LiteBIRD, the next-generation cosmic microwave background (CMB) experiment, aims for a launch in Japan’s fiscal year 2032, marking a major advancement in the exploration of primordial cosmology and fundamental physics. Orbiting the Sun-Earth Lagrangian point L2, this JAXA-led strategic L-class mission will conduct a comprehensive mapping of the CMB polarization across the entire sky. During its 3-year mission, LiteBIRD will employ three telescopes within 15 unique frequency bands (ranging from 34 through 448 GHz), targeting a sensitivity of 2.2 μK-arcmin and a resolution of 0.5° at 100 GHz. Its primary goal is to measure the tensor-toscalar ratio r with an uncertainty δr = 0.001, including systematic errors and margin. If r ≥ 0.01, LiteBIRD expects to achieve a > 5σ detection in the ℓ = 2–10 and ℓ = 11–200 ranges separately, providing crucial insight into the early Universe. We describe LiteBIRD’s scientific objectives, the application of systems engineering to mission requirements, the anticipated scientific impact, and the operations and scanning strategies vital to minimizing systematic effects. We will also highlight LiteBIRD’s synergies with concurrent CMB projects.
KEYWORDS: Analog electronics, Power supplies, Cryogenics, Quantum reading, Time division multiplexing, Sensors, Quantum detection, Digital electronics, Resistors, Cosmic microwave background
CMB-S4 is the next generation, ground-based, cosmic microwave background (CMB) observatory. It is designed to explore the scientific potential contained in the CMB temperature and polarization anisotropies. The goal of CMB-S4 is to observe the mm sky with about 500,000 transition edge sensors (TES). These cryogenic detectors are read out using time division multiplexing (TDM). Two stages of superconducting quantum interference devices (SQUIDs) are used at cryogenic temperatures for multiplexing and amplifying the signals coming from the TESs. This imposes stringent noise requirements to the electronics for readout. In this paper, we discuss the developments and the first tests of an analog front-end differential electronics daughter board. The board is based on an SiGe application-specific integrated circuit (ASIC), the AwaXe v3, developed for the readout of ATHENA’s X-IFU instrument. It provides low-noise amplification (LNA) after the cryogenic multiplexer and supplies the low noise current biasing for the two SQUID stages and TESs. This front-end electronics is expected to improve the noise performances of the CMB-S4 readout chain and help moving towards a differential and compact design.
LiteBIRD is a JAXA strategic L-Class mission designed to search for the existence of primordial gravitational waves produced during the inflationary phase of the Universe. This is achieved through measurements of their imprint on the polarization of the cosmic microwave background (CMB). To fulfill the scientific objectives, observations have to be made over a wide range of frequencies (34 GHz - 448 GHz), which is accomplished by three telescopes: the Low-Frequency Telescope (LFT) led by JAXA and the Middle & High-Frequency Telescopes (MHFT) under European responsibility and led by CNES. To withstand the launch, comply with satellite requirements, and minimize the mass of the mechanical structure, we conducted finite element modeling of the entire MHFT, incorporating both modal and quasi-static load analyses. A nodal thermal study was carried out to evaluate, on the one hand, the static thermal loads of the instruments, and on the other hand the sensitivity of the instruments to sinusoidal disturbances simulating those caused by the ADR cooling system. This paper outlines the methodology employed in designing the mechanical structure of the MHFT, then summarizes the initial results and conclusions drawn from various mechanical and thermal analyses performed on the MHFT.
Antenna-coupled microwave kinetic inductance detectors are emerging as a compelling solution for the next generation of cosmic microwave background (CMB) experiments, which require focal plane arrays with a substantial increase in the number of detectors and multi-band observation capabilities. We present the design and fabrication of multichroic pixels using this architecture, optimized for B-mode polarization observation. The pixel incorporates an improved dual bowtie slot antenna placed at the second focus of an elliptical lens, covering an octave frequency range from 100 GHz to 300 GHz. We aim to achieve bandwidths exceeding 20% for two CMB-atmospheric transparent subbands at 150 GHz and 220 GHz while maintaining adequate linear polarization sensitivity with a cross-polarization level below −17 dB across the entire range. The captured signal is then passed through a superconducting microstrip low-pass filter to remove excessive colors before being fed into the diplexer, where the two bands are separated. These bands are then coupled to the inductive section of MKIDs, effectively modifying the resonant frequency and quality factor of the corresponding resonators. The demonstration sample is fabricated using five photomask layers, employing niobium and aluminum as the superconducting materials, and is currently undergoing testing.
