음이온이 전기 탐침 특성에 미치는 영향

Abstract

Absolute density of negative ions is measured by an electric probe in the MAP-II (Material and Plasma, B=200G) plasmas using a new method without measuring the sheath potential, sheath velocity, temperatures of positive and negative ions, and effective masses of positive ions when there are negative ions among normal positive ion-electron plasma, which are given or assumed traditionally. This new probe method is to be verified by comparing probe data with those by the laser photo-detachment method. This measurement is based upon an approximate analytic formula, which is derived using the measured data of ion and electron saturation currents and electron temperature by assuming the linear dependence of the small change of negative ion densities upon small change of the pressure or flow rate of the added gases for the generation of negative ions. The linearity between the negative ions and the positive ions generated by the added gases is also assumed. With the measured Ⅰ-Ⅴ characteristics over three different pressures of mixed gases for the generation of negative ions, the whole spectrum of negative ion density variations can be deduced by this three-point linearity. Comparison of probe results with those by laser photo-detachment shows the applicability of this new probe method, although the assumptions of small variation of relative sheath factor and effective masses are to be mitigated for the detailed future analysis.