The role of guide field in magnetic reconnection: the case of relativistic magnetic reconnection in pair plasmas

We investigate the guide field effect to magnetic reconnection, in the case of relativistic magnetic reconnection in high-energy astrophysical contexts. In a relativistic current sheet of electron-positron plasmas, two two- dimensional processes are considered: 1) relativistic magnetic reconnection, which accompanies strong particle acceleration around the X-type diffusion region, and 2) the relativistic drift kink instability (RDKI), which fast dissipates magnetic energy. Theories and three-dimensional PIC simulations show that the current sheet is extremely unstable to the RDKI and the magnetic energy is rapidly dissipated into plasma heat. However, when the guide field is introduced, the RDKI is stabilized by magnetic tension and the current sheet is unstable to new obliquely-directed instability, which we call relativistic drift-kink-tearing instability (RDKTI). We found that the RDKTI triggers secondary magnetic reconnection and the relevant particle acceleration. In short, guide field controls the destination of the magnetic energy: plasma heat (by the RDKI) or non-thermal energy (by reconnection acceleration).