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POLARBEAR: Polarization of Background Radiation Huan T. Tran Huan T. Tran UC Berkeley 1 POLARBEAR University of California at Berkeley Kam Arnold Daniel Flannigan Wlliam Holzapfel Jacob Howard Zigmund Kermish Adrian Lee Marius Lungu Mike Myers Roger O'Brient Erin Quealy Christian Reichardt Paul Richards Chase Shimmin Bryan Steinbach Huan Tran Oliver Zahn P.I. University of California at San Diego David Boettger Brian Keating George Fuller Nathan Miller Hans Paar Ian Schanning Meir Shimon Imperial College Andrew Jaffe Daniel O’Dea Laboratoire Astroparticule & Cosmologie Josquin Errard Joseph Martino Radek Stompor P.M. Lawrence Berkeley National Lab Julian Borrill Christopher Cantalupo Theodore Kisner Eric Linder Helmuth Spieler University of Colorado at Boulder Aubra Anthony Nils Halverson Collaboration KEK Masashi Hasumi Haruki Nishino Takayuki Tomaru McGill University Peter Hyland Matt Dobbs Cardiff University Peter Ade Carole Tucker 2 POLARBEAR Concept Polarbear concept Key Technologies for Sensitivity • Large Format Antenna-coupled TES bolometer arrays • Frequency-Multiplexed Readout • Monochromatic – switch focal planes for different frequencies Key designs for Systematic Control • HWP Modulator stepped/continuous • Low Spurious Polarization Optics Eric Chauvin-General Dynamics (Vertex) • Stringent Ground Shielding/monolithic primary Test phase in California- Cedar Flat • Located in Chile for Sky Rotation 3 POLARBEAR Telescope 3.5m Clear aperture (2.5m active) Dragone-Gregorian • 4’ at 150 GHz: Constrain Lensing • Large FOV: 2.4 deg • Relatively compact • Monolithic central primary Cold Reimaging Optics • Flat-telecentric focal plane • Cold Lyot Stop 4 5 POLARBEAR mirrors Primary: RMS 53 micron Secondary: RMS 37 micron 6 POLARBEAR Receiver Cold Reimaging Optics • Three UHMWPE lenses • Cold Lyot Stop •Telcentric Focal Plane Rotating HWP • Skyward of lenses • Field Stop Cryogenics • Cryomech Pulse-tube cooler • Simon-Chase ‘He10’ refrigerator 2m • now demonstrated with APEX/SPT 7 POLARBEAR Array Antenna Filter • 7 Hexagonal wafers in Chile • 2 Wafers at Cedar Flat • 637 Pixels/1274 bolometers @ 150 GHz Bolometer Pixel pair Si Lenslet Si Wafer 8 POLARBEAR Detector performance Receiver Spectrum Polarization Purity Beam map 9 POLARBEAR DfMUX Readout capacitors inductors NIST squids Bolometer wafer FPGA-based Oscillator-Demodulators 10 POLARBEAR Drive HWP rotation mechanism Idler • Single plate Sapphire (not shown) • AR coated with TMM • ~70K 28cm Tooth • Designed for both continuous and stepped rotation • Ball bearing • Belt driven / stepper motor • Optical encoder readout • ~Arcsec repeatability (stepped) Pawl 11 POLARBEAR Groundshielding •Goal: Ground must be suppressed by ~109 •Cylindrically symmetric •Curved panels •Extra tall to shield mountains 12 Systematic errors Foregrounds Atmosphere Polarization Calibration HWPSS Band mismatch Array Temp stability Ghost reflections Ground/sidelobes Telescope flexure Beam Distortions Scan Strategy HWP Small beam size Beam Measurement 13 Scan Strategy • Scan in AZ, fixed EL ~ 1 hour • Re-center scan each hour • Choose centers for uniformity • Choose HWP stepping scheme • Maps ground pickup template each hour 14 Scan Strategy: optimizing polarization uniformity • Sky rotation gives some uniformity • Continuous HWP is ideal-> null many effects • Can choose steps wisely Step HWP 3 times, once per day f1 : Measure of quad-pole nonuniformity polarization coverage f2 : dipole and oct-pole non-uniformity 15 POLARBEAR Parameter Tolerances Instrumental leakage Diff Gain Suppression due to modulation Diff FWHM Diff Diff Diff Pointing Ellipticity Rotation Beam effect Suppression Differential gain Beam constrained 10-3 Diff Ellipticity Suppression With sky rot Suppression w/ stepped HWP Diff Rotation Diff Beam Width Diff Pointing small beams => Peak in leakage at high-l 17 Foregrounds and Scan Regions Scan is targeted at low dust contrast regions as low as ~2uK intensity 150,220 GHz bands Patches chosen to match QUIET 18 POLARBEAR Performance Red error bars: Includes noise increase from subtracting 220 GHz to remove mid lat dust 19 Experiment Summary Frequencies 150/220 GHz Angular resolutions 7’ :90GHz 4’ :150GHz 2.7’:220 Ghz Field centers and sizes Coord w/ QUIET 1000 sq-Deg total Ra/Dec/Sq-Deg Telescope type Gregorian/lenses Refractor, Gregorian, Compactrange etc Polarization Modulations HWP, sky rot Detector type Bolometer/TES Location Atacama Instrument NEQ/U 360/sqrt(1288/4) =20 Observation start date 2010 Planned observing time 1000/250 Projected limit on r 0.025 95% c.l. arcmin at each freq Waveplate, boresight rot., sky rot., scan etc. – list all that apply K s1/2 for both Q and U Elapsed/effective days <10X foreground removal 20 POLARBEAR PolarbearDeployment concept Testing phase at Cedar Flat Test stepped vs continuous HWP Telescope assembly underway Test for atmospheric removal First light in months 21
