Use of High Sensitivity Bolometers for Astronomy: Planck High Frequency Instrument

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. LamarreM . Ade. J R . Piat. Bock. 21 A J Bernards,M e . 1D P , . 3,P 4, M. Giard5, A. Lange6, A. Murphy7, J. P. Torre8, A. Benoit9, R. Bhatia6, F. R. Bouchet10, B. Maffei2, J. L. Puget1, R. Sudiwala2, V. Yourchenko7

Institut d'Astrophysique Spatiale, Orsay, France, email: [email protected], [email protected], [email protected] 2Cardiff University, Wales, email:UK, [email protected], [email protected] 3Jet Propulsion Laboratory, Pasadena, Ca, USA, email: [email protected] 4Universita Sapienza,La Roma, Italy, email: [email protected] CESR, Toulouse, France, email: [email protected] 6Caltech, Pasadena, Ca, USA, email: [email protected], [email protected] 7University of Maynooth, Ireland, email: [email protected], [email protected], 8Service d'Aeronomie, Verrieres le Buisson, France, email: [email protected] CRTBT, Grenoble, France, email: [email protected], 1 °Institut d'Astrophysique Paris,de France, email: [email protected]

Abstract Plance Th . k satellit dedicates ei measuremene th o dt anisotrope th f Cosmie o t th f yo c Microwave Background (CMB) with unprecedented sensitivity and angular resolution. It is a project of the European Space Agency based on a wide international collaboration, including United State Canadiad san n laboratories detectore Th .Higs it f ho s Frequency Instrument (HFI) are bolometers coole . TheimK d r 0 sensitivitdow10 o nt y wil limitee photoe b l th y db n noisf eo the CMB itself at low frequencies, and of the instrument background at high frequencies. The requirements on the measurement chain are directly related to the strategy of observation used satellitee foth r . This impact bolometee sth r desig wels na othes a l r elements cooline Th : g system must present outstanding temperature stability, and the amplification chain must show a flat noise spectrum dow ver no frequenciest w ylo .

INTRODUCTION

The Cosmic Microwave Background (CMB) is the most distant, and therefore the most ancient source of radiation that can be directly observed from Earth in any frequency range satellite Th . e COB measures Eha submillimetes dit r emission, which is nearla tha f o t y perfect blackbod t 2.7ya . Thi3K s emissio s attributeni e th o dt primordial univers ward year0 an e m d abous 00 whe senougol 0 wa t n30 ti h (300) 0K to ioniz hydrogee eth thas nga t constitute expansioe th so t masss mos it e f f no o tDu . universee th , this radiatio red-shiftes nwa Doppley db r effec factoa y b tabouf ro t 1000, and thanks to the cooling due to the expansion, it could travel and reach us through the very transparent neutra s refineit d l an dhydrogen B e discoverCM Th e . th f o y observation by COBE are pillars that support the big bang theory. The CMB is isotropi dowy c leve a sk ove o nf e 10"t o lrt th smal a 5 l scales tine yTh . deviations from

Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp FIGUR e Cosmi . th E1 Lef f o tc p (a)MicrowavMa : e Background obtaine e BOOMERanth y db G experiment e degreon e eemissio B Th lik. eCM e tinbumpe ar nth y f locao s l fluctuatione th f o s brightness temperatur CMBe th f eo . Right (b): Simulatio Plance th f no k capabilit domaie th n yi f no angular frequencies. Smaller details wil measuree b l d wit mucha h better sensitivity (with respeco t t BOOMERanG) on the whole sky. The position of the first peak informs us on the curvature of the universe, whil whole eth e spectrum give much more about other cosmological parameters. uniformity give us unique information on the physics of the primeval universe, on the cosmological parameters describing the geometry of the universe, and on the history of matter and radiation since the Big Bang. resultw Ne s fro balloon-borne mth e experiments BOOMERanG MAXIMd [1an ] A frod an m ] ground-base[2 d experiments using radio detector interferometrd san y [3,4] were recently published. They gave firsa t smale vieth f wlo scale anisotrope th f yo CMB, unveiling the predicted peaks in the power spectrum of its angular distribution. BOOMERane Th showp ma figurn ni B GeCM real(aa s i )l picturr primevaou f eo l universe whe t becamni e transparen infrareo t t d radiation figurd an , e l(b) shows it s predicted spectral distributio spherican ni l harmonics, wit errore hth s bars expected from the Planck-HFI Project. The project Planck of the European Space Agency is intended to be, after COBE and MAP [5], the next generation of CMB experiments, pushing to its limits the knowledge that wil e retrieveb l d fro e CMmth B observation with unprecedented angular resolutio sensitivityd nan .

