Electron Beam Signatures Along the Guide Field during Electron-only Magnetic Reconnection in the PHAse Space MApping (PHASMA) Experiment

The Phase Space Mapping (PHASMA) experiment is designed to investigate distribution functions in electron-only magnetic reconnection events arising from the merger of two flux ropes generated by two pulsed plasma guns. Magnetic reconnection on PHASMA exhibits two distinct phases: a push-type reconnection phase and a pull-type reconnection phase. Prior work has shown the presence of oppositely-directed Alfvenic electron beams on either side of the reconnection X-point (Shi et. al., PRL 2022), and here we present data showing the presence of an electron beam propagating along the guide field (perpendicular to the plane of reconnection) during the pull phase of magnetic reconnection on PHASMA. This measurement was accomplished with a compact retarding field energy analyzer (RFEA) constructed with four wire-mesh grids of Debye-scale resolution (0.125mm per grid hole) to measure electron energy distribution functions (EEDFs) during magnetic reconnection. Electric potential gradients within the RFEA are set to reject ion collection and minimize secondary electron generation (via photoelectric and electron impact effects) with the use of a suppressor grid. A bi-Maxwellian fit to the EEDF obtained with the RFEA aperture directed along the guide field shows the presence of a cold, high-energy electron beam which develops during the pull phase of magnetic reconnection.