Evaluation of a Microchannel Plate Detector Gain Change Over Time Using In‐Flight Data

Abstract

Microchannel plates (MCP) detectors have been extensively used in space to measure particles and photons. The primary radiation causes electron emission inside the MCP small pores that transforms into an electron avalanche. This is due to a bias voltage accelerating the secondary electrons down the pores creating more secondary electrons. The typical gain of 10 ⁷ at the beginning of life decreases with the charge extracted from the MCP. The gain can be recovered by increasing the bias voltage until the charge extracted reaches the end‐of‐life of the MCP (typically several C/cm ² ). The gain decrease with charge extracted experienced by MCP detectors in space instruments affects their overall sensitivity. Since the sensitivity is used to convert the individual counts from the MCP detector into physical quantities of the primary radiation, it is necessary to quantify and track these changes in detector gain. This study shows how in‐flight data from a plasma ion instrument are used to evaluate the gain over time and how to recover the gain loss with bias voltage increase. Since the bias voltage adjustment is occasional, we also show how to estimate the gain as a function of time. Finally, we relate the gain loss or the bias voltage increase required for constant gain with an estimate of the charge extracted from the MCP. These results can be used to evaluate the voltage bias required at the end of the mission, which is useful when designing the detector (e.g., HV standoffs) and the power supplies that bias them.