On the Challenges of Measuring Energetic Particles in the Inner Belt: A Geant4 Simulation of an Energetic Particle Detector Instrument, REPTile‐2

Abstract

Following the retirement of the community supported Van Allen Probes mission, the quest for high‐quality energetic particle measurements in the radiation belts is likely to be taken on by smaller spacecraft like CubeSats in the foreseeable future. Here we introduce the Relativistic Electron Proton Telescope integrated little experiment‐2 (REPTile‐2), a miniaturized (∼1.5 U) solid‐state charged particle telescope that aims to undertake this challenging task. It incorporates detailed pulse‐height analysis to enable 60 electron channels and 60 proton channels and includes anticoincidence detectors to minimize unwanted background contamination. This paper presents a description of the REPTile‐2 design and emphasizes the importance of extensive Geant4‐based analysis to inform the design of a new energetic particle detector and characterize the instrument response. Our analysis shows that REPTile‐2 can measure ∼0.3–∼4 MeV electrons and ∼6.7–35 MeV protons with energy resolution (∆E/E) of 7%–38% for electrons and 1.5%–5% for protons. Results from a Sr‐90/Y‐90 radioactive source test have verified the instrument performance and the validity of the Geant4 simulations. These energetic particle measurements will enable a new scientific understanding of the inner radiation belt, where unwanted contamination from the unforgiving penetration of highly energetic protons (tens of MeV to GeV) is common, and provide detailed quantification of the inner belt electrons and protons in the low‐Earth orbit that is crucial for space weather modeling.

Observations of Relativistic Electron Enhancement and Butterfly Pitch Angle Distributions at Low L (<3)

“…With the PHA data set available, a new binning process is formulated and analyzed using Monte Carlo simulations in the Geant4 toolkit to characterize the behavior of new electron bins. The result of this process is an instrument response function that quantifies the contribution of electrons at each energy to each channel (e.g., Khoo et al., 2022). A similar process was previously used for proton detection from REPT PHA data (Selesnick et al., 2018) and to constrain the electron flux at low L at the energies of the standard REPT data (Li et al., 2015).…”

Design and Instrument Characterization of the High‐Energy Resolution Relativistic Electron Telescope (HERT) Using Geant4 Simulation

“…A particle source can be defined with variety of input parameters such as given energy range, source shape, and angle distribution. Following previous literature (Khoo et al., 2022; Yando et al., 2011), a spherical particle source centered on the middle of first detector with a radius of 85 mm was initially selected for instrument categorization in a more realistic particle environment (Figure 2 left panel). The angular distribution from the source is a cosine distribution so that the particle flux inside the source sphere is isotropic.…”

“…The High Energy Resolution relativistic electron Telescope (HERT) is a miniaturized particle telescope designed for a CubeSat mission in geosynchronous transfer orbit (GTO). HERT follows the heritage from the REPT instrument (Baker et al., 2013, 2021) on the Van Allen Probes and the REPTile instrument (Khoo et al., 2022; Li et al., 2022; Q. G. Schiller et al., 2010; Q. Schiller et al., 2014),on the Colorado Student Space Weather Experiment (CSSWE) (Li et al., 2012, 2013) to provide high energy resolution electron flux measurements for 1–7 MeV electrons. The main design requirements for HERT are the miniaturization (≤3U) and high energy spectral resolution ( dE / E ≤ 12%).…”

“…The High Energy Resolution relativistic electron Telescope (HERT) is a miniaturized particle telescope designed for a CubeSat mission in geosynchronous transfer orbit (GTO). HERT follows the heritage from the REPT instrument (Baker et al, 2013(Baker et al, , 2021 on the Van Allen Probes and the REPTile instrument (Khoo et al, 2022;Li et al, 2022;Q. G. Schiller et al, 2010;Q.…”

Estimation of Geometric Factors for the Particle Detecting Instruments of the Geostationary Satellite GK2A at 128.2°E Longitude Based on Observations of the Outer Radiation Belt During Geomagnetically Quiet Periods

“…Second, the numerical simulation presents a highly idealized response of the instrument and does not consider the actual configuration of the instrument. Because the Monte Carlo simulation used to estimate the detector response is CPU‐intensive, the simulation is often undertaken for a simplified instrument residing isolated within a hypothetical domain (Baker et al., 2014; Khoo et al., 2022; Park et al., 2021; Rodríguez‐Pacheco et al., 2020; Ruffenach et al., 2020; Seon et al., 2020; Siegl et al., 2009; Spence et al., 2010; Yando et al., 2011). This simplification of instrument configuration may lead to inaccurate estimation of geometric factors, especially when there are heavy shadowing effects of charged particle fluxes owing to the presence of a spacecraft platform.…”