Temperature and relative density of atomic hydrogen in a multicusp H− volume source

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Abstract
The Balmer β and γ line shapes have been analyzed to determine the relative density and the temperature of hydrogen atoms in magnetic multicusp plasma generators. Results for a 90-V, 4–40-mTorr, 1–18-A conventional multicusp plasma generator and a 50-V, 4-mTorr, 1–15-A hybrid multicusp plasma generator are presented. The relative number density of hydrogen atoms increased smoothly with pressure and discharge current but never exceeded 10%. The absolute atomic number density in a 90-V 10-A discharge varied in proportion with pressure. The atomic temperature (in the 0.1–0.4-eV range) decreased with pressure and slowly increased with the discharge current. The role of atoms in the processes determining the H− temperature and the H2 vibrational and rotational temperatures is discussed. The results confirm that in multicusp negative-ion sources collisional excitation of ground state atoms and molecules by energetic electrons is the dominant process in Balmer-β and -γ light emission.