Effects of ripple-induced ion thermal transport on H-mode plasma performance

A recent series of dimensionless pedestal identity experiments at JET and JT-60U failed to produce a match in the dimensional pedestal parameters and edge-localized mode (ELM) frequency despite a good match in the main dimensionless plasma parameters. This paper describes the progress made in unders...

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Bibliographic Details
Published in:Plasma physics and controlled fusion 2007-03, Vol.49 (3), p.273-295
Main Authors: Lönnroth, J-S, Parail, V, Hynönen, V, Johnson, T, Kiviniemi, T, Oyama, N, Beurskens, M, Howell, D, Saibene, G, de Vries, P, Hatae, T, Kamada, Y, Konovalov, S, Loarte, A, Shinohara, K, Tobita, K, Urano, H
Format: Article
Language:English
Subjects:
barrier
edge-localized modes
global confinement
jet plasmas
jt-60u
physics
rotation
temperature
tokamaks
toroidal field ripple
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Summary:A recent series of dimensionless pedestal identity experiments at JET and JT-60U failed to produce a match in the dimensional pedestal parameters and edge-localized mode (ELM) frequency despite a good match in the main dimensionless plasma parameters. This paper describes the progress made in understanding these experimental results. First, it is investigated whether differences in the magnetohydrodynamic stability of the pedestal, including those potentially arising from the 10% difference in the aspect ratio between the two tokamaks, can explain the results. The potential effects of differences in plasma rotation between the two machines are also examined. Given the result that these mechanisms fail to explain the experimental observations and the fact that JT-60U features considerably stronger toroidal magnetic field ripple than JET, the bulk of the paper, however, discusses the effects of ripple losses. The analysis shows that ripple losses of thermal ions can affect H-mode plasma performance very sensitively. Orbit-following simulations indicate that losses due to diffusive transport give rise to a wide radial distribution of enhanced ion thermal transport, whereas non-diffusive losses have a very edge-localized distribution. In predictive transport simulations with an energy sink term in the continuity equation for the ion pressure representing non-diffusive losses, reduced performance as well as an increase in the ELM
ISSN:0741-3335
1361-6587
1361-6587
DOI:10.1088/0741-3335/49/3/007