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

Abstract:

The most important feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy. Recently we have reported our initial results on the energy conversion and partitioning in a laboratory reconnection layer [1]. Our experimental study of the reconnection layer is carried out on MRX [2] in the two-fluid physics regime. We have observed that the conversion of magnetic energy occurs across a region significantly larger than the narrow electron diffusion region. A saddle shaped electrostatic potential profile exists in the reconnection plane, and ions are accelerated by the resulting electric field at the separatrices. These accelerated ions are then thermalized by re-magnetization in the downstream region. A quantitative inventory of the converted energy is presented in a reconnection layer with a well-defined, variable boundary. We have also carried out a systematic study of the effects of boundary conditions on the energy inventory. This study concludes that about 50% of the inflowing magnetic energy is converted to particle energy, 2/3 of which is ultimately transferred to ions and 1/3 to electrons. Recently in a reconnection region of similar size (L ~ 3 ion skin depth) in the Earth's magneto-tail, the energy partition was statistically measured by using Cluster satellite data [3]. The observed energy partition is remarkably consistent with the present MRX data, namely, a substantial part of magnetic energy flux being converted to the particle energy flux which is dominated by the ion enthalpy flux with smaller contributions from both the electron enthalpy and heat flux. It is also observed that the observed features of energy conversion and partitioning do not depend on the size of monitoring boundary across the range of sizes tested from 1.5 to 4 ion skin depths.

In collaboration with J. Yoo, J. Jara-Almonte, H. Ji, R. Kulsrud, and C. Myers

[1] Yamada et al. Nat. Commn. 5, 4474 (2014)

[2] Yamada et al, Phys. Plasmas, 4, 1936 (1997)

[3] J. Eastwood et al, Phys. Rev. Lett. 110, 225001 (2013)