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A local thermal equilibrium study of a hydrogen gas has been carried out for temperatures and densities relevant to the expected conditions in the Penning SAS source, which is a negative-ion source presently under investigation by AT-2 at Los Alamos National Laboratory. For the pure hydrogen mixture, it was found that the relative abundance of H/sup -/ ions peaks at about 10,000 K but is extremely low. The inclusion of cesium does improve the H/sup -/ abundance significantly only at low temperatures (less than or equal to5000 K), raising it to about several parts per million, which should be considered low in view of estimates from the sheath physics which is not based on the local thermodynamic equilibrium assumption. Incorporation of the enhancement of dissociative attachment from contributions by higher rotational-vibrational states associated with a nonthermal hot electron component has not been attempted, being an intrinsically nonthermal effect. The higher rotational-vibrational states themselves are, however, fully included.

Local thermodynamic equilibrium study of H/sup -/ abundance in negative-ion source discharges