Laser-Assisted Hμ Spectroscopy for Measurement of Negative Ion Density in a Hydrogen Plasma

AbstractA novel laser-assisted Hμ spectroscopy is proposed to measure negative ion density in a hydrogen plasma. The laser-induced photodetachment of negative ions leads to a decrease in Hμ intensity due to blocking of the mutual neutralization channel associated with generation of H (n=3) atoms. The relationship between the reduced Hμ intensity and the negative ion density is investigated experimentally and analytically. It is observed that the reduced Hμ intensity follows the trend in the negative ion density as a function of pressure, indicating that this spectroscopy holds promise for determining the negative ion density. In addition, a departure from linearity between the reduced Hμ intensity and the negative ion density is also analyzed because it can affect the quantitative determination of the negative ion density in the laser-assisted Hμ spectroscopy. The departure is found to be attributed to the change in the mutual neutralization reaction rates depending on plasma conditions.