Reversed-field flux-trapping in a low-compression theta pinch

Rapid field reversal is employed to trap an initial negative-magnetic-field bias flux in a 300-cm long theta pinch having an inner radius of 10 cm. A large fraction (40%--75%, depending on filling pressure) of the initial bias flux is trapped after the implosion (approx.1 μsec); this fraction then diminishes to a plateau value of 25% to 35% in approximately 2 μsec. During this decay, magnetic probe measurements indicate an average anomalous resistivity one order of magnitude greater than classical. The open-line configurations obtained have large separatrix (zero enclosed flux) radii and are present for the duration of the applied magnetic field. The presence of the reversed bias field lowers the plasma temperature by a factor of two