Improved confinement and current drive of high temperature field reversed configurations in the new translation, confinement, and sustainment upgrade device

Previous work in the translation, confinement, and sustainment (TCS) device [Hoffman, Guo, Slough et al., Fusion Sci. Technol. 41, 92 (2002)] demonstrated formation and steady-state sustainment of field reversed configurations (FRC) by rotating magnetic fields (RMF). However, in TCS the plasma temperature was limited to several 10 s of eV due to high impurity content. These impurities are greatly reduced in the new TCS upgrade device (TCSU), which was built with a bakable, ultrahigh vacuum chamber, and advanced wall conditioning capabilities. This led to dramatic improvements in TCSU with temperatures well over 200 eV, using simple even-parity RMF drive. The higher temperatures, coupled with reduced recycling, allowed plasma to enter into a collisionless, high-ζ (ratio of average electron rotation frequency to RMF frequency) regime. These new FRC states exhibit the following key features: (1) Dramatic improvement in current drive efficiency with ζ approaching 100%, for the first time in TCSU; (2) up to threefold increase in global energy confinement time; and (3) significant reduction in transport rates, accompanied by a striking transition from a Bohm-type transport to a lower hybrid driftlike transport that scales better than gyro-Bohm and is very favorable for the next step FRC development