Abstract Details

brownicc2006.pdf2006-02-21 14:52:37Michael Brown

Novel Spheromak Configurations: Dipole Trapped and m=1 Tilted

Author: Michael R. Brown
Submitted: 2005-12-21 16:48:07

Co-authors: C. Cothran, J. Fung, M. Schaffer, E. Belova

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

Abstract Text:
We have been studying two novel spheromak configurations in the prolate (tilt unstable) $0.4~m$ diameter, $0.6~m$ length flux conserver of the Swarthmore Spheromak Experiment (SSX). The first is a fully tilted, $m=1$ spheromak formed by co-helicity merging of two spheromaks (either right-right or left-left handed). The single tilted configuration is rapidly formed in an Alfv'en time without direct reconnection, presumably by fast three-dimensional reconnection. The final three-dimensional structure is long-lived and apparently well-confined. The second configuration is a single $m=0$ spheromak trapped in an externally applied dipole field produced by a set of $0.5~m$ diameter coils at the midplane. The trapped plasma encircles a large plasma flux core. Most remarkably, this plasma does not tilt, despite the prolate conserver.  Evidently, the combination of the attractive external dipole field, the close-fitting copper flux conserver, and perhaps line-tying stabilize the tilt. Each configuration is characterized by a suite of magnetic probe arrays for magnetic structure {bf B}(r,t), interferometry for $n_e$, and soft x-ray analysis for $T_e$. Three dimensional MHD simulations of these configurations are also being performed.

In addition, ion Doppler spectroscopy (IDS) has been implemented for $T_i$ and flow for both configurations. The SSX IDS instrument measures with $1~mu s$ or better time resolution the width and Doppler shift of the $C_{III}$ impurity (H plasma) $229.7~nm$ line to determine the temperature and line-averaged flow velocity during spheromak merging events. Preliminary results indicate interesting flow dynamics associated with the formation of the $m=1$ tilted spheromak but very little flow or rotation for the $m=0$ dipole trapped spheromak ($le 10~km/s$).

IDS results for both configurations will be presented including Abel inversions of data obtained from several chords. In addition, magnetic structure from a variety of probe arrays and comparison to simulation results will be presented. Dynamical simulations of the dipole trapped spheromak equilibrium indicate gross stability.

Characterization: A1,E3


The University of Texas at Austin

Innovative Confinement Concepts Workshop
February 13-16, 2006
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