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Journal of Low Temperature Physics

, Volume 184, Issue 3–4, pp 824–831 | Cite as

LiteBIRD: Mission Overview and Focal Plane Layout

  • T. Matsumura
  • Y. Akiba
  • K. Arnold
  • J. Borrill
  • R. Chendra
  • Y. Chinone
  • A. Cukierman
  • T. de Haan
  • M. Dobbs
  • A. Dominjon
  • T. Elleflot
  • J. Errard
  • T. Fujino
  • H. Fuke
  • N. Goeckner-wald
  • N. Halverson
  • P. Harvey
  • M. Hasegawa
  • K. Hattori
  • M. Hattori
  • M. Hazumi
  • C. Hill
  • G. Hilton
  • W. Holzapfel
  • Y. Hori
  • J. Hubmayr
  • K. Ichiki
  • J. Inatani
  • M. Inoue
  • Y. Inoue
  • F. Irie
  • K. Irwin
  • H. Ishino
  • H. Ishitsuka
  • O. Jeong
  • K. Karatsu
  • S. Kashima
  • N. Katayama
  • I. Kawano
  • B. Keating
  • A. Kibayashi
  • Y. Kibe
  • Y. Kida
  • K. Kimura
  • N. Kimura
  • K. Kohri
  • E. Komatsu
  • C. L. Kuo
  • S. Kuromiya
  • A. Kusaka
  • A. Lee
  • E. Linder
  • H. Matsuhara
  • S. Matsuoka
  • S. Matsuura
  • S. Mima
  • K. Mitsuda
  • K. Mizukami
  • H. Morii
  • T. Morishima
  • M. Nagai
  • T. Nagasaki
  • R. Nagata
  • M. Nakajima
  • S. Nakamura
  • T. Namikawa
  • M. Naruse
  • K. Natsume
  • T. Nishibori
  • K. Nishijo
  • H. Nishino
  • T. Nitta
  • A. Noda
  • T. Noguchi
  • H. Ogawa
  • S. Oguri
  • I. S. Ohta
  • C. Otani
  • N. Okada
  • A. Okamoto
  • A. Okamoto
  • T. Okamura
  • G. Rebeiz
  • P. Richards
  • S. Sakai
  • N. Sato
  • Y. Sato
  • Y. Segawa
  • S. Sekiguchi
  • Y. Sekimoto
  • M. Sekine
  • U. Seljak
  • B. Sherwin
  • K. Shinozaki
  • S. Shu
  • R. Stompor
  • H. Sugai
  • H. Sugita
  • T. Suzuki
  • A. Suzuki
  • O. Tajima
  • S. Takada
  • S. Takakura
  • K. Takano
  • Y. Takei
  • T. Tomaru
  • N. Tomita
  • P. Turin
  • S. Utsunomiya
  • Y. Uzawa
  • T. Wada
  • H. Watanabe
  • B. Westbrook
  • N. Whitehorn
  • Y. Yamada
  • N. Yamasaki
  • T. Yamashita
  • M. Yoshida
  • T. Yoshida
  • Y. Yotsumoto
Article

Abstract

LiteBIRD is a proposed CMB polarization satellite project to probe the inflationary B-mode signal. The satellite is designed to measure the tensor-to-scalar ratio with a 68 % confidence level uncertainty of \(\sigma _\mathrm{r}<10^{-3}\), including statistical, instrumental systematic, and foreground uncertainties. LiteBIRD will observe the full sky from the second Lagrange point for 3 years. We have a focal plane layout for observing frequency coverage that spans 40–402 GHz to characterize the galactic foregrounds. We have two detector candidates, transition-edge sensor bolometers and microwave kinetic inductance detectors. In both cases, a telecentric focal plane consists of approximately \(2\times 10^3\) superconducting detectors. We will present the mission overview of LiteBIRD, the project status, and the TES focal plane layout.

Keywords

Inflation CMB Polarization Primordial B-mode TES bolometer MKID Satellite 

1 Introduction

Recent developments in the field of low-temperature detectors enable us to probe various fundamental questions in science. One of the science drivers that pushes superconducting detector array technology forward is the measurement of the cosmic microwave background (CMB) polarization.

