Concept Design of Low Frequency Telescope for CMB B-mode Polarization satellite LiteBIRD
Y. Sekimoto, P. A. R. Ade, A. Adler, E. Allys, K. Arnold, D. Auguste, J. Aumont, R. Aurlien, J. Austermann, C. Baccigalupi, A. J. Banday, R. Banerji, R. B. Barreiro, S. Basak, J. Beall, D. Beck, S. Beckman, J. Bermejo, P. de Bernardis, M. Bersanelli, J. Bonis, J. Borrill, F. Boulanger, S. Bounissou, M. Brilenkov, M. Brown, M. Bucher, E. Calabrese, P. Campeti, A. Carones, F. J. Casas, A. Challinor, V. Chan, K. Cheung, Y. Chinone, J. F. Cliche, L. Colombo, F. Columbro, J. Cubas, A. Cukierman, D. Curtis, G. D'Alessandro, N. Dachlythra, M. De Petris, C. Dickinson, P. Diego-Palazuelos, M. Dobbs, T. Dotani, L. Duband, S. Duff, J. M. Duval, K. Ebisawa, T. Elleflot, H. K. Eriksen, J. Errard, T. Essinger-Hileman, F. Finelli, R. Flauger, C. Franceschet, U. Fuskeland, M. Galloway, K. Ganga, J. R. Gao, R. Genova-Santos, M. Gerbino, M. Gervasi, T. Ghigna, E. Gjerløw, M. L. Gradziel, J. Grain, F. Grupp, A. Gruppuso, J. E. Gudmundsson, T. de Haan, N. W. Halverson, P. Hargrave, T. Hasebe, M. Hasegawa, M. Hattori, M. Hazumi, S. Henrot-Versillé, D. Herman, D. Herranz, C. A. Hill, G. Hilton, Y. Hirota, E. Hivon, R. A. Hlozek, Y. Hoshino, E. de la Hoz, J. Hubmayr, K. Ichiki, T. iida, H. Imada, K. Ishimura, H. Ishino, G. Jaehnig, T. Kaga, S. Kashima, N. Katayama, et al. (137 additional authors not shown)
CConcept Design of Low Frequency Telescope for CMBB-mode Polarization satellite LiteBIRD
Y. Sekimoto , P.A.R. Ade , A. Adler , E. Allys , K. Arnold , D. Auguste , J. Aumont ,R. Aurlien , J. Austermann , C. Baccigalupi , A.J. Banday , R. Banerji , R.B. Barreiro ,S. Basak , J. Beall , D. Beck , S. Beckman , J. Bermejo , P. de Bernardis ,M. Bersanelli , J. Bonis , J. Borrill , F. Boulanger , S. Bounissou , M. Brilenkov ,M. Brown , M. Bucher , E. Calabrese , P. Campeti , A. Carones , F.J. Casas ,A. Challinor , V. Chan , K. Cheung , Y. Chinone , J.F. Cliche , L. Colombo ,F. Columbro , J. Cubas , A. Cukierman , D. Curtis , G. D’Alessandro ,N. Dachlythra , M. De Petris , C. Dickinson , P. Diego-Palazuelos , M. Dobbs ,T. Dotani , L. Duband , S. Duff , J.M. Duval , K. Ebisawa , T. Elleflot , H.K. Eriksen ,J. Errard , T. Essinger-Hileman , F. Finelli , R. Flauger , C. Franceschet , U. Fuskeland ,M. Galloway , K. Ganga , J.R. Gao , R. Genova-Santos , M. Gerbino , M. Gervasi ,T. Ghigna , E. Gjerløw , M.L. Gradziel , J. Grain , F. Grupp , A. Gruppuso ,J.E. Gudmundsson , T. de Haan , N.W. Halverson , P. Hargrave , T. Hasebe ,M. Hasegawa , M. Hattori , M. Hazumi , S. Henrot-Versill´e , D. Herman ,D. Herranz , C.A. Hill , G. Hilton , Y. Hirota , E. Hivon , R.A. Hlozek , Y. Hoshino ,E. de la Hoz , J. Hubmayr , K. Ichiki , T. Iida , H. Imada , K. Ishimura , H. Ishino ,G. Jaehnig , T. Kaga , S. Kashima , N. Katayama , A. Kato , T. Kawasaki ,R. Keskitalo , T. Kisner , Y. Kobayashi , N. Kogiso , A. Kogut , K. Kohri ,E. Komatsu , K. Komatsu , K. Konishi , N. Krachmalnicoff , I. Kreykenbohm ,C.L. Kuo , A. Kushino , L. Lamagna , J.V. Lanen , M. Lattanzi , A.T. Lee ,C. Leloup , F. Levrier , E. Linder , T. Louis , G. Luzzi , T. Maciaszek , B. Maffei ,D. Maino , M. Maki , S. Mandelli , E. Martinez-Gonzalez , S. Masi , T. Matsumura ,A. Mennella , M. Migliaccio , Y. Minami , K. Mitsuda , J. Montgomery , L. Montier ,G. Morgante , B. Mot , Y. Murata , J.A. Murphy , M. Nagai , Y. Nagano , T. Nagasaki ,R. Nagata , S. Nakamura , T. Namikawa , P. Natoli , S. Nerval , T. Nishibori ,H. Nishino , C. O’Sullivan , H. Ogawa , H. Ogawa , S. Oguri , H. Ohsaki , I.S. Ohta ,N. Okada , N. Okada , L. Pagano , A. Paiella , D. Paoletti , G. Patanchon , J. Peloton ,F. Piacentini , G. Pisano , G. Polenta , D. Poletti , T. Prouv´e , G. Puglisi ,D. Rambaud , C. Raum , S. Realini , M. Reinecke , M. Remazeilles , A. Ritacco ,G. Roudil , J.A. Rubino-Martin , M. Russell , H. Sakurai , Y. Sakurai , M. Sandri ,M. Sasaki , G. Savini , D. Scott , J. Seibert , B. Sherwin , K. Shinozaki ,M. Shiraishi , P. Shirron , G. Signorelli , G. Smecher , S. Stever , R. Stompor ,H. Sugai , S. Sugiyama , A. Suzuki , J. Suzuki , T.L. Svalheim , E. Switzer ,R. Takaku , H. Takakura , S. Takakura , Y. Takase , Y. Takeda , A. Tartari ,E. Taylor , Y. Terao , H. Thommesen , K.L. Thompson , B. Thorne , T. Toda ,M. Tomasi , M. Tominaga , N. Trappe , M. Tristram , M. Tsuji , M. Tsujimoto ,C. Tucker , J. Ullom , G. Vermeulen , P. Vielva , F. Villa , M. Vissers , N. Vittorio ,I. Wehus , J. Weller , B. Westbrook , J. Wilms , B. Winter , E.J. Wollack ,N.Y. Yamasaki , T. Yoshida , J. Yumoto , M. Zannoni , and A. Zonca Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Science (ISAS), Sagamihara,Kanagawa 252-5210, Japan a r X i v : . [ a s t r o - ph . I M ] J a n The University of Tokyo, Department of Astronomy, Tokyo 113-0033, Japan High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan Cardiff University, School of Physics and Astronomy, Cardiff CF10 3XQ, UK Stockholm University Laboratoire de Physique de l’´Ecole Normale Sup´erieure, ENS, Universit´e PSL, CNRS, Sorbonne Universit´e, Universit´ede Paris, 75005 Paris, France University of California, San Diego, Department of Physics, San Diego, CA 92093-0424, USA Universit´e Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France IRAP, Universit´e de Toulouse, CNRS, CNES, UPS, (Toulouse), France University of Oslo, Institute of Theoretical Astrophysics, NO-0315 Oslo, Norway National Institute of Standards and Technology (NIST), Boulder, Colorado 80305, USA International School for Advanced Studies (SISSA), Via Bonomea 265, 34136, Trieste, Italy Instituto de Fisica de Cantabria (IFCA, CSIC-UC), Avenida los Castros SN, 39005, Santander, Spain School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram, Maruthamala PO,Vithura, Thiruvananthapuram 695551, Kerala, India Stanford University, Department of Physics, CA 94305-4060, USA University of California, Berkeley, Department of Physics, Berkeley, CA 94720, USA Instituto Universitario