Refluxing physics for quasisteady state spheromak sustainment

``Refluxing'' for spheromak sustainment injects helicity during formation, followed by a slowly-decaying, high confinement phase. The plasma is rebuilt before the magnetic flux fully decays, and the cycle repeated as demonstrated in the SSPX experiment [1]. Numerical simulations (NIMROD code) and axisymmetric modeling including transport (CORSICA code) extend the experimental study, improving the confinement phase using bias flux reduction [2]. The free energy in the injected current is reduced, lowering the level of magnetic fluctuations. Flux amplification during buildup is increased above SSPX, achieving higher Te and lengthening the confinement phase duration. Calculations use the SSPX flux-conserver geometry to maintain contact with experiment; some issues with this geometry at high flux amplification are analyzed. Current profile control including edge boundary condition on j/B is considered for limiting internal magnetic mode amplitudes. Opportunities for further improvement of this scenario are identified. [1] B. Hudson, et al., Phys. Plasmas 15, 056112 (2008). [2] E. B. Hooper, et al., Nucl. Fusion 47, 1064 (2007).