The detection of the divergence-free CMB polarization pattern at large angular scales, called the primordial B-mode, provides the direct evidence of the inflation. The signal strength is parameterized as a tensor-to-scalar ratio, r, and this parameter relates to the energy scale of inflation. The current generation experiments have on order of \(\sim \)10\(^3\) transition-edge sensor (TES) bolometers at one to a few observing frequency bands within a single telescope. The next-generation focal plane detector arrays for those experiments aim to populate about \(\sim \)10\(^4\) multi-chroic feeds/pixels in one focal plane.

While ground-based and balloon-borne CMB experiments will continue probing the primordial B-mode with the sensitivity of \(r\sim \)10\(^{-2}\), the role of a future CMB polarization mission would be to characterize the primordial B-mode with a sensitivity of \(\sigma _r<10^{-3}\). LiteBIRD is a proposed satellite mission to JAXA, which is dedicated to probe the inflationary paradigm using measurements of CMB polarization. In this paper, we describe the results of the current conceptual design on the overall mission and discuss the optical and focal plane layout of LiteBIRD.

2 Science Goal

The satellite is designed to measure the tensor-to-scalar ratio with a 68 % confidence level uncertainty of \(\sigma _r<10^{-3}\), including statistical, instrumental systematic, and foreground uncertainties. In this way, LiteBIRD probes the representative large single-field slow-roll inflation models. The design philosophy of LiteBIRD is purely driven by this mission goal. For \(r\ge 10^{-2}\), LiteBIRD measures the power spectral shape in \(2<\ell <200\) with high signal to noise at each \(\ell \)-bin. Information from the shape of the power spectrum would not only tightly constrain the tensor-to-scalar ratio but would also provide a strong confirmation to the inflationary paradigm. For \(r<10^{-2}\), the constraint on the tensor-to-scalar ratio largely comes from the reionization bump, taking advantage of the full sky coverage provided by the satellite platform. We do not rely on de-lensing of the CMB signal to achieve the LiteBIRD scientific goals. However, using external data to de-lens the CMB signal will enhance LiteBIRD’s scientific capabilities.
Table 1

The LiteBIRD sensitivity

Band

Bandwidth

NEP

NET

\(N_\mathrm{bolo}\)

NET\(_\mathrm{arr}\)

Sensitivity with margin

(GHz)

(\(\Delta \nu /\nu \))

(aW/\({\sqrt{\mathrm{Hz}}}\))

(\(\upmu \)K\({\sqrt{\mathrm{s}}}\))

 

(\(\upmu \)K\({\sqrt{\mathrm{s}}}\))

(\(\upmu \)K arcmin)

40

0.30

7.74

225.9

152

18.3

53.4

50

0.30

7.86

136.9

152

11.1

32.3

60

0.23

7.06

106.2

152

8.6

25.1

68

0.23

7.10

82.9

152

6.7

19.6

78

0.23

7.08

64.7

152

5.2

15.3

89

0.23

7.00

52.4

152

4.3

12.4

100

0.23

8.55

79.7

222

5.3

15.6

119

0.30

9.48

52.5

148

4.3

12.6

140

0.30

8.99

42.3

222

2.8

8.3

166

0.30

8.31

36.2

148

3.0

8.7

195

0.30

7.62

34.1

222

2.3

6.7

235

0.30

6.86

35.8

148

2.9

8.6

280

0.30

9.14

55.4

72

6.5

19.0

338

0.30

8.34

78.0

108

7.5

21.9

402

0.23

6.69

154.4

74

17.9

52.3

Total

   

2276

 

3.2

The last column represents the sensitivity to polarization with the units \(\upmu \)K arcmin, and it includes the 3 sources of margin, (i) the observational time of 3 years with the time efficiency of 0.72, (ii) the yield of 0.8, and (iii) \(1.25\times \)NET

3 Mission Overview

The science case and general overview of the mission are described in Hazumi et al. and Matsumura et al. [1, 2, 3].

