Direct Measurements of Electron Heating from Electron-Only Magnetic Reconnection in Laboratory Mini-Magnetospheres

Mini-magnetospheres are ion-scale structures that are ideal for studying the kinetic-scale physics of collisionless space plasmas. Such ion-scale magnetospheres can be found in a wide range of systems, including the Moon, Mars, and Ganymede, and have recently been created in the lab to study kinetic processes like magnetic reconnection [1,2]. We report on the experimental observation of electron heating in electron-only magnetic reconnection in laser-driven laboratory mini-magnetospheres on the Large Plasma Device (LAPD) at UCLA. In this experiment, a fast-flowing plasma impacts a pulsed magnetic dipole embedded within LAPD's magnetized ambient plasma, creating an ion-scale magnetosphere and driving electron-only magnetic reconnection between the background and dipole field lines. The electron velocity distribution is measured across the reconnection region using non-collective Thomson scattering, enabling determination of electron temperature and density. Significant electron heating is observed in the electron diffusion region, increasing from an initial temperature of 1.8 eV to 9.7 eV, corresponding to a 40\% conversion of Poynting flux into electron enthalpy flux. Particle-in-cell (PIC) simulations that provide insights into the heating mechanisms are also presented.

[1] D. B. Schaeffer et al. Physics of Plasmas 29, 042901 (2022)

[2] L. Rovige et al., The Astrophysical Journal 969, 124 (2024)