DETECTION OF LOW-ENERGY NEUTRAL ATOMS IN THE PLANETARY ENVIRONMENTS

Microchannel Plates (MCP) detectors are frequently used in space instrumentation for detecting a wide range of radiation and particles. The capability to detect non-thermal low energy neutral species is crucial for the ELENA (Emitted Low-Energy Neutral Atoms) sensor, which is part of the SERENA package (Search for Exospheric Refilling and Emitted Natural Abundances) on board the MPO spacecraft of the BepiColombo mission of ESA to Mercury, which is scheduled for launch in August 2015. ELENA is a Time of Flight (TOF) sensor, based on a novel concept using an ultra-sonic oscillating shutter (Start section) and MCP detector (Stop detector). The ELENA scientific objective is to monitor the emission of neutral atoms from the surface of Mercury by detecting energetic neutral atoms in the range 10 eV – 5 keV, within 76° FOV, perpendicular to the S/C orbital plane. The surface is scanned thanks to the spacecraft motion. In particular, processes of particle release from the surface will be investigated by identifying particles released via solar wind-induced ion sputtering (with energies > 1eV – < 100 eV) as well as energetic Hydrogen atoms, which are back-scattered solar wind protons, at energies of hundreds eV. MCP absolute detection efficiency for very low energy neutral atoms (E < 30 eV) is a crucial point for this investigation. At the MEFISTO facility of the University of Bern, measurements on three MCP with different coatings have been performed providing the first data of MCP detection efficiencies in the energy range 10eV – 1keV.