|approved||poster_final.pdf||2017-05-17 10:46:21||Matthew Beidler|
Author: Matthew T. Beidler
Requested Type: Poster
Submitted: 2017-03-15 12:26:36
Co-authors: J. D. Callen, C. C. Hegna, C. R. Sovinec, N. M. Ferraro
University of Wisconsin-Madison
517 ERB, 1500 Engineering Driv
Madison , WI 53706
United States of Ame
The nonlinear, extended-magnetohydrodynamic (MHD) code NIMROD is benchmarked with the theory of time-dependent forced magnetic reconnection (FMR) induced by small resonant fields in slab geometry  in the context of visco-resistive MHD modeling. Linear computations agree with time-asymptotic, linear theory of flow screening of externally-applied fields . The inclusion of flow in nonlinear computations can result in mode locking due to the balance between electromagnetic and viscous forces in the time-asymptotic state, which produces bifurcations from a high-slip to a low-slip state as the external field is slowly increased . We reproduce mode locking and unlocking transitions by employing time-dependent externally-applied magnetic fields. Mode locking and unlocking exhibit hysteresis and occur at different magnitudes of applied field. We establish how nonlinearly-determined flow screening of resonant field penetration is affected by the externally-applied field amplitude. These results emphasize that inclusion of nonlinear physics is essential for accurate prediction of field penetration in a flowing plasma. We explore FMR in cylindrical geometry by way of benchmarks between the NIMROD and M3D-C1 extended-MHD codes. Linear computational results of flow-scaling of field penetration display excellent agreement, and exhibit reasonable agreement with analytical predictions derived for an asymptotic dissipation regime . We also compare nonlinear computations to analytical predictions of quasilinear, time-asymptotic, force balance .
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Supported by DOE OFES grants DE-FG02-92ER54139, DE-FG02-86ER53218, DE-AC02-09CH11466, the SciDAC Center for Extended MHD Modeling, and the U.S. DOE FES Postdoctoral Research program administered by ORISE and managed by ORAU under DOE contract DE-SC0014664.