BERYLLIUM PLASMA-FACING COMPONENTS - JET EXPERIENCE

JET has accumulated practical experience of plasma operation in both l imiter and divertor configurations using massive beryllium plasma-faci ng components. These latter have shown evidence, even after a very sho rt operational phase, for localised melting of the beryllium surface. Sustained melting results in substantial transport of the liquid beryl lium metal; there is, however, no evidence for low cycle termal fatigu e under this extreme environment. Design has proceeded by thermal test ing of prototypes with analysis used for interpretation only. For flux densities less than or equal to 5 MW m(-2), T surface less than or eq ual to 1000 degrees C, typically 200 pulses of 6-8 s can be sustained with plastic deformation and no surface fatigue cracking. The latter i s seen for more extreme conditions, i.e. flux densities in excess of 1 4 MW m(-2), pulse lengths less than or equal to 0.5 a surface temperat ure >700 degrees C. Failure of thin cladding of beryllium to heat sink s, which tends to occur along the beryllium to substrate interface, wa s insufficient to produce fatigue effects in the bulk beryllium materi al, at fluxes less than or equal to 10 MW m(-2). (C) 1997 Jet Joint Un dertaking. Published by Elsevier Science S.A.