QUBIC (Q and U bolometric interferometer for cosmology) is an international ground-based experiment dedicated to the measurement of the polarized fluctuations of the cosmic microwave background (CMB). It is based on bolometric interferometry, an original detection technique which combines the immunity to systematic effects of an interferometer with the sensitivity of low temperature incoherent detectors. QUBIC will be deployed in Argentina, at the Alto Chorrillos mountain site near San Antonio de los Cobres, in the Salta province. The QUBIC detection chain consists of 2048 NbSi transition edge sensors (TESs) cooled to 320 mK. The voltage-biased TESs are read out with time domain multiplexing based on superconducting quantum interference devices (SQUIDs) at 1 K and a novel SiGe application-specific integrated circuit (ASIC) at 60 K allowing an unprecedented multiplexing (MUX) factor equal to 128 to be reached. The current QUBIC version is based on a reduced number of detectors (1/4) in order to validate the detection technique. The QUBIC experiment is currently being validated in the lab in Salta (Argentina) before going to the site for observations. This paper presents the main results of the characterization phase with a focus on the detectors and readout system.
The Q and U Bolometric Interferometer for Cosmology (QUBIC) Technical Demonstrator (TD) aiming to shows the feasibility of the combination of interferometry and bolometric detection. The electronic readout system is based on an array of 128 NbSi Transition Edge Sensors cooled at 350mK readout with 128 SQUIDs at 1K controlled and amplified by an Application Specific Integrated Circuit at 40K. This readout design allows a 128:1 Time Domain Multiplexing. We report the design and the performance of the detection chain in this paper. The technological demonstrator unwent a campaign of test in the lab. Evaluation of the QUBIC bolometers and readout electronics includes the measurement of I-V curves, time constant and the Noise Equivalent Power. Currently the mean Noise Equivalent Power is ~ 2 x 10-16W= p √Hz
QUBIC (a Q and U Bolometric Interferometer for Cosmology) is a next generation cosmology experiment designed to detect the B-mode polarisation of the Cosmic Microwave Background (CMB). A B-mode detection is hard evidence of Inflation in the ΛCDM model. QUBIC aims to accomplish this by combining novel technologies to achieve the sensitivity required to detect the faint B-mode signal. QUBIC uses technologies such as a rotating half-wave plate, cryogenics, interferometric horns with self-calibration switches and transition edge sensor bolometers. A Technical Demonstrator (TD) is currently being calibrated in APC in Paris before observations in Argentina in 2021. As part of the calibration campaign, the spectral response of the TD is measured to test and validate QUBIC's spectro-imaging capability. This poster gives an overview of the methods used to measure the spectral response and a comparison of the instrument data with theoretical predictions and optical simulations.
QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that has been designed to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the systematic error control of an interferometer. It will directly observe the sky through an array of 400 back-to-back entry horns whose signals will be superimposed using a quasi-optical beam combiner. The resulting interference fringes will be imaged at 150 and 220 GHz on two focal planes, each tiled with NbSi Transition Edge Sensors, cooled to 320 mK and read out with time-domain multiplexing. A dichroic filter placed between the optical combiner and the focal planes will select the two frequency bands. A very large receiver cryostat will cool the optical and detector stages to 40 K, 4 K, 1 K and 320 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. Polarisation modulation and selection will be achieved using a cold stepped half-wave plate (HWP) and polariser, respectively, in front of the sky-facing horns. A key feature of QUBIC’s ability to control systematic effects is its ‘self-calibration’ mode where fringe patterns from individual equivalent baselines can be compared. When observing, however, all the horns will be open simultaneously and we will recover a synthetic image of the sky in the I, Q and U Stokes’ parameters. The synthesised beam pattern has a central peak of approximately 0.5 degrees in width, with secondary peaks further out that are damped by the 13-degree primary beam of the horns. This is Module 1 of QUBIC which will be installed in Argentina, near the city of San Antonio de los Cobres, at the Alto Chorrillos site (4869 m a.s.l.), Salta Province. Simulations have shown that this first module could constrain the tensor-to-scalar ratio down to σ(r) = 0.01 after a two-year survey. We aim to add further modules in the future to increase the angular sensitivity and resolution of the instrument. The QUBIC project is proceeding through a sequence of steps. After an initial successful characterisation of the detection chain, a technological demonstrator is being assembled to validate the full instrument design and to test it electrically, thermally and optically.
The technical demonstrator is a scaled-down version of Module 1 in terms of the number of detectors, input horns and pulse tubes and a reduction in the diameter of the combiner mirrors and filters, but is otherwise similar. The demonstrator will be upgraded to the full module in 2019. In this paper we give an overview of the QUBIC project and instrument.
