Speeding up charge exchange recombination spectroscopy analysis in support of NERSC/DIII-D realtime workflow

TL;DR

This paper describes the optimization of charge exchange recombination spectroscopy analysis to enable real-time plasma diagnostics at DIII-D, reducing analysis time from 15 minutes to under a minute through parallelization.

Contribution

The authors restructured the CERFIT analysis code to leverage parallel computing with Slurm, achieving a 20x speedup for real-time plasma diagnostics.

Findings

Analysis time reduced from 15 minutes to 51 seconds

Parallelization with Slurm enabled real-time workflow support

Significant time savings for plasma diagnostics and equilibrium reconstruction

Abstract

We report optimization work made in support of the development of a realtime Superfacility workflow between DIII-D and NERSC. At DIII-D, the ion properties measured by charge exchange recombination (CER) spectroscopy are required inputs for a Superfacility realtime workflow that computes the full plasma kinetic equilibrium. In this workflow, minutes matter since the results must be ready during the brief 10-15 minute pause between plasma discharges. Prior to this work, a sample CERFIT analysis took approximately 15 minutes. Because the problem consists of many calculations that can be done independently, we were able to restructure the CERFIT code to leverage this parallelism with Slurm job arrays. We reduced the runtime to approximately 51 seconds -- a speedup of roughly 20x, saving valuable time for both the scientists interested in the CER results and also for the larger equilibrium reconstruction workflow.