[Show abstract][Hide abstract] ABSTRACT: In view of the recent interest in high Z metals as plasma facing materials, high heat load experiments by irradiation of electron beam were performed on CVD tungsten coated molybdenum samples in order to prove the suitability and the load limit of such coating materials. Measurements were made with respect to heat load properties, surface modification and structure change of cross section of the samples. These results indicate that the thermal and adhesion properties between the substrate and coating were good under high heat load (peak temperature was 2500$^\circ$C). It was also shown that enbrittlement by recrystallization was suppressed very much in the high purity CVD tungsten.
[Show abstract][Hide abstract] ABSTRACT: We have also been developing a plasma-wall interaction (PWI) simulator of which plasma source is a steady-state RF helicon wave plasma supply to demonstrate in situ and real-time measurement and to study PWI phenomena. A helical antenna is surrounding a cylindrical quartz tube of which outer diameter is ～5 cm. The antenna is connected to an RF power supply of which power is up to 5kW through a matching box. A set of two coils produces an axial magnetic field of 0.05T at the plasma center. At present, the electron density at the plasma center is up to ～3 x 10^18 m^(-3) and electron temperature is up to ～10eV. Rather high plasma flux density of ～4 x 10^22 m^(-2) s^(-1) to the substrate has been obtained. 64
[Show abstract][Hide abstract] ABSTRACT: 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.