LiteBIRD observes the full sky from the second Lagrange point. The scan strategy consists of the combination of precession and spin of the instrument. We have four parameters to specify the scan strategy, the precession and spin angles, \((\alpha , \beta )\), and the precession and spin rates, \((T_{\mathrm{prec}}, T_{\mathrm{spin}})\). These parameters are chosen as \((\alpha , \beta , T_{\mathrm{prec}}, T_{\mathrm{spin}}) = (65^\circ , 30^\circ , {\sim }90 \text { min}, {\sim }10 \text { min})\), which optimizes crosslinking over the sky and thus minimizes several sources of polarization instrumental systematic effects. With this set of parameters, LiteBIRD covers approximately 50 % of the sky in 1 day and the full sky in 6 months.
Fig. 1

The observing frequency of LiteBIRD (Color figure online)

LiteBIRD has a broad observing frequency range so that it can separate the CMB and foreground emissions without relying on external dataset. The optimization of these bands has relied on various methods. A parametric analysis of the foregrounds [4] led us to choose a frequency coverage from 40 to 402 GHz using 15 bands . The observing frequency bands are summarized in Table 1. While a method such as template subtraction [5] may indicate that such a broad spectral range is not necessary, the current choice of observing frequencies is conservative and allows for checks of self-consistency in the foreground model. Going forward, we will conduct updated studies that reflect more realistic foreground models using the recent Planck results (Fig. 1).

The science goal of LiteBIRD is to probe the large angular scales, i.e., \(\ell <200\), and therefore, we need degree-scale angular resolution at all the observing frequency bands. The observing frequency coverage is split in two, and we have two corresponding telescopes. The low-frequency telescope (LFT) covers the frequency range between 40 and 235 GHz, and the high-frequency telescope (HFT) covers between 280 and 402 GHz. We employ the cross-Dragone design for LFT in order to maximize the field of view (FOV) while minimizing the overall size of the optical system. The 800 mm diameter anamorphic aspheric primary and secondary mirrors achieve the telecentric \(10\times 20\) degree diffraction-limited FOV. The cross-Dragone telescope is known to be susceptible to stray light, and we introduce a 400-mm aperture to control off-axis sensitivity. The aperture is cooled at 4.5 K to minimize the radiative loading to a detector. We place a polarization modulator—a continuously rotating achromatic half-wave plate (HWP)—at the aperture. The polarization modulator is introduced to mitigate the instrumentally induced differential systematic effects as well as the system 1 / f noise in the detector and readout chain. HFT is a refractive telescope that has the FOV of about \(10\times 10\) degrees. It consists of two lenses together with the cryogenically cooled aperture and a second continuously rotating HWP. An overview of the LFT and HFT is shown in Fig. 2.

The cryogenic system consists of a two-stage Stirling cooler to cool the radiation shields and to pre-cool the 4 K Joule Thomson (JT) cooler, which provides the 4.5 K stage and is used to cool the aperture. We make use of the development heritage of these space-compatible coolers from Astro-H/SXS [6]. We have an option to cool mission components to 1.7 K using a \(^3\)He-based JT cooler as necessary. The focal plane is cooled to 100 mK using an adiabatic magnetization refrigerator (ADR) (Fig. 3).
Fig. 2

Left The optical system and the focal plane unit of the LFT and HFT. Right The optical layout of the LFT (Color figure online)

Fig. 3

The focal plane unit for the LFT. The 13 wafers cooled at 100 mK form the LFT focal plane. The wafer with a larger pixel diameter covers the observation frequencies from 40 to 89 GHz, and the wafer with the smaller pixel diameter covers from 100 to 235 GHz. A quasi-optical low-pass filter is placed above each wafer to minimize the thermal loading (Color figure online)

4 Focal Plane Layout

LiteBIRD has two detector options, TES bolometers and microwave kinetic inductance detector (MKID). TES bolometers have been used extensively in ground-based and balloon-borne CMB observations. The currently detected B-mode data points all come from the bolometer-based CMB experiments. The MKID is a relatively new technology that is undergoing rapid progress in the low-temperature detector community. The MKID focal plane layout for LiteBIRD appears in Sekimoto et al. [7]. In this article, we focus on the focal plane layout for LiteBIRD using a TES bolometer.

We have two focal plane configurations that correspond to the two telescopes, the high-frequency telescope and the low-frequency telescope. The focal plane design for the observing coverage of 40–235 GHz is based on the multi-chroic pixel using a sinuous antenna [8]. This multi-chroic pixel technology is implemented in the ground-based CMB experiment, Polarbear-2, Simons Array [9], and SPT-3G. For LiteBIRD, one pixel contains 6 TESs that measure 3 bands with 2 orthogonal linear polarization states simultaneously. The development status of the multi-chroic pixel using a sinuous antenna is in Westbrook et al. [10]. Each sinuous antenna is optically coupled to the telescope through a directly contacting dielectric lenslets. Hemispherical silicon or alumina with an extension of the same material, together with the sinuous antenna, forms a nearly single-mode beam. The lens surface is anti-reflection coated to minimize reflection loss [11]. We divide the 12 bands into two different diameter pixels.

