Analytical Model for the Phase-Space Distribution of Electrons in Guide Field Magnetic Reconnection

Electron distributions measured in situ by the Wind spacecraft has revealed that electrons were trapped in the electromagnetic geometry of the reconnection event encountered in the deep magnetotail [1]. Here we present a new analytical theory that can account for the anisotropic features of the electron distributions observed by Wind [2]. The anisotropy is related to extensive trapping of electrons in parallel electric fields. Trapping is found to be generic in guide-field reconnection, as it is required in order to maintain the condition of quasi- neutrality. In addition to the spacecraft data, evidence of trapping in numerical simulations is also presented. Trapping is effective in controlling the free-streaming of electrons along magnetic fields. Its importance for fast reconnection is discussed and emphasized by observations in the VTF experiment. \\[1ex] [1] J.~Egedal, M.~Oieroset, W.~Fox, and R.~P.~Lin., Phys.~Rev.~Lett., {\bf 94}, 025006 (2005). \\[1ex] [2] J.~Egedal, W.~Fox, N.~Katz, et al., {\sl ``Evidence and theory for trapped electrons in guide field magnetotail reconnection''}, submitted to Journal of Geophysical Research, 2008.