de Microgravedad Ignacio Da Riva (IDR/UPM), Plaza Cardenal Cisneros 3, 28040 - Madrid,Spain Dipartimento di Fisica, Universit`a La Sapienza, P. le A. Moro 2, Roma, Italy and INFN Roma Dipartimento di Fisica, Universit`a degli Studi di Milano, INAF-IASF Milano, and Sezione INFN Milano Lawrence Berkeley National Laboratory (LBNL), Computational Cosmology Center, Berkeley, CA 94720, USA University of California, Berkeley, Space Science Laboratory, Berkeley, CA 94720, USA Institut d’Astrophysique Spatiale (IAS), CNRS, UMR 8617, Universit´e Paris-Sud 11, Bˆatiment 121, 91405 Orsay,France University of Manchester, Manchester M13 9PL, United Kingdom AstroParticle and Cosmology (APC) - University Paris Diderot, CNRS/IN2P3, CEA/Irfu, Obs de Paris, SorbonneParis Cit´e, France Dipartimento di Fisica, Universit`a di Roma ”Tor Vergata”, and Sezione INFN Roma2 DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, U.K. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, U.K. Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge CB3 0HA, U.K. University of Toronto University of Tokyo, School of Science, Research Center for the Early Universe, RESCEU McGill University, Physics Department, Montreal, QC H3A 0G4, Canada Universidad Polit´ecnica de Madrid Stockholm University Univ. Grenoble Alpes, CEA, IRIG-DSBT, 38000 Grenoble, France Lawrence Berkeley National Laboratory (LBNL), Physics Division, Berkeley, CA 94720, USA NASA Goddard Space Flight Center INAF - OAS Bologna, via Piero Gobetti, 93/3, 40129 Bologna (Italy) SRON Netherlands Institute for Space Research Instituto de Astrofisica de Canarias (IAC), Spain Dipartimento di Fisica e Scienze della Terra, Universit`a di Ferrara and Sezione INFN di Ferrara, Via Saragat 1, 44122Ferrara, Italy University of Milano Bicocca, Physics Department, p.zza della Scienza, 3, 20126 Milan Italy University of Oxford Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, The University ofTokyo, Kashiwa, Chiba 277-8583, Japan National University of Ireland Maynooth MPE Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO, 80309, USA Tohoku University, Graduate School of Science, Astronomical Institute, Sendai, 980-8578, Japan The Graduate University for Advanced Studies (SOKENDAI), Miura District, Kanagawa 240-0115, Hayama, Japan The University of Tokyo, Tokyo 113-0033, Japan Institut d’Astrophysique de Paris, CNRS/Sorbonne Universit´e, Paris France Saitama University, Saitama 338-8570, Japan Nagoya University, Kobayashi-Masukawa Institute for the Origin of Particle and the Universe, Aichi 464-8602, Japan ispace, inc. National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan Waseda University Okayama University, Department of Physics, Okayama 700-8530, Japan Kitasato University, Sagamihara, Kanagawa 252-0373, Japan Osaka Prefecture University, Sakai, Osaka 599-8531, Japan Max-Planck-Institut for Astrophysics, D-85741 Garching, Germany University of Erlangen-N¨urnberg SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), MenloPark, CA 94025, USA Kurume University, Kurume, Fukuoka 830-0011, Japan Istituto Nazionale di Fisica Nucleare - Sezione di Ferrara Italian Space Agency (ASI) Centre National d’Etudes Staptiales (CNES), France Yokohama National University, Yokohama, Kanagawa 240-8501, Japan Japan Aerospace Exploration Agency (JAXA), Research and Development Directorate, Tsukuba, Ibaraki 305-8505,Japan National University of Ireland Maynooth Konan University Space Science Data Center, Italian Space Agency, via del Politecnico, 00133, Roma, Italy The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan Optical Science Laboratory, Physics and Astronomy Dept., University College London (UCL) University of British Columbia, Canada National Institute of Technology, Kagawa College INFN Sezione di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa (Italy) Three-Speed Logic, Inc. The University of Tokyo, Department of Physics, Tokyo 113-0033, Japan N´eel Institute, CNRS Mullard Space Science Laboratory, University College London, London San Diego Supercomputer Center, University of California, San Diego, La Jolla, California, USA
ABSTRACT
LiteBIRD has been selected as JAXA’s strategic large mission in the 2020s, to observe the cosmic microwavebackground (CMB) B -mode polarization over the full sky at large angular scales. The challenges of LiteBIRDare the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, whichare derived from the system requirements. The possible paths of stray light increase with a wider FoV and thefar sidelobe knowledge of −
56 dB is a challenging optical requirement. A crossed-Dragone configuration waschosen for the low frequency telescope (LFT : 34–161 GHz), one of LiteBIRD’s onboard telescopes. It has awide field-of-view (18 ◦ × ◦ ) with an aperture of 400 mm in diameter, corresponding to an angular resolution ofabout 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90 ◦ arechosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapeswith serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure aremade of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaledmodel of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reducedfar sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in frontof the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TESdetectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas havebroadband capability. Performance specifications of the LFT and an outline of the proposed verification planare presented. Keywords:
Cosmic microwave background, space program, millimeter-wave polarization, cryogenic telescope
Send correspondence to Y. Sekimoto, E-mail: [email protected] . INTRODUCTION