The focal plane unit for HFT covers the highest three bands using feed-horn coupled TES bolometers, with each pixel measuring at a single-frequency band. The feed-horn technology and detector technology for this focal plane are based on the focal plane arrays developed for SPTpol and Advanced ACTpol [12, 13].

For both focal planes, the TES bolometer signals are measured by the combinations of the cold and warm electronics using a frequency domain superconducting quantum interference device (SQUID) multiplexing system. The dynamic range required at the SQUID input is actively reduced using digital active nulling (DAN) technology [14]. The warm electronics digitally generate combinations of sinusoidal bias carriers, one for each detector, that are then transmitted to the cold electronics [15]. The total required power for the detector readout electronics is maintained at about 100 W. Polarbear-2 and SPT-3G employ similar readout electronics.

5 Project Status

LiteBIRD was proposed to the JAXA strategic large mission category in early 2015, and it was selected for further study. LiteBIRD is currently in transition to the Phase-A1 study toward the system requirement review. The US LiteBIRD team proposed to the NASA mission of opportunity. This proposal was also selected for further study and the US team is currently preparing a Phase A concept study report. During this period, we are iteratively progressing the design of the overall mission and the mission instruments. The current effort aims the target launch year in 2024–2025.

Notes

Acknowledgments

This work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks, JSPS KAKENHI Grant Number 15H05441, MEXT KAKENHI Grant Number 15H05891, and the ISAS strategic development fund from the steering committee for space science. The McGill authors acknowledge funding from the Canadian Space Agency.

