Negative hydrogen ions are extracted from a reflex-type sheet plasma. Electron density and temperature profiles are measured with changing the filling gas pressure, and they are optimized to the H- production at the optimum gas pressure. The optimum gas pressure is 5 mTorr for the discharge current Id =2 A. As the discharge current Id increases, H- current increases linearly corresponding to the density increase in the center region, but saturates above Id =40 A. The maximum extracted H- current density of 4 mA/cm2 is obtained at Id=100 A.
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