We describe the design, construction and performance of a double stage super(3)He- super(4)He refrigerator, built to cool down a multiband bolometric photometer at the MITO telescope. The fridge was ...optimized to work without external pumps, with the main cryostat providing a 4.2 K thermostat at sea level and a 4.0 K one at high mountain pressure conditions. The measured ultimate temperature of the fridge is 290 mK, with a hold time of 81 h. The external heat input on the cold flange is approximately 35 mu W, with the main bath at 4.0 K. The recycle time is 8 h with a heat input on the thermostat during recycling of approximately 6800 J. The cryostat can operate without any relevant changes to performance tilted down to 50 degree from the vertical position, as needed at the telescope focal plane.
High precision measurements of the Cosmic Microwave Background (CMB) represent one of the most difficult challenges in observational cosmology, but promise to unveil the mysteries of the very early ...Universe and of the birth of structures. Three observables are available. The small polarized CMB signal is probably carrying a signature of the early inflationary dynamics of the Universe. It is, however, embedded in overwhelming noise, systematic effects, and polarized foreground. The imprint of the large scale structure in the universe is present in the small-scale anisotropy of the CMB and in its spectral signatures (secondary anisotropy), again mixed with foreground contaminants. Low-level non-Gaussian components of CMB anisotropy and polarization also provide a very promising way to constrain inflation and the physics of ultra-high energies, if foregrounds can be efficiently separated from the measured signal. If measured with high precision, as required by the science issues above, the spectra of CMB anisotropy and polarization also constrain efficiently neutrino properties, hence their interest in this conference. Here we summarize the current status of CMB measurements, dominated by the Planck survey, and delineate the forthcoming activities, needed to exploit the huge scientific potential of precision measurements of the CMB, including the detection of neutrino masses.
After the successful measurements of many ground based, balloon-borne and satellite experiments, which started the era of “Precision Cosmology”, Cosmic Microwave Background (CMB) observations are now ...focusing on two targets: the precision measurement of B-modes in the polarization field, and the measurement of the Sunyaev-Zeldovich effect in distant clusters of galaxies. Polarization measurements represent the best way to probe the very early universe, and the energy scale of inflation. Fine-scale anisotropy measurements, possibly with spectral capabilities, can provide important information on dark matter and dark energy. Here we describe original approaches to these measurements.
We present a short description of the BOOMERANG experiment explaining its scientific goal and the technologies employed. We concentrate then on the analysis of the noise properties, discussing in ...particular the scan synchronous noise. Finally, we present the calibration technique and the sensitivity of all the channels. (Author)
The Planck satellite is dedicated to the measurement of the anisotropy of the Cosmic Microwave Background (CMB) with unprecedented sensitivity and angular resolution. It is a project of the European ...Space Agency based on a wide international collaboration, including United States and Canadian laboratories. The detectors of its High Frequency Instrument (HFI) are bolometers cooled down to 100 mK. Their sensitivity will be limited by the photon noise of the CMB itself at low frequencies, and of the instrument background at high frequencies. The requirements on the measurement chain are directly related to the strategy of observation used for the satellite. This impacts the bolometer design as well as other elements: The cooling system must present outstanding temperature stability, and the amplification chain must show a flat noise spectrum down to very low frequencies. (Author)
Ultra-sensitive bolometric detectors in balloon-borne or satellite missions have the potential to discover low-level non gaussian features in the Cosmic Microwave Background (CMB), due to topological ...defects or to the inflation process. However, the space environment includes a population of cosmic rays (CR), which produce spurious spikes in bolometric signals. In this paper we analyze how CR affect these measurements and the estimates of non-gaussianity and of angular power spectra of the CMB. Using accurate simulations of noise and CR events in bolometric detectors, we find that a de-spiking technique based on outliers removal in the detector signals contributing to the same sky pixel works well in removing CR events larger than the noise. Low level events hidden in the noise produce skewness and kurtosis of the temperatures of the pixels, indicating low-level non-gaussianity. Moreover, when the low-level CR distribution is not known a-priori, the standard noise estimation pipeline produces a positive bias of the power spectrum at high multipoles. In experiments with detector sensitivity better than 100 \(\mu K / \sqrt{Hz}\), in an environment less favorable than the earth stratosphere, the CR-induced non gaussianity is likely to affect significantly the results.
The Planck satellite is a project of the European Space Agency based on a wide international collaboration, including United States and Canadian laboratories. It is dedicated to the measurement of ...the anisotropy of the Cosmic Microwave Background (CMB) with unprecedented sensitivity and angular resolution. The detectors of its High frequency Instrument (HFI) are bolometers cooled down to 100 mK. Their sensitivity will be limited by the photon noise of the CMB itself at low frequencies, and of the instrument background at high frequencies. The requirements on the measurement chain are directly related to the strategy of observation used for the satellite. Due to the scanning on the sky, time features of the measurement chain are directly transformed into angular features in the sky maps. This impacts the bolometer design as well as other elements: For example, the cooling system must present outstanding temperature stability, and the amplification chain must show, down to very low frequencies, a flat noise spectrum. (Author)
PDF
