関本 裕太郎

LiteBIRD is a planned JAXA-led cosmic microwave background (CMB) B-mode satellite experiment aiming for launch in the late 2020s, with a primary goal of detecting the imprint of primordial inflationary gravitational waves. Its current baseline focal-plane configuration includes 15 frequency bands between 40 and 402 GHz, fulfilling the mission requirements to detect the amplitude of gravitational waves with the total uncertainty on the tensor-to-scalar ratio, dr, down to dr < 0.001. A key aspect of this performance is accurate astrophysical component separation, and the ability to remove polarized thermal dust emission is particularly important. In this paper we note that the CMB frequency spectrum falls off nearly exponentially above 300 GHz relative to the thermal dust spectral energy distribution, and a relatively minor high frequency extension can therefore result in even lower uncertainties and better model reconstructions. Specifically, we compared the baseline design with five extended configurations, while varying the underlying dust modeling, in each of which the High-Frequency Telescope (HFT) frequency range was shifted logarithmically toward higher frequencies, with an upper cutoff ranging between 400 and 600 GHz. In each case, we measured the tensor-to-scalar ratio r uncertainty and bias using both parametric and minimum-variance component-separation algorithms. When the thermal dust sky model includes a spatially varying spectral index and temperature, we find that the statistical uncertainty on r after foreground cleaning may be reduced by as much as 30-50% by extending the upper limit of the frequency range from 400 to 600 GHz, with most of the improvement already gained at 500 GHz. We also note that a broader frequency range leads to higher residuals when fitting an incorrect dust model, but also it is easier to discriminate between models through higher X-2 sensitivity. Even in the case in which the fitting procedure does not correspond to the underlying dust model in the sky, and when the highest frequency data cannot be modeled with sufficient fidelity and must be excluded from the analysis, the uncertainty on r increases by only about 5% for a 500 GHz configuration compared to the baseline.

The radio frequency interference (RFI) due to the X-band telecommunication with the LiteBIRD spacecraft was computed using a 3D electromagnetic field simulator to evaluate its field strength at the instrument detectors. First, the level of RFI with different materials for the spacecraft main body was evaluated. The attenuation effects for aluminum (Al) and carbon-fiber-reinforced plastic (CFRP) in comparison with a perfect electric conductor (PEC) were 1.5 dB and 10.5 dB, respectively. Then, the electric field strength for various shield plate structures on the solar panels was evaluated. In the best case, the RFI level could be attenuated by another 31 dB with an optimum design. Finally, the frequency dependence of the RFI was evaluated across the X-band, giving an attenuation slope of − 10 dB/oct, leading to an electric field intensity of − 116.8 dBV/m at the detector position for a frequency of 8.4 GHz.

Abstract LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun–Earth Lagrangian point L2, where it will map the cosmic microwave background polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of $2.2\, \mu$K-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions, and synergies with other projects.

The radio frequency interference (RFI) due to the X-band telecommunication with the LiteBIRD spacecraft was computed using a 3D electromagnetic field simulator to evaluate its field strength at the instrument detectors. First, the level of RFI with different materials for the spacecraft main body was evaluated. The attenuation effects for aluminum (Al) and carbon-fiber-reinforced plastic (CFRP) in comparison with a perfect electric conductor (PEC) were 1.5 dB and 10.5 dB, respectively. Then, the electric field strength for various shield plate structures on the solar panels was evaluated. In the best case, the RFI level could be attenuated by another 31 dB with an optimum design. Finally, the frequency dependence of the RFI was evaluated across the X-band, giving an attenuation slope of - 10 dB/oct, leading to an electric field intensity of - 116.8 dBV/m at the detector position for a frequency of 8.4 GHz.

A methodology to provide the polarization angle requirements for different sets of detectors, at a given frequency of a CMB polarization experiment, is presented. The uncertainties in the polarization angle of each detector set are related to a given bias on the tensor-to-scalar ratio r parameter. The approach is grounded in using a linear combination of the detector sets to obtain the CMB polarization signal. In addition, assuming that the uncertainties on the polarization angle are in the small angle limit (lower than a few degrees), it is possible to derive analytic expressions to establish the requirements. The methodology also accounts for possible correlations among detectors, that may originate from the optics, wafers, etc. The approach is applied to the LiteBIRD space mission. We show that, for the most restrictive case (i.e., full correlation of the polarization angle systematics among detector sets), the requirements on the polarization angle uncertainties are of around 1 arcmin at the most sensitive frequency bands (i.e., approximate to 150 GHz) and of few tens of arcmin at the lowest (i.e., approximate to 40 GHz) and highest (i.e., approximate to 400 GHz) observational bands. Conversely, for the least restrictive case (i.e., no correlation of the polarization angle systematics among detector sets), the requirements are approximate to 5 times less restrictive than for the previous scenario. At the global and the telescope levels, polarization angle knowledge of a few arcmins is sufficient for correlated global systematic errors and can be relaxed by a factor of two for fully uncorrelated errors in detector polarization angle. The reported uncertainty levels are needed in order to have the bias on r due to systematics below the limit established by the LiteBIRD collaboration.

