Controlling surface dust in a tokamak

Methods to measure the inventory of dust particles and to remove dust if it approaches safety limits will be required in next-step tokamaks. A novel electrostatic dust detector, based on a fine grid of interlocking circuit traces, biased to 30 or 50 V, has been developed for the detection of dust on remote surfaces in air and vacuum environments. Impinging dust particles are detected when they create a short circuit between the traces, however this short circuit is temporary suggesting the device may be useful for the removal of dust from specific areas. The fate of the dust particles has been tracked by measurements of mass gain/loss. Heating by the current pulse caused up to 90% of the particles to be ejected from the grid or vaporized, the removal efficiency depending on the experimental geometry. We also report the first attempt at real-time dust detection in NSTX.