High-impedance capacitive divider probe for potential measurements in plasmas

Abstract

It is often desirable, though difficult, to measure electric potential changes within a plasma, including variations due to waves and fluctuations. For a broad range of plasma parameters ac floating potential measurements may be made using the high input impedance probe described in this paper. A capacitive divider with an active buffer circuit is incorporated, such that a 50-Ω line can be driven with a 60-dB dynamic range and 100-MHz bandwidth. Details of the electronic circuit, mechanical construction, and calibration of the probe are given, together with a discussion of the parameter range over which successful measurements may be made.