Optimization of the extraction of H- ions in a magnetized sheet plasma

Abstract

A mass spectrometer is upgraded to compare the current intensity of the extracted H^- ions to the current intensity of the electrons straying and entering the aperture of the spectrometer. The negative ion source used in these experiments have been described in reference 1. A 180°-deflection mass spectrometer is used. Dependence of the H^- current on the bias to the plasma, electrode has been determined. Similarly the dependence of the H^- current on the mass spectrometer coil current was obtained. The electron current detected by tire mass spectrometer as a function of the B-field intensity is shown. This is done to obtain the ratio of the currents of the extracted H^- ions and the extracted electrons and thus obtain the ratio of the ion density to the electron density. Finally, the negative hydrogen ion to electron density ratio as a function of the bias to the plasma electrode for different field intensities were obtained. The ratio n_-/n_e, obtained was higher than results obtained from similar sources. A maximum H^- ion current is obtained when the mass spectrometer B-field is 691 G and when the bias to the plasma electrode is near the value of the plasma floating potential.