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Recent Results from the HSX Stellarator

Author: Gavin M Weir
Requested Type: Consider for Invited
Submitted: 2014-07-02 13:58:05

Co-authors: K.M. Likin, B.J. Faber, S. T. A. Kumar, A. Akerson, C. Deng, E. Chlechowitz, R.S. Wilcox, D.T. Anderson, F.S.B. Anderson, J.N. Talmadge

Contact Info:
HSX Plasma Laboratory
1415 Engineering Drive
Madison, WI   53706
USA

Abstract Text:
In the quasihelically symmetric experiment HSX, the neoclassical transport is comparable to a low-q tokamak and turbulent transport dominates throughout the plasma. Stiffness in the electron heat transport is investigated by measuring the electron temperature response to ECRH modulation through the ECE. Spectral analysis yields a profile of the perturbed amplitude and the resulting transient electron thermal diffusivity is comparable to the steady-state diffusivity. Linear gyrokinetic calculations using the GENE code demonstrate that the Trapped Electron Mode (TEM) is the dominant long-wavelength instability with growth rates that scale linearly with electron temperature gradient. Initial nonlinear gyrokinetic flux tube simulations indicate that the TEM contributes significantly to the heat flux. A new array of magnetic diagnostics has been installed in HSX that is optimized to reconstruct the plasma pressure and current profiles to greater accuracy than previous experimental work. Neoclassical Pfirsch-Schluter impurity ion flows are now measured using CHERS near the core while Reynolds stress measurements suggest that it determines the flows near the edge where measurements of the electric field disagree with neoclassical calculations. Finally, Langmuir probe measurements of density contours within magnetic islands just outside of the LCFS are in good agreement with EMC3-EIRENE calculations, although those of parallel flow show substantial disagreement. Measurements of the plasma potential indicate E x B flow within the magnetic island that is not present in the numerical modeling. This work is supported by DOE grant DE-FG02-93ER54222.

Characterization: 3.0

Comments:

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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