CROSS-FIELD DIFFUSION-COEFFICIENTS MEASURED IN THE JET EDGE FOR CONSTANT PLASMA CURRENT

Recently, JET has been operated with beryllium limiters. This permits a much wider range of operating densities (ne) for a given plasma current Ip than was possible with carbon limiters. The edge value of the cross-field diffusion coefficient Dperpendicular toSOL has been deduced from Langmuir probe measurements of the density scrape-off thickness in the SOL, lambda n. It is thus possible to establish whether Dperpendicular to depends on plasma parameters, independent of any dependence on Ip, q or B. It was found that the experimental results for 3 MA, 2.3 T ohmically heated discharges are in fairly close agreement with the Bohm value i.e. linearly dependent on edge temperature. The edge temperatures and densities are closely coupled, however, and the data can also be reasonably fitted by Dperpendicular toSOL varies as nedge-12/.