LiteBIRD, the Lite (Light) satellite for the study of B -mode polarization and Inflation from cosmic backgroundRadiation Detection, observes the cosmic microwave background (CMB) polarization over the full sky at largeangular scales. Cosmological inflation predicts primordial gravitational waves, which imprinted large-scalecurl ( B -mode) patterns on the CMB polarization map. Measurements of the CMB B -mode signals are knownas the best probe to detect the primordial gravitational waves and to measure the inflation energy. The scientificobjective of LiteBIRD is to test major inflationary models. The power of the B -modes is proportional to thetensor-to-scalar ratio, r . The current upper limit on r is r < . The mission goal of LiteBIRD is to measure r with a precision of δr < . < (cid:96) < (cid:96) is the multipole moment.LiteBIRD has been selected as JAXA’s strategic large mission in the late 2020s. It will be launched with anH3 vehicle for three years of observations at the Lagrangian point (L2) of the Earth-Sun system. It is a spinningsatellite with a precession angle ( α ) of 45 ◦ and spin angle ( β ) of 50 ◦ with spin rate of 0.05 rpm and precessionperiod of 180 minutes, which are optimized from crossing angles and revisits of previously scanned regions. Theconcept design has been studied by researchers from Japan, U.S., Canada, and Europe since September 2016.LiteBIRD observes millimeter waves from 34 GHz to 448 GHz with two instruments, LFT and MHFT.
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Both instruments have the same relative bandwidth of min: max frequencies = 1:5. LFT will explore synchrotronand CMB emission, while MHFT covers CMB emission and will also extend to higher frequencies to explorethe dust contribution. The bands in common between the two telescopes, i.e. 89–161 GHz, allow reductionof systematics associated with the telescopes, and add redundancy. A transmissive half-wave plate (HWP) forpolarization modulation has a limited bandwidth, and so LiteBIRD has two instruments to cover the frequencybands. Both instruments are operated at cryogenic temperature of 5 K to reduce the photon noise. The focalplane design is based on multi-chroic TES detectors at 100 mK operation.
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Cryogenic chain of LiteBIRD isdescribed by Hasebe et al. and Duval et al. Challenges for LiteBIRD are wide field-of-view (FoV) and broadband capabilities of millimeter-wave polar-ization measurements, which are derived from the sensitivity specifications. The wide FoV corresponds to alarge focal plane area; a detector pixel has different spill-over or edge-taper depending on the pixel position onthe focal plane. The possible paths of stray light increase with a wider FoV. A stable system is also required toperform the all sky survey.LiteBIRD is currently under the conceptual study phase. It is important to define preliminary design spec-ifications in order to make progress on the system design. The derivation of the detailed requirements and thedetailed design study are moving in parallel, and affect each other iteratively. In this paper we introduce a listof design specifications in this phase. Based on further simulation-based studies of the error budget allocationover the entire system, the numbers we list for the design specifications may change.
2. OVERVIEW OF LFT
LFT has been designed to meet specifications described in the next section. This section describes a briefoverview of LFT before describing design details. LFT is a wide field-of-view telescope designed to observe theCMB and synchrotron radiation in the frequencies of 34–161 GHz, as shown in Figure 1. The aperture diameteris 400 mm. The angular resolution is 24–71 arcminutes. LFT is operated at cryogenic temperature of 5 K toreduce the optical loading and is surrounded by radiators called V-grooves. The thermal design of LiteBIRDis described in Hasebe et al. LFT has a crossed Dragone antenna made of aluminum. A frame structureat 5 K supports all components: the PMU (polarization modulation unit); focal plane; primary and secondaryreflectors; and absorbers. An earlier design has been updated.A PMU with a transmissive HWP (half-wave plate) is mounted in front of the aperture stop. LFT focalplane is based on multi-chroic TES detectors at 100 mK operation.
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There are interfaces with the LFT PMUand the LFT focal plane.
3. LFT DESIGN SPECIFICATIONS
The performance specifications for LFT are as follows. -grooves30K80K160Kfront hood focal plane (0.1K)primary (5K)PMUframe (5K) aperture(400mm)secondary(5K)
Figure 1. Overview of low frequency telescope (LFT). MHFT and side panels are not shown for clarity.
Frequency coverage
Band sensitivities
LFT shall have the array sensitivities as tabulated in Table 1, which shall satisfy the map-level sensitivity specifications. The sensitivity is limited by the number of pixels, which is closely relatedwith the field of view of the telescope. The noise of the detector in a pixel is limited by the optical loading.
Table 1. Performance specifications of LFT. The bandwidth (BW) is (High − Low)/Center frequency.
Center freq. BW Beam fwhm pixel dia. No. det NET array
Pol. sensitivityGHz [arcmin] [mm] [ µ Krts] [ µ K arcmin]40 0.30 70.5 32 48 18.5 37.450 0.30 58.5 32 24 16.5 33.560 0.23 51.1 32 48 10.5 21.368 0.23 41.6 16 144 9.8 16.968 0.23 47.1 32 24 15.778 0.23 36.9 16 144 7.7 12.178 0.23 43.8 32 48 9.589 0.23 33.0 16 144 6.1 11.389 0.23 41.5 32 24 14.2100 0.23 30.2 16 144 5.1 6.6119 0.30 26.3 16 144 3.8 4.6140 0.30 23.7 16 144 3.6 4.8
Band shape
The frequency bandpasses are defined by a combination of superconducting band-pass filters onthe wafer, and the use of quasi-optical metal-mesh filters in front of the focal plane to reject higherfrequencies. Lower frequencies than the defined band (red-leak) might contribute to sidelobes due to thedistorted beam pattern. The red-leak is rejected only by a superconducting band-pass filter on the wafer. Higher frequencies than the defined band (blue-leak) might contribute to noise due to far-infrared radiation.The blue leak is rejected by both the on-chip filter and the quasi-optical metal mesh filter in front of thefocal plane.