A methodology to provide the polarization angle requirements for different sets of detectors, at a given frequency of a CMB polarization experiment, is presented. The uncertainties in the polarization angle of each detector set are related to a given bias on the tensor-to-scalar ratio r parameter. The approach is grounded in using a linear combination of the detector sets to obtain the CMB polarization signal. In addition, assuming that the uncertainties on the polarization angle are in the small angle limit (lower than a few degrees), it is possible to derive analytic expressions to establish the requirements. The methodology also accounts for possible correlations among detectors, that may originate from the optics, wafers, etc. The approach is applied to the LiteBIRD space mission. We show that, for the most restrictive case (i.e., full correlation of the polarization angle systematics among detector sets), the requirements on the polarization angle uncertainties are of around 1 arcmin at the most sensitive frequency bands (i.e., ≈ 150 GHz) and of few tens of arcmin at the lowest (i.e., ≈ 40 GHz) and highest (i.e., ≈ 400 GHz) observational bands. Conversely, for the least restrictive case (i.e., no correlation of the polarization angle systematics among detector sets), the requirements are ≈ 5 times less restrictive than for the previous scenario. At the global and the telescope levels, polarization angle knowledge of a few arcmins is sufficient for correlated global systematic errors and can be relaxed by a factor of two for fully uncorrelated errors in detector polarization angle. The reported uncertainty levels are needed in order to have the bias on r due to systematics below the limit established by the LiteBIRD collaboration.

LiteBIRD is a JAXA-led international project that aims to test representative inflationary models by performing an all-sky cosmic microwave background radiation (CMB) polarization survey for 3 years at the Sun-Earth Lagrangian point L2. We aim to launch LiteBIRD in the late 2020s. The payload module (PLM) is mainly composed of the Low-Frequency Telescope (LFT), the Mid-Frequency Telescope and High-Frequency Telescope (MHFT), and a cryo-structure. To conduct the high-precision and high-sensitivity CMB observations, it is required to cool the telescopes down to less than 5 K and the detectors down to 100 mK. The high temperature stability is also an important design factor. It is essential to design and analyze the cryogenic thermal system for PLM. In this study, the heat balance, temperature distribution, and temperature stability of the PLM for the baseline design are evaluated by developing the transient thermal model. The effect of the Joule-Thomson (JT) coolers cold tip temperature variation, the periodical changes in subK Adiabatic Demagnetization Refrigerator (ADR) heat dissipation, and the satellite spin that generates the variable direction of solar flux incident are implemented in the model. The effect of contact thermal conductance in the LFT and the emissivity of the V-groove on the temperature distribution and heat balance are investigated. Based on the thermal analysis, it was confirmed that the PLM baseline design meets the requirement of the temperature and the cooling capability of the 4K-JT cooler. In addition, the temperatures of the V-groove and the LFT 5-K frame are sufficiently stable for the observation. The temperature stability of the Low Frequency Focal Plane (LF-FP) is also discussed in this paper.

We developed broadband antireflection structures for millimeter-wave and submillimeter-wave applications, particularly cryogenic applications. The structures were fabricated on silicon using deep reactive ion etching. Three-layer subwavelength structures were fabricated on both sides of a silicon plate with an area of 20 mm2. The transmittances of the structures were measured at 28 K. The average transmittance was 97.6% in the frequency range of 200–450 GHz.

© 2020, The Author(s). Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA’s H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy’s foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun–Earth Lagrangian point, L2, are planned for 3 years. An international collaboration between Japan, the USA, Canada, and Europe is sharing various roles. In May 2019, the Institute of Space and Astronautical Science, JAXA, selected LiteBIRD as the strategic large mission No. 2.

