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Author: Matthew T. Beidler
Requested Type: Poster
Submitted: 2016-02-29 11:50:35

Co-authors: J.D. Callen, C.C. Hegna, C.R. Sovinec, A.L. Becerra, E.C. Howell

Contact Info:
University of Wisconsin-Madison
1500 Engineering Drive
Madison, WI   53706

Abstract Text:
Edge-localized modes (ELMs) deposit large particle and heat fluxes to the diverter region in tokamaks, and are predicted to unfavorably scale up to ITER. However, it has been shown on multiple machines that ELMs can be mitigated or suppressed by externally applied resonant magnetic perturbations (RMPs) that modify the magnetic field at the top of the H-mode pedestal. The effects of RMPs can initiate a forced magnetic reconnection (FMR) process. In FMR, an external magnetic field directed normal to a tearing-stable rational surface penetrates the surrounding plasma and can drive reconnection; this generates a magnetic island in the vicinity of the rational surface. To gain insight into this process, we use the extended-MHD code NIMROD to study FMR in slab [1] and cylindrical [2] magnetic field geometries. By applying a static, spatially-varying magnetic field at the boundary of the simulation domain that induces a component normal to the rational surface for each geometry, we numerically verify the linear and nonlinear analytical predictions given in [1,2]. We also demonstrate progress towards verifying that the addition of flow parallel to the reconnecting component of the magnetic field leads to a screening of the boundary field, in contrast to the case with no equilibrium flow, which demonstrates a fully penetrated field state. The screening process results in a diminished magnetic island consistent with [2], and varies with resistivity, viscosity, and inertia. In particular, we focus on nonlinear simulations of the flow-screening process in a visco-resistive plasma, which is representative of the top of the H-mode pedestal during ELM suppression in current and future tokamak experiments.

[1] T.S. Hahm and R.M. Kulsrud, Phys. Fluids 28, 2412 (1985)
[2] R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)

Supported by OFES DoE grants DE-FG02-86ER53218, DE-FG02-92ER54139.

Please place next to J.D. Callen et al. poster on “Forced Magnetic Reconnection In Tokamak Plasmas"