POLOIDAL MAGNETICS AND DIVERTOR STRIKE POINT CONTROL IN THE COMPACT IGNITION TOKAMAK.

Methods are presented for computing free-boundary MHD equilibrium with prescribed constraints on plasma position, PF (poloidal field) volt-seconds, and divertor strike-point or X-point coordinates. These methods are used to show the feasibility of using external PF coils to position and shape the plasma flux surfaces relative to the divertor plates in the CIT (Compact Ignition Tokamak) and to present a scenario for a swept divertor. Forcing the separatrix flux surface to coincide with four prescribed points in the poloidal plane, over some range of uncertainty in plasma pressure and current profiles, requires four relatively independent coil groups. The degree of independence in these coil groups is often limited by physical constraints on their locations, which can result in large variations in coil currents because of profile uncertainty.