NET PLASMA FACING MATERIALS BEHAVIOUR UNDER EROSION AND REDEPOSITION REGIMES IN PISCES
First wall and divertor target plate materials envisaged for the Next European Torus (NET) have been investigated in the PISCES-A plasma facility at UCLA. Alternative materials included in the present study include SiC-impregnated carbon, 2-D carbon weave with/without CVD-SiC coatings and isotropic graphite (CL5890PT). These samples have been exposed to continuous hydrogen or deuterium plasma bombardment under various conditions, such as ion bombardment energy - from a range where material eroded from the surface freely escapes the plasma (erosion regime) to conditions where electron impact ionisation is important and redeposition of eroded material occurs. The NET erosion yield for SiC-impregnated carbon is a factor of 3 below those of isotropic carbon and 2D weave materials where the plasma bombardment is in the erosion mode. A further factor of 2 reduction in net erosion yield is found when plasma conditions correspond to the redeposition regime. Post-exposure analysis by AES is used to determine compositional changes on the surface. For SiC-impregnated carbon, the initial atomic composition ratio is 4-6 in terms of C/Si atomic ratio. It is found that at 350 C, carbon is preferentially removed by hydrocarbon formation until chemical composition of the surface comes to an equilibrium. The equilibrium surface composition is reached at a fluence around 6 x 1.0 E21 ions/cm2, and corresponding to a C/Si ratio of 1.5. This compositional ratio is then maintained out to a fluence of 3.6 x 1.0 E21 ions/cm2, the highest fluence studied in this experiment.
Bibliographic Reference: REPORT: RT/FUS/88/26 EN (1988) 23 PP. AVAILABLE FROM SERVIZIO STUDI E DOCUMENTAZIONE, ENEA, CENTRO RICERCHE ENERGIA FRASCATI, C.P. 65 - 00044 FRASCATI, ROMA (IT)
Record Number: 1989128045500 / Last updated on: 1990-11-09
Available languages: en