LiteBIRD is a JAXA-led Strategic Large-Class mission designed to search for the existence of the primordial gravitational waves produced during the inflationary phase of the Universe, through the measurements of their imprint onto the polarization of the cosmic microwave background (CMB). These measurements, requiring unprecedented sensitivity, will be performed over the full sky, at large angular scales, and over 15 frequency bands from 34 GHz to 448 GHz. The LiteBIRD instruments consist of three telescopes, namely the Low-, Medium-and High-Frequency Telescope (respectively LFT, MFT and HFT). We present in this paper an overview of the design of the Medium-Frequency Telescope (89{224 GHz) and the High-Frequency Telescope (166{448 GHz), the so-called MHFT, under European responsibility, which are two cryogenic refractive telescopes cooled down to 5 K. They include a continuous rotating half-wave plate as the first optical element, two high-density polyethylene (HDPE) lenses and more than three thousand transition-edge sensor (TES) detectors cooled to 100 mK. We provide an overview of the concept design and the remaining specific challenges that we have to face in order to achieve the scientific goals of LiteBIRD.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. JAXA selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with its expected launch in the late 2020s using JAXA's H3 rocket. LiteBIRD plans to map the cosmic microwave background (CMB) polarization over the full sky with unprecedented precision. Its main scientific objective is to carry out a definitive search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with an insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. To this end, LiteBIRD will perform full-sky surveys for three years at the Sun-Earth Lagrangian point L2 for 15 frequency bands between 34 and 448 GHz with three telescopes, to achieve a total sensitivity of 2.16 μK-arcmin with a typical angular resolution of 0.5° at 100 GHz. We provide an overview of the LiteBIRD project, including scientific objectives, mission requirements, top-level system requirements, operation concept, and expected scientific outcomes.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD has been selected as JAXA's strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of-56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT: 34-161 GHz), one of LiteBIRD's onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90a-▪ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. GroundBIRD is a millimeter-wave telescope to observe the polarization patterns of the cosmic microwave background (CMB). The target science topics are primordial gravitational waves from cosmic inflation and reionization optical depth. Therefore, this telescope is designed to achieve the highest sensitivity at large angular scales, ℓ = 6 - 300. For wide sky observations (∼40% full-sky), scanning at a high rotation speed (120°/s) is important to remove atmospheric fluctuations. Microwave kinetic inductance detector (MKID) is utilized with the fast GroundBIRD rotation since its good time response. We have started the commissioning run at the Teide Observatory in the Canary Islands. We report the performance of the telescope, receiver, and data acquisition system, including cooling achievements, observations of astronomical objects, and observations taken during several days ahead of our main survey observations.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. We are developing a 100-GHz band 109-pixel MKID camera for the Nobeyama 45-m telescope. The camera optics contains plano-convex silicon (Si) lenses with 300-and 154-mm diameters located at the 4-K and 1-K stages, and a vacuum window of 320-mm diameter. Antireflective subwavelength structures (SWSs) for the Si lenses and the vacuum window were designed to reduce surface reflection. Cyclo olefin polymer (COP) was chosen as the base material for vacuum window as the dielectric loss is comparable with high-density polyethylene and it is easy to fabricate. Antireflective SWSs optimized for 100-GHz band were simulated using ANSYS HFSS. A one-layer rectangular pillar was designed for a Si lens of 300-mm diameter and a 320-mm diameter COP window to examine the fabrication process in large areas. For 154-mm diameter Si lens, a 1.2-mm depth tapered structure was used to obtain broadband characteristics. These designed structures were fabricated on both sides using a three-Axis numerically-controlled machine. An end mill and a metal-bonded dicing blade were used for cutting the COP and Si, respectively. W-band vector network analyzer was used for S-parameter measurements of the SWS formed flat surface at an ambient temperature. Average surface reflectance of Si lenses and transmittance of the COP window in the 90-110 GHz range were found at approximately 1% and 98%, respectively.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. The electromagnetic interference (EMI) is becoming an increasingly important factor in the spacecraft design equipped with highly sensitive detectors. This is particularly the case for LiteBIRD, in which the TES bolometers are exposed to space through the optical path. A particular concern is radiative interference caused by the X-band transmission during the ground communication. As the end-to-end verification test will be conducted in a later phase of the development, we need to derisk the concern early using simulation. In this report, we present the result of the EMI effects in the 1-GHz frequency range based on the electromagnetic simulation using a finite difference time domain (FDTD) solver. We modeled the dominant large structures of the spacecraft, calculated the spatial transmission of the antenna power, and estimated the electric field strength at the detector focal plane. The simulation results helped constrain aspects of the LiteBIRD satellite, such as the forward/backward ratio of the transmission antenna, to reduce the coupling between the antenna and the detectors.