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Author: Zz S Riford
Requested Type: Poster
Submitted: 2016-02-15 11:09:58

Co-authors: C.R.Sovinec, J.B.O’Bryan

Contact Info:
University of Wisconsin
241 Langdon St, APT 201
Madison, Wisconsin   53703
United States

Abstract Text:
Non-inductive start-up of toroidal fusion devices, especially spherical tokamaks, is an important area of research for the future of economic fusion power. The evolution and relaxation of the flux ropes formed during non-inductive start-up of the Pegasus Toroidal Experiment have previously been simulated using nonlinear MHD and two-fluid models in the NIMROD code [1]. The formation, evolution, and relaxation of a current rope from one injector was studied and shown to have good agreement with similar experiments in key areas. Most critically, axisymmetric rings are formed by the merging of adjacent current windings and closed flux surfaces form as the plasma relaxes after the injector is shut off. Reexamining the simulations, we find the tokamak-like profile exists in toroidally averaged current profiles prior to shut-off. Recent simulations help investigate a discrepancy in predicted and observed temperatures during non-inductive start-up. Viscous heating with a simplified and with a full Braginskii viscosity model, which was developed since the original simulations, is applied. We continue this work in parallel with experimental research done or planned on the Pegasus device. Recent results and plans for future research and experiments on non-inductive start-up of spherical devices will be presented.

[1] J. B. O'Bryan, C. R. Sovinec, and T. M Bird, "Simulation of Current-Filament Dynamics and Relaxation in the Pegasus Spherical Tokamak," Physics of Plasmas 19, 080701 (2012).