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.
QUBIC, the QU Bolometric Interferometer for Cosmology, is a novel forthcoming instrument to measure the B-mode polarization anisotropy of the Cosmic Microwave Background. The detection of the B-mode signal will be extremely challenging; QUBIC has been designed to address this with a novel approach, namely bolometric interferometry. The receiver cryostat is exceptionally large and cools complex optical and detector stages to 40 K, 4 K, 1 K and 350 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. We discuss the thermal and mechanical design of the cryostat, modelling and thermal analysis, and laboratory cryogenic testing.
QUBIC (the Q and U Bolometric Interferometer for Cosmology) is a ground-based experiment which seeks to improve the current constraints on the amplitude of primordial gravitational waves. It exploits the unique technique, among Cosmic Microwave Background experiments, of bolometric interferometry, combining together the sensitivity of bolometric detectors with the control of systematic effects typical of interferometers. QUBIC will perform sky observations in polarization, in two frequency bands centered at 150 and 220 GHz, with two kilo-pixel focal plane arrays of NbSi Transition-Edge Sensors (TES) cooled down to 350 mK. A subset of the QUBIC instrument, the so called QUBIC Technological Demonstrator (TD), with a reduced number of detectors with respect to the full instrument, will be deployed and commissioned before the end of 2018.
The voltage-biased TES are read out with Time Domain Multiplexing and an unprecedented multiplexing (MUX) factor equal to 128. This MUX factor is reached with two-stage multiplexing: a traditional one exploiting Superconducting QUantum Interference Devices (SQUIDs) at 1K and a novel SiGe Application-Specific Integrated Circuit (ASIC) at 60 K. The former provides a MUX factor of 32, while the latter provides a further 4. Each TES array is composed of 256 detectors and read out with four modules of 32 SQUIDs and two ASICs. A custom software synchronizes and manages the readout and detector operation, while the TES are sampled at 780 Hz (100kHz/128 MUX rate).
In this work we present the experimental characterization of the QUBIC TES arrays and their multiplexing readout chain, including time constant, critical temperature, and noise properties.
QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that aims to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the immunity to systematic effects of an interferometer. It will directly observe the sky through an array of back-to-back entry horns whose beams will be superimposed using a cooled quasioptical beam combiner. Images of the resulting interference fringes will be formed on two focal planes, each tiled with transition-edge sensors, cooled down to 320 mK. A dichroic filter placed between the optical combiner and the focal planes will select two frequency bands (centred at 150 GHz and 220 GHz), one frequency per focal plane. Polarization modulation will be achieved using a cold stepped half-wave plate (HWP) and polariser in front of the sky-facing horns.
The full QUBIC instrument is described elsewhere1,2,3,4; in this paper we will concentrate in particular on simulations of the optical combiner (an off-axis Gregorian imager) and the feedhorn array. We model the optical performance of both the QUBIC full module and a scaled-down technological demonstrator which will be used to validate the full instrument design. Optical modelling is carried out using full vector physical optics with a combination of commercial and in-house software. In the high-frequency channel we must be careful to consider the higher-order modes that can be transmitted by the horn array. The instrument window function is used as a measure of performance and we investigate the effect of, for example, alignment and manufacturing tolerances, truncation by optical components and off-axis aberrations. We also report on laboratory tests carried on the QUBIC technological demonstrator in advance of deployment to the observing site in Argentina.
Remnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines.
The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane.
The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results.
In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner.
Big Bang cosmologies predict that the cosmic microwave background (CMB) contains faint temperature and polarisation
anisotropies imprinted in the early universe. ESA's 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.
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.
CNES (French Space Agency) continuously drives the development of detectors for Space based Astronomy. Several detector concepts are developped by French Laboratories, from far infrared to mm wavelength. This paper gives a status on these developments as well as an overview of the associated roadmap.
The Q and U Bolometric Interferometer for Cosmology (QUBIC) is a ground-based interferometer that aims to meet one of the major challenges of modern cosmology in the detection of B-mode polarization anisotropies in the Cosmic Microwave Background.B-mode anisotropies originate from tensor fluctuations of the metric produced during the inflationary phase of the early Universe. Their detection would therefore constitute a major step towards understanding the primordial Universe. The expected level of these anisotropies is however so small that detection requires instruments with high sensitivity and extremely good control of systematic effects. The QUBIC instrument is based on the novel concept of bolometric interferometry, and exploits the sensitivity advantages of bolometric detectors along with the greater control of systematics offered by interferometry.The instrument will directly observe the sky through an array of entry horns whose signals will be combined optically onto an array of bolometers cooled to around 300mK. The whole set-up is located inside a cryostat. The sensitivity of the instrument is maximised if equivalent baselines produce identical fringe patterns on the focal plane. This requires the minimization of wavefront aberrations for a wide field-of-view and a fast system.In this poster we present the quasi-optical design and analysis of the dual reflector designed to do this. We report on the loss of sensitivity for different levels of optical aberration in the combiner. The sensitivity of the QUBIC instrument is comparable with that of an imager with the same number of horns but with much greater control over systematics.
