The Spin-plane double probe instrument (SDP) is part of the FIELDS instrument suite of the Magnetospheric Multiscale mission (MMS). Together with the Axial double probe instrument (ADP) and the Electron Drift Instrument (EDI), SDP will measure the 3-D electric field with an accuracy of 0.5 mV/m over the frequency range from DC to 100 kHz. SDP consists of 4 biased spherical probes extended on 60 m long wire booms 90∘ apart in the spin plane, giving a 120 m baseline for each of the two spin-plane electric field components. The mechanical and electrical design of SDP is described, together with results from ground tests and calibration of the instrument.

/pdf/the-spin-plane-double-probe-electric-field-instrument-for-22mzx2keqx.pdf

The Spin-Plane Double Probe Electric Field Instrument for MMS

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ∼15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the “highest quality” events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

https://link.springer.com/content/pdf/10.1007%2Fs11214-013-0013-7.pdf

The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission

The nature of small-scale turbulent fluctuations in the solar wind is investigated using a comparison of Cluster magnetic and electric field measurements to predictions arising from models consisting of either kinetic Alfven waves or whistler waves. The electric and magnetic field properties of these waves from linear theory are used to construct spacecraft-frame frequency spectra of (|δE|/|δB|) s/c and (|δB ∥|/|δB|) s/c , allowing for a direct comparison to spacecraft data. The measured properties of the small-scale turbulent fluctuations, found to be inconsistent with the whistler wave model, agree well with the prediction of a spectrum of kinetic Alfven waves with nearly perpendicular wavevectors.

https://iopscience.iop.org/article/10.1088/2041-8205/745/1/L9/pdf

Identification of kinetic alfven wave turbulence in the solar wind

The European Space Agency's Cluster programme is designed to study the small-scale spatial and temporal characteristics of the magnetospheric and near-Earth solar wind plasma. The programme is composed of four identical spacecraft which will be able to make physical measurements in three dimensions. The relative distance between the four spacecraft will be varied between 200 and 18000 km during the course of the mission. This paper provides a general overview of the scientific objectives, the configuration and the orbit of the four spacecraft and the relation of Cluster to other missions.

Cluster - Science and Mission Overview

Highlights are presented from studies of the electric field data from various regions along the CLUS- TER orbit. They all point towards a very high coherence for phenomena recorded on four spacecraft that are sepa- rated by a few hundred kilometers for structures over the whole range of apparent frequencies from 1 mHz to 9 kHz. This presents completely new opportunities to study spatial- temporal plasma phenomena from the magnetosphere out to the solar wind. A new probe environment was con- structed for the CLUSTER electric field experiment that now produces data of unprecedented quality. Determination of plasma flow in the solar wind is an example of the capability of the instrument.

/pdf/first-results-of-electric-field-and-density-observations-by-3gl4gmasmp.pdf

First results of electric field and density observations by Cluster EFW based on initial months of operation

The electric-field and wave experiment (EFW) on Cluster is designed to measure the electric-field and density fluctuations with sampling rates up to 36000 samples s-1. Langmuir probe sweeps can also be made to determine the electron density and temperature. The instrument has several important capabilities. These include (1) measurements of quasi-static electric fields of amplitudes up to 700 mV m-1 with high amplitude and time resolution, (2) measurements over short periods of time of up to five simualtaneous waveforms (two electric signals and three magnetic signals from the seach coil magnetometer sensors) of a bandwidth of 4 kHz with high time resolution, (3) measurements of density fluctuations in four points with high time resolution. Among the more interesting scientific objectives of the experiment are studies of nonlinear wave phenomena that result in acceleration of plasma as well as large- and small-scale interferometric measurements. By using four spacecraft for large-scale differential measurements and several Langmuir probes on one spacecraft for small-scale interferometry, it will be possible to study motion and shape of plasma structures on a wide range of spatial and temporal scales. This paper describes the primary scientific objectives of the EFW experiment and the technical capabilities of the instrument.

M Thomsen

Papers

The electric field and wave experiment for the cluster mission