The impact of boundary shaping on reverse-field-pinch equilibria

This work explores the impact of boundary shaping on access into and out of quasi-single helicity states in reverse-field-pinch (RFP) plasmas. Experiments have shown that RFP plasmas can self-organize to a quasi-single helicity equilibrium with a helical axis. These states have improved confinement and lower magnetic turbulence levels compared to a standard RFP plasma [D.F. Escande, et al., {\it Phys. Rev. Lett.}~{\bf 85}, 1662 (2000)]. The VMEC code can obtain these similar equilibria with a helical axis and a symmetric boundary [J.D. Hanson, et al., {\it Nucl. Fusion} ~{\bf 53}, 083016 (2013)]. These equilibria all have circular, or nearly-circular cross-sections. In this work we analyze the impact of 2D-shaping of the boundary on RFP equilibria. Particular attention is paid to the impact on access to quasi-single helicity states.