EROSION - REDEPOSITION AND IMPURITY TRANSPORT IN THE SCRAPE-OFF LAYER OF THE FT TOKAMAK
Impurity transport processes, particle and impurity fluxes in the scrape-off layer (SOL) of the FT machine have been studied by means of two graphite probes acting as catcher targets. Targets are analyzed after 217 deuterium FT discharges (68% flat top discharges, 32% disruption shots, and 1 runaway shot) using SEM, SAES, and SIMS surface techniques. SAES and SIMS analyses indicate that the main metallic impurities are Cr, Mn, Fe, and Ni. Weight loss measurements of the graphite probes evidence that the erosion of each sample is greater than the redeposition of the metallic film. Impurity fluxes due mainly to disruptions, runaway electrons, or PDC processes were observed to range from 6.5.10**15 to 1.2.10**16 atoms/cm**2 . discharge on the ion drift side, and from 7.3.10**15 to 1.1.10**16 atoms/cm**2 . discharge on the electron drift side, at an average distance of 21 cm from the center line of the plasma. The e-folding length lambda-imp of the SOL for the impurity flux was also estimated to lie in the range 9.8 < lambda-imp <or=12.5 cm.
Bibliographic Reference: 7TH INTERNATIONAL CONFERENCE ON PLASMA-SURFACE INTERACTIONS IN CONTROLLED FUSION DEVICES, PRINCETON (UK), MAY 5-9, 1986 PP. 21-33 WRITE TO SERVIZIO STUDI E DOCUMENTAZIONE - ENEA, CENTRO RICERCHE ENERGIA FRASCATI, C.P. 65 - 00044 FRASCATI, ROMA (ITALY), ME
Record Number: 1989125045000 / Last updated on: 1987-07-01
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