PIC simulation study of merging processes of two spheromak-like plasmoids

Two different types of merging processes of spheromak-like plasmoids (SPs) without any external guide-field (toroidal) component, which are confined in a rectangular conducting vessel, have been investigated by means of two-dimensional PIC simulation, i.e., counter-helicity merging and co-helicity merging processes. The merging time scale is given by the transit time for ion sound wave to travel from the center of SP in the initial profile to the reconnection point for both cases. Through the counter-helicity SP merging process, toroidal magnetic field energy is effectively converted to thermal energy, while the energy transfer rate is suppressed to lower value for the co-helicity case because most of the toroidal magnetic field energy does not dissipate in the merging process. The reconnection process is impulsive for both cases, and, thus, the released energy is locally distributed around field lines connected to a reconnection point and forms the high temperature region with a spatial structure dependent on Larmor radius and the merging processes. © 2019 The Japan Society of Plasma Science and Nuclear Fusion Research.