The knee frequency of the post-demodulation 1 /f noise should be below 0 . .
05 rpmpin rate, precession angle α = 45 ◦ and spin angle β = 50 ◦ ). The knee frequency of the raw 1 /f noiseshould be well below 3.1 Hz (46 rpm × f knee is 20 mHz for individual detectors and 100 , mHz for the commonmode. Data loss and operational duty cycle
The operating life of the instruments should be long enough to per-form observations for 3 years. The system shall have an operational duty cycle of 85 % for science obser-vations, including all downtime for cryogenic cycling, detector operation preparation, and data transfer.Data loss due to cosmic ray glitches should be less than 5 %.
Angular resolution
The angular resolution of each detector response should be sufficient to cover the requiredangular scales of 2 < (cid:96) < (cid:96) is the spherical harmonic index. It shall have a FWHM of 80 (cid:48) or better. Angular resolution should be better than 30 (cid:48) at 100 GHz, for measuring the recombinationbump, which is the prominent structure at degree scales in the B -mode power spectrum coming from theprimordial gravitational waves. It shall also be better than 80 (cid:48) at 40 GHz, for dealing with point sources. Pointing offset knowledge
The pointing offset knowledge should be less than 2 . (cid:48) .
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Far sidelobe knowledge
The extended component of the far sidelobe should be known at a precision levelof −
56 dB.
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Radiation from the Galactic plane through the far sidelobes contaminates the signal andtherefore the inferred power spectrum. The far sidelobe is currently defined as the domain located above0.2 rad.
Small scale feature of sidelobe
The small-scale features of the far sidelobes should be known at a precisionlevel of −
33 dB, more specifically defined by the following equation: (intensity/0 .
05 %) × (diameter/30 (cid:48) ) ,where the diameter is the FWHM of the small-scale features due to possible optical ghosts or opticalmultiple reflections. Near sidelobe knowledge
The beam pattern of near sidelobes (out to 10 ◦ from the co-polar beam peak)should be known at a precision level of −
30 dB. Also, it should be confirmed to be consistent with itsdesigned pattern at a precision level of 10 % or better.
Beam stability knowledge
The beam-shape stability over time, should be better than 0.46 % (synchronous)/ 2 %( random) for beam width, and better than 1.7 (cid:48)(cid:48) (synchronous) / 16 (cid:48)(cid:48) (random) for pointing, betterthan 0 .
086 % (synchronous) / 2 . −
46 dB at sidelobes around several to 30 degrees. The time scale of the synchronous beam fluctuation is163 msec for LFT in which HWP rotates by 45 ◦ , while ”random” is a component that fluctuates randomlyover time. They correspond to “differential beam shape” and are also related to optical qualities of theinstrument in the broad sense. Note that in the case of a perfect polarization modulator, differentialbeam effects are negligibly small. Therefore beam stability specifications are tied to imperfections of thepolarization modulation system. Knowledge of polarization efficiency
The polarization efficiency knowledge should be better than 0 . Absolute polarization angle knowledge (monopole)
The absolute polarization angle knowledge on thestable monopole component should be better than 2 . (cid:48) .
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Polarization modulation
The modulation frequency should be > × .
76 Hz, which assures 4 modulation (atleast) during beam-size excursions of 30 (cid:48) . The modulation frequency should be < × . Modulation synchronous instrumental polarization knowledge
The 4 f synchronous instrumental po-larization knowledge should be better than 0 . able 2. Optical specifications of LFT antenna Aperture diameter 400 mmField of view 18 ◦ × ◦ Strehl ratio > .
95 at 161 GHzFocal plane telecentricity < . ◦ Focal ratio 2 . < F/ < . < < −
30 dBRotation of polarization angle across FoV < ± . ◦ Gain variation in time
The gain variation in time for a single detector should be better than 10 % assumingthat the gain parameter is updated every 1200 sec (which corresponds to a 0.05 rpm rotation period). Theeffective differential gain should be smaller than 0 . ◦ ) / 0 . There are other specifications. According to the system design, heat dissipation of LFT is limited to 4 mW,which includes the PMU and temperature control of the LFT optical components. The minumum eigen-frequencyfor LFT is assumed to be 100 Hz and 50 Hz for axial and lateral axes, respectively; however, this might beoptimized by a combined design with the cryo-structure of the payload module (PLM). LFT is designed towithstand quasi-static loads of 20 g for the axial and lateral axes. EMC/EMI specifications have been studiedwith simulations.
4. OPTICAL DESIGN4.1 Antenna design
After trade-off studies of various optical configurations among crossed-Dragone, offset-Gregorian, and open-Dragone,
24, 25 we concluded that the crossed-Dragone antenna is the best option for LFT because of the wide-fieldof view and the low cross polarization. Multiple reflections of crossed-Dragone antennas have been describedearlier. A crossed-Dragone antenna of LFT has been designed with anamorphic aspherical surfaces to achieve thespecifications listed in Table 2. The anamorphic aspherical surface is described with the following equation forboth the primary mirror (PM) and the secondary mirror (SM): z m = C m,x x m + C m,y y m (cid:113) − (1 + k m,x ) C m,x x m − (1 + k m,y ) C m,y y m + (cid:88) i =2 A m,i (cid:2) (1 − B m,i ) x m + (1 + B m,i ) y m (cid:3) i , (1)where m = PM, SM, C m,x and C m,y are curvatures for the x and y directions, k m,x and k m,y are conic constantsin the x and y directions, and A m,i and B m,i are aspherical coefficients. Table 3. Optical parameters of anamorphic aspherical surfaces. C m,x /mm − C m,y /mm − k m,x k m,y y m, /mm z m, /mm θ m /deg.PM − . × − − . × − − . × − × − − . − . − .
