Physics Basis for a Spherical Torus Power Plant
S.C. Jardin, C.E. Kessel, J. Menard, T.K. Mau, R. Miller, F. Najmabadi, V. Chan, L. Lao, Y.R. Linliu, R.L. Miller, T. Petrie, P. Politzer, and A.D. Turnbull
Date of PPPL Report: November 1999
Submitted to: Fusion Engineering and Design
The spherical torus, or low-aspect-ratio tokamak, is considered as the basis for a fusion power plant. A special class of wall-stabilized high-beta high-bootstrap fraction low-aspect-ratio tokamak equilibrium are analyzed with respect to MHD stability, bootstrap current and external current drive, poloidal field system requirements, power and particle exhaust and plasma operating regime. Overall systems optimization leads to a choice of aspect ratio A = 1:6, plasma elongation k = 3:4, and triangularity delta = 0:64. The design value for the plasma toroidal beta is 50%, corresponding to betaN = 7:4, which is 10% below the ideal stability limit. The bootstrap fraction of 99% greatly alleviates the current drive requirements, which are met by tangential neutral beam injection. The design is such that 45% of the thermal power is radiated in the plasma by Bremstrallung and trace Krypton, with Neon in the scrapeoff layer radiating the remainder.