The Cherenkov Telescope Array ( ) is a future gamma-ray observatory that is planned to significantly improve upon the sensitivity and precision of the current generation of Cherenkov telescopes. The observatory will consist of several dozens of telescopes with different sizes and equipped with different types of cameras. Of these, the FlashCam camera system is the first to implement a fully digital signal processing chain which allows for a traceable, configurable trigger scheme and flexible signal reconstruction. As of autumn , a prototype FlashCam camera for the medium-sized telescopes of nears completion. First results of the ongoing system tests demonstrate that the signal chain and the readout system surpass requirements. The stability of the system is shown using long-term temperature cycling.

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Observations of ultraviolet light is the key to understand high temperature processes in the universe like hot plasma, accretion processes or illuminated protoplanetary discs around UV sources. Furthermore these observation contribute to major cosmological questions, like the distribution of baryonic matter or the formation of the milky way, as pointed out by Gomez de Castro et al. 1 Driven by the idea to participate in the Russian World Space Observatory we started to develop a position sensitive micro channel plate detector (MCP) for spectroscopy in the range of 160 nm to 300 nm. Although we are not part of this project we still build a MCP detector prototype. In this paper we will present the general design of the detector and mainly focus on the aspect of our photocathode, while the electronics will be explained in more detail in the paper "Characterisation of low power readout electronics for a UV microchannel plate detector with cross-strip readout" (Paper number 9144-116) by Marc Pfeifer.Keywords: micro channel plate detector, caesium telluride photocathodes THE MCP DETECTORS DESIGNThe Institute of Astronomy and Astrophysics Tübingen has a long tradition in developing ultraviolet sensitive detectors and based on the heritage of the 1990's flight of ORFEUS we develop a position sensitive, solarblind, photon counting micro channel plate detector. Even if there is an ongoing progress in the development of CCD detectors for all wavelengths, they are victims of their high performance in the optical band, which generates a high noise compared to the desired UV band. By using solar-blind photocathodes our MCP detector avoids this problem and doesn't need extensive shielding or additional filters for a low signal-to-noise-ratio which, in combination with their fast readout, makes such a detector still leading in ultraviolet spectroscopy. Working principleDepending on the field of use, there are two concepts for MCP detectors, either a sealed detector with a semitransparent photocathode coated on an entrance window or an open-faced detector with an opaque photocathode directly on the micro channel plates. As the MCPs work with high voltage in the range of several thousand volts, they need to be operated under vacuum conditions with a pressure below 1 × 10 −5 mbar to avoid damage by accelerated particles. Therefore open-faced detectors only work in space, while sealed detectors can be operated everywhere, also in non-astronomical fields. Furthermore the photocathodes degrade under oxygen exposure, 2 so they need to be stored under vacuum conditions (or inert gas), which complicates the use of open-faced detectors, as they need a sealed envelope until the detector is in space. As shown in fig. 1 and fig. 2 any incoming photon that hits the photocathode, releases an electron which is accelerated towards the micro channel plates, where it creates an avalanche of additional electrons. Depending on the MCP configuration and applied voltage a gain factor of 1 × 10 5 to 1 × 10 7 is achieved. This electron cloud hits a cha...