Theory Weekly Highlights for January 2017

January 27, 2017

Sonic toroidal rotation (including full centrifugal effects) is being added to CGYRO to study the influence of heavy impurities on gyrokinetic stability and transport. Sonic toroidal rotation, which arises in tokamaks from torque due to neutral beam injection, produces a strong centrifugal force that pushes the ions toroidally outward, causing them to redistribute non-uniformly around a flux surface. As a result of quasi-neutrality, a poloidally-varying electrostatic potential is generated to balance the density asymmetry. In CGYRO, the poloidal variation of the induced electrostatic poential is computed from the quasi-neutrality relation, which is a nonlinear equation for multi-species plasmas, using Newton's method, as in NEO. The Coriolis drift and the centrifugal drift have been implemented and benchmarked with the GKW code for simple test cases. Both terms are found to have a stabilizing influence on ITG modes and TEMs. Implementation and benchmarking of the centrifugal trapping terms is in progress.

January 20, 2017

Using NIMROD code modifications to allow larger number of runaway electron orbits to be followed, a simulation of a rapid-shutdown in DIII-D by shell-pellet injection was repeated to examine runaway electron losses. The modeling had previously shown that the outermost flux-surfaces remain intact through much of the thermal quench following deposition of the impurities directly into the core. Nevertheless, when the flux surfaces finally break up, the modeling shows that nearly all the confined runaway electrons are lost in short time. With over 20k runaway electrons orbit tracked, less than 0.05% remained confined past the end of the thermal quench. This scenario in which seed runaways are dumped to the divertor without accompanying large heat loads is a promising result for disruption mitigation.

January 13, 2017

As reported in the May 27 and Oct 7 2016 highlights (see Theory Weekly Highlights for October 2016 and Theory Weekly Highlights for May 2016), the TGLF reduced model computes growth rates for Alfven eigenmodes (AEs) driven by energetic particles (EPs) that are in good agreement with GYRO. A new code, TGLFEP, developed to quickly compute the profile for the local critical EP beta given the thermal plasma profiles is now available. TGLFEP should prove useful in the development of a practical critical EP gradient transport model. This work was described in a recent APS-DPP invited talk by Ron Waltz.

January 06, 2017

A new OMFIT module was developed that allows for automated running of the M3D-C1 extended-magnetohydrodynamics code. The module was developed with the help of the OMFIT code-camp (See Highlight from November 18 2016 at Theory Weekly Highlights for November 2016). Through an intuitive graphical user interface, the user is able to select equilibrium files, pre-process them according to M3D-C1 needs, and then select a variety of linear calculations to perform. OMFIT then launches the autoC1 python script on a specified server and the desired calculations are performed without additional user input. This capability will allow for automated stability and 3D response calculations for equilibria created within OMFIT and for simplified analysis of M3D-C1 results with other codes (e.g., TRIP3D, EMC3-EIRENE). It will also facilitate parameter scans required for uncertainty quantification and verification & validation. Finally, this automated M3D-C1 capability may allow for between-shot linear stability and/or response calculations to help guide DIII-D experiments once between-shot kinetic EFIT is available.

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