771 346.223 42.45664FP 550.924 343.223 90 A m, B m, A m, B m, A m, B m, A m, B m, PS − . × − − . × − × − − . − . × − − . − . × − − . × − × − − . − . × − -1.157 − . × − − . ray diagram of LFT is shown in Figure 2, which has an aperture diameter of 400 mm and an FoV of 18 ◦ × ◦ . The aperture diameter is derived from the requirement of the angular resolution of 80 (cid:48) at 40 GHz. The FoVcorresponds to the focal plane area of 420 mm ×
210 mm, which is roughly proportional to the sensitivity. Thismeets the sensitivity requirement in Table 1.Optical rays are designed to have 640 mm diameter at the aperture from the focal plane to keep enough edgetapers at both primary and secondary reflectors. The Strehl ratio at 161 GHz is larger than 0.95, as shownin Figure 3. Rotation of the polarization angle for the y -axis polarization across the field of view is shown inFigure 3. The rotation is estimated to < ± . ◦ according to the ray tracing simulation with a finite resistivity.The derived optical parameters are tabulated in Table 3.The allocated volumes of LFT and MHFT are shown in Figure 4. The field of view of LFT is maximizedunder the volume constraint. Crossed-Dragone antennae with f/2.5, 3.0, and 3.5 are compared. The volume isroughly proportional to the f-number. Under the volume constraint, the smaller values are preferable, but, thestray light is larger. We chose f/3.0 for LFT, considering focal-plane dimensions and feed parameters.We updated the design of a crossed-Dragone antenna reported by. The f/3.0 and the crossing angle of theoptical axes of 90 ◦ have been chosen after an extensive study of stray light (on the right of Figure 2).Figure 5 shows the stray light with the crossing angles; At the crossing angle of 110 ◦ , the direct path fromthe feed to the sky is small, but there are many triple reflection paths. At 82 ◦ , there are large direct paths. Thenthe 90 ◦ angle moderates for both the triple reflections and direct paths.The detector hood and front hood whose height of 500 mm reduces stray light to far sidelobes as shownin Figure 2. The y -direction of the focal plane in the focal plane coordinate (Figure 6) is limited by multiplereflections or stray light. The x -direction is limited by the 5 K allocated area of LiteBIRD, as shown in Figure 4.Primary and secondary mirrors have rectangular shapes of 835 ×
795 mm and 872 ×
739 mm, respectively,with serrations to reduce diffraction patterns from the edges of mirrors. The mirror sizes were reduced from theprevious design because the 2 K cold aperture stop was removed due to limitations of the cooling capacity andthen the length between the aperture and the main reflector was reduced. The optical design is based on feedparameters as tabulated in Table 4. y-axis detectorhoodfront hood primarysecondaryaperturestop Figure 2. (Left) Ray tracing diagram of Low Frequency Telescope (LFT). Blue, Red, and Green lines show θ y = +4 . ◦ , θ y = 0 ◦ , θ y = − . ◦ , respectively. (Right) Possible stray light paths of LFT. Red lines show direct paths. Blue and greenlines show triple reflections. Physical optics simulations of LFT with GRASP10 have been studied in the same way by Imada et al. Lowerfrequencies make it relatively difficult to meet the far sidelobe requirement due to diffraction effects. Figure 7shows the impact of the feed sidelobes. igure 3. (Left) Map of Strehl ratio of LFT antenna at 161 GHz. (Right) Rotation of polarization angle of y -axispolarization across the field of view in units of degrees. mm Z YPLM 5K Coordinate mm MHFT
750 95017001700
LFT xyz
Figure 4. (Left) Usable volume of LFT and MHFT and the PLM coordinate. V-grooves are also shown. The most innerV-groove is at 30 K. The top of the truss is the 5 K structural interface for LFT and MHFT. (Right) Allocated area ofLFT and MHFT and the PLM coordinate.
The LFT antenna pattern assuming a Gaussian feed is shown in the left panels of Figure 7, while the feedsimulated with HFSS is shown in the right ones. Upper panels show the antenna pattern of a pixel near theprimary reflector, while lower ones show that of near the aperture. It is clear that the direct path from the feedsidelobe contributes the far sidelobe of LFT at a level of −
60 dB. The feed sidelobe of a pixel near the aperturecontributes the point-like sidelobe due to triple reflections (feed → primary → secondary → primary → sky:shown in green). Note that there are discrepancies of the feed sidelobes at a level around −
20 dB between theHFSS simulation and the room-temperature measurement of the sinuous/lens feed. We have simulated the antenna pattern at 30 GHz, as shown in Figure 8, since a bandpass filter cannot cut offsharply at a specific frequency, e.g., 34 GHz, which causes a red leak to the sidelobe. The feed here is polarized
Figure 5. Stray light with the crossing angle of the optical axes of the crossed-Dragone configuration.able 4. Frequency bands and feed parameters. The bandwidth (BW) is (High − Low)/Center frequency. The number(No.) of detectors is two times the number of pixels because of two orthogonal polarization detections.
Type Center freq. BW Low High Pixel dia. Beam waist No. pix No. det.[GHz] [GHz] [GHz] [mm] radius [mm]1 40 0.30 34 46 32 11.64 24 4860 0.23 53 67 32 11.64 24 4878 0.23 69 87 32 11.64 24 482 50 0.30 43 58 32 11.64 12 2468 0.23 60 76 32 11.64 12 2489 0.23 79 99 32 11.64 12 243 68 0.23 60 76 16 5.82 72 14489 0.23 79 99 16 5.82 72 144119 0.30 101 137 16 5.82 72 1444 78 0.23 69 87 16 5.82 72 144100 0.23 89 112 16 5.82 72 144140 0.30 119 161 16 5.82 72 144 x y z y
420 210
Figure 6. LFT focal plane pixel arrangement. There are eight square (10 cm ×
10 cm) tiles. Red, yellow, and green, bluepixels correspond Type 1, 2, 3, and 4 of Table 4, respectively. The LFT focal plane coordinate is shown in black arrows.The scales are shown in units of millimeters. along the x axis, and located at ( x, y ) = ( −
88 mm, +44 mm) with a diameter of 24 mm, which is different fromthe current design, but the qualitative effects are the same. Several features, originating from the diffraction atthe mirror edges, are shown within circles in both panels. These features are at a higher level than that of thenominal diffracted point spread function (PSF).The current simulations take into account the reflectors, the aperture stop and the front baffle with perfectabsorbers. The followings items will be considered for further studies, which might generate additional side-lobes. • Actual absorbers have finite reflections on the aperture stop, front hood, detector hood, frame, and panels.The absorbers covering the optical cavity and the focal plane are not ideal and they have frequencydependence as well as angle dependence of reflectance. • There are multiple reflections (i.e. ghost effects) or multiple scattering among the HWP, the focal plane,the aperture stop, quasi-optical LP Filters, and the absorbers.
