The laser photodetachment technique in its combination with probe measurements is applied for the determination of the electronegativity and the concentration of the negative hydrogen ions in the expansion plasma volume of an inductively driven two-chamber plasma source. Both the implementation of the method and the obtained results are discussed in the study. The variations of the gas pressure and the applied rf power in the experiments are in the ranges p = (0.3–5) Pa and P = (200–700) W, respectively. The results for an almost constant—with the gas pressure—electronegativity and its increase with the applied power are in agreement with theoretical estimations. The obtained nonmonotonic variation of the concentration of the negative ions with increasing gas pressure correlates with the gas pressure dependence of the electron density in the expansion plasma region of the source.
Use of electrical measurements for non-invasive estimation of plasma electron density in the inductively coupled SPIDER ion source