Pinch plasmas in the open flux column with sheared flows based on the gun-spherical torus using the dropping liquid metal central conductor

We have experimentally investigated the open flux column (OFC) region surrounding the closed flux regions of spherical torus (ST) produced by coaxial helicity injection (CHI) in the HIST device. This gun-produced ST magnetic configurations can be explained by two-fluid equilibrium calculations. The OFC plasma has the high density and the diamagnetic toroidal field which is stabilized by the poloidal shear flow. We propose that the dropping liquid metal as central post is used to carry the axil current instead of the conventional metal central conductor. If we can increase the external toroidal field produced by the axial current in the liquid metal, the density and the ion temperature of the long OFC plasma is expected to increase effectively by pinch effects. We will present the characteristics of OFC and the sheared flow profiles produced on HIST in comparison with the two-fluid equilibrium calculation. Furthermore, we will explore the possibility of formation of OFC pinch plasma in the reactor parameter regime.