Progress in reducing ICRF-specific impurity release in ASDEX upgrade and JET. (August 2017)

• Record Type: Journal Article
• Authors: Bobkov, V.; Aguiam, D.; Baruzzo, M.; Borodin, D.; Borodkina, I.; Brezinsek, S.; Coffey, I.; Colas, L.; Czarnecka, A.; Delabie, E.; Dumortier, P.; Durodie, F.; Dux, R.; Faugel, H.; Fünfgelder, H.; Giroud, C.; Goniche, M.; Hobirk, J.; Herrmann, A.; Jacquot, J.; Jacquet, Ph.; Kallenbach, A.; Krivska, A.; Klepper, C.C.; Lerche, E.; Menmuir, S.; Milanesio, D.; Maggiora, R.; Monakhov, I.; Nave, F.; Neu, R.; Noterdaeme, J.-M.; Ochoukov, R.; Pütterich, Th.; Reinke, M.; Tuccilo, A.; Tudisco, O.; Van Eester, D.; Wang, Y.; Yang, Q.; Zhang, W.;
• Is Part Of: Nuclear materials and energy. Volume 12(2017)
• Page Start: 1194
• Page End: 1198
• Publication Date: 2017-08
• Subjects: ICRF -- RF sheath -- Three-strap -- 3-strap -- ASDEX Upgrade -- JET -- ILW -- A2 antenna -- ILA -- Sputtering; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2016.10.026
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: ICRF antenna design and tuning in ASDEX Upgrade has a major influence on W release. 3-strap antenna with W-coated limiters has reduced RF image currents and W sputtering. ITER-like antenna in JET-ILW produces less W than A2 antenna. Role of SOL impurity transport modifications by convective cells in JET-ILW is small. Abstract: Use of new 3-strap ICRF antennas with all-tungsten (W) limiters in ASDEX Upgrade results in a reduction of the W sources at the antenna limiters and of the W content in the confined plasma by at least a factor of 2 compared to the W-limiter 2-strap antennas used in the past. The reduction is observed with a broad range of plasma shapes. In multiple locations of antenna frame, the limiter W source has a minimum when RF image currents are decreased by cancellation of the RF current contributions of the central and the outer straps. In JET with ITER-like wall, ITER-like antenna produces about 20% less of main chamber radiation and of W content compared to the old A2 antennas. However the effect of the A2 antennas on W content is scattered depending on which antennas are powered. Experiments in JET with trace nitrogen (N2 ) injection show that a presence of active ICRF antenna close to the midplane injection valve has little effect on the core N content, both in dipole and in -90° phasing. This indicates that the effect of ICRF on impurity transport across the scape-off-layer is small in JET compared to the dominant effect on impurity sources leading to increased impurity levels during ICRF operation.