Electrostatic Dust Detection and Removal in Tokamaks

The inventory of in-vessel dust particles in next-step tokamaks will increase with the rise in stored energy and pulse duration. Dust levels will need to be measured and controlled for safety reasons and to avoid plasma contamination. A novel electrostatic dust detector has been developed with a sensitivity appropriate for the carbon dust levels expected in next-step devices.$^{23}$ Higher sensitivity is desired for real-time measurements in contemporary tokamaks that have less dust. We report on results from a larger area, more sensitive detector. A 2\textquotedblright~x 2\textquotedblright~circuit board has two interlocking combs of copper traces spaced by 25 microns and biased at 30-50 V. The carbon test dust is delivered to the circuit board by a mesh tray vibrated at 60 Hz. The impinging dust creates a short circuit and the resulting current pulse is recorded. We will present results on the dust detection sensitivity and dust removal efficiency of these new detectors in three environments: air, vacuum, and inert gas. \newline $^{2}$ C. Voinier \textit{et al.}, J. Nucl. Mater. 346 (2005) 266-271. \newline $^{3}$ C. Parker \textit{et al.}, PPPL Report, PPPL-4169.