Experimental Study of Energy Confinement as a Function of Magnetic Well in HSX

The Helically Symmetric eXperiment (HSX) is an optimized stellarator that has demonstrated excellent neoclassical transport properties [1]. However, strong anomalous electron heat fluxes have been observed in the outer plasma region (r/a $>$ 0.3), likely due to density gradient driven Trapped-Electron-Mode (TEM) turbulence [2]. This work explores how changing the magnetic field geometry between the standard configuration and a configuration with an enhanced magnetic well (Well configuration) affects energy transport and TEM-driven turbulence in HSX. The stored energy is compared between the two magnetic geometries. A power balance analysis with uncertainty propagation is carried out for both configurations to obtain experimental heat fluxes to compare with nonlinear GENE simulations. Previous results for the standard configuration of HSX suggest good agreement between GENE-simulated and experimental heat fluxes [3]. Moreover, GENE simulations for the Well configuration will be presented here.

[1] J. M. Canik et al., Phys. Rev. Lett. 98, 085002 (2007)

[2] B. J. Faber et al., Phys. Plasmas 22, 072305 (2015)

[3] J. C. Smoniewski, PhD. thesis, UW-Madison (2021)