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Techniques to extend FRC lifetimes for magnetized target fusion implosions in FRCHX

Author: Glen Wurden
Requested Type: Consider for Invited
Submitted: 2012-12-07 15:11:26

Co-authors: C. Grabowski, J. H. Degnan, D. J. Amdahl, M. Domonkos, E. L. Ruden, W. M. White, M. H. Frese, S. D. Frese, J. F. Camacho, S. K. Coffey, M. Kostora, J. McCullough, W. Sommars, B. Bauer, S. R. Fuelling, K. Yates, A. G. Lynn

Contact Info:
Los Alamos National Laboratory
PO Box 1663
Los Alamos, New Mexico   87545
United States

Abstract Text:


We are working to improve the field reversed configuration (FRC) plasma lifetime in FRCHX, so that sufficient warm plasma exists (and can therefore be compressed) during the 25 microseconds it takes to implode the aluminum liner on FRCHX at the Shiva Star facility in Albuquerque. We are using every measure that we can think of, aiming for a 50-100% increase, over the present 10-12 usec measured flux decay times in the trapping (liner) region of the experiment. We will report on progress along these lines. Up to four implosion shots are planned during 2013.

We have identified a number of issues which limit the present lifetime. These include the amount of flux trapping during the initial FRC formation, symmetry of the initial theta-pinch preionization plasma, losses in the capture region (incomplete capture of the existing FRC), poor aspect ratio of the magnetic geometry of the capture region (inadequate length), spin-up of the plasma and subsequent n=2 instability development, a tendency for the plasma to go off-center at late times in the capture region, and possible plasma wall interactions during translation or with metallic aperture structures at either end of the liner.

During the past year [1-2], we have tested both a low power and high power RF prepreionization system. We have switched from static fill, to a gas puff prefill. We have added a set of control “bias” rings at the upper end of FRCHX, to attempt to modify the radial electric fields on flux lines near the FRC separatrix. We have scanned the values of the magnetic fields produced by the translation and mirror coils….and identified that we must split these coil sets (and capacitor bank) so that we can independently control these fields. Finally, we will install a Russian coaxial plasma gun (loaned from EMC2), as strongly suggested by results from the Tri Alpha Energy C-2 experiment, to symmetrically stabilize the n=2 instability without having touse conventional quadrapole coils.

[1] G. A. Wurden, “Field Reversed Configuration Formation for High Energy Density Experiments”, LA-UR-12- 22573, oral talk, ICOPS 2012, Edinburgh, Scotland, July 10, 2012.
[2] J. H. Degnan et al., “Recent Magneto-Inertial Fusion Experiments on FRCHX", ICC/P6-002, IAEA Fusion Energy Conference, San Diego, CA, Oct. 2012.

Characterization: 1.1,1.2

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