A. Tartari

QUBIC: The QU Bolometric Interferometer For Cosmology

The primordial B-mode polarisation of the Cosmic Microwave Background is the imprints of the gravitational wave background generated by inflation. Observing the B-mode is up to now the most direct way to constrain the physics of the primordial Universe, especially inflation. To detect these B-modes, high sensitivity is required as well as an exquisite control of systematics effects. To comply with these requirements, we propose a new instrument called QUBIC (Q and U Bolometric Interferometer for Cosmology) based on bolometric interferometry. The control of systematics is obtained with a close-packed interferometer while bolometers cooled to very low temperature allow for high sensitivity. We present the architecture of this new instrument, the status of the project and the self-calibration technique which allows accurate measurement of the instrumental systematic effects.

The Large-Scale Polarization Explorer (LSPE)

The LSPE is a balloon-borne mission aimed at measuring the polarization of the Cosmic Microwave Background (CMB) at large angular scales, and in particular to constrain the curl component of CMB polarization (B-modes) produced by tensor perturbations generated during cosmic inflation, in the very early universe. Its primary target is to improve the limit on the ratio of tensor to scalar perturbations amplitudes down to r = 0.03, at 99.7% confidence. A second target is to produce wide maps of foreground polarization generated in our Galaxy by synchrotron emission and interstellar dust emission. These will be important to map Galactic magnetic fields and to study the properties of ionized gas and of diffuse interstellar dust in our Galaxy. The mission is optimized for large angular scales, with coarse angular resolution (around 1.5 degrees FWHM), and wide sky coverage (25% of the sky). The payload will fly in a circumpolar long duration balloon mission during the polar night. Using the Earth as a giant solar shield, the instrument will spin in azimuth, observing a large fraction of the northern sky. The payload will host two instruments. An array of coherent polarimeters using cryogenic HEMT amplifiers will survey the sky at 43 and 90 GHz. An array of bolometric polarimeters, using large throughput multi-mode bolometers and rotating Half Wave Plates (HWP), will survey the same sky region in three bands at 95, 145 and 245 GHz. The wide frequency coverage will allow optimal control of the polarized foregrounds, with comparable angular resolution at all frequencies.

SAGACE : The spectroscopic active galaxies and clusters explorer

The SAGACE experiment consists of a mm/sub-mm telescope with a 3-m diameter primary mirror, coupled to a cryogenic multi-beam differential spectrometer. SAGACE explores the sky in the 100-760 GHz frequency range, using four diffraction-limited bolometer arrays. The instrument is designed to perform spectroscopic surveys of the Sunyaev- Zeldovich effects of thousands of galaxy clusters, of the spectral energy distribution of active galactic nuclei, and of the [CII] line of a thousand galaxies in the redshift desert. In 2008 a full phase-A study for a national small mission was completed and delivered to the Italian Space Agency (ASI). We have shown that taking advantage of the differential operation of the Fourier Transform Spectrometer, this ambitious instrument can operate from a Molniya orbit, and can be built and operated within the tight budget of a small mission. Copyright

A template of atmospheric O2 circularly polarized emission for cosmic microwave background experiments

We compute the circularly polarized signal from atmospheric molecular oxygen. The polarization of O 2 rotational lines is caused by the Zeeman effect in the Earths magnetic field. We evaluate the circularly polarized emission for various sites suitable for cosmic microwave background (CMB) measurements: the South Pole and Dome C (Antarctica), Atacama (Chile) and Testa Grigia (Italy). We present and discuss an analysis of the polarized signal within the framework of future CMB polarization experiments. We find a typical circularly polarized signal (V Stokes parameter) of ∼50―300 μK at 90 GHz looking at the zenith. Among the sites, Atacama shows a lower polarized signal at the zenith. We present maps of this signal for the various sites and we show typical elevation and azimuth scans. We find that Dome C presents the lowest gradient in polarized temperature: ~0.3 μK deg ―1 at 90 GHz. We also study the frequency bands of observation: around ν ≃ 100 GHz and ν ≃ 160 GHz, we find the best conditions because the polarized signal vanishes. Finally, we evaluate the accuracy of the templates and the signal variability in relation to our knowledge of and the variability of the Earths magnetic field and atmospheric parameters.

A template of atmospheric

We compute the circularly polarized signal from atmospheric molecular oxygen. The polarization of O 2 rotational lines is caused by the Zeeman effect in the Earths magnetic field. We evaluate the circularly polarized emission for various sites suitable for cosmic microwave background (CMB) measurements: the South Pole and Dome C (Antarctica), Atacama (Chile) and Testa Grigia (Italy). We present and discuss an analysis of the polarized signal within the framework of future CMB polarization experiments. We find a typical circularly polarized signal (V Stokes parameter) of ∼50―300 μK at 90 GHz looking at the zenith. Among the sites, Atacama shows a lower polarized signal at the zenith. We present maps of this signal for the various sites and we show typical elevation and azimuth scans. We find that Dome C presents the lowest gradient in polarized temperature: ~0.3 μK deg ―1 at 90 GHz. We also study the frequency bands of observation: around ν ≃ 100 GHz and ν ≃ 160 GHz, we find the best conditions because the polarized signal vanishes. Finally, we evaluate the accuracy of the templates and the signal variability in relation to our knowledge of and the variability of the Earths magnetic field and atmospheric parameters.

