Abstract
Time-resolved measurements of deposition in current tokamaks are crucial to gain a predictive understanding of deposition with a view to mitigating tritium retention and deposition on diagnostic mirrors expected in next-step devices. Two quartz crystal microbalances have been installed on NSTX at a location 0.77m outside the last closed flux surface. This configuration mimics a typical diagnostic window or mirror. The deposits were analyzed ex-situ and found to be dominantly carbon, oxygen, and deuterium. A rear facing quartz crystal recorded deposition of lower sticking probability molecules at 10% of the rate of the front facing one. Time resolved measurements over a 4-week period with 497 discharges, recorded 29.2 {micro}g/cm{sup 2} of deposition, however surprisingly, 15.9 {micro}g/cm{sup 2} of material loss occurred at 7 discharges. The net deposited mass of 13.3 {micro}g/cm{sup 2} matched the mass of 13.5 {micro}g/cm{sup 2} measured independently by ion beam analysis. Monte Carlo modeling suggests that transient processes are likely to dominate the deposition.
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