Runaway electron (RE) losses during DIII-D rapid shutdown simulations with NIMROD have been compared for a variety of injection scenarios. For the same equilibrium, edge localized “Massive Gas Injection-like” (MGI) injection more thoroughly deconfines REs during the thermal quench than more uniform “pellet-like” injection. Toroidally uniform and toroidally localized MGI injection on the low-field-size show about the same RE behavior during the thermal quench (TQ), although the TQ happens earlier when the source is localized. For high-field-side injection, a significant fraction of the REs are deconfined just prior to (instead of during) the TQ, due to pre-TQ MHD modes that appear to produce RE losses without increasing radial heat transport enough to trigger a TQ. The reason for this difference will be studied in further simulations.
A new wiki page (https://fusion.gat.com/theory/Shortfall) has been created to coordinate current efforts to understand the systematic under prediction of transport and turbulence levels in the near-edge region (ρ >= 0.7) of DIII-D L-modes by both gyrofluid and gyrokinetic models. While results reported in Rhodes et al. [Nucl. Fusion 51 063022 (2011)] showed that transport predictions by TGLF, GYRO, and GEM all systematically under predict transport at ρ=0.75 in a well-diagnosed L-mode discharge, new simulations performed by the GENE code appear to reproduce the transport levels within experimental uncertainties. Because GYRO and GENE solve similar sets of equations, and have been shown to predict similar results in other studies, a new effort in the ITPA transport and confinement working group to perform detailed cross-comparisons of linear and nonlinear predictions for this discharge between multiple codes (including GYRO and GENE) has begun. In order to facilitate these comparisons and to encourage additional researchers and modelers to participate in this effort, the equilibrium profiles and magnetic geometry data (both Miller parameterizations and EFIT gfile) have been made publicly available on the wiki page, as well as the results of GYRO linear convergence and physics studies. The wiki page will be updated with results from additional codes as they become available. Contributions from additional codes or models are encouraged, along with the use of this profile data for other benchmarking studies.
A new 3D local analytic equilibrium solver is being developed for use with the neoclassical code NEO to explore the effects of non-axisymmetry on the transport. The solver is based on the formalism developed by C. Hegna (UWM), which is analogous to a 3D extension of the Miller formalism for shaped axisymmetric equilibria. Unlike a global equilibrium solver, this method allows for systematic studies of the effects of 3D flux-surface shaping parameters. A local 3D equilibrium is determined by constructing a magnetic coordinate mapping on a magnetic surface, which is consistent with the MHD equilibrium equations. Parameterizations based on a model consisting of a 2D axisymmetric component and a small non-axisymmteric perturbation are being considered. As a first result, a solution for a circular plasma with a ripple-like single toroidal Fourier harmonic perturbation has been obtained. Extensions to more general geometry are in progress.
These highlights are reports of research work in progress and are accordingly subject to change or modification