Characteristics of Floating Potential in Negative Ion Plasma

We proposed the floating potential method to estimate the negative ion density in a negative ion plasma. The floating potential in a negative ion double plasma was examined as a function of negative ion concentration and compared with the theoretical value calculated from the sheath equation including negative ions. Here, the negative ion plasma was produced by introducing SF6 gas into a Xe (Ar) double plasma. The negative ion density mormalized to the ion density was estimated from the reduction of the electron saturation current. It was found that the observed floating potential agree with the theoretical values qualitatively.