SCRAPE-OFF LAYER PARAMETERS IN JET WITH BERYLLIUM LIMITERS

Scaling of edge particle flux and temperature with central density in JET has been studied in ohmic and auxiliary heated beryllium limiter discharges, using Langmuir probes in the edge. Data has been obtained over a much wider density range than previously, and it is found that flux density scales almost linearly with central density. The edge temperature, on the other hand, is almost constant at low densities, but falls rapidly when gas puffing is used in the edge to achieve high densities. A global power balance assuming T(i) = T(c) suggests a shortfall in power to the edge, particularly at low densities, suggesting T(i) > T(e). The consequence of high T(i) on limiter sputtering is considered.