A COMPARISON OF LIFETIMES OF BERYLLIUM, CARBON, MOLYBDENUM AND TUNGSTEN AS DIVERTOR ARMOR MATERIALS

An assessment of lifetime as a function of plasma temperature was made for the plasma-facing materials, Be, C, Mo and W. This analysis was based on the erosion by D/T neutrals and by D+/T+ ions. A Maxwellian energy distribution was applied for the impinging neutral particles, whilst the energy distribution of the impinging ions, a Maxwellian shifted by sheath potentials, was used to calculate the erosion. For carbon material, the analysis was made for the two cases: (a) with chemical erosion by forming hydrocarbon species and (b) neglecting chemical erosion. This study was performed for divertor relevant conditions: high flux density > 10(19) cm-2 s-1 and low plasma temperature < 50 eV. The results show that at plasma temperatures between 2 and 10 eV, the erosion of C (no chemical erosion) is about factor of 10 to 1000 smaller than that of Be. The C erosion (including chemical erosion) is of the same order of magnitude as that of Be. The lifetimes of Be, C, Mo, and W as well as the limitation of operation temperatures were compared and the implications discussed.