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • T. Matsumura
    • 1
  • Y. Akiba
    • 23
  • K. Arnold
    • 29
  • J. Borrill
    • 26
    • 32
  • R. Chendra
    • 25
  • Y. Chinone
    • 26
  • A. Cukierman
    • 26
  • T. de Haan
    • 26
    • 32
  • M. Dobbs
    • 9
  • A. Dominjon
    • 12
  • T. Elleflot
    • 27
  • J. Errard
    • 21
  • T. Fujino
    • 31
  • H. Fuke
    • 1
  • N. Goeckner-wald
    • 26
  • N. Halverson
    • 3
  • P. Harvey
    • 26
  • M. Hasegawa
    • 5
  • K. Hattori
    • 7
  • M. Hattori
    • 24
  • M. Hazumi
    • 5
    • 7
  • C. Hill
    • 26
  • G. Hilton
    • 15
  • W. Holzapfel
    • 26
  • Y. Hori
    • 26
  • J. Hubmayr
    • 15
  • K. Ichiki
    • 11
  • J. Inatani
    • 12
  • M. Inoue
    • 17
  • Y. Inoue
    • 23
  • F. Irie
    • 31
  • K. Irwin
    • 22
  • H. Ishino
    • 16
  • H. Ishitsuka
    • 23
  • O. Jeong
    • 26
  • K. Karatsu
    • 4
  • S. Kashima
    • 12
  • N. Katayama
    • 7
  • I. Kawano
    • 1
  • B. Keating
    • 27
  • A. Kibayashi
    • 16
  • Y. Kibe
    • 16
  • Y. Kida
    • 16
  • K. Kimura
    • 5
  • N. Kimura
    • 17
  • K. Kohri
    • 5
  • E. Komatsu
    • 10
  • C. L. Kuo
    • 22
  • S. Kuromiya
    • 18
  • A. Kusaka
    • 32
  • A. Lee
    • 26
    • 32
  • E. Linder
    • 32
  • H. Matsuhara
    • 1
  • S. Matsuoka
    • 25
  • S. Matsuura
    • 6
  • S. Mima
    • 19
  • K. Mitsuda
    • 1
  • K. Mizukami
    • 31
  • H. Morii
    • 5
  • T. Morishima
    • 24
  • M. Nagai
    • 28
  • T. Nagasaki
    • 5
  • R. Nagata
    • 5
  • M. Nakajima
    • 18
  • S. Nakamura
    • 31
  • T. Namikawa
    • 24
  • M. Naruse
    • 20
  • K. Natsume
    • 31
  • T. Nishibori
    • 1
  • K. Nishijo
    • 1
  • H. Nishino
    • 5
  • T. Nitta
    • 28
  • A. Noda
    • 1
  • T. Noguchi
    • 12
  • H. Ogawa
    • 17
  • S. Oguri
    • 5
  • I. S. Ohta
    • 8
  • C. Otani
    • 19
  • N. Okada
    • 17
  • A. Okamoto
    • 1
  • A. Okamoto
    • 16
  • T. Okamura
    • 5
  • G. Rebeiz
    • 26
  • P. Richards
    • 26
  • S. Sakai
    • 1
  • N. Sato
    • 5
  • Y. Sato
    • 1
  • Y. Segawa
    • 23
  • S. Sekiguchi
    • 12
  • Y. Sekimoto
    • 12
  • M. Sekine
    • 12
  • U. Seljak
    • 32
  • B. Sherwin
    • 32
  • K. Shinozaki
    • 1
  • S. Shu
    • 12
  • R. Stompor
    • 2
  • H. Sugai
    • 7
  • H. Sugita
    • 1
  • T. Suzuki
    • 5
  • A. Suzuki
    • 26
  • O. Tajima
    • 5
  • S. Takada
    • 13
  • S. Takakura
    • 18
  • K. Takano
    • 18
  • Y. Takei
    • 1
  • T. Tomaru
    • 5
  • N. Tomita
    • 30
  • P. Turin
    • 26
  • S. Utsunomiya
    • 1
  • Y. Uzawa
    • 14
  • T. Wada
    • 1
  • H. Watanabe
    • 23
  • B. Westbrook
    • 26
  • N. Whitehorn
    • 26
  • Y. Yamada
    • 16
  • N. Yamasaki
    • 1
  • T. Yamashita
    • 31
  • M. Yoshida
    • 5
  • T. Yoshida
    • 1
  • Y. Yotsumoto
    • 1
  1. 1.Japan Aerospace Exploration Agency (JAXA)SagamiharaJapan
  2. 2.Laboratoire Astroparticule et Cosmologie (APC)Paris Cedex 13France
  3. 3.University of ColoradoBoulderUSA
  4. 4.Delft University of TechnologyDelftThe Netherlands
  5. 5.High Energy Accelerator Research Organization (KEK)TsukubaJapan
  6. 6.Kansei Gakuin UniversityNishinomiyaJapan
  7. 7.Kavli Institute for the Physics and Mathematics of The Universe (WPI)The University of TokyoChibaJapan
  8. 8.Konan UniversityKobeJapan
  9. 9.Canadian Institute for Advanced ResearchMcGill UniversityMontrealCanada
  10. 10.Max-Planck-Institut fur AstrophysikGarchingGermany
  11. 11.Nagoya UniversityNagoyaJapan
  12. 12.National Astronomical Observatory of Japan (NAOJ)TokyoJapan
  13. 13.National Institute for Fusion ScienceGifuJapan
  14. 14.National Institute of Information and Communications Technology (NICT)TokyoJapan
  15. 15.National Institute of Standards and TechnologyBoulderUSA
  16. 16.Okayama UniversityOkayamaJapan
  17. 17.Osaka Prefecture UniversitySakaiJapan
  18. 18.Osaka UniversitySuiteJapan
  19. 19.RIKENSendaiJapan
  20. 20.Saitama UniversitySaitamaJapan
  21. 21.Institut Lagrange de Paris (ILP)Sorbonne UniversitesParisFrance
  22. 22.Stanford UniversityStanfordUSA
  23. 23.The Graduate University for Advanced Studies (SOKENDAI)HayamaJapan
  24. 24.Tohoku UniversitySendaiJapan
  25. 25.Tokyo Institute of TechnologyTokyoJapan
  26. 26.University of California, BerkeleyBerkeleyUSA
  27. 27.University of California, San DiegoLa JollaUSA
  28. 28.University of TsukubaTsukubaJapan
  29. 29.University of Wisconsin-MadisonMadisonUSA
  30. 30.University of TokyoTokyoJapan
  31. 31.Yokohama National UniversityYokohamaJapan
  32. 32.Lawrence Berkeley National LaboratoryBerkeleyUSA

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