F. Pajot, D. Prele, J. Zhong, Y. Atik, B. Bélier, L. Bergé, G. Bordier, E. Bréelle, L. Dumoulin, C. Evesque, F. Gadot, B. Leriche, S. Marnieros, J. Martino, M. Piat, S.-C. Shi, F. Voisin
The achievement of the Planck and Herschel space missions in the submillimeter and millimeter range was made
possible by a continuous effort on detector developments. Now limited by the intrinsic fluctuations of the radiation
coming from the astronomical sources themselves, the sensitivity improvement requires the development of large arrays
of detectors filling the focal plane of the telescopes. We present here the development of a TES array using NbSi sensors
on SiN membranes. The readout electronics is based on SQUIDs and a cooled SiGe ASIC multiplexer. The detector is
coupled with the input radiation by means of antenna. The present goal performance is adapted for the realisation of a
ground based millimeter camera.
Future space experiments will require large arrays of sensitive detectors in the submillimeter and millimeter range.
Superconducting transition-edge sensors (TESs) are currently under heavy development to be used as ultra sensitive
bolometers. In addition to good performance, the choice of material depends on long term stability (both physical and
chemical) along with a good reproducibility and uniformity in fabrication. For this purpose we are investigating the
properties of co-evaporated NbSi thin films. NbSi is a well-known alloy for use in resistive thermometers. We present a
full low temperature characterization of superconductive NbSi films. In order to tune the critical temperature of the NbSi
thermometers down to the desired range, we have to adjust the concentration of niobium in the NbSi alloy. Tests are
made using 4He-cooled cryostats, 300mK 3He mini-fridges, Resistance Bridges and commercial SQUID. Measured
parameters are the critical temperature, the sharpness of the transition. Noise measurements are on-going.
Bolometers cooled to very low temperature are currently the most sensitive detectors for low spectral resolution
detection of millimetre and sub-millimetre wavelengths. The best performances of the state-of-the-art bolometers allow
to reach sensitivities below the photon noise of the Cosmic Microwave Background for example. Since 2003, a french
R&D effort called DCMB ("Developpement Concerte de Matrices de Bolometres") has been organised between different
laboratories to develop large bolometers arrays for astrophysics observations. Funded by CNES and CNRS, it is intended
to get a coherent set of competences and equipments to develop very cold bolometers arrays by microfabrication. Two
parallel developments have been made in this collaboration based on the NbSi alloy either semi-conductive or
superconducting depending on the proportion of Nb. Multiplexing schemes have been developed and demonstrated for
these two options. I will present the latest developments made in the DCMB collaboration and future prospects.
This paper presents an ultra low noise instrumentation based on cryogenic electronic integrated circuits (ASICs :
Application Specific Integrated Circuits). We have designed successively two ASICs in standard BiCMOS SiGe 0.35 μm
technology that have proved to be operating at cryogenic temperatures. The main functions of these circuits are the
readout and the multiplexing of SQUID/TES arrays. We report the cryogenic operation of a first ASIC version dedicated
to the readout of a 2×4 pixel demonstrator array. We particularly emphasize on the development and the test phases of an
ultra low noise (0.2 nV/√Hz) cryogenic amplifier designed with two multiplexed inputs. The cryogenic SiGe amplifier
coupled to a SQUID in a FLL operating at 4.2 K is also presented. We finally report on the development of a second
version of this circuit to readout a 3×8 detectors array with improved noise performances and upgraded functionalities.
The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric detectors
cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture consists in
several stages cooled using different active coolers. These generate weak thermal fluctuations on the HFI thermal
stages. Without a dedicated thermal control system these fluctuations could produce unwanted systematic effects,
altering the scientific data. The HFI thermal architecture allows to minimise these systematic effects, thanks to
passive and active control systems described in this paper. The passive and active systems are used to damp
the high and low frequency fluctuations respectively. The results of the simulation of these active and passive
control systems are presented here. These simulations based on the use of thermal transfer functions for the
thermal modelling can then be used for finding the optimal working point of the HFI PID active thermal control
system.
