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Electromagnetic stabilization of tokamak microturbulence in a high- β regime

Author
Abstract

The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low- β JET L-mode discharge illustrates the relation between ITG stabilization and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high- β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high- β generalization of comparable observations found at low- β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

Year of Publication
2015
Journal
Plasma Physics and Controlled Fusion
Volume
57
Issue
1
Number of Pages
014032
DOI
10.1088/0741-3335/57/1/014032
PId
e0af60be4a46d18811b729f6beb4c203
Alternate Journal
Plasma Phys. Control. Fusion
Label
OA
Attachment
Journal Article
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