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Hybrid simulations of counter-helicity spheromak merging

Author: Elena V Belova
Requested Type: Poster Only
Submitted: 2014-05-30 15:45:14

Co-authors:

Contact Info:
PPPL
MS 18, PPPL
Princeton, NJ   08543
USA

Abstract Text:
Hybrid simulations of counter-helicity spheromak merging have been performed using the HYM code and compared with MHD simulations. Initial ion temperature was assumed to be uniform, and thermal ion Larmor radius was relatively small. It has been found that for large resistivity (Lundquist number S~500), there were significant differences between hybrid and MHD simulations. In particular, in the MHD runs, spheromaks move towards the midplane, and merge completely in about 10 Alfven times, whereas in hybrid simulations with the same plasma parameters, the spheromaks moved towards midplane initially, but then bounced back, and there were no complete reconnection. For lower resistivity with S~1500, the hybrid simulation results were generally similar to the MHD simulations, and spheromaks were completely reconnected forming an FRC by about 6 Alfven times. The hybrid simulations show outward radial shift of the reconnection X-point, which is related to generation of a quadrupole field, and has also been observed in 2D Hall-MHD simulations. Relatively large toroidal ion velocities up to 2.5Va are generated due to ‘sling-shot’ effect both in MHD and hybrid simulations. Hybrid simulations also show much wider ion velocity profiles, compared to MHD.

Characterization: 1.2

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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