Noble gas enrichment studies at JET

Adequate helium exhaust has been achieved in reactor-relevant ELMy H-mode p lasmas in JET performed in the MKII AP and MKII GB divertor geometry. The d ivertor-characteristic quantities of noble gas compression and enrichment h ave been experimentally inferred from Charge Exchange Recombination Spectro scopy measurements in the core plasma, and from spectroscopic analysis of a Penning gauge discharge in the exhaust gas. The retention of helium was fo und to be satisfactory for a next-step device, with enrichment factors exce eding 0.1. The helium enrichment decreases with increasing core plasma dens ity, while the neon enrichment has the opposite behaviour, Analytic and num erical analyses of these plasmas using the divertor impurity code package D IVIMP/NIMBUS support the explanation that the enrichment of noble gases dep ends significantly on the penetration depth of the impurity neutrals with r espect to the fuel atoms. Changes of the divertor plasma configuration and divertor geometry have no effect on the enrichment. (C) 2001 Published by E lsevier Science B.V.