Sherwood 2015

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approvedsherwood_2015_final.pdf2015-01-19 15:59:59Nicholas Roberds

Simulation of a Disruption Using NIMROD

Author: Nicholas A Roberds
Requested Type: Poster Only
Submitted: 2015-01-19 15:57:18

Co-authors: J. Hebert, M. Cianciosa, L. Guazzotto, J.D. Hanson

Contact Info:
Auburn University
2045 Wire Rd. #85
Auburn, AL   36832

Abstract Text:
Low-q disruptions are seen in tokamaks when the edge q approaches 2, placing a limit on the maximum current. However in the Compact Toroidal Hybrid (CTH) device, a tokamak-stellarator hybrid, low q-disruptions do not occur until the edge q approaches 3/2. In these low-q runs, CTH is operating in a regime where most of the rotational transform is due to the plasma current, not the helical stellarator field.
Previously, numerical simulations have described tokamak low-q disruptions as a non-linear coupling of tearing modes [1]. First, the unstable m=2, n=1 tearing mode grows, flattening the current and pressure profiles within the 2/1 island. This change to the equilibrium is such that it destabilizes the m=3, n=2 mode. Higher m modes, each with a rational surface closer to the magnetic axis, are successively destabilized in this way so that the disruption manifests as a front that advances inwards rapidly. This front breaks up good flux surfaces and leaves behind a wake of stochastic magnetic fields. The heat is then lost due to rapid parallel heat transport along field lines.
We wish to explore a CTH low-q disruption using NIMROD [2] for numerical simulation. Presently, a simulation of a low-q disruption in a tokamak having a CTH wall is shown and the results are compared to previous studies on tokamak low-q disruptions by simulation. This will serve as a starting point for future work, where we will explore the effect of the CTH helical field on the evolution of low-q disruptions.

[1] A. Bondeson, Nucl. Fusion 26, 929 (1986)
[2] C.R. Sovinec, A.H. Glasser, T.A. Gianakon, D.C. Barnes et al, J. Comput. Phys. 195, 355 (2004).

This material is based upon work supported by Auburn University and the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG02-03ER54692.


March 16-18, 2015
The Courant Institute, New York University