Aniello Mennella

1=f noise and other systematic effects in the Planck-LFI radiometers

We use an analytic approach to study the susceptibility of the Planck Low Frequency Instrument radiometers to various systematic eects. We examine the eects of fluctuations in amplifier gain, in amplifier noise temperature and in the reference load temperature. We also study the eect of imperfect gain modulation, non-ideal matching of radiometer parameters, imperfect isolation in the two legs of the radiometer and back-end 1=f noise. We find that with proper gain modulation 1=f gain fluctuations are suppressed, leaving fluctuations in amplifier noise temperature as the main source of 1=f noise. We estimate that with a gain modulation factor within1% of its ideal value the overall 1=f knee frequency will be relatively small (<0.1 Hz).

Offset balancing in pseudo-correlation radiometers for CMB measurements

Radiometeric CMB measurements need to be highly stable and this stability is best obtained with differential re- ceivers. The residual 1/f noise in the differential output is strongly dependent on the radiometer input offset which can be can- celled using various balancing strategies. In this paper we discuss a software method implemented in the PLANCK-LFI pseudo- correlation receivers which uses a tunable gain modulation factor, r, in the sky-load difference. Numerical simulations and experimental data show how proper tuning of the parameter r ensures a very stable differential output with knee frequencies of the order of few mHz. Various approaches to calculate r using the radiometer total power data are discussed with some examples relevant to PLANCK-LFI. Although the paper focuses on pseudo-correlation receivers and the examples are relative to PLANCK-LFI, the proposed method and its analysis is general and can be applied to a large class of differential radiometric receivers.

PLANCK: Systematic effects induced by periodic fluctuations of arbitrary shape

A fundamental requirement in the new generation of high resolution Cosmic Microwave Background imaging experiments is a strict control of systematic errors that must be kept at K level in the nal maps. Some of these errors are of celestial origin, while others will be generated by periodic fluctuations of the satellite environment. These environment instabilities will cause fluctuations in the measured signal output thus generating correlated eects in the reconstructed maps. In this paper we present an analytical study of the impact of periodic signal fluctuations on the measured sky maps produced by the Planck survey. In particular we show how it is possible to estimate analytically the damping factor of the peak-to-peak amplitude of the fluctuation at the instrument output after the projection in the nal maps.

Noise properties of the Planck-LFI receivers

The Planck Low Frequency Instrument (LFI) radiometers have been tested extensively during several dedicated campaigns. The present paper reports the principal noise properties of the LFI radiometers. A brief description of the LFI radiometers is given along with details of the test campaigns relevant to determination of noise properties. Current estimates of flight sensitivities, 1/f parameters, and noise effective bandwidths are presented. The LFI receivers exhibit exceptional 1/f noise, and their white noise performance is sufficient for the science goals of Planck.

The Optical Design of the Background Emission Anisotropy Scanning Telescope (BEAST)

We present the optical design of the Background Emission Anisotropy Scanning Telescope (BEAST), an offaxis Gregorian telescope designed to measure the angular distribution of the cosmic microwave background radiation (CMBR)at30and 41.5 GHzonangularscalesrangingfrom 20 0 to10 � .Theapertureof thetelescope is1.9m, and our design meets the strict requirements imposed by the scientific goals of the mission: the beam size is 20 0 at 41.5 GHz and 26 0 at 30 GHz, while the illumination at the edge of the mirrors is lower than � 30 dB for the central horn.Theprimarymirror isanoff-axissectionofaparaboloid,andthesecondaryanoff-axissectionofanellipsoid.A spinning flat mirror located between the sky and the primary provides a two-dimensional chop by rotating the beams around an ellipse on the sky. BEAST uses a receiver array of cryogenic low noise InP High Electron Mobility Transistor (HEMT) amplifiers. The baseline array has seven horns matched to one amplifier each and one horn matchedtotwoamplifiers(twopolarizations)foratotalofnineamplifiers.Twohornsoperatearound30GHz,andsix operate around 41.5 GHz. Subsequent campaigns will include 90 GHz and higher frequency channels. Subject heading gs: cosmic microwave background — cosmology: observations — telescopes

Recent Developments in Astrophysical and Cosmological Exploitation of Microwave Surveys

In this paper, we focus on the astrophysical results and the related cosmological implications derived from recent microwave surveys, with emphasis to those coming from the Planck mission. We critically discuss the impact of systematic effects and the role of methods to separate the cosmic microwave background (CMB) signal from the astrophysical emissions and each different astrophysical component from the others. We then review the state-of-the-art diffuse emissions, extragalactic sources, cosmic infrared background and galaxy clusters, addressing the information they provide to our global view of the cosmic structure evolution and for some crucial physical parameters, as the neutrino mass. Finally, we present three different kinds of scientific perspectives for fundamental physics and cosmology offered by the analysis of on-going and future CMB projects at different angular scales dedicated to anisotropies in total intensity and polarization and to absolute temperature.

