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epr2014_mcam.pdf2014-08-15 08:17:18Matthew ArchMiller

Vacuum rotational dependence of disruptive behavior and vertical stability in the Compact Toroidal Hybrid

Author: Matthew C ArchMiller
Requested Type: Consider for Invited
Submitted: 2014-06-11 17:02:03

Co-authors: M. R. Cianciosa, D. A. Ennis, J. D. Hanson, G. J. Hartwell, J. D. Hebert, J. L. Herfindal, S. F. Knowlton, X. Ma, D. A. Maurer, M. D. Pandya, N. Roberds, P. Traverso

Contact Info:
Auburn University
206 Allison Laboratory
Auburn University, AL   36849

Abstract Text:
There is renewed interest in understanding if the addition of strong 3D magnetic shaping applied to axisymmetric fusion plasmas can improve their robustness against disruptions [1]. The Compact Toroidal Hybrid (CTH) is a stellarator/tokamak hybrid device that can operate over a wide range of magnetic configurations. The disruptive behavior of current-carrying discharges in CTH can be reproducibly modified by the presence of modest levels of externally generated rotational transform, but both the amount of vacuum transform required and the character of the observed disruption suppression depend on the type of disruption. In the case of density limit disruptions, we observe that the density at the disruption scales with the plasma current and that the disruptive density limit increases by up to a factor of 3 over the Greenwald limit across the range of applied vacuum transform. A threshold vacuum transform level beyond which density limit disruptions are completely avoided is not observed. This differs from the behavior of low-q disruptions, which can occur at high current when 1.1 < q(a) < 2.0. These low q disruptions cease to occur if the vacuum transform is raised above approximately 0.07 despite the fact that q(a) < 2.0. In the low q disruptions, a strong m = 3, n = 2 MHD precursor is observed prior to disruption with little m = 2, n = 1 kink activity, whereas for density limit disruptions a strong tearing m = 2, n = 1 fluctuation is seen. Finally, disruptions in CTH have been triggered when the position of elongated plasmas is allowed to drift vertically in the absence of position control. The application of a weak poloidal field of the stellarator equilibrium has been demonstrated to reduce and eliminate the vertical drift of elongated current-carrying toroidal discharges that would otherwise be vertically unstable [2].
[1] A. H. Boozer, Phys. Plasmas, 16, 058102 (2009).
[2] M. C. ArchMiller, et al., Phys. Plasmas, 21, 056113 (2014).

Characterization: 3.0


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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