IMPURITY TRANSPORT STUDIES IN WENDELSTEIN VII-A
The transport behaviour of impurities in typical net current free neutral beam heated plasmas in W VII-A has been studied for both oxygen as the main plasma impurity and A1 as a tracer impurity. Comparison with a 1D impurity transport and radiation code shows that the main features of the impurity transport are consistent with neoclassical predictions. Some details, however, seem to require additional anomalous transport during short time intervals. This may be due to a distortion of the magnetic configuration around resonant magnetic surfaces induced either by pressure driven currents or by modulations of the helical field. An oxygen influx from the walls at least of the same order of magnitude as the oxygen influx from the neutral injection (about 3x10**18 s**-1) has to be assumed in order to explain the measured central oxygen radiation. Discharges with cold gas feed, which lead to broad plasma density profiles, indicate a substantial reduction of the central impurity radiation. Also the calculated central impurity density is considerably smaller in this case. No conclusive evidence for a different impurity transport behaviour for co- and counter neutral beam injection has been found. This is probably due to the almost perpendicular neutral injection.
Bibliographic Reference: 5TH INTERNATIONAL WORKSHOP ON STELLARATORS, SCHLOSS RINGBERG, BAVARIA (GERMANY), SEPT. 24-28, 1984 VOL. I, PP. 259-277, EUR 9618 EN (1985) FS, VOL. I AND VOL. II, 787 P., BFR 3500 (BOTH VOLUMES), EUROFFICE, LUXEMBOURG, POB 1003
Record Number: 1989124120300 / Last updated on: 1987-01-01
Available languages: en