"Multistage ion heating during high guide field reconnection associated with plasmoid formation"

 The series of experiments of the torus plasma merging have made clear the following high guide field reconnection characteristics such as, (i)significant ion heating in the downstream area, (ii) quadrupole electrostatic potential structure formation for ion heating and ion acceleration. Here, in this report, several ion heating events are observed in the early reconnection phase during our torus plasma merging experiment, TS-6. The novel 288CH extensive/high-resolution ( Δr = 1.5cm, Δz = 1.0cm) ion doppler spectroscopy system and newly developed high resolution magnetic probe array ( Δz = 1.1cm ) clearly detected the process of pull-type plasmoid production and ion heating synchronizing with plasmoid's movements. As the two initial torus plasmas are formed, magnetic flux surface which is close to X-point ( z = 0) starts to expand, ejecting mass of plasmas continuously. Subsequently, several X-points are formed, and the ion heating occurs downstream. When the plasmoid vanishes, ions are heated intensively, and finally significant heating occurs during the main toroidal plasmas merging. This series of ion heating in early reconnection phase should be suppressed to achieve effective energy conversion through magnetic reconnection.