Microchannel Plate Efficiency to Detect Low Velocity Dust Impacts

Abstract

Recent space experiments suggest that electron and ion energy analyzers using microchannel plates (MCPs) as detectors are also registering direct hits by nanodust particles. To allow the analysis and interpretation of these putative dust events, the detection efficiency of MCPs has to be characterized. We report on a series of experiments to investigate the detection efficiency of MCP detectors to direct impacts for both positively and negatively charged micron and submicron sized iron particles. A double-stack MCP detector in a chevron configuration was mounted as a target in a dust accelerator. A range of particle velocities and masses were used for a comprehensive examination. The MCP detected and produced definite signals associated with confirmed particle impacts of the MCP for both positively and negatively charged dust particles. The detection efficiency was found to be (6 ± 1)% for positively charged dust and (9 ± 3)% for negatively charged dust particles with a characteristic mass of 6.0 × 1011μ (10−15 kg) and speed of 100 m/s. The examined particle velocity range accurately replicates Rosseta's interaction with dust grains emanating from comet 67P/ Churyumov-Gerasimenko's nucleus. Additionally, the MCP detection efficiency for low velocity particles shows a possible underestimate of higher speed nanograin signals from Cassini's electron plasma spectrometer during its flyby through Enceladus' active south pole.