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.
COSMO (COSmic Monopole Observer) is an experiment aimed at the searching for spectral distortions in the CMB (Cosmic Microwave Background) between 120 and 300 GHz. COSMO will be operated from Concordia Station on the Antarctic plateau. The experiment is based on a cryogenic Martin-Puplett interferometer whose superconductive detectors are KIDs (Kinetic Inductance Detectors). The interferometer produces interferograms proportional to the difference between the sky and an internal reference black body. The sky signal has a fast modulation to compensate for the atmospheric fluctuations. A key requirement of the readout is an ultra-fast rate to track the signal modulation and also for detector diagnostic. The readout architecture is based on an IQ transceiver generating a comb of test tones tuned to each detector. We developed a modular readout based on commercial components for reliability and fast prototyping. We were able to reach and sustain a readout rate higher than 60 kHz for 18 detectors. In this contribution a general description of the architecture, together with the main performances in terms of amplitude and phase noise are given.
A new facility instrument open to the scientific community is MISTRAL. The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a millimetric multi–pixel camera, mounted at the Gregorian focus of the Sardinia Radio Telescope (SRT), working in the W-band that will be able to study many scientific cases, from the ‘missing baryons’ problem to extragalactic astrophysics, morphology of galaxy cluster and the search of the Cosmic Web through high angular resolution measurements of the Sunyaev-Zel’dovich effect. We present the current state of the map-making and data filtering software that we plan to use for future observations. This software aims to analyze the simulated observations of a target, filter the data from instrumental noise and produce a map, employing a customized common mode removal.
The LiteBIRD mission is a next generation CMB space mission which aims at detecting CMB polarization produced by primordial gravitational waves, with a sensitivity for the tensor to scalar ratio δr < 0.001. A polarization modulator unit (PMU) represents a critical and powerful component to avoid 1/f noise contributions and mitigate differential systematic uncertainties in orthogonal polarization sensitive detectors on both Mid- and High- Frequency Telescopes.
Each PMU is based on a continuously transmissive rotating half-wave plate (HWP), held by a superconducting magnetic bearing operating in the 5K environment. The dynamical behaviour of the system during the rotation must be monitored, since it can introduce systematic effects during the measurements. In this contribution, we present the development of custom cryogenic capacitive sensors, used to monitor the spinning rotor. A set of these sensors allows to monitor the levitation height and wobbling of the rotor, with accuracy of ~ 5 μm and ~ 0.1′, respectively. A thermistor mounted on the rotor can be coupled with one of these capacitors, so that it can be properly biased and read.
The LiteBIRD mission is dedicated to the search for primordial B modes in the Cosmic Microwave Background (CMB) polarization. To achieve unprecedented sensitivity and accuracy in this measurement, the control of instrument systematics is paramount. In this context, we describe the development of microwave absorbers needed to mitigate the straylight within the telescope tubes of the LiteBIRD Mid- and High-Frequency Telescopes (MHFT). A baseline solution has been designed and validated using HFSS simulations, consistently demonstrating sub-percent level specular reflectance across the entire 90-448 GHz band of the MHFT under a broad variety of incidence conditions, representative of the actual optical environment predicted for the two telescopes. Leveraging consolidated technologies, a prototype has been manufactured and characterized in laboratory, demonstrating a promising reflectance mitigation despite the deviation from the nominal geometry. Ongoing parallel efforts involve a comprehensive investigation (both through simulations and laboratory measurements) of the requirements to be finalized in order to define the practical implementation of the baseline design. This activity will ultimately ensure the alignment with allocated thermo-mechanical requirements along with the compliance with the desired electromagnetic performance. The presented studies not only solidify the feasibility of the straylight mitigation approach, but also inform the finalization of the optical tube design, in view of the conclusion of the CNES Phase A study of LiteBIRD.
In this work, we present the design and manufacturing of the two multi-mode antenna arrays of the COSMO experiment and the preliminary beam pattern measurements of their fundamental mode compared with simulations.
COSMO is a cryogenic Martin-Puplett Fourier Transform Spectrometer that aims at measuring the isotropic y-type spectral distortion of the Cosmic Microwave Background from Antarctica, by performing differential measurements between the sky and an internal, cryogenic reference blackbody. To reduce the atmospheric contribution, a spinning wedge mirror performs fast sky-dips at varying elevations while fast, low-noise Kinetic Inductance detectors scan the interferogram.
Two arrays of antennas couple the radiation to the detectors. Each array consists of nine smooth-walled multi-mode feed-horns, operating in the 120−180 GHz and 210−300 GHz range, respectively. The multi-mode propagation helps increase the instrumental sensitivity without employing large focal planes with hundreds of detectors. The two arrays have a step-linear and a linear profile, respectively, and are obtained by superimposing aluminum plates made with CNC milling. The simulated multi-mode beam pattern has a ~ 20° − 26° FWHM for the low-frequency array and ~16° FWHM for the high-frequency one. The side lobes are below −15 dB.
To characterize the antenna response, we measured the beam pattern of the fundamental mode using a Vector Network Analyzer, in far-field conditions inside an anechoic chamber at room temperature. We completed the measurements of the low-frequency array and found a good agreement with the simulations. We also identified a few non-idealities that we attribute to the measuring setup and will further investigate. A comprehensive multi-mode measurement will be feasible at cryogenic temperature once the full receiver is integrated.
The Millimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a new high resolution, wide field-of-view camera that was successfully installed in May 2023 at the Sardinia Radio Telescope (SRT). SRT is a 64m fully steerable gregorian radio telescope, and it underwent an upgrade funded by a National Operational Program (PON) with the aim to expand the fleet of receivers of the radio telescope in order to cover frequency up to the W–band. The W-band sky has been extensively studied by Cosmic Microwave Background experiments, both ground-based (ACT, SPT) and satellite-based (WMAP, Planck). However, their resolution is limited to ≈1′ from ground telescopes and ≈10′ from satellite at best. With this new instrument, we aim to map the microwave sky at a resolution of ≈12′′, a capability only shared by few instruments in the world, unlocking the exploration of a plethora of science cases from the recently upgraded SRT. The heart of MISTRAL is a ≈90mm silicon focal plane populated with 415 cryogenic Lumped Elements Kinetic Inductance Detectors (LEKIDs). These detectors are copuled with the telescope using a cold (4K) re-imaging optical system, producing a diffraction limited field-of-view of 4 ′. The system is enclosed in a custom, four stage cryostat, built with strict requirements on its size, in order to fit on the rotating turret that allows to switch the receivers to be quickly moved in and out of the gregorian focus position. The sub-K stage cools the detectors down to 200-240 mK. MISTRAL is now installed on the gregorian focus of SRT and is undergoing the technical commissioning, and will soon enter the scientific commissioning phase. In this contribution we will survey the subsystems of MISTRAL and their performance at the focus of the radio telescope, and report the current status of the technical commissioning.
LiteBIRD, a forthcoming satellite mission, aims to measure the polarization of the Cosmic Microwave Background (CMB) across the entire sky. The experiment will employ three telescopes, Transition-Edge Sensor (TES) bolometers and rotating Half-Wave Plates (HWPs) at cryogenic temperatures to ensure high sensitivity and systematic effects mitigation. This study is focused on the Mid- and High-Frequency Telescopes (MHFT), which will use rotating metal mesh HWPs. We investigate how power variations due to HWP differential emissivity and transmittance combine with TES nonlinear responsivity, resulting in an effective instrumental polarization. We present the results of simulations for the current HWP design, modeling the TES deviation from linearity as a second-order response. We quantify the level of acceptable residual nonlinearity assuming the mission requirement on the tensor-to-scalar ratio, δr < 0.001. Moreover, we provide an accuracy requirement on the measurement of TES responsivity nonlinearity level for MHFT channels. Lastly, we present possible mitigation methods that will be developed in future studies.
The MISTRAL instrument is a cryogenic, W-band camera consisting of 415 lumped element kinetic inductance detectors. In a significant milestone achieved in May 2023, MISTRAL was successfully installed at the Gregorian focus of the Sardinia Radio Telescope, a 64m aperture telescope in Italy. MISTRAL has a focal plane of ~ 94mm in diameter, resulting in an instantaneous field of view ~ 4 arcmin. To preserve the high angular resolution of the telescope, which is ~ 12 arcsec, the focal plane sampling has been tuned to 4.2 mm, corresponding to a pixel separation of ~ 10.6 arcsec. The remarkable combination of high angular resolution and wide instantaneous field of view makes MISTRAL an exceptionally versatile tool for continuum surveys of wide areas of the sky. Its unique capabilities significantly enhance the observational capacity of the Sardinia Radio Telescope. The lumped element kinetic inductance detectors of MISTRAL are obtained from a titanium-aluminum bilayer 10 + 30nm thick on a single 100 mm–diameter Silicon wafer with thickness 235 μm. They exhibit a critical temperature of 945mK and are optimized to operate within the temperature range of 200 to 240 mK. The feedline is made of an aluminum 21nm thick and has a critical temperature of 1.35 K. We discuss the design, electrical, and optical characterization of the detector array, placing specific emphasis on the yield, the pixel identification on the array, the optical performance, and the calibration procedures.
KEYWORDS: Reflectivity, Transmittance, Mirrors, Monte Carlo methods, Fourier transforms, Refractive index, Error analysis, Terahertz radiation, Signal to noise ratio, Interferometers
In many astrophysical instruments, optical elements and absorbers are extensively used and can alter the status of input polarized light. In particular in mm-wave experiments the lack of knowledge of material properties is becoming the most critical issue in controlling systematic effects. We developed a pipeline of test and analysis to characterize absorbing materials through the measurement of reflectance and transmittance spectra over a broad range of frequencies (from 200 GHz to 800 GHz) and incident angles (up to 70°). Spectra were acquired with a Martin-Puplett interferometer, coupled with a cryogenic bolometer detector. The setup is characterized by using a Neoprene sample (1 mm thick). The aliasing, the reproducibility and the incidence angle error are analyzed to evaluate the impact on the measurements. Individual one-day sessions ensure the capability to characterize transmittance/reflectance with high signal-to-noise: error < 0.5% in the 300-800 GHz band and ∼ 2% in the 200-300 GHz. A Monte Carlo-based fitting method is used to retrieve the physical properties of the sample. The thickness 1.005±0.016 mm is compatible with the one measured with calipers. The measured refractive index at 200 GHz is n=2.416±0.032.
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