Control of plasma shape and performance of the PBX‐M tokamak experiment in high‐β t /high‐β p regimes

The highly indented plasmas of the PBX‐M tokamak experiment [P l a s m a P h y s i c s a n d C o n t r o l l e d N u c l e a r F u s i o n R e s e a r c h (IAEA, Vienna, 1989), Vol. 1, p. 97] have reached plasma regimes of both high volume‐averaged beta (β t ), and high‐beta poloidal (β p ), and sho...

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Published in:Physics of fluids. B, Plasma physics Plasma physics, 1990-06, Vol.2 (6), p.1271-1279
Main Authors: Bell, R. E., Asakura, N., Bernabei, S., Chance, M. S., Duperrex, P.‐A., Fonck, R. J., Gammel, G. M., Greene, G., Hatcher, R. E., Holland, A., Jardin, S. C., Jiang, T.‐W., Kaita, R., Kaye, S. M., Kessel, C. E., Kugel, H. W., LeBlanc, B., Levinton, F. M., Okabayashi, M., Ono, M., Paul, S. F., Powell, E. T., Qin, Y., Roberts, D. W., Sauthoff, N. R., Sesnic, S., Takahashi, H.
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Language:English
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Summary:The highly indented plasmas of the PBX‐M tokamak experiment [P l a s m a P h y s i c s a n d C o n t r o l l e d N u c l e a r F u s i o n R e s e a r c h (IAEA, Vienna, 1989), Vol. 1, p. 97] have reached plasma regimes of both high volume‐averaged beta (β t ), and high‐beta poloidal (β p ), and show evidence of the suppression of external surface modes by the passive stabilizing system. Values of β t up to 4.0 I/a B (% MA/m T) with T i (0)≊4 keV have been obtained. A magnetohydrodynamic analysis of plasmas with β p =2.0 indicates that these plasmas are near the threshold of the second stability regime. A value of β t of 6.8% has been reached with T i (0)>5 keV and an indentation of 28%. Control of plasma shape is accomplished with a feedback system that uses a moment expansion about a single equilibrium and is augmented by time‐dependent waveforms to redefine plasma shape. Diagnostics to measure the safety factor q have been developed and used to make accurate measurements of q(r) and to verify changes made in q(0).
ISSN:0899-8221
2163-503X
DOI:10.1063/1.859542