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Van Allen Probes
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Electric Field and Waves Suite (EFW)

EFW will study the electric fields in near-Earth space that energize radiation particles and modify the structure of the inner magnetosphere.

This investigation consists of a set of four spin-plane electric field (E-field) antennae and a set of two spin-axis stacer (tubular, extendable) booms. The investigation will provide understanding of the electric fields associated with particle energization, scattering and transport, and the role of the large-scale convection electric field in modifying the structure of the inner magnetosphere.

EFW Science Investigation Objectives:

Measure electric fields associated with a variety of mechanisms causing particle energization, scattering and transport in the inner magnetosphere, including:

  • Energization by the large-scale convection E-field
  • Energization by substorm injection fronts propagating in from the magnetotail
  • Radial diffusion of energetic particles mediated by ultra-low frequency (ULF) magnetohydrodynamic (MHD) waves
  • Transport and energization by intense magnetosonic waves generated by interplanetary shock impacts upon the magnetosphere
  • Coherent and stochastic acceleration and scattering of particles by small-scale, large-amplitude plasma structures, turbulence and waves (electromagnetic and electrostatic ion cyclotron waves, kinetic Alfven waves, solitary waves, electron phase space holes, zero frequency turbulence).

Why Measure E on Van Allen Probes?

  • The dynamics of the Earth’s radiation belts are all about particle energization, scattering, and transport; in other words, particle acceleration.
  • In collisionless plasmas, such as the Earth’s radiation belts, the electromagnetic field is responsible for all observed particle acceleration.

Particle acceleration occurs in the radiation belts at a variety of spatial and temporal scales:

  • ...from the large-scale E-field associated with the global circulation of plasma in the magnetosphere, down to small-scale structures in plasma density,
  • ...from the slow pumping of particles by ULF waves, to the scattering and energization by high-frequency whistlers.

EFW Instrument:

Spin Plane Booms
Image of Spin Plane Booms

Axial Booms
Image of Axial Booms

EFW Data Products:

Key Measurement Quantities:

  • Spin plane component of E at DC - 12 Hz (0.05 mV/m accuracy)
  • Spin axis component of E at DC - 12 Hz (~3 mV/m accuracy)
  • E- and B-field spectra for nearly-parallel and nearly-perpendicular to B components between 1 Hz and 12 kHz at 6-second cadence
  • Spacecraft potential estimate covering cold plasma densities of 0.1 to ~100 cm-3 at 1-second cadence
  • Burst recordings of high-frequency E- and B-field waveforms, as well as individual sensor potentials for interferometric analyses

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