Pulse-by-pulse Measurements of Dynamic Retention and Deposition in NSTXI
Authors: C.H. Skinner, H.W. Kugel, A.L. Roquemore, R. Maingi, and W.R. Wampler
Date of PPPL Report: June 2006
Submitted to: Journal of Nuclear Materials
Presented at the Seventeenth International Conference on Plasma Surface Interaction in Controlled Fusion Devices (PSI-17), 22 - 26 May 2006, Hefei Anhui, China.
Three quartz crystal microbalances have been deployed in NSTX to measure deposition/erosion in plasma-shadowed areas at the upper & lower divertor and outboard mid-plane. These show a complex pattern of material gain and loss. At the time of a plasma discharge a transient increase in mass of order ∼0.1 μg cm-2 is observed that decays in the interpulse period to a level either higher, lower or similar to that prior to the discharge. The first discharge of the day always shows a long term step-up in mass. Some correlations of mass gain with plasma duration, stored energy, and change in the plasma shape are observed. Following a day's plasma operations, a slow decay in mass is observed. The results are interpreted in terms of dynamic retention and erosion/deposition.