Updated Design of the CMB Polarization Experiment Satellite LiteBIRD

Abstract: 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: A satellite for the studies of B-Mode polarization and inflation from cosmic background radiation detection

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

LiteBIRD: A Satellite for the Studies of B-Mode Polarization and Inflation from Cosmic Background Radiation Detection

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 \u3b4r&lt; 0.001 , where \u3b4r is the total error on the tensor-to-scalar ratio r. The required angular coverage corresponds to 2 64 \u2113 64 200 , where \u2113 is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3&nbsp;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 \u3bc K arcmin with a typical angular resolution of 0.5 18 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

The LiteBIRD Satellite Mission: Sub-Kelvin Instrument

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 \u201cB-mode\u201d (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\u2013235 GHz) with four frequency arrangements of trichroic pixels. An orthomode-transducer-coupled corrugated horn array will cover high-frequency bands (280\u2013402 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

Concept Study of Optical Configurations for High-Frequency Telescope for LiteBIRD

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\u20133.2% at 101\u2013448 GHz

LiteBIRD: an all-sky cosmic microwave background probe of inflation

The Litebird mission will map polarized fluctuations in the cosmic microwave background (CMB) to search for the signature of gravitational waves from inflation, potentially opening a window on the Universe a fraction of a second after the Big Bang. CMB measurements from space give access to the largest angular scales and the full frequency range to constrain Galactic foregrounds, and Litebird has been designed to take best advantage of the unique window of space. Litebird will have a powerful ability to separate Galactic foreground emission from the CMB due to its 15 frequency bands spaced between 40 and 402 GHz and sensitive 100-mK bolometers. Litebird will provide stringent control of systematic errors due to the benign thermal environment at the second Lagrange point, L2, 20-K rapidly rotating half-wave plates on each telescope, and the ability to crosscheck its results by measuring both the reionization and recombination peaks in the B-mode power spectrum. Litebird would be the next step in the series of CMB space missions, COBE, WMAP, and Planck, each of which has given landmark scientific discoveries. The 4,736 detectors are distributed between three 5-K cooled telescopes, called the Low-, Medium-, and High-frequency telescopes (LFT, MFT, and HFT), with 31 arc-min resolution at 140 GHz. Litebird will map 20 times deeper than Planck, with a total error of \u3b4r &lt; 0.001, conservatively assuming equal contributions of statistical error, systematic error, and margin. Litebird will be designed to discover or disfavor the best motivated inflation models \u2013 singlefield models that naturally explain the observed value of the spectral index of primordial density perturbations, with a characteristic scale of the potential comparable to or larger than the Planck scale. Litebird will also measure the optical depth to reionization to cosmicvariance-limited error, enabling ground-based high-resolution CMB experiments to measure the sum of neutrino masses. The proposed mission will be a partnership. Japan Aerospace Exploration Agency (JAXA) will provide the launch, spacecraft, Joule-Thomson coolers, LFT and its wave-plate. Europe will build the MFT and HFT, their waveplates, and the 100-mK cooler. Canada will contribute the 300-K detector readout electronics. The U.S. will build the detector arrays, cold readout electronics, and the 1.8-K cooler likely through a NASA mission of opportunity cost capped at $75M. In May 2019, JAXA selected Litebird as a \u201cstrategic L-class\u201d mission for launch in early 2028. The total mission cost is estimated to be approximately$500M, and therefore the U.S. contribution is highly leveraged. Finally, Litebird technologies have been tested or will be tested in the near future on ground-based experiments. Litebird\u2019s ability to measure the entire sky at the largest angular scales with 15 frequency bands is complementary to that of ground-based experiments such as South Pole Observatory, Simons Observatory, and CMB-S4, which will focus on deep observations of low-foreground sky. Litebird can provide valuable foreground information for ground-based experiments and ground-based experiments can improve Litebird\u2019s observations with high-resolution lensing data