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD is JAXA Strategic Large Mission for the late 2020s that aims to observe the large-scale B-mode polarization pattern of the cosmic microwave background. One of its telescopes, the Low Frequency Telescope (LFT), has a crossed-Dragone design and observes at 34-161 GHz with a field of view of 18° x 9°. Because a miscalibration of the polarization angles mixes E- and B-mode polarization, we have measured the variation of the polarization angles in the field of view of a 1/4-scaled LFT antenna at 140-220 GHz, which corresponds to 35-55 GHz for the full-scale LFT, considering a scaling of the wavelength. We placed a collimated-wave source near the scaled-LFT aperture and rotated the polarization angle of the LFT feed. The measurements were explained well with a simple Jones matrix calculation, and the fitting errors of the polarization angles were less than 0.1'. We also measured the polarization angles by rotating the polarization direction in the scaled-LFT aperture, and the results were consistent with the angles measured by rotating the feed polarization at the ±10"level, except at the lowest frequencies. The polarization angle at the edges of the focal plane varied from that at the center by up to around a degree, with larger variation at lower frequencies. We evaluated the polarization angles for both Pol-X and Pol-Y feeds, and the results with Pol-Y showed a trend consistent with ray-tracing simulations. The results for Pol-X showed the opposite trend of the polarization rotation direction and larger angle variations.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. GroundBIRD is a ground-based experiment for a precise observation of the cosmic microwave background (CMB) polarizations. To achieve high sensitivity at large angular scales, we adopt three features in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID), and cold optics. The rotation scanning strategy has the advantage to suppress 1/f noise. It also provides a large sky coverage of 40%, which corresponds to the large angular scales of l∼ 6. This allows us to constrain the tensor-to-scalar ratio by using low l B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 145 GHz and 23 are for 220 GHz. This array is currently under development, and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. To show the technical feasibility of high-frequency and broadband anti-reflection (AR) coating for silicon optics in millimeter wavelengths, we fabricated a prototype of the four-layer sub-wavelength structure (SWS) using a combination of deep reactive ion etching (DRIE) and dicing processes. We also fabricated a three-layer SWS using a multi-layer DRIE technique. The described processes allow to obtain physical prototypes that are close enough to those designed that their simulated reflectances are slightly worse than expected. The simulations of the obtained three- and four-layer prototype showed the averaged reflectances of 5.2 % at 150–450 GHz and 3.7 % at 100–450 GHz, while the designed SWSs showed 1.6 % and 2.0 %, respectively.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. We are developing a detector array for astronomical observations in the 100-GHz band using microwave kinetic inductance detectors (MKIDs) and a readout system for the array with frequency sweeping scheme, which uses a frequency sweeping probe signal instead of a fixed-frequency probe signal. This scheme enables us to simultaneously obtain the resonance spectra of MKIDs in an array and to derive the resonance frequencies corresponding to the power of incoming radiation. It has the advantage of the dynamic range being higher than the standard scheme and the derived resonance frequencies not being affected by changes of the gain or delay in the transmission line. The resonance profile measured, however, can be distorted by frequency sweeping, and hence, it is necessary to evaluate the effect of frequency sweeping on the resonance spectrum. We made measurements using the scheme with several frequency-sweep velocities and checked its effect on the resonance frequency and the quality factor. A slow frequency sweep causes only small differences in the resonance spectrum compared to an ideal profile, and hence suitable for astronomical applications.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. LiteBIRD is a JAXA-led L-Class mission aimed at the study of B-mode polarization of the cosmic microwave background. Measurements on 15 bandwidth from 34 to 448 GHz are made on two instruments, low-frequency telescope and medium- and high-frequency telescope. To reach the desired sensitivities, more than 4500 transition edge sensors detectors, used on both instruments, will be continuously cooled to 100 mK. The cryogenic design based on shield cooling and mechanical coolers is presented in this paper. Shield cooling will be done with passive cooling and 15 K pulse tube coolers. A single cryogenic chain will cool both instruments. A 4 K stage is cooled by a 4He Joule–Thomson cooler from Japanese Aerospace Exploration Agency, pre-cooled by Stirling coolers. Multistage adiabatic demagnetization refrigerator will be optimized to provide continuous cooling at 1.75 K, 300 mK and 100 mK with 2.2 µW of cooling power on the latter stage. Seven ADR stages provided by NASA (USA) and CEA (France) are required. Details on the thermal design, preliminary sizing and expected performance are presented.

