Coupled BOUT++ Simulations of ELM–Detachment Interactions in the DIII-D Tokamak

Detached divertor operation is essential for managing heat flux in future high-power tokamaks, but large edge-localized modes (ELMs) can penetrate detached plasmas and compromise material integrity. We present a two-stage simulation framework using BOUT++ to investigate ELM–detachment interactions in a DIII-D QCE-like discharge. First, a 2D axisymmetric steady-state solution is computed using the BOUT++/Hermes-3 fluid model, incorporating impurity radiation, ionization, recombination, recycling, and neutral transport. Cross-field transport coefficients are tuned to match upstream experimental profiles, and fixed-fraction impurity radiation (C, Ne, Ar) is applied to achieve detachment. This solution then serves as the background for 3D nonlinear simulations using the BOUT++/6-field model to resolve ELM-driven turbulence and transient heat and particle fluxes. Solver performance for the 2D transport simulations was improved through hypre preconditioning and timestep control, yielding converged results in a few hours on 10 CPUs. Radiation had minimal effect on upstream turbulence at ELM time scales, underscoring the time-scale separation between ELM dynamics and background transport. These simulations offer insights into ELM-induced reattachment and divertor design optimization.

This work was performed under the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 and was supported by the SciDAC ABOUND Project, SCW1832.