|icc2006_milroy.pdf||2006-02-21 12:04:41||Richard Milroy|
Antisymmetric RMF Current Drive in FRCs
Author: Richard D Milroy
Submitted: 2005-12-19 16:08:58
Co-authors: H.Y. Guo, A.L. Hoffman, L.C. Steinhauer
RPPL, University of Washington
14700 NE 95th Street
Redmond, WA 98052
Rotating Magnetic Fields (RMF) are the only method yet developed that have been shown to both form FRCs with low applied power levels, and to sustain them in steady state. A major concern with applying RMF to FRCs has been that even small transverse magnetic fields tend to open field lines and possibly compromise confinement. Calculations have shown that both electron and ion orbits are confined due to the cyclic nature of the field line opening, but electron thermal conduction could still be rapid unless the edge density was maintained extremely low. It was proposed, and shown by numerical calculations that field line closure could be maintained if the RMF was applied in an anti-symmetric configuration, as long as the ratio of vacuum RMF, Bw, to external confinement field, Be, was low. Recent experiments on the TCS device showed greatly improved field line closure related energy confinement when using anti-symmetric RMF, even with large ratios of Bw/Be. Calculations showed that this highly encouraging result was due to the desirable and naturally occurring partial penetration of the RMF and strong reduction in its radial component.
Due to the importance of this result for FRCs, we have extended the previous analysis of anti-symmetric current drive to include a more accurate representation of the RMF antenna geometry and FRC shape. This model is used to determine the sensitivity of field line opening to imperfections in the simple plus-minus RMF asymmetry, and its dependence on the depth of RMF penetration and the ratio of Bw/Be. Anti-symmetric RMF will be tested in hotter plasmas in the new TCS/upgrade experiment.
 S. A. Cohen and R. D. Milroy, Phys. Plasmas, 7, 2539, (2000)
 H. Y. Guo, A. L. Hoffman, and L. C. Steinhauer, Phys. Plasmas 12, 062507 (2005)