DESIGN OF STP-3(M) REVERSED-FIELD PINCH WITH HIGH CURRENT DENSITY

An air-core transformer has been used in the STP-3(M) reversed field pinch to minimize toroidal asymmetry of the magnetic fields as well as to obtain good accessibility of diagnostics. A one-turn poloidal coil coaxially surrounds both the plasma and the thick conducting shell for close coupling with plasma and for reducing field errors at the inner shell gaps. A bi-polar flux swing has been applied to drive a high plasma current with low primary current. Optimization of the poloidal and toroidal circuits has been performed using a simple circuit model. The STP-3(M) has thus been operated with current density higher than 8 MA/m 2 for as long as 6 ms.