Author: Nicholas A. Roberds
Requested Type: Poster
Submitted: 2016-02-15 13:13:30
Co-authors: J. D. Hanson, C. R. Sovinec, D. A. Maurer and L. Guazzotto
644 W. Magnolia Ave., Apt. D38
Auburn, AL 36832
Sawtoothing is sometimes seen in the Compact Toroidal Hybrid (CTH) on SXR signals. The CTH is a small stellarator-tokamak hybrid with a five field period, L=2 stellarator magnet coil. A clear correlation between the sawtooth period and the strength of the helical stellarator field is observed experimentally. Many previous studies have investigated the effect of two dimensional profile shaping on the properties of sawteeth [1,2,3]. Also, experience from past numerical studies of sawtoothing suggests that a resistive MHD model with a highly anisotropic heat flux is adequate for quantitatively recovering many properties of sawteeth in smaller tokamaks with relatively low temperatures . Here, we study the effect of three dimensional shaping from the helical stellarator field on sawteeth by evolving extended resistive MHD equations with NIMROD  for a sequence of configurations with increasing helical field strength. A correlation between sawtooth period and helical field strength is seen in the results. Careful attention to numerical convergence was required to obtain the results and these considerations are relevant to simulations of other phenomena in non-axisymmetric devices such as perturbed tokamaks or stellarators.
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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.