© 2019 IEEE. Polarization of the cosmic microwave background (CMB) has crucial information on the inflationary universe. To detect these signals, it is necessary to suppress far sidelobes of a telescope, which contaminate the CMB signals with strong foreground radiation, such as the Galactic plane. LiteBIRD is the only funded CMB observation satellite for the 2020s, and the low frequency telescope (LFT; 34-161 GHz) is one of its telescopes. We measured near-field antenna patterns of the LFT using its 1/4-scaled model and examined far sidelobes up to 60° from the peaks. To cover the 20° field of view of the LFT, we investigated the antenna patterns at the edges of the focal plane as well as at the center. The measurement frequencies were 140-220 GHz, which correspond to the lowest bands (35-55 GHz) of the full-scale LFT. The measurements were consistent with the simulated far-sidelobe patterns at least -50 dB level, and showed that far sidelobes for two orthogonal polarization directions are consistent with each other down to -40 dB level. We also measured the cross-polarization patterns, and their peak level was less than -20 dB.

© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE). Radiative cooling with thermal isolation shields can provide a reliable cooling system for instruments onboard satellites in orbit. We report the optimization study for the cryogenic architecture of the LiteBIRD satellite using radiative cooling. A trade study that changed the number of thermal shields and shield emissivity were conducted. The heat flow from 300 to 4.5 K, including active cooling by mechanical cryocoolers, was evaluated among the trade designs. We found that the design that consists of low-emissivity four-layer thermal shields is optimum in terms of thermal performance and system design. The optimum design achieved a heat load of 29.9 mW for the 4.5-K cooling stage, whereas the requirement was 30 mW with the assumed cryogenic system.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. The Advanced Technology Centre (ATC) of National Astronomical Observatory of Japan is developing microwave kinetic inductance detectors (MKIDs) for large-array pixel cameras for millimeter and sub-millimeter astronomy. We investigated single-crystal Nb thin layers to form superconducting microresonators. We compared the performances of MKIDs based on crystalline Nb structure and those based on polycrystalline Nb. We carried out the entire manufacture of the detectors in the ATC clean room. DC magnetron sputtering is used to grow single-crystal Nb films on r-plane sapphire substrates at an elevated temperature of 800 °C. The residual resistivity ratio (RRR) measured on these single-crystal Nb layers reached values ranging from 40 to 80. We made MKIDs with this crystalline Nb layer, and we measured internal quality factors of the detectors up to 10 6 . The measurement of the noise power spectral density of these MKIDs gave a low value of − 95 dBc/Hz from 100 Hz to 100 kHz. The internal quality factor Q i and the fractional resonance frequency change δf r /f r of MKIDs with respect to the temperature variation are usually following the extended Mattis–Bardeen equations. However, we noticed a deviation from the theoretical prediction for temperature lower than 1 K (in our case). This deviation has already been observed on Al MKIDs and explained by a theory taking into account the Kondo effect and the kinetic inductance contribution. We demonstrated that our measurements on single-crystal Nb MKIDs are also in agreement with the same theory.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. LiteBIRD is a candidate satellite for a strategic large mission of JAXA. With its expected launch in the middle of the 2020s with a H3 rocket, LiteBIRD plans to map the polarization of the cosmic microwave background radiation over the full sky with unprecedented precision. The full success of LiteBIRD is to achieve δr< 0.001 , where δr is the total error on the tensor-to-scalar ratio r. The required angular coverage corresponds to 2 ≤ ℓ≤ 200 , where ℓ is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3 years at a Lagrangian point L2 will be carried out for 15 frequency bands between 34 and 448 GHz with two telescopes to achieve the total sensitivity of 2.5 μ K arcmin with a typical angular resolution of 0.5 ∘ at 150 GHz. Each telescope is equipped with a half-wave plate system for polarization signal modulation and a focal plane filled with polarization-sensitive TES bolometers. A cryogenic system provides a 100 mK base temperature for the focal planes and 2 K and 5 K stages for optical components.

