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Advances in the Theory of Stellarator Plasma Physics

Author: Chris C Hegna
Requested Type: Poster Only
Submitted: 2012-12-07 15:39:18

Co-authors: A. Bader, M. Rorvig, M. G. Schlutt

Contact Info:
University of Wisconsin
1500 Engineering Drive
Madison, WI   53706
USA

Abstract Text:
Recent work has advanced the theory of stellarator plasma physics in a number of areas. In this presentation, we discuss three specific topics: extended MHD modeling and magnetic island physics, optimization of stellarators against ion temperature gradient instabilities and edge/divertor modeling.

Numerical simulations of MHD equilibrium and nonlinear stability of 3-D magnetic configurations have been performed using the extended MHD code NIMROD [1,2]. Both current and pressure driven instability effects have been investigated. In particular, simulations of Ohmic driven discharges of the CTH experiment have been able to reproduce a number of experimentally observed features including the prominence of n/m = ½ islands when the rotational transform exceeds 0.5. Additionally, the theory of flow induced island healing has extended to include a broad range of collisionality regimes [3,4]. These theoretical results have been compared favorably to LHD observations with the theory predicting the observed island/flow phenomenology, providing a prediction for the onset of island healing and correctly anticipating the presence of hysteresis in the healing/mode penetration process [5].

With the goal of improving the anomalous transport properties of stellarators, the effects of 3-D shaping on microinstability properties are studied. In particular, the role of curvature and local shear on ITG stability is addressed using local 3-D equilibrium theory [6] to construct configurations with a variety of 3-D shaping. Local ITG stability is sensitive to the spatial properties of the magnetic drift frequency which is influenced by the depth and extent of the bad curvature along a field line, the local shear and the geodesic curvature . Efforts to quantify ITG stability with an analytically derived proxy function are presented.

The edge/divertor properties of 3-D configurations of interest to the HSX stellarator are investigated using the EMC3-EIRENE code. Simulations have shown that for configurations with significant magnetic islands outside the plasma confinement region, prominent counter streaming parallel flows are present. These flows are thought to affect the ability of stellarator experiments to obtain high recycling regimes. The effects of varying magnetic configuration and simulation parameters will be discussed.

[1] M. G. Schlutt et al, Nucl. Fusion 52, 103023 (2012)
[2] M. G. Schlutt et al, submitted to Phys. Of Plasmas (2012).
[3] C. C. Hegna, Nucl. Fusion 51, 113017(2011).
[4] C. C. Hegna, Physics of Plasmas 19, 056101 (2012).
[5] Y. Narushima et al, to be submitted to Nuclear Fusion (2013).
[6] C. C. Hegna, Phys. Plasmas 7, 3921 (2000).

This work is supported by US DOE contracts DOE-SC0006103 and DE-FG02-99ER54546.

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