Two dimensional simulations of the vibrational state distributions in low pressure hydrogen plasmas with an isothermal neutral gas and gas temperature gradients*

Low pressure hydrogen plasmas are of interest in fundamental plasma phenomena and applications including surface processing and negative ion beams. As negative ions form in the plasma volume through dissociative attachment of vibrationally excited hydrogen molecules, it is important to understand their response to gas temperature gradients, known to form at high power densities. In this study, two dimensional fluid-kinetic simulations using the Hybrid Plasma Equipment Model, including a new reaction set that accounts for gas temperature dependencies in determining heavy particle reaction rates with all of the vibrational levels of the ground electronic state, are used to study the influence of these temperature gradients. The results demonstrate that the incorporation of spatially resolved gas temperatures has a significant impact on the distribution of atomic hydrogen and the vibrational states, but has a relatively smaller impact on the negative ions. These results are important for future studies of low pressure hydrogen plasmas in technological plasma sources that generate spatial gas temperature gradients.