© ISSTT 2019 - 30th International Symposium on Space Terahertz Technology, Proceedings Book. All rights reserved. LiteBIRD is a satellite for polarization observation of the Cosmic Microwave Background. We have carried out near-field antenna pattern measurement of one of its telescopes, the Low Frequency Telescope, in 1/4 scale. We have investigated the far-sidelobes at the center and at the edges of the 20-degree field of view. The measured far-sidelobe patterns are consistent with the simulated one at −50 dB level, and the patterns for two orthogonal polarization directions are consistent with each other down to −40 dB level.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. Inflation is the leading theory of the first instant of the universe. Inflation, which postulates that the universe underwent a period of rapid expansion an instant after its birth, provides convincing explanation for cosmological observations. Recent advancements in detector technology have opened opportunities to explore primordial gravitational waves generated by the inflation through “B-mode” (divergent-free) polarization pattern embedded in the cosmic microwave background anisotropies. If detected, these signals would provide strong evidence for inflation, point to the correct model for inflation, and open a window to physics at ultra-high energies. LiteBIRD is a satellite mission with a goal of detecting degree-and-larger-angular-scale B-mode polarization. LiteBIRD will observe at the second Lagrange point with a 400 mm diameter telescope and 2622 detectors. It will survey the entire sky with 15 frequency bands from 40 to 400 GHz to measure and subtract foregrounds. The US LiteBIRD team is proposing to deliver sub-Kelvin instruments that include detectors and readout electronics. A lenslet-coupled sinuous antenna array will cover low-frequency bands (40–235 GHz) with four frequency arrangements of trichroic pixels. An orthomode-transducer-coupled corrugated horn array will cover high-frequency bands (280–402 GHz) with three types of single frequency detectors. The detectors will be made with transition edge sensor (TES) bolometers cooled to a 100 milli-Kelvin base temperature by an adiabatic demagnetization refrigerator. The TES bolometers will be read out using digital frequency multiplexing with Superconducting QUantum Interference Device (SQUID) amplifiers. Up to 78 bolometers will be multiplexed with a single SQUID amplifier. We report on the sub-Kelvin instrument design and ongoing developments for the LiteBIRD mission.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. The high-frequency telescope for LiteBIRD is designed with refractive and reflective optics. In order to improve sensitivity, this paper suggests the new optical configurations of the HFT which have approximately 7 times larger focal planes than that of the original design. The sensitivities of both the designs are compared, and the requirement of anti-reflection (AR) coating on the lens for the refractive option is derived. We also present the simulation result of a sub-wavelength AR structure on both surfaces of silicon, which shows a band-averaged reflection of 1.1–3.2% at 101–448 GHz.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. Pyramid-type antireflective subwavelength structures for large-diameter (>30cm) silicon lenses are promising for broadband astronomical observations. The refractive index and dielectric loss tangent of the lens material, columnar crystal silicon which is manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd., were measured at around 30 K using a Martin–Puplett-type Fourier transform spectrometer. The measured refractive index and dielectric loss tangent between 200 GHz and 1.6 THz were ∼ 3.42 and 1–5 × 10 - 4, respectively. Three different pyramid-type structures with a period of 265μm and depth of 600μm were simulated to obtain their reflectance using an electromagnetic field simulator, HFSS. The structures were fabricated on both sides of a 100-mm-diameter plane-convex lens made of columnar crystal silicon with a 150-mm radius of curvature using a metal-bonded V-shaped blade and a dedicated three-axis machine. The fabrication errors in the period and depth were less than 10μm. The reflectance of the lens flat surface was measured using a vector network analyzer to be between - 8 and - 17 dB in the range of 110–170 GHz, which was consistent with the result from the simulation.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. Cosmic microwave background (CMB) radiation is an afterglow from the Big Bang. CMB contains rich information about the early stage of the universe. In particular, odd-parity patterns (B-mode) in the CMB polarization on a large angular scale would provide an evidence of the cosmic inflation. The aim of the GroundBIRD experiment is to observe the B-mode on large angular scales from the ground. One of the most novel characteristics of the telescope used for this experiment is its rapid rotational scanning technique. In addition, the telescope uses cold optics and microwave kinetic inductance detectors. We have developed a telescope mount with a three-axis rotation mechanism (azimuth, elevation, and boresight) and measured the vibration at the focal plane stage at 20 RPM scan rotation rate. We also performed focal plane detector tests on this mount. The tests confirmed the expected response from the geomagnetism associated with the mount rotation. We have also developed a design for the magnetic shields and a detector array on a 3-in wafer. The preparations to begin the observations at the Teide Observatory in the Canary Islands in 2018 are proceeding smoothly.

