Abstract

The 1989 JET experimental campaign assessed the properties of beryllium as a plasma-facing material. This campaign had three phases: (i) an all graphite phase to recommission the tokamak, (ii) a phase with beryllium evaporation on graphite to isolate the effect of oxygen gettering and (iii) a beryllium limiter phase. Beryllium evaporation removed oxygen from the plasma and reduced carbon concentrations by a factor of two. Strong deuteron pumping was obtained which resulted in a significant, long-term improvement in density control and eliminated the deconditioning effect of disruptions. The use of beryllium limiters reduced the plasma radiation, increased the density limit, reduced the incidence of disruptions and enhanced the deuteron pumping. In the beryllium phases impurity influxes were lower during ICRH heating which permitted the first ICRH-only H-modes. The deuteron pumping allowed heavy gas fuelling to be used to reduce impurity levels of limiter and X-point plasmas.

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