Plans for Experimental Validation of GENE-Predicted Turbulence-Reduced HSX Configurations

The Helically Symmetric Experiment (HSX) has been shown to be dominated by anomalous transport, most likely density gradient-driven Trapped-Electron-Mode (TEM) turbulence [1]. Recent gyrokinetic studies using the GENE code have found promising coil-generated magnetic configurations with improved TEM stability [2]. Ongoing computational work also indicates certain configurations may have reduced nonlinear heat flux. Plans for testing these promising configurations are presented here. A set of planned experiments is laid out which include auxiliary coil current scans, profile matching, on and off axis heating, and working gas experiments. An array of diagnostic measurements will be used to discern possible changes in transport physics in these configurations as compared with the standard HSX configuration. The diagnostics and analysis methods discussed include reflectometry, ECE spectroscopy, CXRS, interferometry, and power balance. The goal of these experiments is to ascertain whether the GENE-predicted improvements in heat flux saturation and TEM stability are physically realizable, and validate the method of optimization that provided these configurations in the first place.

[1] B. J. Faber et al., Phys. Plasma 22, 072305 (2015)

[2] M. J. Gerard et al., Nucl. Fusion 63, 056004 (2023)