The aperture stop at 4.8 K with an inner diameter of 400 mm is made of millimeter absorber, TK-RAM
32, 33 on an aluminum plate. This works to make good beam shape for a relatively low edge taper of about 3 dBconfiguration. ray : no stray lightRed : direct pathGreen : pri-sec-priBlue : sec-pri-sec
Feed : Gaussianposition (-190, -87)
Angular distance in degrees I n t en s i t y i n d B i
10 20 30 40 50 60 70 80 90 100 Angular distance in degrees10 20 30 40 50 60 70 80 90 100Angular distance in degrees10 20 30 40 50 60 70 80 90 100Angular distance in degrees10 20 30 40 50 60 70 80 90 100 Gray : no stray lightRed : direct pathGreen : pri-sec-priBlue : sec-pri-sec
Feed : HFSSposition (-190, -87)
Gray : no stray lightRed : direct pathGreen : pri-sec-priBlue : sec-pri-sec
Feed : Gaussianposition (-190, +87)
Gray : no stray lightRed : direct pathGreen : pri-sec-priBlue : sec-pri-sec
Feed : HFSSposition (-190, +87) -50-40-30-20-10010203040 I n t en s i t y i n d B i -50-40-30-20-10010203040 I n t en s i t y i n d B i -50-40-30-20-10010203040 I n t en s i t y i n d B i -50-40-30-20-10010203040 Figure 7. Optical simulation of far-field beam pattern of LFT at 34 GHz. Gray shows the nominal beam pattern withoutstray light, red shows the direct path from the focal plane to sky, green shows triple reflections (feed − primary − secondary − primary − sky), and blue shows triple reflections (feed − secondary − primary − secondary − sky). (Top,Left) A pixel near the primary reflector around ( x, y ) = ( −
190 mm, −
87 mm) with a Gaussian feed. (Top, Right) A pixelnear the primary reflector with HFSS simulation of sinuous antenna. The feed sidelobe contributes the far sidelobe ofLFT due to direct path (Red). (Bottom, Left) A pixel near the aperture stop around ( x, y ) = ( −
190 mm, +87 mm) witha Gaussian feed. (Top, Right) A pixel near the aperture stop with HFSS simulation of sinuous antenna. The feed sidelobecontributes the far sidelobe of LFT due to triple reflections (feed − primary − secondary − primary − sky: Green). Millimeter absorbers to reduce reflections are attached on the inside surface of the 5 K frame, which plays arole of a cavity. Eccosorb AN72 and HR10 are candidates for such absorbers; however, they have large TML (totalmass loss) and CVCM (collected volatile condensable materials). According to the NASA outgass database, AN72 washed with ethanol shows reasonable TML and CVCM.The front-hood, as shown in Figure 9, is made of millimeter absorber Eccosorb AN72 and aluminum plate.
Temperature stability of the optical components of LFT is required to meet the specification of the single detector f knee = 20 mHz, which corresponds to 50 seconds. The noise equivalent temperature (NET) of each detector isaround 50 µ K/ √ Hz, so the noise is integrated to ∆ T = 7 µ K in the 50 seconds. It is necessary to meet thefollowing constraint: (∆ T ) (cid:29) N o (cid:88) o =1 ( δT o × η o × (cid:15) o × (optical efficiency)) , (2)where N o is the number of optical components, δT o is the temperature stability of the optical components, η o isthe optical load fraction and, (cid:15) o is the emissivity of the optical components. The optical efficiency of the feed isa) (b) Figure 8. Physical optical simulation for 30 GHz, which is out of the band. (a) 2D map. The features from the diffractionat the mirror edges can be found at the right side of the main lobe. (b) 1D cut.Table 5. specifications for temperature stability on the scale of 50 seconds of LFT optical components. The optical loadfraction ( η o ) is a typical value, because it depends on the focal plane position, the feed sidelobe, and frequency. (cid:15) o is theemissivity of the optical components. Components Temperature [K] η o (cid:15) o Stabilitymin. max. [mK]Front hood 5 6 0.004 0.99 3PMU/HWP 4.5 20 0.63 0.01 0.5PMU mount 4.5 20 0.004 0.99 0.7Around aperture stop 4.5 4.8 0.2 0.99 0.025 K frame 4.5 5 0.1 0.99 0.03LFT reflectors 4.5 5 0.9 0.002 1.6Detector hood 1.8 2 0.08 0.99 0.04Low-pass filter 1.7 2 0.9 0.01 0.3assumed to be 0.69. The noise contribution of each optical component is assumed less than 2 µ K. The derivedspecifications on the stability of the LFT optical components are shown in Table 5. Those specifications give arough estimate for temperature stability of δT o /T o ∼ − in the worst case, but, more accurate estimates arerequired, because the optical load fraction ( η o ) depends on the focal plane position, the feed sidelobe and thefrequency, as described in section 4.2 and in Figure 7.The temperature of the aperture stop, and other optical components, are planned to be stabilized with heatersto reduce the 1 /f noise level.
5. STRUCTURE DESIGN
The structural design of LFT is shown in Figure 9. The frame and reflectors of LFT are made of aluminum inorder to shrink similarly within 0.4 % from 300 K to 5 K. Structural and thermal stability of the telescope isrequired for the all sky survey of CMB polarization observations. Aluminum has good thermal conductance at5 K and is mechanically stable. The frame has structural interfaces at 5 K with PMU and the focal plane, whichis operated at 0.1 K. The fastener between the reflector and the frame is planned to use SUS (stainless steel)bolts. The SUS bolts generate local deformations with an area of several mm, which does not affect on the globalshape of the reflectors. The telescope is supported by trusses made of aluminum on the 5 K interface plate. Thetotal mass of LFT, including the trusses, the PMU and the focal plane, is estimated to be 200 kg. able 6. Alignment specifications of LFT. All values are maxima.
Requirement Primary (M1) Secondary (M2) Frame CombinedMechanical shape error 15 µ m r.m.s. 15 µ m r.m.s. 30 µ m r.m.s.Alignment dx ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± δx of − µ m, δy of − µ m, δz of 22 µ m, which are all reasonably small. Then, we can plan the ground verification and calibration withoutdirectional constraints due to gravitational effects. According to a scaled model (see Section 8), the alignmentcan be achieved with careful design and assembly.The surface roughness of the reflectors are designed to be 2–4 µ m in R a on the scale of 10 mm, which reducesinfrared radiation, mainly from the Galactic plane. According to the Ruze fomula η e = exp (cid:104) − (cid:0) π(cid:15)λ (cid:1) (cid:105) , infraredradiation more than 5–10 THz (30–60 µ m) can be scattered.The telescope is tightly covered with aluminum and absorbers to reduce the stray light from the inner surfaceof the 30 K V-groove (see Figure 1). The absorber, made of plastic and carbon, is adhered to a panel withepoxy, then the panel is fixed to the 5 K frame. The cryogenic contraction of the absorber and the epoxy will becarefully designed not to deform the frame. aperture stop focal planeprimary reflectorsecondaryreflectorframe PMU front hoodOpticalaxis Figure 9. (Left) Lateral view of structural design of LFT. The side panel is covered with millimeter absorbers. (Right)Top view of LFT.
