Physics:
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Abstract
Mass spectrometry is a useful diagnostic technique for monitoring plasma species and plasma-surface interactions. In order to maximize tie sensitivity of measurements of hydrogen-fueled fusion plasmas or hyrjrogen-based discharge cleaning ana etching plasmas, the ion sources of mass spectrometers are operated at or near the high pressure limit of 10 Torr do" Pa), such high ambient pressures of hydrogen give rise to high background levels of residual gases such as HjO, CO, and CH 4 , due to surface reactions on the ion source electrodes. For a commonly used ion source configuration, the residual gas production is a linear function of the ambient K2 pressure. Hydrogen conditioning can reduce the absolute residual gas levels. Steady-state residual gas production is observed in a conditioned ion source, which is related to a balance of diffusion and sorption on the electrode surfaces.