There is one PEACE (Plasma Electron and Current Experiment) instrument on each of the four Cluster spacecraft.

A PEACE instrument is designed to measure the electron velocity distribution in the vicinity of its host spacecraft, covering an energy range of 0.7 eV to about 30 keV and detecting electrons arriving from all possible directions (i.e. 4*pi steradians of solid angle).

Each PEACE instrument has two sensor heads, LEEA and HEEA, which are mounted on opposite sides of the spacecraft such that the instantaneous field of view of one is the same as that seen by the other half a spacecraft rotation period later. LEEA and HEEA differ only in geometric factor (HEEA admits more electrons than LEEA in an identical plasma). Both sensors sample 4*pi steradians per spin. The full energy range is divided into 88 levels. Each sensor is typically set up to sample an energy range of 60 contiguous levels. Both LEEA and HEEA can be used to sample any group of 60 or 30 levels within the full range of 88 levels. Although neither sensor can cover the full energy range, full coverage of the energy range can be achieved by using both together. HEEA will normally cover the upper part of the energy range, since its larger geometric factor enables it to make better measurements of the more diffuse electron population expected at higher energies. When the energy ranges of the two sensors overlap, an appropriate combination of data from the two sensors produces data with an effective 4*pi steradian coverage in the overlap region, every half spin.

Each PEACE instrument makes an onboard calculation of moments (for a restricted energy range) and a spacecraft potential estimate, once every spin.

When Normal Mode telemetry is available, the Moments data and Spacecraft Potential estimate are transmitted to ground, together with Pitch Angle Distributions and a Low Energy Distribution. When Burst Mode Telemetry is available, PEACE can also transmit selected 3-dimensional velocity distribution data.
 

Read about the PEACE Hardware

Return to PEACE Instrument Page

Return to PEACE Home Page
 

Last Updated on22/04/99
By Andrew Fazakerley