Fast wave current drive in H mode plasmas on the DIII-D tokamak

Current driven by fast Alfven waves is measured in H mode and VH mode plasmas on the DIII-D tokamak for the first time. Analysis of the poloidal flux evolution shows that the fast wave current drive profile is centrally peaked but sometimes broader than theoretically expected. Although the measured...

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Bibliographic Details
Published in:Nuclear fusion 1999-10, Vol.39 (10), p.1421-1432
Main Authors: Petty, C.C, Baity, F.W, deGrassie, J.S, Forest, C.B, Luce, T.C, Mau, T.K, Murakami, M, Pinsker, R.I, Politzer, P.A, Porkolab, M, Prater, R
Format: Article
Language:English
Subjects:
Carrier concentration
Density (specific gravity)
Electric currents
Electromagnetic waves
Tokamak devices
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Summary:Current driven by fast Alfven waves is measured in H mode and VH mode plasmas on the DIII-D tokamak for the first time. Analysis of the poloidal flux evolution shows that the fast wave current drive profile is centrally peaked but sometimes broader than theoretically expected. Although the measured current drive efficiency is in agreement with theory for plasmas with infrequent ELMs, the current drive efficiency is an order of magnitude too low for plasmas with rapid ELMs. Power modulation experiments show that the reduction in current drive with increasing ELM frequency is due to a reduction in the fraction of centrally absorbed fast wave power. The absorption and current drive are weakest when the electron density outside the plasma separatrix is raised above the fast wave cut-off density by the ELMs, possibly allowing an edge loss mechanism to dissipate the fast wave power since the cut-off density is a barrier for fast waves leaving the plasma.
ISSN:0029-5515
1741-4326
DOI:10.1088/0029-5515/39/10/305