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064505-3 Rath, Onofri, and Barnes
force have to approximately cancel. Therefore, the majority of potential energy cannot become kinetic but is transferred to the currents flowing in the wall and then dissipated ohmi- cally. The faster the energy is dissipated, the faster the insta- bility grows.
Beam-driven FRC plasmas are generally unstable to axial displacements (i.e., transversely stable) because of the need for a midplane-peaked vacuum field to maintain suffi- cient elongation to avoid the tilt instability. Conductors are then placed in such a way to ensure that the instability is wall-stabilized, so that feedback control becomes feasible.
In general, the minimum number of conductors and their maximum distance to the plasma that is required to ensure wall-stabilization depends on the axial profile of the equilib- rium field. For an infinitesimal perturbation from a perfectly flat equilibrium field, an infinitesimal amount of restoring force is sufficient, so there are no theoretical lower bounds. In practice, the equilibrium field is constrained by the need to avoid other instabilities. However, the experimental data available so far are insufficient to derive an experimental lower bound. At Tri Alpha Energy, the C-2U device operates with an equilibrium field of about 750 G, with a midplane peak at about 800 G. In this configuration, a wall at r 1⁄4 80 cm (twice the separatrix radius) provides sufficient restor- ing force in both simulations and experiments.
Phys. Plasmas 23, 064505 (2016) The authors gratefully acknowledge the support of Tri
Alpha Energy’s investors and team members.
1E. V. Belova, S. C. Jardin, H. Ji, M. Yamada, and R. Kulsrud, “Numerical study of tilt stability of prolate field-reversed configurations,” Phys. Plasmas 7(12), 4996–5006 (2000).
2M. W. Binderbauer, T. Tajima, L. C. Steinhauer, E. Garate, M. Tuszewski, L. Schmitz, H. Y. Guo, A. Smirnov, H. Gota, D. Barnes, B. H. Deng, M. C. Thompson, E. Trask, X. Yang, S. Putvinski, N. Rostoker, R. Andow, S. Aefsky, N. Bolte, D. Q. Bui, F. Ceccherini, R. Clary, A. H. Cheung, K. D. Conroy, S. A. Dettrick, J. D. Douglass, P. Feng, L. Galeotti, F. Giammanco, E. Granstedt, D. Gupta, S. Gupta, A. A. Ivanov, J. S. Kinley, K. Knapp, S. Korepanov, M. Hollins, R. Magee, R. Mendoza, Y. Mok, A. Necas, S. Primavera, M. Onofri, D. Osin, N. Rath, T. Roche, J. Romero, J. H. Schroeder, L. Sevier, A. Sibley, Y. Song, A. D. Van Drie, J. K. Walters, W. Waggoner, P. Yushmanov, K. Zhai, and TAE Team, “A high performance field-reversed configuration,” Phys. Plasmas 22(5), 056110 (2015).
3N. Iwasawa, A. Ishida, and L. C. Steinhauer, “Linear gyroviscous stability of field-reversed configurations with static equilibrium,” Phys. Plasmas 8(4), 1240 (2001).
4H. Ji, M. Yamada, R. Kulsrud, N. Pomphrey, and H. Himura, “Studies of global stability of field-reversed configuration plasmas using a rigid body model,” Phys. Plasmas 5(10), 3685 (1998).
5N. Rath, M. Onofri, and D. C. Barnes, “Modeling feedback control of unstable separatrix location in beam-driven field-reversed configurations,” Nucl. Fusion (submitted).
6L. C. Steinhauer, “Review of field-reversed configurations,” Phys. Plasmas 18(7), 070501 (2011).
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