HFI SCIENTIFIC CAPABILITIES

The six spectral bands of the High Frequency Instrument (HFI, see Table 1) cover the frequency range between 100 and 1000 GHz with an angular resolution of about 5 arcmin s sensitivitIt . channelsB y e statisticawil CM th e limited b le y b th , n i l, fluctuations [6] of the CMB itself [7], which makes it a kind of ultimate experiment. It will also measure the polarization of the CMB in three channels, which will give independent and unique information on the CMB anisotropy [8]. achievee b Thin ca sd B kin onl accuracf removindy CM o y b e th n varioue yo g th s foregrounds formed by the evolving universe situated between us and the warm primordial universe emittin CMBe gth . Amon emissioe th g e these se dusf nd e o w ,an t galaxn froow d r yan m ou othen i s r ga galaxies. Cluster galaxiesf so , that contain high

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Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp TABL . EPlanc1 k HFI performances. Central Frequency (GHz) 100 143 217 353 545 857 Beam Full width Half Maximum arcmin 9.2 7.1 5.0 5.0 5.0 5.0 Numbe unpolarizef ro d detectors 4 4 4 4 4 4 Number of polarized detectors - 8 8 8 - - Total sensitivity (3T/T) liK/K 2.2 2.4 3.8 15 17 8000 sensitivitQ d an U y (8T/T) /xK/K - 4.8 7.6 30 - - Flux sensitivity mJy 9.0 12.6 9.4 20 46 52 temperature gas detected in the X-rays, distort the CMB by inverse Compton scattering. This is the Sunyaev-Zeldovich Effect (SZE), that makes clusters of galaxies good tracer dynamice th universf e so th f so t largea e scales. Six bands in the HFI and four more in the LFI are needed to separate these various components thanks to their spectral and spatial signature. An additional benefit of the increase in complexity resulting from this approach is that all these astrophysical sources wil e knowb l n much better, whic mann i s hi y case f majoo s r interesr fo t astronomy. Planck has to be considered not only as the third generation of CMB satellites firse t alsth t s bu ,osub-Terahert a survey zsk moderf yo n astronomy. Several thousand galaxiesf so younf o , g stellar objects clusterf o , galaxief so s wil observee lb d wayw ne . a Nearl n i y every fiel f astronomdo y will benefit fro resultss mit , froe mth study of the solar system (Trans-Neptunian objects for example) to the large scale structur universe th f eo e (SZE results) insighcole w welth s ne da , n s componento a tl s of galaxies, a possible candidate for dark matter. The Planck project is committed to well-definef deliveo t se ra d product scientifie th o st c communit t largeya .

REQUIREMENTS AND DESIGN OF HFI DETECTION SYSTEM

Planck will be put in a "halo" orbit around the L2 Lagrangian point of the Sun- Earth system Eartt e aboua , th millio 5 f h1. o t (Figursatellite m nk Th . e2) e will rotate at 1 RPM around an axis nearly anti-solar, allowing its field of view to scan large

Sun

Birth-Moon L3

scan

FIGUR . ESchemati2 c representatio Plance th f no k orbi scannind an t g strategy.

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Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp 0 fspih 2*fspin 3*f$pin 4-*fspin 5*fspin 6*fspiri frequence

FIGURE 3. The scientific signal is periodic at the frequency of the spin rate of the satellite (1 RPM). The first 5000 harmonics contain useful information, which determines the working frequency range of the bolometers: from 0.016Hz to about lOOHz.

circles in the sky. Every 60 min, the axis of rotation will be shifted by 2.5 arcmin, in order to follow the movement of the Earth around the Sun. In six months the successive circles will cover the full sky. The useful data from the telescope is therefore a quasi-periodic signal, with a period of one minute. The signal from the detection chain must therefore be stable from one observatio sourc a nex e [9]f e no th .on to et Lowe r frequenciee th filtere e n b i n t ca sdou data reduction process. This stabilit majoa s yi r requiremen cryogenice th r e fo th t d san electronic HFf scae so LTh n deg/srat6 s ei . Wit arcmih5 n beams response th , e timf eo the bolometers must be less than a few milliseconds (see Table 2). This is the driving requiremen choice bolometerse th th r f efo o t particularn I . understoos wa t i , d froe mth beginning of the project that only very low temperature (100 mK or less) would allow to reach this speed for the large bolometers needed in the millimeter range. This choice is consistent wit requiremene hth t thasensitivite th t y mus limitee photoe b t th y db n HFnoise th I n ewavelengti h range. The absorber of the bolometers is of the spider web type [10] for unpolarized detectors. For polarized channels, the bolometers are sensitive to polarization thanks to an absorber made with parallel wires (J. Bock). NTD Ge thermometers with

TABL . ERequire2 d bolometer performances. Frequ. Optical Load Maximum NEP Goal time Maximum time (GHz) (pW) 1017WHz1/2 constant (ms) constant (ms) 100 1.0 1.2 3.9 7.8 143 1.1 1.5 2.9 5.7 217 1.1 1.8 2.2 4.4 353 1.0 2.2 2.2 4.4 545 5.0 6.0 2.2 4.4 857 16.0 13.5 2.2 4.4 143P 0.57 1.1 3.0 5.7 217P 0.54 1.3 2.2 4.4