O_2

Room temperature VNA calibration to measure cryogenic devices can be inadequate when the loss of the unavoidable thermal decoupling line is order of magnitude higher than the DUT one. We present a cryogenic calibration setup with an accuracy at the level of some tens of milli-dB for S21 parameter.

circularly polarized emission for CMB experiments

We have developed a correlation radiometer at 33 GHz devoted to the search for the residual polarization of the Cosmic Microwave Background (CMB). The two instruments outputs are a linear combination of two Stokes parameters. The instrument is therefore directly sensitive to the polarized component of the radiation (rispectively linear and circular). The radiometer has a beamwidth of 7 or 14 degree, but it can be coupled to a telescope increasing the resolution. The expected CMB polarization is at most a part per million. The polarimeter has been designed to be sensitive to this faint signal, and it has been optimized to improve its long term stability, observing from the ground. In this contribution the performances of the instrument are presented, together with the preliminary tests and observations.We have developed a correlation radiometer at 33 GHz devoted to the search for residual polarization of the Cosmic Microwave Background (CMB). The two instruments`s outputs are linear combination of two Stokes Parameters (Q and U or U and V). The instrument is therefore directly sensitive to the polarized component of the radiation (respectively linear and circular). The radiometer has a beam-width oif 7 or 14 deg, but it can be coupled to a telescope increasing the resolution. The expected CMB polarization is at most a part per milion. The polarimeter has been designed to be sensitive to this faint signal, and it has been optimized to improve its long term stability, observing from the ground. In this contribution the performances of the instrument are presented, together with the preliminary test and observations.

Measurement accuracy of S-parameters in W band at cryogenic temperature

The main objective of this activity is to develop new focal plane coupling array concepts and technologies that optimise the coupling from reflector optics to the large number of detectors for next generation sub millimetre wave telescopes particularly targeting measurement of the polarization of the cosmic microwave background (CMB). In this 18 month TRP programme the consortium are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays which will be demanded to reach the required sensitivity of future CMB polarization missions. One major development was to have multichroic operation to potentially reduce the required focal plane size of a CMB mission. After research in the optimum telescope design and definition of requirements based on a stringent science case review, a number of compact focal plane architecture concepts were investigated before a pixel demonstrator consisting of a planar mesh lens feeding a backend Resonant Cold Electron Bolometer RCEB for filtering and detection of the dual frequency signal was planned for manufacture and test. In this demonstrator the frequencies of the channels was chosen to be 75 and 105 GHz in the w band close to the peak CMB signal. In the next year the prototype breadboards will be developed to test the beams produced by the manufactured flat lenses fed by a variety of antenna configurations and the spectral response of the RCEBs will also be verified.

Dual output polarimeter devoted to the study of the Cosmic Microwave Background

In this activity, we develop novel focal plane detector pixels for the next generation CMB B mode detection missions. Such future mission designs will require focal plane pixel technologies that optimizes the coupling from telescope optics to the large number of detectors required to reach the sensitivities required to measure the faint CMB polarization traces. As part of an ESA Technical Research Programme (TRP) programme we are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays to reduce the focal plane size requirement. The concept of replacing traditional single channel pixels with multi frequency pixels will be a key driver in future mission design and the ability to couple radiation effectively over larger bandwidths (30 - 100%) is a real technical challenge. In the initial part of the programme we reviewed the science drivers and this determined the technical specifications of the mission. Various options for focal plane architectures were considered and then after a tradeoff study and review of resources available, a pixel demonstrator was selected for design manufacture and test. The chosen design consists of a novel planar mesh lens coupling to various planar antenna configurations with Resonant Cold Electron Bolometer (RCEB) for filtering and detection of the dual frequency signal. The final cryogenic tests are currently underway and a final performance will be verified for this pixel geometry.

Next generation sub-millimeter wave focal plane array coupling concepts: An ESA TRP project to develop multichroic focal plane pixels for future CMB polarization experiments

Big Bang cosmologies predict that the cosmic microwave background (CMB) contains faint temperature and polarisation anisotropies imprinted in the early universe. ESAs PLANCK satellite has already measured the temperature anisotropies1 in exquisite detail; the next ambitious step is to map the primordial polarisation signatures which are several orders of magnitude lower. Polarisation E-modes have been measured2 but the even-fainter primordial B-modes have so far eluded detection. Their magnitude is unknown but it is clear that a sensitive telescope with exceptional control over systematic errors will be required. QUBIC3 is a ground-based European experiment that aims to exploit the novel concept of bolometric interferometry in order to measure B-mode polarisation anisotropies in the CMB. Beams from an aperture array of corrugated horns will be combined to form a synthesised image of the sky Stokes parameters on two focal planes: one at 150 GHz the other at 220 GHz. In this paper we describe recent optical modelling of the QUBIC beam combiner, concentrating on modelling the instrument point-spread-function and its operation in the 220-GHz band. We show the effects of optical aberrations and truncation as successive components are added to the beam path. In the case of QUBIC, the aberrations introduced by off-axis mirrors are the dominant contributor. As the frequency of operation is increased, the aperture horns allow up to five hybrid modes to propagate and we illustrate how the beam pattern changes across the 25% bandwidth. Finally we describe modifications to the QUBIC optical design to be used in a technical demonstrator, currently being manufactured for testing in 2016.