Development of the High-resolution FUV Detector for the BepiColombo Mission

Abstract

The PHEBUS (Probing of Hermean Exosphere By Ultraviolet Spectroscopy) instrument on Mercury Planetary Orbiter in the BepiColombo mission is a dual FUV-EUV spectrometer (EUV: 55-155 nm, FUV: 145-315 nm). We are now developing the compact detector system sensitive to FUV airglow emissions of the Mercury. The FUV detector is required to have high spatial resolution (512×512 pixels) so that the wavelength resolution of the PHEBUS instrument should be 2 nm at the FUV range. The FUV detector consists of a Cs2Te photocathode, microchannel plates (MCPs), and a resistive anode encoder. In a position-sensitive system with a resistive anode encoder, the spatial resolution is determined by the signal-to-noise ratios at the anode terminals. Therefore, a high and stable electron gain of MCPs allows the position determination of each photoelectron event with high spatial resolution. We studied a method for achieving a high and stable electron gain. We fabricated a test model of the FUV detector incorporating a clamped pair of MCPs (V-stack) followed by a gap and a clamped triplet of MCPs (Z-stack) in cascade. We investigated the effect of the negative inter-stack potential on the PHD and the spatial resolution by means of calculation and experiments. As a result, the negative inter-stack potential made the electron gain more stable and the spatial resolution higher by ~14%. In this paper we report the specific performance of the test model of the FUV detector.

Ecliptic North‐South Symmetry of Hydrogen Geocorona

“…The detector unit consists of five‐stage microchannel plates and a resistive anode. It is identical to the Far Ultraviolet (FUV) detector unit in the Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS) instrument on the Mercury Planetary Orbiter as part of the BepiColombo mission (Murakami et al, ), except for the photocathode material. The detector plane of LAICA includes a CsI photocathode whereas PHEBUS/FUV has a Cs 2 Te photocathode.…”