Formation of Electric Potential in Counter-helicity Spheromak Merging

We studied merging formation process of Field-Reversed Configuration (FRC). In this method, an FRC is formed by merging of two spheromaks with opposing toroidal magnetic fields through magnetic reconnection, named ``counter-helicity spheromak merging.'' During this merging, the reconnection electric field has not only the toroidal component but also the radial component which accelerate/ decelerate unmagnetized ions in inboard or outboard direction depending on opposing toroidal magnetic field polarities of initial spheromaks, called case-O and case-I mergings. Based on electrostatic potential and ion velocity measurements, the generated radial electric field significantly affects ion outflow profiles, causing significant unbalance between inboard and outboard outflows from the X-point. In case-O, direction of radial electric field is inward, and in case-I, that is outward. The difference in electric field direction and that in Hall effect probably cause asymmetry between case-O and case-I mergings. The asymmetry is maintained after the merging completion, causing difference between magnetic fluxes of case-O and case-I FRCs.