Measurement of negative ion density in a magnetized sheet plasma by DC laser photodetachment method

Abstract

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 (Hâ ^–â ) by a volume production process. The H^–â â  density in a sheet plasma was measured by photodetachment current from Hâ ^–â Â 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.