HYDROGEN AND IMPURITY FLUXES IN THE SCRAPE OF LAYER OF THE TOKAMAK-DE-VARENNES

Hydrogen and impurities were collected in the scrape off layer by means of retractable Be probes: facing the plasma, or facing the ion or electron drift direction. A first set of probes was exposed to a variety of plasma conditions, a second set to 17 well-controlled discharges, with a TiC test limiter in use, and a third set was subjected to 88 well-controlled discharges with the usual graphite limiters only. These samples were analyzed by use of AES, RBS, PIXE and ERD E X B. H, C, O and metal fluxes are typically 7 X 10(18), 4 X 10(19), 2 X 10(19) and 2 X 10(18) m-2 s-1, the relative quantities being different than those measured in the plasma, suggesting a more efficient shielding for C. Depth profiles of H, O and metals are presented and show the effect of co-deposition. From the H depth profile, an average central ion temperature of almost-equal-to 625 eV has been estimated.