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Aspect ratio scan of CT merging in SSX

Author: Tim Gray
Requested Type: Consider for Invited
Submitted: 2009-12-04 15:39:25

Co-authors: M. Brown, C. Cothran, V. Lukin, G. Marklin, C. Myers, E. Belova, M. Schaffer

Contact Info:
Swarthmore College
500 College Ave.
Swarthmore, PA   19081
USA

Abstract Text:
Interest in plasma merging in the fusion community has grown recently. The Swarthmore Spheromak Experiment (SSX) studies plasma merging by forming two spheromaks with magnetized coaxial plasma guns, and injecting them into the opposite sides of a flux conserver. The flux conserving boundaries are provided by highly conducting copper walls. Four different geometries have been studied in SSX, including trapezoidal oblate ($L/R = 1.2$) geometry, and three cylindrical geometries, slightly prolate ($L/R = 2.0$), prolate ($L/R = 3.0$), and super prolate ($L/R = 10$). The helicity of the spheromaks can be individually chosen, allowing for both co- and counter-helicity merging, both of which have been tried. Dynamic activity in the magnetic fields and dynamic flows are observed during the merging process. After the merging phase, complex activity subsides and the plasma settles into an equilibrium state. In the case of co-helicity merging, these equilibrium states match the minimum energy Taylor states ($nabla times B = lambda B$) calculated for the geometries. Counter-helicity merging often ends in more complicated states, possibly consistent with lowest energy states of the generalized helicity. Simulations of co- and counter-helicity merging in the $L/R = 3.0$ geometry using the HiFi and HYM codes provide insight to the merging process in this geometry. However, merging in the less prolate geometries seems to proceed by a different route during both co- and counter-helicity merging. Preliminary results in the super prolate ($L/R = 10$) will be presented.

noindent*Supported by US DOE and NSF.

Characterization: A1,A2

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