Flux confinement measurements in large field-reversed configuration equilibria

The poloidal magnetic flux φ in large field-reversed configuration plasmas is examined experimentally. A wide range of initial equilibrium conditions, with 1≤φ≤8 mWb, is produced by varying the reverse bias magnetic field strength. The flux confinement time τφ at first improves with bias, albeit with field-null resistivities an order of magnitude larger than classical. A further increase in bias results in a reduction of τφ, which is inconsistent with either classical or anomalous diffusion theory. The data suggest the importance of nondiffusive processes such as instabilities or formation dynamics.