Interpretation and implementation of an ion sensitive probe as a plasma potential diagnostic

Abstract

An ion sensitive probe (ISP) is developed as a robust diagnostic for measuring plasma potentials (Φ[subscript P]) in magnetized plasmas. The ISP relies on the large difference between the ion and electron gyroradii (ρ[subscript i]/ρ[subscript e] ∼ 60) to reduce the electron collection at a collector recessed behind a separately biased wall distance ∼ ρ[subscript i]. We develop a new ISP method to measure the plasma potential that is independent of the precise position and shape of the collector. Φ[subscript P] is found as the wall potential when charged current to the probe collector vanishes during the voltage sweep. The plasma potentials obtained from the ISP match Φ[subscript P] measured with an emissive probe over a wide range of plasma conditions in a small magnetized plasma.