Conversion of magnetic energy to plasma kinetic energy during guide field magnetic reconnection in the laboratory*

Magnetic reconnection is a fundamental process that leads to fast conversion of stored magnetic energy to plasma kinetic energy. The energy conversion is mediated by an electric field given by the generalized Ohm’s law. We present laboratory measurements showing the 2-D structure of energy conversion during magnetic reconnection in the two-fluid regime with a guide field comparable to the upstream reconnecting field [1]. We find that the electrons are energized in two separate regions of the reconnection layer by the parallel electric field, E_||.  E_|| energizes electrons in the electron diffusion region (EDR) and outside the EDR near the separatrices. In contrast, the energy deposition on ions is driven by the perpendicular electric field and is strongest in the vicinity of the high-density separatrices where electrons move against the electric field. The perpendicular electric field is sufficiently strong to impulsively energize the ions. An energy balance calculation shows that about 40% of the magnetic energy is converted into particle energy, 2/3 of which is transferred to ions and 1/3 to electrons. Additional analysis shows that the energy deposited on electrons manifests as thermal energy, part of which increases electron temperature, while the rest is most likely transported to the exhaust by heat conduction. The energy deposited on ions enhances ion temperature, with loss due to charge exchange collisions and thermal conduction.

References

[1] Bose et al. submitted (2023).