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Gyrokinetic turbulence modeling of a high performance scenario in JT-60SA

Author
Abstract

Local gyrokinetic simulations are used to model turbulent transport for the first time in a representative high-performance plasma discharge projected for the new JT-60SA tokamak. The discharge features a double-null separatrix, 41 MW of combined Neutral Beam Heating (NBH) and Electron Cylotron Heating (ECH), and a high predicted ratio of the normalized plasma kinetic to magnetic pressure B. When considering input parameters computed from reduced transport models, gyrokinetic simulations predict a turbulent heat flux well below the injected 41 MW. Increasing the background gradients, on the other hand, can trigger a non-zonal transition (NZT), causing heat fluxes to no longer saturate. Furthermore, when considering fast ions in the simulations, a high-frequency mode is destabilized that substantially impacts the turbulence. The NZT is avoided by reducing the electron pressure by 10% below its nominal value, and the fast-ion resonance is removed by reducing the fast-ion temperature. The thus-obtained simulation features broadband frequency spectra and density and temperature fluctuation levels dn/n ≈ 1-2%, dT/T ≈ 1-6% that should be measurable with fluctuation diagnostics planned for JT-60SA. The temperature profile is fixed by the critical main-ion temperature gradient as a consequence of the high stiffness; heat fluxes increase by a factor of ten when increasing the main ion temperature gradient by 17%. Despite large gradients, it is demonstrated that, due to the large B, retaining compressional magnetic field fluctuations and in particular, the contribution of the pressure gradient in the vB drifts, is crucial to achieving non-zero heat fluxes.

Year of Publication
2024
Journal
Nuclear Fusion
Volume
64
Issue
2
Number of Pages
026005
DOI
10.1088/1741-4326/ad0c0a
PId
ca6631b4e8dfda41237ec2ab1d1da64a
Alternate Journal
Nucl. Fusion
Label
OA
Journal Article
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