Plasmoid dynamics in reconnection turbulence

Circular structures of the parallel current, hereafter referred to as plasmoids, are found to form, merge, and dissipate recurringly in gyrokinetic simulations of driven reconnection turbulence in a strong guide field. A Krook term is used to force the system via a two-dimensional reconnecting current sheet, and the energy thus injected is partly transferred into the plasmoids. The plasmoids, which can be thought of as flux ropes in a guide field scenario, are attracting or repelling each other, depending on the signs of the associated currents; this mechanism, which highlights the importance of temporal effects and intermittency in reconnection setups, is described quantitatively. In this context, dependencies on physical parameters (such as the plasma pressure $\beta$ or the ion temperature $T_i$) are compared with linear reconnection physics in current sheets. Another important aspect of plasmoid dynamics is the occurrence of mergers. Such events underscore the need for (gyro)-kinetic descriptions, since it causes the parallel velocity space to undergo a significant departure from the usual Maxwellian distribution.