Detection efficiency of microchannel plates 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 plates (MCP). These detectors are sensitive not only to the incident energetic charged particles themselves but also to the final end-product energy deposited by energetic electrons, ions, and X-rays/gammas. The resulting radiation-induced background noise can potentially contaminate the science signal. This issue constitutes undoubtedly one of the main challenges together with the radiation hardness of the electronics for particle instruments onboard future missions to Jupiter like the European Space Agency (ESA) 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 MCP 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–noise ratio (SNR) of the instrument, and, hence, ensure that the instrument will return useful scientific data when operated in the Jovian magnetosphere. We describe and report in the present paper the results of an experiment in which we measured the response of Photonis MCP detectors to 300–1500 keV electrons and 500 keV photons (gamma rays) using a Van de Graff electron gun available at ONERA, Toulouse, France. The efficiency of the tested MCP for high-energy electrons is about 20–30% below 100 keV and is reduced to 10% for electron energies greater than 100 keV. The efficiency of the tested MCP for the gamma radiation of 500 keV energy is approximately 0.1%.