Tokamak plasma magnetics

High-β (approximately 5-30%) tokamak equilibria have been found and the external magnetic field structures required to attain and hold them have been studied. The high-β equilibria can be a natural consequence of intense heating by an auxiliary power source such as neutral beams, if the heating is rapid compared to the magnetic diffusion time scale. Since magnetic fluxes are ''frozen in'' for such equilibria, they are called flux-conserving-tokamak (FCT) equilibria. FCT equilibria are shown to exist and satisfy the local (Mercier) stability criterion with β-values ranging up to 28%. For slighly D-shaped cross-sections, simple and efficient poloidal field systems are described which properly control and shape the plasma and admit poloidal divertors at the apexes of the natural D-shaped cross-sections. The poloidal field system may also have the property (STATIC concept) of shielding (by a factor of about 6) superconducting toroidal field coils from flux changes. Finally, the toroidal field ripple effects that enhance the ion heat conduction and cause a substantial fraction of alpha particles to drift out of the plasma are briefly discussed. (author)