Electrostatic dust detection on remote surfaces

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/cm2.