NUKLEONIKA 2006, 51(1):29-35

In this paper we analyze the possibility to use the reflex discharge plasma as a volume source of negative hydrogen ions. The basic internal parameters like the temperature T_e and the density ne of the electrons, the density n_i of the positive hydrogen ions, the density n_- of the negative hydrogen ions, and the negative ion fraction n_-/n_e are measured and discussed. The operating conditions are optimized within the pressure range 0.1-10 Pa, the discharge power 20-140 watt, and the magnetic field 0-150 gauss. The experiment shows that the enhanced magnetic ionization is the most effective within the pressure range from 0.7 to 4.0 Pa. When p » 1 Pa the cold electron temperature T_e is 0.77 eV, the cold electron density ne is 4.2 ´ 10¹⁸ m^-3 and the negative ion density n_- is as high as 0.8 ´ 10¹⁷ m^-3.
The negative ion fraction n_-/n_e increases from 1.4% for p = 0.1 Pa to almost 2.2% within the pressure range 1-4 Pa. The positive ion density scales with the power, while the negative ion density and the negative ion fraction seems to saturate at higher power levels.