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Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp FIGURE 4. Left: The solar panels cover the bottom part of the satellite. The thermal architecture allow passivelo st y coo telescope th l . RighteK dow0 4 : o nThret e differrent active cooler needee sar o dt coo bolometere th l s dow 0.o . nt 1 K impedanc abouf sensitive eo th M 0 e 1 tQ ar e elements requiree Th . d performancee ar s liste Tabln di . e2 readoue Th t electronic limitine th se b mus gt detectioe factono t th f o r n chainA . specially developed amplifier [11] using tunabl biacold C eA san d J-FET preamplifier show nVHz"5 sa 172 noise dow 10". o nt 2Hz e PlancTh k desig thermae s driveni th y nb l requirements. Thank s stablit o t se orientation with respect to the sun, the moon and the earth, it was possible to obtain an efficient passive coolin science th f go e payloa lesr o sd K (sedow0 5 e o nFigurt . e4) J-T expansion of hydrogen using sorption pumps cools both LFI and HFI down to 20 K. Mechanical compressors provide helium for the 4 K J-T compressor. The open loop helium3/helium4 dilution cooler provides both the cooling of the bolometers down to 100 mK and cools an intermediate stage at 1.6 K by J-T expansion of the helium mixture e internaTh . l architecturI focaHF l e planth f eo e uni s showi t n no Figure show s righe 5A .th tn no sectio thif no s figure, radiation fro varioue mth s stages loads the bolometers. This radiation must be very stable, because any fluctuation in the range of useful frequencies (0.016 to 100 Hz) could be taken as coming from the sky. This implies very good temperature stabilit varioue th f yo s stageHFI-focae th f o s l

stagK m plane0 (directl10 e e unit th nkHz"0 r y2 : fo connecte bolometers)e th o dt , 2

28 |uKHz'1/2 fo17 r the 1.6 K stage, and 10 juKHz'172 for the 4 K stage.

CONCLUSIONS

Fundamental fluctuation flue th x f reachino s detectore gmaith e th ne parametesar r limitin instrumene gth t sensitivity. Photo radiatioB CM n e noisnth itself eo f limite sth

575

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FIGURE 5. The focal plane unit of the HFI consists of three stages at 4 K, 1.6 K, and 0.1 K. The coupling of the bolometer with the telescope is made thanks to corrugated horns at 4 K. These stages radiate on the detectors and contribute to the background as well as the telescope (right).

sensitivit three th en yi most sensitive channels scannine Th . g strategy plays alsoa major part in the derivation of the bolometer requirements, since it gives, for signal and noises, the relation between the time domain and the domain of angular scales. A bolometee studth f yo r requirement Fouriee th n si r domai nefficienn provea e b o dt tool for several aspects of the instrument design. undew no Plancrs i construction I kHF launca r fo ,earl n hi y 2007 e thane th W .l kal technical and scientific persons who contributed to the design of this instrument.

REFERENCES

1. P. de Bernardis et al., Aflat universe from high resolution maps of the CMBR, Nature, v404, 2000, p.955 2. A. T. Lee et al., A high spatial resolution analysis of the MAXIMA-1 cosmic microwave background anisotropy data, astro-ph/0104459 3. A. D. Miller et al, A Measurement of the Angular Power Spectrum of the CMBfrom 1=100 to 400, Accepted by ApJL, Astro-ph/9906421 . HaversoW . N t al. n. e 4 , DASI first results: MeasurementA Cosmice oth f Microwave background Angular Power Spectrum, Astro-ph/0104489 5. M. Halpera and D. Scott, Future Microwave Background Experiments, Astro-ph/9904188 . LamarreM . J . ,6 Photon Noise Photometricn i Instruments Infraredr Fa d Submillimetert a an Wavelengths, Appl. Opt. 25, 870 (1986) 7. J. M. Lamarre et al., The High Frequency Instrument of PLANCK: Design and Performances, Astro. LettCommunicationsd An . , pp.161-17, vol37 . 0 (2000) . BouchetR . F . Puget8 . LamarreL . . M J , . J , cosmice Th , microwave background: from detector signals to constraints on the early universe physics, in The primordial universe, Binetruy et al. Editors sciencesP ED , Uliss Le , , Paris, 2000 . 103-22,pp 0 9. M. Piat et al., Proceedings of LTD8, Dalfsen, the Netherlands, 1999, NIMA, 444, pp. 419-422 (2000). 10. A. D. Turner et al., SisN4 micromesh bolometer array for sub-millimeter astrophysics, accepted for publicatio Applien i d Optics, 2001. 11. S. Gaertner et al., A new readout system for bolometers with improved low frequency stability, Astron. &Astrophys. Sup, 126, 151-160, 1997.

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