Iterative Calculation of Plasma Density from a Cylindrical Probe Characteristic

A novel method is proposed for treating cylindrical probe characteristics to obtain plasma density. The method consists of exponential extrapolation of the transitional part of the I-V curve to the floating potential for the ion saturation current, other than the existing theories which use the ion branch, and an iterative sheath thickness correction procedure for improved accuracy. The method was tested by treating Langmuir probe I-V characteristics obtained from inductively coupled Ar discharges at various pressures, and comparing the present results with those deduced by existing theories. It was shown that the plasma densities obtained by the present method are in good agreement with those calculated by the Allen-Boyd-Reynolds (ABR) theory, suggesting the effectiveness of the proposed method. Without need of manual setting and adjustment of fitting parameters, the method may be suitable for automatic and real time processing of probe characteristics.