Plasma surface interaction under the high ion temperature discharges in TRIAM-1M

Material exposure experiments were carried out in the superconducting high field tokamak TRIAM-1M using the surface probe system. TEM observation of the exposed specimens clearly showed the anisotropic radiation damage due to charge exchange (CX) hydrogen neutrals and the analysis of damage structure enabled to estimate the mean flux (from lower side; 4.2*10^17m^-2s^-1sr^-1). This anisotropy could be explained as the effect of grad-B drift. TEM observation also showed that the surface was covered with deposition consisted of fine crystals (~EDS analysis, only Mo (limiters and divertor plates material) and no stainless-steel composition; Fe, Cr, Ni (the vessel wall material) were detected in the deposition. This fact indicates that the vessel wall had been covered with Mo deposition in the long history. The amount of deposited Mo was estimated quantitatively and the distribution in the radial direction was discussed. The surface modification will change the initial hydrogen recycling property. It is especially important for long pulse discharges because the plasma density control is greatly influenced by recycled hydrogen. In addition, damage (melting) due to fast electrons was observed. This evidence indicates that intense heat load is possible in the SOL even during limiter discharges