The Medium and High Energy Neutral Atoms (MH-ENA) detector for the BepiColombo Mission to Mercury

The charge-exchange interaction of energetic plasma of solar wind or magnetospheric origin with the exospheric gas around Mercury has the potential of generating strong energetic neutral atom (ENA) emission. The temporal evolution on short time scales of the solar wind-magnetosphere interaction as well as the magnetospheric plasma dynamics could be studied through the analysis of the flux of such energetic neutrals. The MH-ENA detector is part of the Neutral Particle Analyzer (NPA) to be proposed for the BepiColombo mission to Mercury. MH-ENA is a nadir-pointing 2-D sensor with an instantaneous FOV of 88 deg x 60deg. Its design is optimized for the detection of energetic neutrals, from 1 keV to >30 keV. The detector consists of a pinhole-focusing ENA camera. First, the environmental ions are suppressed by a biased HV collimated pin-hole telescope. The collimated energetic neutrals traverse a thin carbon foil (< 1 g/cm2), causing an up-streaming SE emission, that are collected by a dedicated MCP to generate the START signal. After a short (~1cm) flight, particles then hit a 2D detection system, which generates the STOP signal for Time-of-flight measurement, as well as the positional information for determining the velocity direction.