Evidence of Relaxation and Spontaneous Transition to a High-Confinement State in High-$\ensuremath{\beta}$ Steady-State Plasmas Sustained by Rotating Magnetic Fields

Evidence of Relaxation and Spontaneous Transition to a High-Confinement State in High- $β$ Steady-State Plasmas Sustained by Rotating Magnetic Fields

H. Y. Guo, A. L. Hoffman, L. C. Steinhauer, K. E. Miller, and R. D. Milroy

Phys. Rev. Lett. 97, 235002 – Published 6 December 2006

Abstract

Evidence of relaxation has appeared, for the first time, in the extremely high- $β$ , steady-state field-reversed configuration plasma states driven by rotating magnetic fields (RMF) in the translation, confinement, and sustainment experiment. The plasma self-organizes into a near-force-free state in the vicinity of the magnetic axis, with significant improvement in confinement. Associated with this change in magnetic topology is the appearance of an axial RMF component; this would, in turn, generate a current drive in the poloidal direction, thus sustaining the magnetic helicity. A newly developed two-dimensional “equilibrium-lite” model is employed to analyze the magnetic properties of the final high-confinement state, and shows a large $q$ and a significant magnetic shear in the core.