Electron Phase‐Space Holes in Three Dimensions: Multispacecraft Observations by Magnetospheric Multiscale

Abstract

Electron phase‐space holes are kinetic plasma structures commonly observed in space plasmas on Debye length scales. Near the Earth's duskside flank at 10 Earth radii, a series of 32 electron holes (EHs) are detected within a 1‐s window on all four Magnetospheric Multiscale spacecraft. The spacecraft separation of <7 km is similar to the expected EH size in this region. Length, width, amplitude, and relative positions are determined for individual EHs using a cylindrically symmetric model fit to Magnetospheric Multiscale E field measurements. The model shows good agreement with observed E fields far from the EH center. Deviations in E⊥ from the model are present near the center, indicating observed EHs have complex, sometimes irregular, internal structure. Perturbation magnetic fields δB modeled assuming an E × B0 electron current reproduce the measured parallel perturbation in most cases, although there is a systematic variation due to geometric and finite gyroradius effects. Many EHs in this event have large amplitude for their size, reaching the theoretical lower limit in length parallel to the background magnetic field, which requires the electron phase‐space density to approach 0 in the center. It is possible that EHs of this type have recently formed, eventually weakening or becoming longer over time. This study provides the most detailed measurements of EHs to date. Their derived properties are largely in agreement with expectations from previous research. It remains unclear whether the few notable differences are due to rapid time evolution or are specific to the local environment.

Plasma Waves near the Electron Cyclotron Frequency in the Near-Sun Solar Wind

“…Waves near the edges would suggest growth due to instabilities associated with mixing plasma populations (e.g. (Malaspina et al 2015;Holmes et al 2018)). Waves near the magnetic structure center suggest that a property of the plasma within the flux tube is driving the instability.…”

Electron Acceleration and Thermalization at Magnetotail Separatrices

“…The ESWs can roughly be divided into two groups based on their phase speeds, one slower group with v ph <5×10 3 km/s and one faster group with v ph >13×10 3 km/s. Many of the ESWs have significant perpendicular electric fields, which suggests they are three‐dimensional structures, with perpendicular length scales comparable to the parallel length scales (Holmes et al, ; Steinvall et al, ; Tong et al, ). If the shape of an ESW were double Gaussian, all four spacecraft would observe the same l pp but potentially different electric fields depending on their relative position perpendicular to the ESW propagation direction.…”

Collisionless Magnetic Reconnection and Waves: Progress Review

“…At the magnetopause the potentials of EWs are in general lower than those of ESWs (Graham et al, 2016b). With MMS, four-spacecraft interferometry has become routinely applicable, resulting in unambiguous estimates of speeds and parallel length scales, and 3-D characterization of the wave structures (Holmes et al, 2018;Tong et al, 2018;Steinvall et al, 2019b). Phase speeds of EWs and ESWs are highly dependent on their generation mechanism.…”