Neutral Resonant Ionization by Excited States in Optically Thick Plasmas

Ionization from surfaces of low work function explains many properties of both sputter sources of heavy anions and H$^{-}$ from RF plasma sources for heating magnetically confined plasmas. Surface ionization fails to fully account for intensities and operational peculiarities of either type of ion source, however. A blue plasma above cesium-sputtered material is well associated with intense stable anion beams used in accelerator mass spectrometry (AMS). A theory of neutral resonant ionization within this excited Cs plasma was developed [1] to explain a lack of isotopic fractionation seen in low energy AMS [2]. A similar theory of resonant ionization in hydrogen plasma is possible in which H(2s) atoms, sustained by the optical density of hydrogen for Lyman $\alpha $ radiation, have a path to gas phase production of H$^{-}$(1s$^{2})$ at high rates. The theory depends at present on data from multiple decades of unrelated experiments. Implications of the theory are used to suggest supportive or discrediting experiments.\\[4pt] [1] J.S. Vogel AIP Conf. Proc. 1515: 89 (2013).\\[0pt] [2] J.S. Vogel, et al. NIM B294: 340 (2013).