Theory Weekly Highlights for August 2015

August 28, 2015

The Neoclassical Ion-Electron Solver (NIES) code has been modified to read axisymmetric equilibria from the two-fluid extended magnetohydrodynamics (MHD) code M3D-C1. This allows for the calculation of stationary neoclassical distribution functions, and thus the conductivity, poloidal flows, and bootstrap currents, deep in the banana regime. Calculation of Sauter-like conductivity and bootstrap current coefficients has been done for a DIII-D equilibrium and shows excellent agreement with the Sauter values and previously published NIES results for realistic JSOLVER equilibria. This coupling between NIES and M3D-C1 will permit the investigation of a novel second-order Larmor radius effect present in up-down asymmetric equilibria that has been recently identified by J.J Ramos. Additional future work will involve modifying the closely related DK4D code to read the same M3D-C1 equilibria, allowing for the calculation of distribution functions, bootstrap currents, and other physical quantities of interest, at finite collisionality. Furthermore, these results will be coupled back into M3D-C1, providing a drift-kinetic closure for the MHD equations.

August 21, 2015

Support for Uncertainty Quantification (UQ) workflows has been added to OMFIT. The new capabilities are used in the EFIT module to produce Monte-Carlo variations of a nominal equilibrium within the uncertainty of the experimental data (variations of pressure, magnetic probes, flux loops, diamagnetic flux, F-coil, MSE, current). With the help of the new UQ tools within OMFIT, the resulting ensemble of equilibria can be analyzed to provide confidence level for any of the quantities of interest (e.g. pressure or q profile). Support for UQ analyses in OMFIT is generic and can be easily applied to existing OMFIT workflows.

August 14, 2015

Jeff Candy attended the 24th International Conference on the Numerical Simulation of Plasmas in Golden, Colorado, and gave a talk on “The Gaussian Radial Basis Function Method for Plasma Kinetic Theory”.

Dr. Defeng Kong, from ASIPP in Hefei, China, is visiting GA Theory for a month to collaborate on pedestal physics studies for EAST and CFETR using the ELITE code and EPED model.

August 07, 2015

Analysis of NIMROD simulations of massive gas injection (MGI) that include a pre-MGI plasma rotation ~10 kHz, reveal several key features that correspond closely to DIII-D observations. In particular, the radiated power versus time and toroidal angle shows that light, initially centered at the injection location (15⁰), begins rotating at a frequency just below 1kHz during the pre-thermal quench. The rotating pattern continues into the thermal quench, but the primary radiated power flash is approximately 180⁰ separated from the rotating structure. This is consistent with magnetics observations on DIII-D that the n=1 mode is born anti-aligned with the gas valve then rotates at a frequency just under 1kHz until the TQ. The final mode phase at the time of the TQ then determines the location of the radiated power peak. The rotating simulation also shows a shorter, higher amplitude radiated power flash compared with the non-rotating simulations, which is more consistent with DIII-D data. Finally, at 10kHz initial rotation, the dominant direction of impurity spreading reverses from the stationary case to correspond to the rotation direction, in contrast with results at lower rotation (~1kHz) reported in the May 15, 2015 highlight. These results may explain some apparent discrepancies in the rate of impurity spreading between DIII-D and the stationary simulations, and increases confidence in the model's ability to predict radiation asymmetry for mitigated ITER disruptions.

A new EFIT version “06/21/2015” with enhanced features was provided to NSTX-U.

These highlights are reports of research work in progress and are accordingly subject to change or modification