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approvedabstract_draft.pdf2016-02-12 11:32:26Eric Howell


Author: Eric C Howell
Requested Type: Poster
Submitted: 2016-02-12 11:31:27

Co-authors: C.R. Sovinec

Contact Info:
University of Wisconsin-Madison
2334 Chalet Gardens Road Apt.
Fitchburg, WI   53711
United States

Abstract Text:
The nonlinear evolution of the 1/1 mode is responsible for sawtooth activity in tokamaks. Nonlinear simulations are one tool used to study the onset, evolution, and saturation of the sawtooth. Comprehensive simulations of the sawtooth requires the accurate modeling of a number of non-ideal effects such as two-fluid and energetic particle effects. Here we focus of the two-fluid effects, which modify the stability of the 1/1 internal kink mode in multiple ways. Two-fluid effects introduce drifts, which reduce the growth rate and can stabilize the kink. Two-fluid effects also allow the electron and ion dynamics to decouple, allowing for fast reconnection. This increases the linear growth rate of internal kink.
We present the results of a two-fluid verification exercise using the NIMROD code [Sovinec and King, JCP 229, 5803]. Linear calculations of the 1/1 kink are performed in cylindrical screw-pinch equilibria. The linear growth rates are compared to the analytic theory of Zakahrov and Rodgers, PFB 4, 3285 (ZR). In cases without a pressure gradient, the numerical solution agrees with the analytic theory to within 5%. Results are also shown for cases with a finite pressure gradient.
Growth rates from analytic theory are computed with a shooting code that matches the solution of the ZR inner layer equation to the ideal outer-layer solution. The code is needed to calculate the growth rate at moderate ion sound gyro-radius where the ZR dispersion relation, valid for asymptotically large ion sound gyro-radius, is not appropriate.

*Work Supported by the US DoE grant DE-FC02-08ER54974.