Impact of selective ion transmission on measurement by retarding field analyzer

The impact of selective ion transmission on the use of retarding field analyzers (RFAs), which is attributed to the ion Larmor motion, was investigated. Depending on the ion Larmor radius and ion guiding center position, selective transmission limits the parallel and perpendicular ion velocities inside the RFA volume. The velocity limitation flattens I-V curve, leading to an overestimation of the parallel ion temperature. However, the overestimation can be reduced to an acceptable level using the slope in a large grid potential region. The influence of selective transmission depends on both parallel and perpendicular ion temperatures. This nature likely allows the simultaneous determination of two ion temperatures by the best fit of the experimental data, even from a single I-V curve. Applicability of this method was investigated using a radio frequency plasma.