Intrinsic momentum transport in up-down asymmetric tokamaks

Journal article

Recent work demonstrated that breaking the up-down symmetry of tokamak flux surfaces removes a constraint that limits intrinsic momentum transport, and hence toroidal rotation, to be small. We show, through MHD analysis, that ellipticity is most effective at introducing up-down asymmetry throughout the plasma. We detail an extension to GS2, a local $\delta f$ gyrokinetic code that self-consistently calculates momentum transport, to permit up-down asymmetric configurations. Tokamaks with tilted elliptical poloidal cross-sections were simulated to determine nonlinear momentum transport. The results, which are consistent with experiment in magnitude, suggest that a toroidal velocity gradient, $(\partial u_{\zeta i} / \partial \rho) / v_{th i}$, of 5% of the temperature gradient, $(\partial T_{i} / \partial \rho) / T_{i}$, is sustainable. Here $v_{th i}$ is the ion thermal speed, $u_{\zeta i}$ is the ion toroidal mean flow, $\rho$ is the minor radial coordinate normalized to the tokamak minor radius, and $T_{i}$ is the ion temperature. Since other intrinsic momentum transport mechanisms scale poorly to larger machines, these results indicate that up-down asymmetry is the most feasible method to generate the current experimentally-measured rotation levels in reactor-sized devices.

Authors: Ball, J; Parra, F; Barnes, M; Dorland, W; Hammett, G

• Publication status: Published
• Publisher: Institute of Physics Publishing
• Journal: et al. Plasma Phys. Control. Fusion
• Volume: 56
• Issue: 9
• Pages: 095014
• Publication date: 2014-03-13
• DOI: 10.1088/0741-3335/56/9/095014
• EISSN: 1361-6587
• ISSN: 0741-3335
• Language: English
• Keywords: physics.plasm-ph