Plasma formation and equilibrium in a high β tokamak

Abstract

The formation and equilibrium of a high β tokamak in the Columbia High Beta Tokamak (HBT) (Plasma Physics and Controlled Nuclear Fusion Research 1986, in press) is documented using magnetic probes as the principle diagnostic. The formation from a toriodal field stabilized Z pinch is simulated with 2-D resistive magnetohydrodynamic (MHD) equations. From the measurement of the magnetic field by high-impedence internal magnetic probes, the poloidal flux, toroidal current, and safety factor are calculated. In addition, the plasma position and cross-sectional shape are determined. The tokamak has a major radius of about 0.24 m, a minor radius of about 0.05 m, and a toroidal current density of about 106 A/m2. The high β tokamak plasma is observed to have an outward shift in major radius of both the magnetic center and the peak of the toroidal current density. The magnetic center moves inward in major radius after 20–30 μsec, presumably because the plasma maintains major radial equilibrium as its pressure decreases because of the radiation of impurity atoms.