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تسجيل مستخدم جديدA Double Vacuum Window Mechanism for Space-borne Applications
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We present a vacuum window mechanism that is useful for applications requiring two different vacuum windows in series, with one of them movable and resealable. Such applications include space borne instruments that can benefit from a thin vacuum window at low ambient pressures, but must also have an optically open aperture at atmospheric pressures. We describe the implementation and successful operation with the EBEX balloon-borne payload, a millimeter-wave instrument designed to measure the polarization of the cosmic microwave background radiation.
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Measuring the faint polarization signal of the cosmic microwave background (CMB) not only requires high optical throughput and instrument sensitivity but also control over systematic effects. Polarimetric cameras or receivers used in this setting oft
en employ dielectric vacuum windows, filters, or lenses to appropriately prepare light for detection by cooled sensor arrays. These elements in the optical chain are typically designed to minimize reflective losses and hence improve sensitivity while minimizing potential imaging artifacts such as glint and ghosting. The Primordial Inflation Polarization ExploreR (PIPER) is a balloon-borne instrument designed to measure the polarization of the CMB radiation at the largest angular scales and characterize astrophysical dust foregrounds. PIPERs twin telescopes and detector systems are submerged in an open-aperture liquid helium bucket dewar. A fused-silica window anti-reflection (AR) coated with polytetrafluoroethylene (PTFE) is installed on the vacuum cryostat that houses the cryogenic detector arrays. Light passes from the skyward portions of the telescope to the detector arrays though this window, which utilizes an indium seal to prevent superfluid helium leaks into the vacuum cryostat volume. The AR coating implemented reduces reflections from each interface to <1% compared to ~10% from an uncoated window surface. The AR coating procedure and room temperature optical measurements of the window are presented. The indium vacuum sealing process is also described in detail and test results characterizing its integrity to superfluid helium leaks are provided.
IDeF-X HD is a 32-channel analog front-end with self-triggering capability optimized for the readout of 16 x 16 pixels CdTe or CdZnTe pixelated detectors to build low power micro gamma camera. IDeF-X HD has been designed in the standard AMS CMOS 0.35
microns process technology. Its power consumption is 800 micro watt per channel. The dynamic range of the ASIC can be extended to 1.1 MeV thanks to the in-channel adjustable gain stage. When no detector is connected to the chip and without input current, a 33 electrons rms ENC level is achieved after shaping with 10.7 micro seconds peak time. Spectroscopy measurements have been performed with CdTe Schottky detectors. We measured an energy resolution of 4.2 keV FWHM at 667 keV (137-Cs) on a mono-pixel configuration. Meanwhile, we also measured 562 eV and 666 eV FWHM at 14 keV and 60 keV respectively (241-Am) with a 256 small pixel array and a low detection threshold of 1.2 keV. Since IDeF-X HD is intended for space-borne applications in astrophysics, we evaluated its radiation tolerance and its sensitivity to single event effects. We demonstrated that the ASIC remained fully functional without significant degradation of its performances after 200 krad and that no single event latch-up was detected putting the Linear Energy Transfer threshold above 110 MeV/(mg/cm2). Good noise performance and radiation tolerance make the chip well suited for X-rays energy discrimination and high-energy resolution. The chip is space qualified and flies on board the Solar Orbiter ESA mission launched in 2020.
This thesis discusses two different approaches for the measurement of cosmic-ray antiparticles in the GeV to TeV energy range. The first part of this thesis discusses the prospects of antiparticle flux measurements with the proposed PEBS detector.
The project allots long duration balloon flights at one of Earths poles at an altitude of 40 km. GEANT4 simulations were carried out which determine the atmospheric background and attenuation especially for antiparticles. The second part covers the AMS-02 experiment which will be installed in 2010 on the International Space Station at an altitude of about 400 km for about three years to measure cosmic rays without the influence of Earths atmosphere. The present work focuses on the anticoincidence counter system (ACC). The ACC is needed to reduce the trigger rate during periods of high fluxes and to reject external particles crossing the tracker from the side or particles resulting from interactions within the detector which would otherwise disturb the clean charge and momentum measurements. The last point is especially important for the measurement of antinuclei and antiparticles.
Space observatories for gravitational radiation such as LISA are equipped with dedicated on-board instrumentation capable of measuring magnetic fields with low-noise conditions at millihertz frequencies. The reason is that the core scientific payload
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We present the fabrication and optical testing of a fine grating on a ZnS substrate to be used as a wideband infrared spectral disperser and for which the primary application is measurement of the composition of the atmospheres of transiting exoplane
ts using space-borne infrared astronomical telescopes. A grating with a blaze angle of 2.1 deg. and pitch of 166.667 midron was constructed on a roughly flat 10 mm x 10 mm substrate with a maximum thickness of 1 mm. To obtain high accuracy, the sample was fabricated on a ZnS monocrystal using a high performance processing machine at Canon Inc. The surface roughness measured with a microscope interferometer was 2.6 nm rms. The shape of the fabricated grating edges was examined with a scanning electron microscope. The diffraction efficiency was evaluated by optical experiments at {lambda} = 633 nm, 980 nm, and 1550 nm, and compared with the efficiencies calculated using a Fourier Modal Method. The results showed that the differences between the diffraction efficiencies obtained from experiment and by calculation were between just 0.9 % and 2.4 %. We concluded that the quality of the fabricated ZnS grating was sufficiently high to provide excellent diffraction efficiency for use in the infrared wavelength region. We also present the design of a spectral disperser in CdTe for future more advanced performance.
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