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. We are developing a superconducting camera based on microwave kinetic inductance detectors (MKIDs) to observe 100-GHz continuum with the Nobeyama 45-m telescope. A data acquisition (DAQ) system for the camera has been designed to operate the MKIDs with the telescope. This system is required to connect the telescope control system (COSMOS) to the readout system of the MKIDs (MKID DAQ) which employs the frequency-sweeping probe scheme. The DAQ system is also required to record the reference signal of the beam switching for the demodulation by the analysis pipeline in order to suppress the sky fluctuation. The system has to be able to merge and save all data acquired both by the camera and by the telescope, including the cryostat temperature and pressure and the telescope pointing. A collection of software which implements these functions and works as a TCP/IP server on a workstation was developed. The server accepts commands and observation scripts from COSMOS and then issues commands to MKID DAQ to configure and start data acquisition. We made a commissioning of the MKID camera on the Nobeyama 45-m telescope and obtained successful scan signals of the atmosphere and of the Moon.

© 2002-2011 IEEE. We have prepared two kinds of Al resonators using thin films made by evaporation or sputtering and studied temperature behavior of their quality factors and resonance frequencies with the help of the extended Mattis-Bardeen (M-B) equations and its approximated analytical expressions. We have found that temperature behavior of both the internal quality factor Q-i and resonance frequency shift δ f-r/f-r measured in evaporated Al thin-film resonators are well agreed with those calculated by the analytical expressions of the complex conductivity given by the M-B theory. In the Al thin-film resonators made by sputtering, Q-i and δ f-r/f-r show a peak and a bump near 0.17 K in the respective temperature dependence. It is found that 1/Q-i is well approximated by a-b\ln T below 0.15 K, where T is the temperature. This type of temperature dependence strongly indicates the existence of the magnetic impurity scattering of residual quasi-particles due to the Kondo effect. It is shown that the temperature dependence of Q-i and δ f-r/f-r observed in the sputtered Al resonators can be well fitted by the theory taking the Kondo effect and kinetic inductance of the residual quasi-particles into account.

© 2018 Optical Society of America. A side-fed crossed Dragone telescope provides a wide field of view. This type of telescope is commonly employed in the measurement of cosmic microwave background polarization, which requires an image-space telecentric telescope withalarge focal plane over broadband coverage. We report the design of a wide field-of-view crossed Dragone optical system using anamorphic aspherical surfaces with correction terms up to the 10th order. We achieved a Strehl ratio larger than 0.95 over 32 × 18 square degrees at 150 GHz. This design is an image-space telecentric and fully diffraction-limited system below 400 GHz. We discuss the optical performance in the uniformity of the axially symmetric point-spread function and telecentricity over the field of view. We also address the analysis to evaluate the polarization properties, including the instrumental polarization, extinction rate, and polarization angle rotation. This work is a part of a program to design a compact multi-color wide-field-of-view telescope for LiteBIRD, which is a next-generation cosmic microwave background (CMB) polarization satellite.

© 2017 IEEE. The Advanced Technology Center (ATC) of NAOJ is developing a millimeter-wave camera with Microwave Kinetic Inductance Detectors (MKID) for wide field of view observations. We made a prototype array for the 45m telescope of Nobeyama Radio Observatory, NAOJ. This design is a 90-110 GHz band camera composed of a silicon lens array coupled to double-slot antennas connected to MKIDs. In this paper, we report on the development of the Al MKIDs array that we fabricated and characterized. MKID internal quality factors Qi measured at 85 mK achieve values of 7x105. We present the temperature- and power-dependence of these quality factors and the temperature-dependence of the fractional frequency shift. Noise Power Spectrum Density shows an average level of -90 dBc/Hz on 1kHz-1MHz band. At the end of December 2016, the prototype has been installed on the 45m telescope of Nobeyama Radio Observatory (NRO). A test observation in real conditions gave us the possibility to verify and to calibrate the setup of the entire camera. We now plan to upgrade the camera up to a 110 pixels version before next year observations run.

