Structural response of tungsten and molybdenum to high heat fluxes

Refractory metals like tungsten and molybdenum are regarded as candidate materials for divertor plate applications in fusion devices of the next generation. During operation these materials would supposedly be subjected to severe thermal shocks in the course of plasma disruptions. In order to determine the cracking and melting behaviour of tungsten and molybdenum high heat flux experiments were carried out by use of the JT-60 Neutral Beam Injection Test Stand. Material samples were subjected to hydrogen beam pulses with power densities of 82 and 200 MW/m2 and pulse lengths in the range of 45 to 200 ms. After the experiments the tungsten samples showed crack formation already at the lowest heat loads but the material has a very high threshold for melting which was reached at a pulse of 200 MW/m2 for 85 ms. Molybdenum did not show obvious crack formation but has a considerably lower melting threshold than tungsten. (author). 8 refs.; 5 figs.; 1 tab