Plasma Particle Experiment Suite (PPE)

The PPE suite consists of four electron sensors (LEP-e, MEP-e, HEP, and XEP) and two ion sensors (LEP-i and MEP-i). The electron sensors can measure electrons from 10 eV to 20 MeV, while the ion sensors can measure ions from 10 eV/q to 180 keV/q with mass discrimination. Figure 1 shows the energy range of each plasma/particle instrument, together with plasma/particle populations in the inner magnetosphere. The energy ranges of the sensors are designed to overlap each other to provide seamless energy spectra for a wide energy range. The specifications of the PPE sensors are summarized in Tables 1 and 2.

For electron, both HEP and XEP sensors mainly detect relativistic electrons of the radiation belts. These sensors are used to derive the radial profile of the phase space density. Since the anisotropy of the distribution function of hot electrons is free energy for plasma waves, observations of the distribution function by LEP-e and MEP-e are important to clarify how plasma waves are excited in the inner magnetosphere. It was difficult to measure particles with energies lower than tens of keV inside the radiation belts, because of serious contamination by energetic particles [Liu et al., 2005]. Newly developed technologies of reducing the background contamination have been applied to ERG  PPE to allow detailed measurements of tens-of-keV electrons [S. Kasahara et al., 2009].

The LEP-i and MEP-i sensors are ion energy-mass spectrometers. Several ion species can be discriminated with a time-of-flight (TOF) method which also provides effective reduction of the contamination noise due to high-energy particles. In particular, a new technology enables full solid angle measurements of ions up to 180 keV/q [Kasahara et al., 2006]. These ion data will be used to study the evolution of ring current ions. Recent computer simulations showed that the ion hole contributes nonlinear evolution of EMIC waves [Shoji and Omura, 2011], and the ring distribution of ions causes magnetosonic mode waves [Chen et al., 2010]. Measurements by the ERG  satellite will reveal what plasma instabilities excite these waves. Moreover, ion measurements with mass discrimination are necessary for determining the composition of ring current particles and understanding how plasma pressure distributions change the field configuration of the inner magnetosphere during space storms.

Figure 1: Energy range of the plasma and particle experiment instruments.

Table 1: Specifications of PPE (1)
SensorEnergy RangeField of View (elevation x azimuth)Energy ResolutionAngular Resolution (elevation x azimuth)Energy ChannelsAzimuthal SectorsElevation SectorsBitMass AnalysisMass RangeMass Resolution
ElectronXEP400 keV - 20 MeV±10°25 keV20° x 22.5°1816-16---
HEP-L70 keV - 1 MeV 10° x 180°15% at 70 keV, 10% at 100 keV5° x 10°16 (total)161516---
HEP-H700 keV - 2 MeV10° x 180°10% at 2 MeV10° x 10°161516---
MEP-e10 keV - 80 keV5° x 360°10%5° x 5°16323216---
LEP-e10 eV -19 keV2.86° x 270°8.8%2.86° x 22.6° (2.86° x 3.75° fine)3216(12+10+1)16---
IonMEP-i10 keV/q - 180 keV/q5° x 360°15%10° x 22°1616161651-32 AMU M/ΔM=6
LEP-i10 eV/q - 25 keV/q5° x 290°14%5° x 22.5°321516124-H+, He++, He+, O+

Table 2: Specifications of PPE (2)
SensorMeasurement TechniquesWeight (kg)Size (mm)Power (W)
ElectronXEPSi solid-state detector (SSD) + gadolinium silicon oxide scintillator telescope / Anticoincidence detection for noise rejection4.5190φ x 2505.0
HEPMultistacked Si SSD telescope / Coincidence detection for noise rejection3.0200φ x 2008.0
MEP-eCusp-type electrostatic energy analyzer with Si avalanche photo diode / Energy coincidence detection for noise rejection8.0300φ x 40012.0
LEP-eTophat-type electrostatic energy analyzer / Radiation shields for noise suppression6.0200φ x 3009.0
IonMEP-iCusp-type electrostatic energy + Time-of-flight (TOF) type mass analyzer + Si SSD / TOF coincidence detection for noise rejection9.0400φ x 40012.0
LEP-iTophat-type electrostatic energy analyzer + TOF type mass analyzer / TOF coincidence detection for noise rejection7.0200φ x 30010.0
Particle MDP-4.5114 x 253 x 17113.0

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