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Author: Isabel Krebs
Requested Type: Poster
Submitted: 2018-03-01 09:08:20

Co-authors: K. Bunkers, S.C. Jardin, N.M. Ferraro, L.L. Lao, C.R. Sovinec

Contact Info:
Princeton Plasma Physics Laboratory
P.O. Box 451
Princeton, NJ   08543-0

Abstract Text:
As part of the effort to develop predictive capabilities for tokamak disruption modeling with the 3D nonlinear MHD code M3D-C^1, we are carrying out a detailed benchmark activity with the 3D nonlinear MHD code NIMROD and are validating the simulation results against experimental data on Vertical Displacement Events (VDEs) in DIII-D.
The benchmark with NIMROD is based on an NSTX VDE case and uses a rectangular 2D resistive wall model. Linear M3D-C^1 simulations have been performed where the values of the wall resistivity and the temperature at the wall have been varied. The dependency of the linear growth rate of the VDE on the wall resistivity approaches a linear relation for small values of the wall resistivity. When the wall resistivity reaches values comparable to the resistivity in the open field line region, stabilizing response currents in this region take over the role of determining the VDE growth. The results are compared to the results of linear NIMROD simulations as well as to the initial phase of 2D nonlinear M3D-C^1 simulations. A benchmark of 2D and 3D nonlinear simulations is underway.
For the validation of M3D-C^1 simulation results against experimental data, a DIII-D discharge is chosen during which the injection of an impurity pellet initiates a VDE. The 2D resistive wall is based on a simplified model of the DIII-D first wall. 3D nonlinear simulations are prepared by performing a set of 2D nonlinear scoping simulations. The time trace of the position of the magnetic axis and flux loop signals in the 2D nonlinear simulations are compared to the experimental data. We examine the influence of the scrape-off layer width and temperature on the evolution of the VDE. Its width is self-consistently determined by the chosen heat diffusion anisotropy. For wider scrape-off layers, the larger temperatures cause the VDE to be slowed down by response currents in the open field line region.
This work is supported by the US DoE through the CTTS SciDAC program.