Momentum losses by charge exchange with neutral particles in H-mode discharges at JET

TitleMomentum losses by charge exchange with neutral particles in H-mode discharges at JET
Publication TypeJournal Article
Year of Publication2011
AuthorsT.W Versloot, P.C de Vries, C. Giroud, M. Brix, M.G von Hellermann, P.J Lomas, D. Moulton, M.O Mullane, I.M Nunes, A. Salmi, T. Tala, I. Voitsekhovitch, K.D Zastrow
JournalPlasma Physics and Controlled Fusion
Volume53
Issue6
Number6
Pagination065017
Date PublishedJun
Type of ArticleArticle
ISBN Number0741-3335
KeywordsASDEX UPGRADE, density, DIII-D, EDGE, IONS, PLASMAS, THRESHOLD, TOKAMAK, TRANSPORT
Abstract

The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Gamma(0)/n(e) similar to 1.2ms(-1)) and maximum fuelled case (Gamma(0)/n(e) similar to 2.5ms(-1)). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a similar to 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral-ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10% of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.

DOI10.1088/0741-3335/53/6/065017
Division

FP

Department

PDG

PID

c1924357188fac45d3284683f43bc265

Alternate TitlePlasma Phys. Control. Fusion

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