Survivability of dust in tokamaks: Dust transport in the divertor sheath

The survivability of dust being transported in the magnetized sheath near the divertor plate of a tokamak and its impact on the desired balance of erosion and redeposition for a steady-state reactor are investigated. Two different divertor scenarios are considered. The first is characterized by an energy flux perpendicular to the plate q(0) similar or equal to 1 MW/m(2) typical of current short-pulse tokamaks. The second has q(0) similar or equal to 10MW/m(2) and is relevant to long-pulse machines like ITER or Demonstration Power Plant. It is shown that micrometer dust particles can survive rather easily near the plates of a divertor plasma with q(0) similar or equal to 1MW/m(2) because thermal radiation provides adequate cooling for the dust particle. On the other hand, the survivability of micrometer dust particles near the divertor plates is drastically reduced when q(0) similar or equal to 10MW/m(2). Micrometer dust particles redeposit their material non-locally, leading to a net poloidal mass migration across the divertor. Smaller particles (with radius similar to 0.1 mu m) cannot survive near the divertor and redeposit their material locally. Bigger particle (with radius similar to 10 mu m) can instead survive partially and move outside the divertor strike points, thus causing a net loss of divertor material to dust accumulation inside the chamber and some non-local redeposition. The implications of these results for ITER are discussed. (C) 2014 AIP Publishing LLC.