Horn-Shaped Structure Attached To The Ring-Shaped Ion Velocity Distribution During Magnetic Reconnection With A Guide Field

The characteristic feature of a "horn-shaped velocity distribution" in magnetic reconnection in the presence of a guide field is investigated by means of simulation and theory. Particle simulations show that a horn-shaped velocity structure is formed in the downstream, concomitant with a ring-shaped velocity distribution studied in the preceding works. The theory which explains the motion of ions responsible for the horn-shaped structure is constructed as an extension of the basic theory for the ring-shaped structure. In the extended theory, ions are accelerated in the inflow direction by an electrostatic field in the separatrix, and thus the gyration speed of such ions in the downstream is larger than that for the basic theory. Test particle simulations confirm that some ions behave as in the extended theory and form the horn-shaped velocity structure. (C) 2019 The Japan Society of Plasma Science and Nuclear Fusion Research