A SPACE SOLAR PATROL APPARATUS FOR PHOTOMETRIC MEASUREMENTS AT A PHOTON-ENERGY RANGE OF 8 eV TO 8 keV

Abstract

At the Vavilov State Optical Institute (SOI) a special apparatus and a methodology have been developed which enable one to measure absolute fluxes from the full disk of the Sun in the VUV, the EUV and the soft X-ray spectral ranges (0.14–157 nm). The apparatus allows one to carry out absolute spectral measurements using simultaneous operation of the radiometer and spectrometers. The radiometer is equipped with a special disk on which several filters are fitted (foils, thin films and crystals). This enables one to carry out measurements in the spectral range of 0.14–157 nm. The EUV grating spectrometer with normal incidence provides five spectral channels with a channel width of 35 nm each for measurements in the spectral range under 155 nm. The spectral range of 1.8–60 nm can be covered by a soft X-ray grazing grating spectrometer. All instruments are equipped with the same detectors, namely with the open secondary electron multipliers (SEM) with photocathodes made of BeO which were developed at the SOI. This photocathode has a good sensitivity in the spectral range under 150 nm and its sensitivity falls practically down to zero at wavelengths greater than 160 nm. The SEM has a high amplification (up to 108) and is stable to atmospheric influence. The stability of the SEM could be controlled by the radiation of the isotope 55 Fe (0.2 nm). There are plans to use this complex for mutual calibration of various synchrotron sources. Moreover it is planned to launch the Space Solar Patrol mission at the Russian Module of the International Space Station.