Abstract
We develop a new procedure that combines the kinetic orbit runaway electron code (KORC) and the NIMROD extended-magnetohydrodynamic code to simulate runaway electrons (REs) in the post-disruption plateau. KORC integrates guiding-center orbits, with a barycentric-based binary search strategy providing initial guesses for the Newton-Raphson logical-to-physical coordinate inversion, ensuring reliable particle-to-mesh mapping in NIMROD, whose fields remain static for the present study. Samples are drawn in accord with experimental parallel current profiles of RE beams during the plateau phase. Deposition in NIMROD is verified through comparison with a Python-based finite-element code that ensures periodicity in the poloidal direction and continuity at the magnetic axis. Accurate representation of near-axis fields requires finer mesh resolution to prevent under- and overshoots in current density from orbit inaccuracies. Yet, at a fixed particle count, increasing mesh resolution amplifies statistical noise in the deposited fields. An orbit-averaging method accumulates partial current deposits over multiple kinetic steps and reduces the statistical noise with little added computational cost. By coupling kinetic routines from KORC directly into the NIMROD codebase, these developments lay essential groundwork for future self-consistent KORC-NIMROD coupling.
| Original language | English |
|---|---|
| Article number | 083908 |
| Journal | Physics of Plasmas |
| Volume | 32 |
| Issue number | 8 |
| DOIs | |
| State | Published - Aug 1 2025 |
Funding
This work uses the DIII-D National Fusion Facility, a DOE Office of Science user facility (Award No. DE-FC02-04ER54698). This manuscript has been authored in part by UT-Battelle, LLC (Contract No. DE-AC05-00OR22725) with the U.S. Department of Energy (DOE). The U.S. government retains and the publisher, by accepting the work for publication, acknowledges that the U.S. government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the submitted manuscript version of this work, or allow others to do so, for U.S. government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). We thank Dr. E. C. Howell for discussions on constructing NIMROD equilibrium files from EFIT files, and initial assistance with code compilation. Dr. V. Izzo for sharing an initial particle data file and discussing the original implementation of particle advancement in NIMROD. Dr. C. C. Kim for early discussions on the original δ f PIC implementation in NIMROD. This research used resources of the Experimental Computing Laboratory (ExCL) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy (Contract No. DE-AC05-00OR22725). This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated (Contract No. DE-AC02-05CH11231).