Simulations of Temperature-Gradient-Driven Trapped Electron Modes on HSX

The ongoing upgrade to the HSX stellarator at University of Wisconsin-Madison will provide access to higher core electron temperatures and larger electron temperature gradients. The inherent geometric properties of HSX combined with strong electron heating will likely destabilize temperature-gradient-driven trapped electron modes (TEM). Flux-tube gyrokinetic simulations have been performed using the GENE code to study microturbulence characteristics at the larger temperature gradients and temperature ratios. A notable feature of the nonlinear simulations are distinct, long wavelength electrostatic potential structures. These structures show strong similarities with structures observed previously in density-gradient-driven TEM simulations for HSX [1].

The HSX upgrade will also provide new diagnostic capabilities, opening up new opportunities for turbulence validation studies. In particular, a new correlated electron cyclotron emission (CECE) diagnostic will be installed to study electron temperature fluctuations. The application of a CECE synthetic diagnostic to the simulation data will be presented.

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