Download Three-scale structure of diffusion region of magnetic reconnection in

Three-scale structure of diffusion region of magnetic reconnection in the
presence of cold ion component
A. Divin 1, V. Semenov 1, I. Zaytsev 1
1. Saint-Petersburg State University, Saint-Petersburg, Russia,
Recent observations of magnetotail and magnetopause reconnection reported
events with plasma containing hot and cold ion components of comparable densities
[Andre and Cully, 2012]. It was suggested that such ion distribution alters properties
of the magnetic reconnection regions at the magnetopause [Toledo‐Redondo et.
al., 2016]. Motivated by these recent findings, we performed two-dimensional kinetic
Particle-in-Cell (PIC) numerical simulations of magnetic reconnection in plasma
containing a mixture of ion populations having different temperatures. The study was
primarily focused on inspecting various kinetic effects and peculiarities of particle
acceleration in symmetric 2D reconnection in such conditions. Diffusion region
displays three-scale structure, with the cold Ion Diffusion Region (cIDR) scale
appearing in-between the EDR and IDR scales. The structure and the strength of the
Hall magnetic field depends weakly on cold ion temperature or density, and is rather
controlled by the conditions (B, n) upstream the reconnection region. The cold ions
are accelerated predominantly transverse to the magnetic field by the Hall electric
fields inside the IDR, leading to a large ion pressure anisotropy, which is unstable to
ion Weibel-type or mirror-type mode. Extended Electron Diffusion Region (EEDR) is
substantially shorter in cold ion mediated run, which we attribute to gyrotropization of
electrons in the EDR due to cold ion instability. Despite comparable reconnection
rates produced, we find that the overall evolution of reconnection in the presence of
cold ion population is more dynamic compared to the case with a single hot ion
component.
References
André, M., & Cully, C. M. (2012). Low‐energy ions: A previously hidden solar
system particle population. Geophysical Research Letters, 39(3).
Toledo‐Redondo, S., André, M., Vaivads, A., Khotyaintsev, Y.V., Lavraud, B.,
Graham, D.B., Divin, A. and Aunai, N., (2016). Cold ion heating at the dayside
magnetopause during magnetic reconnection. Geophysical Research Letters, 43(1),
pp.58-66.