved emission spectroscopy shows that in the expansion t he radial hydrogen emission profiles are broader than the argon profil es. The addition of hydrogen appears to change the characteristic shoc k behavior of pure argon. For both the argon and the hydrogen system i t is shown that the uppermost levels are in Saha equilibrium with thei r adjacent continuum. The measurements are in agreement with the view that association of hydrogen atoms at the vessel walls results in a re entry flow of hydrogen molecules in the plasma beam.