6. LFT POLARIZATION MODULATION UNIT (PMU)
A polarization modulation unit with a transmissive sapphire HWP has been developed for LiteBIRD (Figure10).
The progress of the PMU is separately reported. The PMU/HWP is placed in front of the aperturestop or entrance pupil of 400 mm diameter. The HWP continuously rotates with 46 rpm = 0 .
77 Hz. PMU usessuperconducting magnets for levitation. The eddy current and magnetic hysteresis dissipate and increase thetemperature of the rotating HWP from 5 K to 20 K. The HWP rotation axis is tilted by 5 ◦ with respect to theoptical axis to mitigate multiple reflections including optical ghosts between the HWP and the focal plane.We have derived following the interface specifications on LFT PMU and focal plane from the LFT specifica-tions (Section 3) and system designs during ISAS pre-phase A2.
2, 3
1. The optical effects of the observation frequency of 34–161 GHz due to the PMU are minimized to meet thenear and far sidelobes specifications of LFT. igure 10. LFT Polarization Modulation Unit (PMU). The sapphire half-wave plate is shown in blue.
2. The opaque 20 K parts of PMU are designed to reduce the optical loading.3. The mass of PMU is 30 kg.4. The heat loads to the 5 K stage including the PMU wire harness are less than 3 mW.5. AC magnetic field variation and DC magnetic field are minimized to reduce the effects on the focal plane.
7. LFT FOCAL PLANE detector hood (2K)LFT frame (5K) Focal plane interface bracket
Figure 11. (Left) LFT focal plane assembly. (Right) Structural interface between the focal plane and LFT.
The LFT focal plane has been designed and developed with antenna-coupled TES detectors. The lensand sinuous antenna have broadband capability. The focal plane with AlMn TES is cooled to 100 mK withADRs. The cold readout with SQUID amplifiers is also cooled to 100 mK. Cosmic ray mitigation has beenextensively investigated.
39, 40
The progress of the LFT focal plane is separately reported. The focal plane consists of eight square (10 cm ×
10 cm) tiles, as shown in Figure 11. The focal plane isshielded with a hood at 2 K to reduce stray light (see Figure 2). A quasi-optical metal-mesh low-pass filter isput in front of square modules to reduce thermal loads from far-infrared radiation of the Galactic plane and the0 K radiation of PMU. A magnetic shield to reduce magnetic variation from the PMU covers the focal planeexcept for the optical input. The structural interface at 5 K between the focal plane and LFT is designed asshown in Figure 11.The following interface specifications on the focal plane are flown down from the LFT specifications andsystem designs.1. The optical efficiency of each detector is higher than 0.69.2. The return loss of the feeds in the in-band frequencies is better than −
10 dB.3. The main beam width of the feeds is consistent with the Gaussian beam radius defined in Table 4 within5 %.4. The sidelobes of each detector are less than −
17 dB. Figure 7 shows the effects of the feed sidelobes.5. The optical cross talk among pixels is less than 0.03 %.6. The lower frequency edges of 34 GHz and 60 GHz of the 40 GHz band and the 68 GHz band, respectively,have sharper cut-offs to reduce the contamination of sidelobes of the lower frequencies. Figure 8 shows thebeam pattern at 30 GHz.7. The polarization efficiency of the feeds should be higher than 98 %, which corresponds to the cross polar-ization of < −
17 dB.8. The polarization angle of each detector across the frequency band changes by less than ± ◦ .9. The detector noise is basically the photon noise limit of the cosmic microwave background of 2.7 K. TheNET is tabulated in Table 1.10. The common mode 1 /f knee noise of the detector module is stable to be better than 100 mHz.11. The 1 /f knee of each detector is stable to be better than 20 mHz.12. Micro-vibration of the 5 K interface is less than 30 µ G/ √ Hz and 80 µ G/ √ Hz over 10–200 Hz and 200–500 Hz, respectively. Under this condition, the focal plane shall perform the required sensitivity. Thisrequirement is based on the experience of the Hitomi X-ray satellite.
13. The detector yield including the readout electronics is larger than 80 %.14. The dead time fraction due to cosmic ray glitches is less than 0.05.15. The mass of the focal plane assembly is assumed to be 17 kg without the magnetic shield.16. The first eigen-frequency of the focal plane is required to larger than 141 Hz for all three axes.
8. SCALED MODEL DEMONSTRATION
A quarter (1/4)-size scaled model of the LFT antenna has been designed and developed to verify the wide-fielddesign. Measured frequencies are also scaled, so the antenna pattern of the scaled model reveals that of the fullsize.The near-field measurement system with the scaled LFT has been developed as shown in Figure 12. Mea-sured amplitude and phase data are transformed to far fields. Figure 12 shows far-field beam patterns at threefocal positions (see Figure 6), center, top-right edge, and bottom-right edge, at the frequency of 220 GHz, whichcorresponds to 55 GHz in the full size LFT. We confirmed the suppression of far sidelobes based on the scaledmodel measurements.Rotation of polarization angle over the field of view is another key parameter for the wide-field design. Adedicated compact antenna test range (CATR), or a collimated millimeter-wave source has been developed to /4 LFT front hoodNear fieldscanner focal planescanner
450 mm
Figure 12. (Left) LFT quarter (1/4) scaled model and the near-field measurement system. (Right) Far-field patternsof the quarter LFT at the center (top) and edges (middle and bottom) of the focal plane, measured at 220 GHz, whichcorresponds to 55 GHz in the full model. measure the polarization angle across the wide field of view of the 1/4 LFT. The polarization angle of the 1/4-scaled LFT has been measured with a resolution of 0.1 (cid:48) . The polarization angle of polarization x or horizontalpolarization was measured to rotate by around 60 (cid:48) across the focal plane, while the angle of polarization y orvertical polarization rotates by around 30 (cid:48) across the focal plane.The structural design of the LFT antenna has been studied with the 1/4-scaled LFT. The frame structureof the 1/4-LFT as shown in Figure 13, was assembled with plates and rectangular bars. The reflector alignmentof the assembled 1/4 LFT was measured with a coordinated machine (Mitsutoyo Legex 12128), as shown inFigure 13. The fitted curve of the optical surfaces referring to the aperture center is different from the designedvalues by 36 µ m and 22 (cid:48)(cid:48) at the maximum. The measured alignment met the quarter values of the alignmentrequirement of Table 6. ApertureFocal PlanePrimarySecondaryFrame
Figure 13. (Left) LFT quarter (1/4) scaled model. (Right) Measurement of reflector surfaces with a coordinated machine. . VERIFICATION PLAN
Verification and calibration of a cryogenic telescope at the ground facilities before launch are challenging. Averification plan is tabulated in Table 7. Two development models (DM/EM and FM ∗ .) are planned. Table 7. Verification plan of LFT.
