RADIOTELESCOPES

Author: SÁNCHEZ COLÍN ANGEL ENRIQUE.
Year: 2005.
University: GRANADA [www.ugr.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: UNIVERSIDAD DE GRANADA.

Summary: Since the early 90, members of the Max-Planck Institute for Radio Astronomy (MPlfR), in Bonn, Germany, have been developing radiometers based arrangements bolómetros for astronomical observations in the ongoing millimeter wavelengths and submillimetre. By submillimetre range, we understand that part of the electromagnetic spectrum with wavelengths between [0.1 -1 mm]. This corresponds to the number of wave in the interval [10-100 cm-1] and frequency of [0.3-3 THz]. The new arrangement with 295 bolómetros, LABOCA (Large Bolometer Camera), operating at 300 mK, represent the settlement of more sensitive detectors in the continuum for wavelengths of 870 m. It will be installed next year in the submillimetre telescope of 12 meters in diameter for the project APEX / Atacama Pathfinder Experiment), located at the project site ALMA (Atacama Large Milimeter Array), Chajnantor-Chile. LABOCA operates at wavelengths where there is a significant absorption by water vapor in the Earth's atmosphere. Therefore, with its large size, there will be a great burden of heat due to radiation heat catering and a good driving through the conductive pathways to produce the signal. All bolómetros astronomical need to be characterized, and proven to be subjected to measures calibration under laboratory conditions before being installed on the telescope. For this reason, it is particularly important to know their spectral response. This thesis consists of two research problems: performance and improvements in thermal contact (Thermal Shunts) and the construction of two sources of radiant type submillimetre black bodies (Blackbodiesm that can be operated in a high vacuum spectrometer, which is intended calibration. Owing their early work, a thermal detector in cryogenics, you need to be very well protected from extraneous thermal loads outside the system. For this purpose, thermal contacts are required. contacts terms are mechanisms that combine high thermal conductivity with a perfect electrical isolation. An important task of this thesis is the design and construction of thermal compact contacts, which are compatible with the design of LABOCA. thermal conductivity of the material decreases rapidly at temperatures less than 1 K, so by measuring the conductance in compact designs with minimal power dissipation, presents a challenge pilot. contact thermal Several versions were built and characterized experimentally by the method of heat flux at steady state at temperatures (4.2 and 1.3) K is a cryostat for 4He and 0.3K in a refrigerated for 3He. relatively large range of temperatures for our data, enabling a deeper understanding of the physical processes in the operation of each mechanism. Even without a single layer of material in the cavity of a black body which has high absorption and therefore high emisivida on Banda total submillimetre wavelengths; for calibration purposes, a source with these thermal characteristics and emisivida near the unit can be constructed, moderately applying a layer of absorbing material inside the cavity, which then is the black body desired. sources Two radiant type black bodies, were built and adapted in Interferometer Martín-Puplett, which serves as a system of spectral calibration in the laboratory bolómetros of MPlfR. sources operating conveniently (77 and 300) K. conduits high vacuum maintained in the interferometer, are intended to prevent complications at the time of measurement; produced by absorbing water vapor in the atmosphere and to reduce because of evaporation of liquid nitrogen content in the body black to 77 K. However, the operation in these conditions, entails finding lubricants that are suitable for high vacuum and that can be used in the internal mechanisms of the interferometer, as s 8 on: 70f shafts and sliding into the screw endless allowing the movement of the mirror. Especially important for this regard, it is the bearing that supports a polarizing revolving wire grids, which acts as a modulator for both black bodies. To test the calibration system, we use a bolómetro semiconductor with a thermistor germanium, NTD-Ge (Neutron-Transmutation-Doped Germanium), mounted on a cryostat for 4He, operating at 1.3K. Eventually, it took a measurement with a bolómetro test consistent with the design of LABOCA. Comprised of a settlement of seven bolómetros superconductors VSB (Voltage-biased Superconducting Bolometer) and a thermistor done with double layer and molybdenum alloy Oro-Paladio, operating at 0.3K with a refrigerator absorption 3He . signals were obtained through a flow sensor SQUID (Superconducting Quantum Interference Device), mounted on the cold plate of a cryostat for 4He to 1.3K. inteferogramas which were obtained and their corresponding spectra we confirmed the full functionality of the interferometer.