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Modern Solar Facilities – Advanced Solar Science, 27–30 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 LYRA - a solar UV radiometer using diamond detectors A. Theissen1,* , A. BenMoussa2 , U. Schühle1 , J.-F. Hochedez2 , and W. Schmutz3 1 Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany 2 Royal Observatory of Belgium, Brussels, Belgium 3 Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center (PMOD/WRC), Switzerland * Email: theissen@mps.mpg.de Abstract. LYRA, the Lyman-α radiometer, is a high–cadence (100 Hz) solar VUV radiometer which will measure disk–integrated irradiances in 4 wavelength channels. Special emphasis is given on novel detectors based on diamond which will be tested for the first time in space. Two kinds of detectors are employed: MSM– and PiN–type detectors. Their particular advantage compared to silicon detectors lies in their solar blindness with a UV/visible reduction ratio of at least four orders of magnitude, which simplifies the design of UV instruments. 1 Introduction Three areas of research are particularly dependent on monitoring the UV solar irradiance: since the solar UV irradiance is the main source of energy deposited in the Earth’s atmosphere and governs its thermal and chemical structure, it provides valuable data for atmospheric studies, e.g. in investigating its ozone balance (Egorova et al. 2004). It is also a main indicator for the radiation and particle environment in space (’Space Weather’), impacting Earth orbiting satellites, ground-based telecommunication, and other technologies. Last but not least, it is a main source of information about physical processes on the Sun itself. Past, present and future missions dedicated to solar irradiance monitoring all show a particular strength in terms of wavelength coverage, spectral resolution, cadence, time coverage or mission lifetime (for an overview, see Table 1 in Hochedez et al. 2006). LYRA will be unique in adding the capability of very high cadence measurements, aiming at a highest possible cadence of 100 Hz, i.e. providing a set of measurements every 10 ms. As LYRA will regularly monitor solar eclipses, it will also scan the vertical absorption profile of the Earth’s atmosphere, where high cadence translates into a high spatial resolution. A main driver of the mission is the first time use of novel diamond photoconducting and semiconducting technologies in space. Together with other instruments, most notably SWAP (’Sun Watcher with APS detectors and image Processing’, Berghmans et al. 2006) which will provide EUV images, LYRA is part of the Proba2 (project for on-board autonomy) spacecraft of the European Space Agency (ESA), a mission aimed at demonstrating novel space technologies and due for launch in late 2007. This proceedings paper gives a short description of the mission and diamond detectors. 28 A. Theissen et al.: LYRA - A solar UV radiometer using diamond detectors Figure 1. Sketch of a LYRA unit with 4 wavelength channels (left) and photograph of the LYRA instrument and its 3 radiometer units (right). More detailed information and a complete list of publications can be found on the web-site at http://lyra.oma.be. 2 Instrument description LYRA will measure the disk–integrated solar irradiance in four wavelength bands: 1–20 nm (Zirconium filter channel), 17-70 nm (Aluminium filter channel), 115–125 nm (Ly–α line), and 200–220 nm (Herzberg continuum). The spectral filter transmittances are plotted in Fig. 2. LYRA consists of three almost identical units (they only have minor differences in detectors, see Sect. 3) of which any two can operate simultaneously. This allows an intercomparison of the performance of each unit for calibration purposes, and monitoring of eventual degradation with time. UV LEDs in each unit provide additional calibration. Figure 1 shows a sketch of one unit, consisting of collimator, 3–mm precision apertures, filters, detectors and calibration UV LEDs, together with a photograph of the assembled instrument with all three units. Detectors are designed and fabricated in Belgium by IMOMEC together with the National Institute for Materials Science (NIMS) in Tsukuba, Japan. The optical, electronical and mechanical design is provided by the Physikalisch-Meteorologisches Observatorium Davos (PMOD) in Switzerland. The unobstructed field of view is 2.06 deg on a circular detector sensitive area with 4.2 mm diameter. 3 Diamond detectors Key elements of the LYRA design are novel solar–blind detectors based on diamond. Solar blindness stems from the fact that diamond is a wide bandgap semiconductor with a gap energy of ≈ 5.5 eV at room temperature. This translates into a...

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