BEHAVIOR OF BORON-CARBIDE MATERIALS IN TEXTOR AND UNDER ELECTRON-BEAMIRRADIATION

Boron-carbon materials have been exposed to high heat fluxes in the TE XTOR tokamak and in the JUDITH electron beam facility. The materials w ere a B4C Coat Mix bulk material, a conversion-type B4C coating, and a plasma-sprayed B4C coating on graphite EK98. The boron-carbide Coat M ix limiter showed, due to the low thermal conductivity of 11 W/mK, sur face melting already at a heat flux of about 1.5 kW/cm(2) after 0.4 s. Both in the tokamak experiments and the electron beam tests the surfa ce temperature stayed close to the melting temperature under continued heating. The conversion coated limiter and specimens had a very irreg ular coating thickness and surface structure. At heat fluxes of 2.6 kW /cm(2) melting of the coating was reached after 0.5 s. The thermal beh aviour and evaporation of impurities into the plasma were comparable t o the Coat Mix limiter but shifted to higher heat fluxes. Both limiter s fractured under the applied heat loads. The plasma sprayed coating s howed early melting of the coating and agglomeration of the molten car bide to droplets on the graphite.