The Energetic Particle Experiment on Plasma Observatory

Plasma Observatory is a candidate mission of the European Space Agency (ESA) with a possible mission selection foreseen in 2026 and possible mission adoption in 2029. The mission aims to investigate cross-scale coupling and plasma energization across key regions of the magnetosphere, including: the bow shock, magnetopause, magnetotail and transition regions. To achieve this aim, Plasma Observatory will investigate the rich range of interesting plasma phenomena in these regions in the Earth’s magnetosphere, using a constellation of seven sister spacecraft. This allows configuration of the spacecraft in two nested tetrahedra to probe coupling on both ion and fluid scales. Since energetic particles are sensitive tracers of energization processes, altering the energy (or velocity) of both ions and electrons, measuring these effects in situ and at high cadence is of high importance for the mission. Energetic electrons and ions will be measured by the Energetic Particle Experiment (EPE). Here we present the instrument, which is a compact, dual-particle telescope, solid state detector design originally based on ELFIN’s EPD instrument. Using three telescopes (sensor heads), it achieves near 3-D distributions for ions and electrons (135 x 360 deg). The development consists of deflecting magnets on the ion side (to screen out electrons) and Aluminized Kapton foil covers to screen out low energy ions on electron side. The baseline energy range (30-600 keV) for both species (with a goal for 20-600 keV at spin cadence) is targeted on low-end, suprathermal energies (minimising the effective gyro-scales for the computation of moments, PAD (e) and VDF determination). An extended energy range of up to 1.5 MeV at lower cadence is possible for ions.  This arrangement allows the potential for spatial differences to be resolved on at least ion to fluid scales and to sense plasma boundaries. Detector layering is based on expected dynamic energy range and allows coincident/anti-coincident logic to be applied to separate out the higher energy species.