Formation of anomalous velocity distribution based on the pickup-like ion motions during magnetic reconnection

By means of electromagnetic particle simulations, we investigate ion effective heating during magnetic reconnection in the presence of a guide field. Our simulations have demonstrated ring-shaped or arc-shaped, i.e., incomplete ring-shaped velocity distributions of protons.

The behaviors of ions forming the ring-shaped or arc-shaped velocity distribution are theoretically explained on the basis of the pickup-like motion of protons as the main component ion. Upon entering the downstream across the separatrix, ions behave as nonadiabatic. They suddenly feel the electromagnetic field in the downstream and move in the outflow direction while rotating around the guide magnetic field. As a result, a ring-shaped or an arc-shaped velocity distribution is formed, which means that ions are effectively heated.

Recently in particle simulations, we find further anomalous velocity distribution such as horn-shaped structure attached to the ring-shaped distributions and double-ring-like distributions. We generalize the above theory of the nonadiabatic motion in order to clarify the formation mechanism of further anomalous distribution, which would lead to enhancement of the ion heating.