Gridded Energy Analyzers for Measurement of Non-Thermal Electron Acceleration during Magnetic Reconnection

Magnetic reconnection has long been known to produce energetic electrons, though few laboratory investigations of this phenomenon have been conducted. Two versions of gridded electron energy analyzers (EEA) (1,2) are developed to measure the high-energy tail of the electron energy distribution produced during reconnection in the Magnetic Reconnection Experiment (MRX). The EEA uses a series of biased grids to filter incoming electrons by parallel energy. In the first version (1), the selector grid voltage is swept from -40 V to 0 V at 1 MHz, a frequency required to discern sub-Alfvénic changes. This EEA is verified by reference to a triple Langmuir probe in a Maxwellian plasma. The EEA is able to successfully identify a nonthermal tail with a temperature three times that reported by the Langmuir probe. However, results are limited to times in which the magnetic field was aligned with the EEA, for otherwise the sweeping voltage would generate a large polarization current. A multi-channel design in development (2) avoids this issue by using up to ten separate collectors which can be set independently. Upon completion, the new EEA will be tested on MRX and be used to determine the nonthermal parallel distribution tail temperature. These results will pave the way for more comprehensive studies of nonthermal electron production in MRX and in the upcoming Facility for Laboratory Reconnection Experiments (FLARE) (3).

(1) Byungkeun Na, Adam Robbins, Jongsoo Yoo, Hantao Ji, submitted (2023)

(2) Stephen Majeski, private communications (2022); William Fox, private communications (2022)

(3) H. Ji et al. Nature Reviews Physics 4, 263 (2022)