Experimental studies of equilibrium in the toroidal Extrap T1 experiment

Experimental studies of a toroidal, high-beta plasma discharge with a non-circular cross-section are described. In Extrap T1, four toroidal, current-carrying rings outside the plasma discharge current channel produce a separatrix which bounds the plasma. Plasma currents of up to 40 kA are induced, operating with a toroidal field of up to 0.2 T. The major radius of the device is 0.45 m and the average minor radius of the current channel is about 40 mm. The discharge pulse is approximately 100 μs long. For the discharges reported here, the peak current density on the discharge axis is about 9 MA m-2, which corresponds to an on-axis safety factor q0 of about 0.1. The plasma density is in the range n ≅ 0.2 to 1 x 1021 m-3, and the electron temperature is in the range Te ≅ 10 to 30 eV. Magnetic flux plots of the experiment have been studied using magnetic probes and current and pressure profiles have been derived from the magnetic data. (orig.)