© The Authors, published by EDP Sciences, 2018. Our understanding of physics at very early Universe, as early as 10-35 s after the Big Bang, relies on the scenario known as the inflationary cosmology. Inflation predicts a particular polarization pattern in the cosmic microwave background, known as the B-mode yet the strength of such polarization pattern is extremely weak. To search for the B-mode of the polarization in the cosmic microwave background, we are constructing an off-axis rotating telescope to mitigate systematic effects as well as to maximize the sky coverage of the observation. We will discuss the present status of the GroundBIRD telescope.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. The Lite satellite for the studies of B-mode polarization and Inflation from the cosmic microwave background (CMB) Radiation Detection (LiteBIRD) is a next generation CMB satellite dedicated to probing the inflationary universe. It has two telescopes, Low Frequency Telescope (LFT) and High Frequency Telescope (HFT) to cover wide observational bands from 34 GHz to 448 GHz. In this presentation, we report the optical design and characterization of the LFT. We have used the CODE-V to obtain the LFT optical design based on a cross- Dragonian telescope. It is an image-space telecentric system with an F number of 3.5 and 20 x 10 degrees2 field of view. The main, near and far side lobes at far-field have been calculated by using a combination of HFSS and GRASP 10. It is revealed that the LFT telescope has good main lobe properties to satisfy the requirements. On the other hand, the side lobes are affected by the stray light that stems from the triple reflection and the direct path from feed. In order to avoid the stray light, the way to block these paths is now under study.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. The conceptual thermal design of the payload module (PLM) of LiteBIRD utilizing radiative cooling is studied. The thermal environment and structure design of the PLM strongly depend on the precession angle α of the spacecraft. In this study, the geometrical models of the PLM that consist of the sunshield, three layers of Vgrooves, and 5 K shield were designed in the cases of α = 45°, 30°, and 5°. The mission instruments of LiteBIRD are cooled down below 5 K. Therefore, heat transfers down to the 5 K cryogenic part were estimated in each case of α. The radiative heat transfers were calculated by using geometrical models of the PLM. The conductive heat transfers and the active cooling with cryocoolers were considered. We also studied the case that the inner surface of the V-groove is coated by a high-emissivity material.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD is a space-borne project for mapping the anisotropy of the linear polarization of the cosmic microwave background (CMB). The project aims to measure the B-mode pattern in a large angular scale to test the cosmic inflation theory. It is currently in the design phase lead by an international team of Japan, US, Canada, and Europe. We report the current status of the design of the electrical architecture of the payload module of the satellite, which is based on the heritages of other cryogenic space science missions using bolometers or microcalorimeters.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD is a candidate for JAXA's strategic large mission to observe the cosmic microwave background (CMB) polarization over the full sky at large angular scales. It is planned to be launched in the 2020s with an H3 launch vehicle for three years of observations at a Sun-Earth Lagrangian point (L2). The concept design has been studied by researchers from Japan, U.S., Canada and Europe during the ISAS Phase-A1. Large scale measurements of the CMB B-mode polarization are known as the best probe to detect primordial gravitational waves. The goal of LiteBIRD is to measure the tensor-to-scalar ratio (r) with precision of r < 0:001. A 3-year full sky survey will be carried out with a low frequency (34 - 161 GHz) telescope (LFT) and a high frequency (89 - 448 GHz) telescope (HFT), which achieve a sensitivity of 2.5 μK-arcmin with an angular resolution 30 arcminutes around 100 GHz. The concept design of LiteBIRD system, payload module (PLM), cryo-structure, LFT and verification plan is described in this paper.

© 2017 IEEE. A broadband antireflective subwavelength structure was developed suitable for large diameter silicon or alumina lenses used in the optical systems of superconducting cameras. In this study, a broadband antireflective subwavelength structure that can be easily fabricated with a dicing blade was designed. The model comprised both a pyramidal section (550 μ m in depth) and a straight section (150 μm in depth) to simplify fabrication with a metal bonded V-shaped blade and a normal straight dicing-blade. The simulated transmittance between 97 and 334 GHz was > 90%, which is comparable to that with a 700-μ m-depth tapered structure. The structure was fabricated on a flat surface, and transmittance at cryogenic temperatures was measured using a Fourier transform spectrometer. The measured average transmittance between 186 and 346 GHz was approximately 95%, and the experimental result is in good agreement with the simulation results.

� 2016 IEEE. We have developed a broadband corrugated horn in the 120-270 GHz and a horn array in the 80-180 GHz bands. The geometry of corrugations is so simple that the horn array can be directly machined from a bulk of aluminum with an end mill. The cross polarization and near sidelobe levels are less than-20 and-30 dB, respectively. The return loss is less than-15 dB in most design frequency bands, and the beam pattern is symmetric. The beam pattern and the return loss are measured in the 120-170 GHz range at room temperature. They are in good agreement with the simulation. It is possible to reduce reflection at the aperture surface and to reduce the weight by carving the unnecessary part. This design provides an octave bandwidth of the corrugated horn array at reasonable machining time.

We developed a broadband 4 pixels corrugated horn array with simple corrugation design. Because of the simple geometry of corrugations, the horn array can be directly machined from a bulk of aluminum with an end-mill. The design achieved over an octave-band (80 - 180 GHz) with good beam shape and -20 dB cross-polarization have been realized at all frequencies. All horns of the array have got similar beam pattern and return loss with simulation. This design provides an octave bandwidth of the corrugated horn array at reasonable cost.