Experimental investigation of three-component magnetic reconnection by use of merging spheromaks and tokamaks

A laboratory experiment of magnetic reconnection has been developed in the Tokyo University Spherical Torus (TS-3) [Y. Ono et al., Phys. Fluids B 5, 3691 (1993)] merging device, using two colliding plasma toroids with cohelicity and counterhelicity. The conventional two-component reconnection was extended experimentally to three-component reconnections by introducing a new field component $B_X$ parallel to the X-line, an external force and a reconnection-driven global equilibrium transition. Selective ion heating accompanied by a field-aligned jet was documented during the counterhelicity reconnection without $B_X,$ indicating its direct energy-conversion into the ion thermal energy. Ion heating, current-sheet resistivity and reconnection rate all increase significantly with decreasing $B_X$ and with increasing the external force, indicating three-component and driven effects of reconnection. The anomalous sheet-current dissipation and the ion heating are both found to depend on whether the current-sheet is compressed shorter than the ion gyroradius or not.