Electrostatic dust detection on remote surfaces

Abstract

The inventory of dust in next-step magnetic fusion devices will be regulated for safety reasons, however diagnostics to measure in-vessel dust are still in their infancy. Advances in dust particle detection on remote surfaces are reported. Grids of interlocking circuit traces with spacing in the range 125–25 μm were biased to 30 V. Impinging dust creates a short circuit and the resulting current pulse was recorded. The detector response was measured with particles scraped from a carbon fiber composite tile and sorted by size category. The finest 25 μm grid showed a sensitivity more than an order of magnitude higher than the 125 μm grid. The response to the finest particle categories (5–30 μm) was two orders of magnitude higher than the largest (125–250 μm) category. Longer duration current pulses were observed from the coarser particles. The results indicate a detection threshold for fine particles below 1 μg/cm 2.