Erosion and Deposition, and Their Influences on Plasma Behavior (Material Transport in Tokamak)

Very high photon and particle fluxes to plasma-facing surfaces (PFS) in a fusion reactor cause materials’ erosion. The eroded materials which are mostly neutral particles enter into boundary plasma. Subsequently, they are ionized and gyrated along magnetic field lines. Since in the boundary plasma, the magnetic field lines attach to PFS with tiny contact angles, most of the gyrated ions return to the surface to make deposited layers close to the eroded location. While the direct long-range transfer of the eroded materials does not likely occur. However, repetitive processes of erosion and deposition transport the eroded materials in long distance. In present divertor tokamaks, the inner first wall and the outer divertor are mostly net eroded, while the inner divertor net deposited. The outer first wall is either eroded or deposited depending on location. This chapter focuses on erosion, deposition, and transport of eroded materials in tokamaks with separation of carbon wall and metallic walls.