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High Flux FRC Facility for Stability, Confinement, and Sustainment Studies

Author: John Slough
Requested Type: Consider for Invited
Submitted: 2009-12-03 01:09:18

Co-authors: A.L. Hoffman, R.D. Milroy, L.C. Steinhauer

Contact Info:
Univerity of Washington
Box 352400
Seattle, WA   98195

Abstract Text:
A new FRC facility is proposed to leverage recent advances from both field reversed theta pinch (FRTP) and rotating magnetic field (RMF) studies. The suitability of the FRC as a fusion plasma depends most critically on the ability to form a stable FRC with sufficient energy confinement so that the plasma can either be brought to fusion gain conditions via pulsed compression, or increased in size and flux for heating and sustainment into a steady state. Past FRC scaling has shown that stable FRCs can be formed at low flux where ion kinetic effects dominate. The confinement was observed to scale roughly with the FRC poloidal flux up to a value of the kinetic parameter s/E ~ 0.5, where s is the average number of ion gyro-radii between the FRC null and separatrix and E is the elongation. While it should be possible to achieve sufficient confinement within the kinetic regime for fusion at high density, the low density, steady state approach will require s/E values well in excess of unity. The first step for any pursuit of fusion in this regime must consequently be the stable formation of the FRC at high s. To date, long-lived FRC equilibria have been achieved at high s with prolate FRCs formed in a FRTP. The proposed high flux FRC facility will therefore employ the FRTP as the primary formation methodology. The facility will also accommodate RMF for sustainment. There have been significant improvements in the FRTP formation since the last large FRC facility – LSX - was terminated in 1992. Most notably is the dynamic formation and merging of FRCs, which was first demonstrated in the IPA experiments, and later corroborated at larger scale elsewhere. It has been found that this new formation technology appreciably increases both FRC flux and lifetime. With dynamic formation, the resultant FRC is achieved in a chamber remote from the formation region, and thus provides for a process whereby the FRC can be wrought into a range of elongations from oblate to prolate over a wide span in density and temperature. A key goal of the high flux FRC facility will be to form FRCs with poloidal fluxes sufficiently large to fully confine high energy ion orbits introduced from either neutral or neutralized ion beams (p > 20 mWb). A primary concern is the stability of the FRC during formation at high flux. FRC stability has been found in numerical calculations where a subpopulation of high energy particles is present in sufficient numbers. The accumulation of adequate numbers through neutral beam injection requires far too long to stabilize modes such as the tilt, which can grow on Alfvenic timescales. Rapid injection of plasma with a high, directed energy will be investigated as a method to provide this kinetic component during formation. Other techniques for enhancing FRC stability will also be investigated including the promising application of rotating magnetic barrier fields for dynamic stabilization of both the rotation and tilt instabilities.

Characterization: A1


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Innovative Confinement Concepts Workshop
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