KEYWORDS: Cryogenics, Control systems, Bolometers, Temperature metrology, Satellites, Space telescopes, Sensors, Thermography, Electronic filtering, Anisotropy
The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric
detectors cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture
consists in several stages cooled using different active coolers. These generate weak thermal fluctuations
on the HFI thermal stages. Without a dedicated thermal control system these fluctuations could produce
unwanted systematic effects, altering the scientific data. The HFI thermal architecture allows to minimise
these systematic effects, thanks to passive and active control systems described in this paper. The
passive and active systems are used to damp the high and low frequency fluctuations respectively. The
last results regarding the tests of the HFI passive and active thermal control systems are presented here.
The thermal transfer functions measurement between active coolers and HFI cryogenic stages will be
presented first. Then the stability of the temperatures obtained on the various cryogenic stages with PID
regulations systems will be checked through analysis of their power spectrum density.
The High Frequency Instrument of the Planck satellite is dedicated to the measurement of the anisotropy of the Cosmic Microwave Background (CMB). Its main goal is to map the CMB with a sensitivity of ΔT/T=2.10-6 and an angular resolution of 5 arcmin in order to constrain cosmological parameters. Planck is a project of the European Space Agency based on a wide international collaboration, including United States and Canadian laboratories. The architecture of the satellite is driven by the thermal requirements resulting from the search for low photon noise. Especially, the passively cooled telescope should be at less than 50K, while a cascade of cryo-coolers will ensure the cooling of the HFI bolometers down to 0.1K. This last temperature will be produced by a gravity insensitive 3He/4He dilution cooler. This will be achieved at the L2 Lagrangian point of the Sun-Earth system. The whole sky will be observed two times in the 14 months mission with a scanning strategy based on a 1RPM rotation of the satellite. In addition to the cosmological parameters that can be derived from the CMB maps, Planck will deliver nine high sensitivity submillimeter maps of the whole sky that will constitute unique data available to the whole astronomical community.
Michel Piat, Jean-Michel Lamarre, Julien Meissonnier, Jean-Pierre Torre, Philippe Camus, Alain Benoit, Jean-Pierre Crussaire, Peter Ade, James Bock, Andrew Lange, Ravinder Bhatia, Bruno Maffei, Jean Puget, Rashmi Sudiwala
KEYWORDS: Sensors, Bolometers, Optical filters, Connectors, Control systems, Cryogenics, Signal to noise ratio, Signal detection, Temperature metrology, Spatial resolution
The Planck-High Frequency Instrument (HFI) will use 48 bolometers cooled to 100mK by a dilution cooler to map the Cosmic Microwave Background (CMB) with a sensitivity of ΔT/T~2.10-6 and an angular resolution of 5 minutes of arc. This instrument will therefore be about 1000 times more sensitive than the COBE-DMR experiment. This contribution will focus mainly on the thermal architecture of this instrument and its consequences on the fundamental and instrumental fluctuations of the photon flux produced on the detectors by the instrument itself. In a first step, we will demonstrate that the thermal and optical design of the HFI allow to reach the ultimate sensitivity set by photon noise of the CMB at millimeter wavelength. Nevertheless, to reach such high sensitivity, the thermal behavior of each cryogenic stages should also be controlled in order to damp thermal fluctuations that can be taken as astrophysical signal. The requirement in thermal fluctuation on each stage has been defined in the frequency domain to degrade the overall sensitivity by less than 5%. This leads to unprecedented stability specifications that should be achieved down to 16mHz. We will present the design of the HFI thermal architecture, based on active and passive damping, and show how its performances were improved thanks to thermal simulations.
We have developed a new readout system for bolometers optimized for the Planck Surveyor experiment, a satellite mission dedicated to survey the Cosmological Microwave Background. The bolometer resistance is measured in a bridge with a capacitance load, using a periodic square wave bias current in order to remove the 1/f noises of the electronics. The use of a capacitance allows to reduce the transient signal and to get rid of the Johnson noise. The bias voltages are fully controlled by computer, and the lock-in detection is digital. This system has been implemented and successfully tested on the Diabolo ground- based astronomical experiment. Using the advantages of our readout system, we have built and fully tested an engineering model of the space qualifiable electronics which fulfills the scientific and technical requirements of the Planck Surveyor bolometric instrument: low noise system down to 0.1 Hz, electrical power consumption lower than 40 Watts and volume lower than 15 liters. Our presentation will consist in a full description of this readout system and a review of the current test results. Our system could also be adapted, with some modifications, to other space born instruments which use bolometers.
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