Increased confinement improvement in a reversed-field pinch using double-pulsed poloidal current drive

The pulsed poloidal current drive (PPCD) [J. S. Sarff et al., Phys. Rev. Lett. 72, 3670 (1994)] experiment is conducted in a reversed-field pinch device, the toroidal pinch experiment RX (TPE-RX) after providing an auxiliary power supply system with increased energy in the main power supply system for the PPCD. The PPCD system thus provides double-pulsed operation with higher current in the toroidal coil than that in single-pulsed PPCD operation in TPE-RX [Y. Yagi et al., Plasma Phys. Controlled Fusion 44, 335 (2002)]. The central electron temperature, ion temperature, and electron density increase during PPCD, and there is, on average, a fivefold improvement in energy confinement, tau(E), relative to standard discharges. Double-pulsed PPCD yields better performance than that of single-pulsed PPCD operation where twofold improvement in tau(E) was obtained. It is shown that the enhancement factor of tau(E) in the double-pulsed PPCD experiment in TPE-RX is consistent with the trends, observed previously, versus magnetic fluctuation amplitude and versus Deltagamma, where Deltagamma is the difference in gamma[=(1-F)/Theta] between the start and the end of the PPCD period. (C) 2003 American Institute of Physics.