Study of Energy Conversion and Partitioning in the Magnetic Reconnection Layer in Laboratory and Space Plasmas

Abstract:

The essential feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy [1]. This talk addresses this key unresolved question; how is magnetic energy converted to plasma kinetic energy during reconnection? The mechanisms responsible for the energization of plasma particles in the magnetic reconnection layer have been investigated in the MRX device together with quantitative evaluation of conversion of magnetic energy to ions and electrons. An analysis is made in terms of two-fluid physics based on the measurements of two-dimensional profiles of 1) electric potential, 2) flow vectors of electrons and ions, and 3) the electron temperature, T_e and the ion temperature, T_i in the layer [2,3]. It is shown that more than 50 % of magnetic energy is converted to plasma particles, of which 2/3 transferred to ions and 1/3 to electrons, at a remarkably fast speed (~0.2V_A) in the reconnection layer [3]. In a reconnection region of effectively similar size in the Earth’s magnetotail, the energy partition was recently measured during multiple passages of the Cluster satellites [4]. The half length of the tail reconnection layer (L) was estimated to be 2000–4000 km namely 3–6d_i; the scale length is very similar to the MRX case, L ~ 3d_i. Reconnection in the magneto-tail is driven by an external force, i.e., the solar wind, and the boundary conditions are very similar to the MRX setup. The observed energy partition is notably similar, namely, more than 50% of the magnetic energy flux is converted to the particle energy flux, which is dominated by the ion enthalpy flux, with smaller contributions from the electron enthalpy and heat flux. A broad implication will be discussed.

Work supported by DOE, NASA, and NSF. Fig.1: Measured ion flow vectors in the reconnection plane with measured 2-D profile of the plasma potential φ_p. The thin lines are measured poloidal flux counters.

[1] M. Yamada, R. Kulsrud, & H. Ji, Rev. Mod. Phys. 82, 603–664 (2010). [2] J. Yoo et al, Phys. Plasmas 21, 055706 (2014), [3] M. Yamada et al, Nature Communications (2014) [4] J. P. Eastwood et al., Phys. Rev. Lett. 110, 225001 (2013)