Abstract Details
Abstracts
Author: Benjamin J Faber
Requested Type: Consider for Invited
Submitted: 2025-02-21 17:35:41
Co-authors: M.J. Gerard, H.O.M. Hillebrecht, B. Geiger
Contact Info:
University of Wisconsin-Madison
1500 Engineering Dr
Madison, WI 53706
USA
Abstract Text:
Global gyrokinetic simulations with the GENE-3D code are applied to the realistic HSX plasmas for the first time.
Linear flux tube simulations have indicated that trapped-electron-mode (TEM) driven turbulence is likely the primary driver of turbulent transport in HSX, due to large electron-to-ion temperature ratios and electron pressure gradients from electron cyclotron resonance heating.
However, the low magnetic shear in HSX calls into question the validity of the flux tube approach as flux tube domains often have unphysically large radial box lengths.
Furthermore, due to the small plasma volume and large geometric variations, flux tube simulations are at the upper limit of validity of the gyrokientic ordering parameter.
Fully global gyrokinetic simulations using experimentally-measured plasma pressure profiles with the GENE-3D code nonetheless demonstrate good agreement with flux tube simulations.
Agreement is observed across of a range of turbulent statistics, including radial correlation lengths of fluctuating quantities and agreement in gyroBohm-normalized heat and particle fluxes.
Global simulations also confirm the observation of zonal-flow-like structures in the electrostatic potential.
A clear difference in turbulent dynamics across the plasma minor radius is observed when the instability drive changes nature from temperature gradient drive to density gradient drive, with stronger zonal flow signatures observed in the density-gradient-drive region.
Differences in confinement are also seen when the main ion species is varied from hydrogen to helium.
In particular, a stronger electromagnetic fluctuation, absent in the hydrogen simulations, is observed in helium simulations, matching a similar experimental observation of hydrogren and helium HSX plasmas.
This verifies the applicability of flux tube simulations as a fast analogue for transport modeling in HSX and as a tool for assessing gyrokinetic turbulence in optimized low-shear stellarators.
Characterization: 4.0
Comments: