Toroidal and poloidal asymmetry in carbon deposition on gaps of plasma facing tiles

Abstract

In order to characterize and mitigate the carbon deposition in gaps between plasma facing tiles, a simulation calculation is performed for transport of hydrocarbons in the plasma density and potential distribution of the gap calculated using 2D gyro-kinetic model. The plasma distribution is strongly asymmetric between toroidal and poloidal gaps, depending the magnetic angle and the gap width. Ionized hydrocarbons are deposited in the gap edge where the toroidal and poloidal asymmetry is found, whereas neutral species are reflected repeatedly at the side surface so that they are deposited deeply in the gap and are found at the bottom. For low temperatures (<10eV) the asymmetry is small due to dominant contribution of the neutral species to the deposition. Small tilt of the tile surface hides the poloidal gap from direct access of both plasma hydrogen ions and returning hydrocarbons, so that the deposition on the plasma-open side is suppressed.