Interpretation and implementation of an ion sensitive probe as a plasma potential diagnostic on Alcator C-Mod

R. Ochoukov, D.G. Whyte, B. Lipschultz, B. Labombard, S. Wukitch

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An ion sensitive probe (ISP) is developed as a robust diagnostic for measuring plasma potentials (Φ ) in magnetized plasmas of Alcator C-Mod. The ISP relies on the large difference between the ion and electron gyro-radii (ρ /ρ ∼ 60) to reduce electron collection at a collector recessed at a distance ∼ρ behind a separately biased wall. We develop a new ISP method based on voltage sweeping to measure Φ that is independent of the precise position and shape of the collector: Φ is found to be the wall voltage when net current to the collector vanishes during an increasing voltage sweep. We have designed and installed an ISP to study Φ and radio frequency (RF) sheath rectification on Alcator C-Mod. Preliminary results show that the ISP is a viable plasma potential diagnostic in Alcator C-Mod plasmas and Φ measurements are in good agreement with independent results obtained with an emissive probe.
Original languageEnglish
JournalJournal of Nuclear Materials
Issue number1 SUPPL
Publication statusPublished - 1 Aug 2011

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