Improved operation of the SSPX spheromak

We present significant advances in the performance and understanding of the sustained spheromak physics experiment (SSPX). High performance discharges are obtained by adjusting the injected current and bias magnetic flux to produce a flat to slightly peaked radial current profile, consistent with reducing the drive for tearing and other MHD modes. Wall conditioning and density control are also essential for obtaining high performance discharges. With these optimizations, plasmas with peak electron temperatures of ~350 eV, edge magnetic fluctuation levels less than 1% and core thermal diffusivities (χe)