Particle Beams in the Vicinity of Magnetic Separatrix According to Near‐Lunar ARTEMIS Observations

Abstract

We study characteristics of ion and electron beams observed during 101 crossings of the near-separatrix region by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in the magnetotail. We found that accelerated ion beams are observed under any level of geomagnetic activity. A duration of earthward moving ion beams is statistically longer (≤ 10 min) than a duration of tailward ion beams (≤ 4 min), which can be due to the transient character of ion acceleration in the vicinity of the near-Earth neutral line (NENL). Energetic characteristics of earthward and tailward ion beams are similar indicating similar acceleration conditions at ion kinetic scales at both sides of an X line independently of its location. Conversely, electron velocity distributions observed near magnetic separatrix earthward of the distant neutral line (DNL) differ from those observed tailward of the NENL. Earthward of the DNL a scattered and thermalized electron population without energetic field-aligned beams is observed near the separatrix. On the contrary, tailward of the NENL field-aligned electron beams accelerated to a few kiloelectron volts are detected. These observations show that near DNL the electron scattering and thermalization dominate over the direct acceleration, whereas stronger electric fields in the NENL produce substantial population of field-aligned kiloelectron volt electrons.

MMS Observations of Reconnection Separatrix Region in the Magnetotail at Different Distances From the Active Neutral X‐Line

“…Before 0419 UT the electron density is low (e) and spacecraft potential is large-(f) with indications that electron density dropped down by a factor 2 below its lobe values between 0418 and 0419 UT. Maximal parallel energy of accelerated electrons ∼500 eV was attained at ∼0418:20 (c), such rather low value is typical for distant reconnection events observed tailward of lunar orbit (Grigorenko et al, 2019). Energy-dispersed energetic proton beam developed since 0418:10 UT (h) and the gradual increase of electron density was observed (e).…”

Space plasma physics science opportunities for the lunar orbital platform - Gateway

“…It is then exposed not to the solar wind but to the terrestrial magnetotail plasma environment, offering the possibility to study in-situ magnetotail dynamics and its dependence on solar and geomagnetic activity (e.g., Kallio and Facskó, 2015;Kallio et al, 2019). Phenomena such as plasmoids released from the near-Earth magnetotail and propagating anti-Sunward, hot plasma flows, energetic particle bursts, plasma waves, magnetic reconnection and plasma sheet dynamics can thus be studied in-situ (e.g., Parks et al, 2001;Nakamura, 2006;Taylor et al, 2006;Nagai et al, 2009;Du et al, 2011;Artemyev et al, 2017;Grigorenko et al, 2019;Sitnov et al, 2019;Kronberg et al, 2021).…”

Energetic Ions Downtail of the Reconnection Site

“…Grigorenko et al. (2019) studied ion and electron beams observed by the ARTEMIS probes near the plasma sheet boundary layer (PSBL). They found no significant differences in characteristics between earthward and tailward ion beams, nor between beams observed on open or closed field lines.…”

“…They showed that typical ion energy spectra obtained in the outflows are characterized by increased fluxes at energies above 10 keV compared to the ion spectra in the background plasma sheet, while the spectral shape was non-Maxwellian with a pronounced high energy tail. Grigorenko et al (2019) studied ion and electron beams observed by the ARTEMIS probes near the plasma sheet boundary layer (PSBL). They found no significant differences in characteristics between earthward and tailward ion beams, nor between beams observed on open or closed field lines.…”