The Medium Energy Electron Telescope (MEET): Geant4‐Based Instrument Design and Analysis

Abstract

While the recent Van Allen Probes mission has provided a wealth of trapped particle measurements, questions still arise from analysis of their data. In particular, 10–100s of keV electrons exhibit dynamics not well understood with current data. Injections of 33–80 keV electrons can occur during both storm and quiet times as shown by Van Allen Probes data. However, due to the Probes' orbit, they can not distinguish precipitation during these events, necessary to quantify injection rates. Analysis of a Low Earth Orbit (LEO) mission measuring these electron populations found enhancements not explained with current injection sources. Future measurements including the quasi‐trapped and precipitating populations are necessary to resolve these dynamics. We present the Medium Energy Electron Telescope to resolve these uncertainties surrounding 10–100s of keV electrons in the inner belt. This solid‐state particle telescope is optimized for these measurements in the high‐flux inner belt environment, with flight heritage from prior instruments. However, novel instrument design is required to measure these populations at fine energy resolution and fit the instrument into a 1U volume, including that of the detectors, electronics, instrument housing, and collimator components. The design is guided by Geant4 analysis and consideration for expected fluxes using the AE9 and AP9 models for a LEO mission and associated tradeoffs are discussed. We develop 59 energy channels with fine nominal resolution (<20%) for 30–800 keV electrons and show proton measurement capabilities for 1.1–>60 MeV populations. Instrument saturation and proton contamination are quantified by analysis of the instrument's response.