Slow Formation of Field-Reversed Configuration by Use of Two Merging Spheromaks

A novel slow formation method of field-reversed configuration (FRC) has been developed by magnetic reconnection of two force-free spheromaks with opposite toroidal magnetic field. The merging process cancels their opposite magnetic helicities, realizing a non-Taylor relaxation from the force-free state to the high-β FRC state with zero helicity. A significant increase in the ion temperature has been documented up to 180eV during this fully anti-parallel reconnection. The dissipated toroidal magnetic energy of the merging toroids is transformed mostly to the ion thermal energy, revealing a unique relaxation mechanism to the high-β equilibrium. The merging toroids are found to relax either to an FRC or to a new spheromak, depending on whether their total helicity is larger or smaller than a critical value.