Contamination in electron observations of the silicon detector on board Cluster/RAPID/IES instrument in Earth's radiation belts and ring current

Abstract

Since more than 15 years, the Cluster mission passes through Earth's radiation belts at least once every 2 days for several hours, measuring the electron intensity at energies from 30 to 400 keV. These data have previously been considered not usable due to contamination caused by penetrating energetic particles (protons at >100 keV and electrons at >400 keV). In this study, we assess the level of distortion of energetic electron spectra from the Research with Adaptive Particle Imaging Detector (RAPID)/Imaging Electron Spectrometer (IES) detector, determining the efficiency of its shielding. We base our assessment on the analysis of experimental data and a radiation transport code (Geant4). In simulations, we use the incident particle energy distribution of the AE9/AP9 radiation belt models. We identify the Roederer L values, L⋆, and energy channels that should be used with caution: at 3≤L⋆≤4, all energy channels (40–400 keV) are contaminated by protons (≃230 to 630 keV and >600 MeV); at L⋆≃1 and 4–6, the energy channels at 95–400 keV are contaminated by high‐energy electrons (>400 keV). Comparison of the data with electron and proton observations from RBSP/MagEIS indicates that the subtraction of proton fluxes at energies ≃ 230–630 keV from the IES electron data adequately removes the proton contamination. We demonstrate the usefulness of the corrected data for scientific applications.

Adiabatic Invariants Calculations for Cluster Mission: A Long‐Term Product for Radiation Belts Studies

“…Since the RAPID/IES electron flux measurements are subject to contamination in the radiation belts region, it is necessary to perform a background data correction to avoid erroneous values during the next steps. In the present paper we use the empirical contamination coefficients described in detail in Kronberg et al () and Smirnov, Kronberg, Latallerie, et al (). Kronberg et al () derived empirical percentages of contamination for different values on all IES energy channels.…”

“…In the present paper we use the empirical contamination coefficients described in detail in Kronberg et al () and Smirnov, Kronberg, Latallerie, et al (). Kronberg et al () derived empirical percentages of contamination for different values on all IES energy channels. The contamination coefficients for Channels 1 and 3 are shown in Table .…”

“…It should be noted that the IES detector was not specifically designed for radiation belts studies and as such is subject to background contamination by the high‐energy electrons ( 400 keV) and inner‐zone protons. However, the recently developed background correction techniques proved to efficiently remove the contamination thus making an enormous data set available for the inner‐magnetospheric science (Kronberg et al, ; Smirnov, Kronberg, Latallerie, et al, ).…”

Extension of an Empirical Electron Flux Model From 6 to 20 Earth Radii Using Cluster/RAPID Observations

“…Contamination less than 10% is not considered to be significant, as it is within error bar of RAPID measurements. The flux data used in the model have not been corrected for contamination; users should be aware of the contamination issue above 95 keV and refer to Kronberg et al () for further insight into the problem. One further issue affects the fluxes from RAPID/IES, namely, a very low nonzero background (well below the one‐count‐per‐second level), that is, likely due to solar cycle‐modulated cosmic rays and has been quantified in detail by Kronberg et al (, see also Smirnov et al, ).…”

“…The new model introduced below is a first attempt to extend the current models radially outward from GEO and is based on electron observations made by the C4 ( Space Weather Daly (2018). Additionally, it has been shown that in the inner magnetosphere, there is contamination of the RAPID/IES fluxes due to energetic electrons and ions present in the radiation belts and ring current (Kronberg et al, 2016. This contamination varies with radial location and energy channels, although in the region L* = 6-9, the contamination is greatest in the top three energy channels and is dominated by >400-keV electrons.…”