Interpretation of ion velocity distributions measured with a retarding field energy analyzer (RFEA) in a inductively coupled helicon plasma

A Retarding Field Energy Analyzer (RFEA) with a grounded surface in a plasma will be surrounded by a sheath that distorts the ion distribution function (IDF) measured at the probe relative to the IDF in the plasma. We investigate this by comparing two simple 1D models to a 3D PIC simulation of an RFEA in a plasma with parameters similar to the Njord helicon device. In addition we have shown that the opening angle of the probe has an significant effect on the low energy part of the measured IDF.