The Electron Drift Instrument for MMS

Abstract

The Electron Drift Instrument (EDI) on the Magnetospheric Multiscale (MMS) mission measures the in-situ electric and magnetic fields using the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and, to a lesser extent, the gradient in the magnetic field. Although these two quantities can be determined separately by use of different electron energies, for MMS regions of interest the magnetic field gradient contribution is negligible. As a by-product of the drift determination, the magnetic field strength and constraints on its direction are also determined. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument on MMS.

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

“…The MMS spacecraft has spent a large amount of time in the magnetosheath and has crossed the magnetopause many times to capture the dynamics of the magnetic reconnection (Burch et al, 2015), and it has provided many observations of mirror mode structures in the magnetosheath. One of the unique features of MMS mission is the high time resolution of particle and field measurements when the spacecraft is in burst mode (Baker et al, 2016;Ergun et al, 2016;Fuselier et al, 2016;Le Contel et al, 2014;Lindqvist et al, 2014;Pollock et al, 2016;Russell et al, 2014;Torbert et al, 2016). Using burst mode MMS data, there have been recent studies of whistler waves in the magnetosheath associated with mirror mode structures (Breuillard et al, 2017).…”

Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission

“…Additionally, 65,536 S/s AC-coupled electric field data were used to identify Langmuir oscillations in the vicinity of the whistler waves. Data from the Fast Plasma Instrument (FPI) [Burch et al, 2015], electron drift instrument (EDI) [Torbert et al, 2014], and flux gate magnetometer [Russell et al, 2014] provide context for the waves with respect to the reconnection geometry. We show that the whistler mode waves are confined to the boundary layer and propagate along the magnetosphere-side separatrix of the X line.…”

Stable reconnection at the dusk flank magnetopause

“…All of the observations presented here are from MMS-4. The Electron Drift Investigation (EDI) [Torbert et al, 2016] operating in the ambient mode (corresponding to an electron energy of 500 eV) is used to measure electron counts to determine the streaming direction of electrons from the reconnection site, i.e., to locate the direction of the reconnection site relative to MMS. Moments of the ion distributions (particularly, the flow velocity in the magnetosheath), plasma composition, and the identification of the boundary layers and magnetopause current layer are from the Hot Plasma Composition Analyzer (HPCA) instrument [Young et al, 2014].…”

“…These measurements are also used to determine the pitch angle of particles streaming parallel or antiparallel with respect to the local magnetic field. The Electron Drift Investigation (EDI) [Torbert et al, 2016] operating in the ambient mode (corresponding to an electron energy of 500 eV) is used to measure electron counts to determine the streaming direction of electrons from the reconnection site, i.e., to locate the direction of the reconnection site relative to MMS. Omnidirectional electron flux from the Fast Plasma Investigation Dual Electron Spectrometer (FPI-DES) [Pollock et al, 2016] is also used to identify regions during this encounter with the magnetopause.…”