Detection efficiency of micro channel plates and channel electron multiplier detectors to penetrating radiation in Space

Abstract

Space-based instruments for detection of photons, plasma, and energetic neutral atom imaging include electron multiplier detectors that are subject to increased transient noise, long-term degradation and even potential failure due to the substantial fluxes of high-energy particles that penetrate the instrument in the space environment. The most commonly used electron multiplier detectors are Multi-Channel Plate (MCP) and Channel Electron Multiplier (CEM). These detectors are sensitive not only to the incident energetic charged particles themselves but they are also sensitive to the final end-product energy deposited by energetic electrons, ions, and X-rays. The resulting radiation-induced background noise can potentially swamp the science signal. This issue constitutes undoubtedly the main challenge for particle instruments onboard future missions to Jupiter like the European Space Agency Jupiter ICy moon Explorer (JUICE), and requires dedicated and innovative radiation mitigation techniques (e.g., multiple coincidence, anti-coincidence) far beyond the simple passive shielding techniques commonly used to protect electronics and other subsystems against Total Ionizing Dose (TID). The accurate response (i.e., efficiency) of MCPs and CEMs detectors against high-energy particles is however not well known, with limited estimates available in the literature. This makes it complicated in particular to reliably predict the Signal to Noise ratio of the instrument, and, hence, ensure that the instrument will return useful scientific data when operated in the Jovian magnetosphere. Here, we first use real measurements from the Galileo Plasma spectrometer (PLS) instrument to derive the background noise measured by CEMs in the Jovian environment. These measurements are used in combination with Geant4 simulations in order to estimate the efficiency of CEMs against high-energy electrons. We then present the results of an experiment in which we measured and compared the response of MCP and CEM detectors to keV-MeV electrons and keV X-rays using a Van de Graff electron gun available at ONERA, Toulouse, France. These experimental tests were funded by the french space agency CNES in support of the JUICE mission and in particular for the contribution of the Institut de Recherche en Astrophysique et Planétologie to the Particle Environment Package (PEP).