May 8-10

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Abstracts

Author: Valerie A Izzo
Requested Type: Poster
Submitted: 2023-03-23 19:41:23

Co-authors: D.B. Weisberg, C. Paz-Soldan

Contact Info:
Fiat Lux
425 W Beech St.
San Diego, CA   92101
USA

Abstract Text:
NIMROD modeling of the planned passively-driven runaway electron mitigation coil (REMC) for DIII-D [1] shows the important effect of the magnetic boundary conditions on the spectrum of the external fields and the coupling of the applied fields all the way to the magnetic axis. In the simulations, an impurity induced thermal quench (TQ) produces magnetic field stochastization all the way to the core, and the effect of the passive coil on the early phase of flux-surface re-healing is examined. Prior modeling of only the CQ phase with a perfectly conducting wall [2] found that the coil fields destroyed only the outer flux surfaces, with a good confinement region remaining in the core. The new simulations show that the coil fields can affect reformation even of the flux surfaces closest to the axis when a resistive wall boundary condition is used. In that case, both the poloidal and toroidal spectrum of modes broadens at the boundary when the applied fields are unfrozen from the walls, allowing the coil to maintain resonance over a wider range of safety factor profiles. A corresponding reduction in localized field amplitudes near the coil reduces RE strikes on the wall in the immediate vicinity of the coil. The simulations also show that the 3D coil fields produce an external distortion of the plasma shape, with the height of the separatrix varying by as much as 15 cm toroidally, corresponding to the varying vertical position of the coil along the inner wall.

[1] D.B. Weisberg , C. Paz-Soldan , Y.Q. Liu, A. Welander and C. Dunn, Nucl. Fusion 61 (2021) 106033
[2] V.A. Izzo, I. Pusztai, K. Särkimäki, A. Sundström, D.T. Garnier, D. Weisberg, R.A. Tinguely, C. Paz-Soldan, R.S. Granetz, & R. Sweeney, Nucl. Fusion 62 (2022) 096029.

Comments:
Not a special instruction, just a comment on the abstract submission web-form: I tried to use my institutional email (val@fiatlux.energy) and the web-form rejected it as an invalid email address.