Stochastic energy diffusion of electrons in a plasma by an electron cyclotron wave

The investigation of the energy diffusion process of the electrons in a magnetized plasma due to an electron cyclotron wave in perpendicular propagation with respect to the magnetic field is performed. Starting from the description of the relativistic electron motion by means of an action‐angle Hamiltonian H(I,θ,t), the Fokker–Planck–Kolmogorov (FPK) approach to the diffusion is considered for a globally stochastic regime of the system. In this regime, the phase correlation process is analyzed, and the characteristic decay time is estimated analytically. The action diffusion coefficient D(I) is derived and compared with a local quasilinear expression. With explicit reference to the low‐density regime, where D increases with I, and is very close to the quasilinear coefficient, the solution of the diffusion equation is compared with the results obtained by direct numerical integration of the motion equations for a statistically significant ensemble of particles. A good agreement with the local quasilinear FPK diffusion is observed. In addition, when the amplitude of the perturbation is varied, oscillations of the average action values around the quasilinear results are found on the long time scale.

Modeling the frequency response of microwave radiometers with QUCS

Characterization of the frequency response of coherent radiometric receivers is a key element in estimating the flux of astrophysical emissions, since the measured signal depends on the convolution of the source spectral emission with the instrument band shape. Laboratory Radio Frequency (RF) measurements of the instrument bandpass often require complex test setups and are subject to a number of systematic effects driven by thermal issues and impedance matching, particularly if cryogenic operation is involved. In this paper we present an approach to modeling radiometers bandpasses by integrating simulations and RF measurements of individual components. This method is based on QUCS (Quasi Universal Circuit Simulator), an open-source circuit simulator, which gives the flexibility of choosing among the available devices, implementing new analytical software models or using measured S-parameters. Therefore an independent estimate of the instrument bandpass is achieved using standard individual component measurements and validated analytical simulations. In order to automate the process of preparing input data, running simulations and exporting results we developed the Python package python-qucs and released it under GNU Public License. We discuss, as working cases, bandpass response modeling of the COFE and Planck Low Frequency Instrument (LFI) radiometers and compare results obtained with QUCS and with a commercial circuit simulator software. The main purpose of bandpass modeling in COFE is to optimize component matching, while in LFI they represent the best estimation of frequency response, since end-to-end measurements were strongly affected by systematic effects.

Thermal Models of the Planck/LFI QM/FM Instruments

The ESA Planck mission is the third generation (after COBE and WMAP) space experiment dedicated to the measurement of the Cosmic Microwave Background (CMB) anisotropies. Two instruments will be integrated onboard: the High Frequency Instrument (HFI), an array of bolometers, and the Low Frequency Instrument (LFI), an array of pseudo-correlation HEMT radiometers. In this paper we will discuss the development of analytical and numerical models to estimate the thermal behavior of LFI, both in steady-state and transient conditions. We then describe their application to the qualification model (QM) tests. QM test data were also used to calibrate the numerical models. Finally, we show some examples about how these models can be used in predicting the instrument performances and the impact of thermal systematic effects on the scientific results.

Data analysis of the Planck/LFI ground-test campaign

The ESA Planck mission is the third generation (after COBE and WMAP) space experiment dedicated to the measurement of the Cosmic Microwave Background (CMB) anisotropies. Planck will map the whole CMB sky using two instruments in the focal plane of a 1.5 m off-axis aplanatic telescope. The High Frequency Instrument (HFI) is an array of 52 bolometers in the frequency range 100-857 GHz, while the Low Frequency Instrument (LFI) is an array of 11 pseudo-correlation radiometric receivers which continuously compare the sky signal with the reference signal of a blackbody at ~ 4.5 K. The LFI has been tested and calibrated at different levels of integration, i.e. on the single units (feed-horns, OMTs, amplifiers, waveguides, etc.), on each integrated Radiometric Chain Assembly (RCA) and finally on the complete instrument, the Radiometric Array Assembly (RAA). In this paper we focus on some of the data analysis algorithms and methods that have been implemented to estimate the instrument performance and calibration parameters. The paper concludes with the discussion of a custom-designed software package (LIFE) that allows to access the complex data structure produced by the instrument and to estimate the instrument performance and calibration parameters via a fully graphical interface.