Measurement of negative ion density in a magnetized sheet plasma by DC laser photodetachment method
A magnetized sheet plasma produced with the combination of a pair of Helmholtz coils and a pair of permanent magnets can create an ideal condition to produce the negative hydrogen ion (H–) by a volume production process. The H– density in a sheet plasma was measured by photodetachment current from H– upon irradiation of an 808 nm semiconductor laser. The maximum sensitivity of the photodetachment signal for the sheet plasma was about 0.4 μA/cm2W. The measured photodetachment current at the center of the plasma was one-third of that measured at 1 mm from the center. The photodetachment center showed a monotonic increase against increasing magnetic field up to 60 Gauss.