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reusch_epr14_final.pdf2014-08-07 08:12:30Joshua Reusch

A Direct Comparison of Single-Fluid MHD Simulations to the MST RFP

Author: Joshua A Reusch
Requested Type: Consider for Invited
Submitted: 2014-05-30 10:44:14

Co-authors: J.K. Anderson, D.J. Den Hartog, C.B. Forest, C.M. Jacobson, K.J. McCollam, J.S. Sarff

Contact Info:
UW - Madison
1150 University Ave.
Madison, WI   53706
USA

Abstract Text:
In recent years, extensive nonlinear simulations of the Madison Symmetric Torus (MST) reversed-field pinch (RFP) have been performed in single-fluid, visco-resistive MHD at experimentally relevant Lundquist numbers (S≈4×10^6). Such high-S simulations are challenging because the RFP's low safety factor allows a large number of resonant magnetic perturbations to nonlinearly couple, strongly affecting the time evolution of the magnetic equilibrium. Qualitatively, the simulations (cylindrical, zero-β simulations performed with the DEBS code) now reproduce many features of the MST discharge with striking accuracy. In particular, the long-timescale evolution of the magnetic equilibrium is well reproduced, including the sharp, quasiperiodic bursts of MHD activity known as sawteeth. While these results suggest the simulations are doing a “good job” of reproducing the experiment, no comprehensive quantitative assessment has been attempted to date. We have now made a quantitative assessment of many parameters of interest for these high S simulations using several different validation metrics. These metrics have been applied to simulations using two different resistivity models. The two models yield similar results, but the metrics allow for quantitative assessment of their relative performance for each parameter. From this exercise we have gained insight into how agreement and disagreement between the simulated and measured data is represented by each metric, aiding in the selection of appropriate metrics to include in a single composite metric. We have also begun constructing such a metric, which reduces the set of validation metrics for each simulation to a zero-D quantity for straightforward comparison of the relative performance of many different simulations. This work is supported by the US DOE and the CMSO.

Characterization: 2.0

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Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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