DM/EM FMLFT-antenna tests at room temperatureShape measurements with a 3D coordinated machine (cid:88) (cid:88)
Millimeter-wave antenna pattern with horns (cid:88) (cid:88)
V-grooves/MHFT diffraction (cid:88) − LFT-antenna cryogenic tests at 5 KStrain measurements (cid:88) − Deformation measurements: photogrammetry or laser sensing optional optionalMillimeter-wave antenna pattern with horns optional optionalLFT AIV and calibration with FP and PMUAntenna pattern (cid:88) (cid:88)
Polarization angle (cid:88) (cid:88)
Frequency response (cid:88) (cid:88)
The antenna pattern of LFT before integration with the focal plane will be tested at room temperature. Apossible method is a near-field beam measurement or a CATR measurement. Diffraction effects due to V-grooves and structures of MHFT will be evaluated and modeled to be smallenough ( < −
60 dB) as designed at room temperature. A structure thermal model (STM) of the mission payloadis constructed and tested with mechanical coolers to verify structural and thermal performance. It will be usedto measure the electromagnetic effects of V-grooves at room temperature.Then, the cryogenic deformation of LFT will be measured to be small enough, as designed. There are a fewmethods to measure cryogenic deformation of LFT: 1) strain measurements with strain gauges; 2) photogram-metric measurements; and 3) laser reflection measurements.To verify the requirements of LFT and to calibrate LFT with the focal plane and the PMU, we have aplan to build a beam measurement system in a cryogenic environment. There are three methods to measurecryogenic beam patterns, polarization angles and spectral response (Table 8). One approach is near-field beammeasurements in front of the front hood of LFT. To obtain the far-field pattern from the near-field measurements,the phase distribution must be retrieved with a reference source. Another method is direct measurement of far-field pattern with a collimated source or a compact antenna testrange (CATR), which needs larger volume for the cryogenic environment, as shown in Figure 14. This concepthas three merits over the phase retrieval near-field beam measurement.1. The polarization angle of LFT is also measured with a collimated beam, as demonstrated by H. Takakuraet al. 2020. ∗ DM: demonstration model, EM: engineering model, FM: flight modelTable 8. Possible cryogenic RF measurements. CATR: compact antenna test range. CW : continuous wave/coherentsource.
Near Field CATR with CW CATR with blackbodyPhase retrieval necessary unnecessary unnecessaryVolume compact large largeTime longer fast fasterStanding wave no concern little concern no concernPol. angle difficult possible possibleSpectral response difficult possible − .6m4KCATRLFT 30K100K Vacuum chamberGonio stage Figure 14. Schematic drawing of cryogenic set-up with a CATR (compact antenna test range), which moves three-dimensionally with two Gonio stages. It is planned to measure co-polar and cross-polar beam pattens, polarization angle,and spectral response of LFT with CW and blackbody sources.
2. The frequency spectral response is measured with a broadband coherent source. A few broadband photo-mixers have been demonstrated at millimeter-wave frequencies.
45, 46
3. It is possible to measure beam patterns with continuum sources as well as coherent sources. Beam mea-surements with a continuum source are faster than those of multiple frequencies with coherent sources.In either method, it is crucial to de-couple the mechanics at room temperature from the sources at cryogenictemperature, or to develop moving mechanics operated at low temperature.
10. SUMMARY
Based on the performance specifications of LFT, a wide field-of-view design has been studied as well as structuraland thermal designs. A 1/4-scaled model of LFT has been developed to verify the design. The measured beampattern was consistent with the optical model at a level of −
50 dB. Interface specifications of the LFT PMUand LFT focal plane are presented. The verification scheme of LFT is planned as the ISAS/JAXA pre-phase Aactivity.
ACKNOWLEDGMENTS
This work is supported in Japan by ISAS/JAXA for Pre-Phase A2 studies, by the acceleration program of JAXAresearch and development directorate, by the World Premier International Research Center Initiative (WPI)of MEXT, by the JSPS Core-to-Core Program of A. Advanced Research Networks, and by JSPS KAKENHIGrant Numbers JP15H05891, JP17H01115, and JP17H01125. The Italian LiteBIRD phase A contribution issupported by the Italian Space Agency (ASI Grants No. 2020-9-HH.0 and 2016-24-H.1-2018), the NationalInstitute for Nuclear Physics (INFN) and the National Institute for Astrophysics (INAF). The French LiteBIRDphase A contribution is supported by the Centre National d’Etudes Spatiale (CNES), by the Centre Nationalde la Recherche Scientifique (CNRS), and by the Commissariat `a l’Energie Atomique (CEA). The Canadiancontribution is supported by the Canadian Space Agency. The US contribution is supported by NASA grantno. 80NSSC18K0132. Norwegian participation in LiteBIRD is supported by the Research Council of Norway(Grant No. 263011). The Spanish LiteBIRD phase A contribution is supported by the Spanish Agencia Estatalde Investigaci´on (AEI), project refs. PID2019-110610RB-C21 and AYA2017-84185-P. Funds that support thewedish contributions come from the Swedish National Space Agency (SNSA/Rymdstyrelsen) and the SwedishResearch Council (Reg. no. 2019-03959). The German participation in LiteBIRD is supported in part bythe Excellence Cluster ORIGINS, which is funded by the Deutsche Forschungsgemeinschaft (DFG, GermanResearch Foundation) under Germany’s Excellence Strategy (Grant No. EXC-2094 - 390783311). This researchused resources of the Central Computing System owned and operated by the Computing Research Center atKEK, as well as resources of the National Energy Research Scientific Computing Center, a DOE Office of ScienceUser Facility supported by the Office of Science of the U.S. Department of Energy.
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