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Huan T. Tran UC Berkeley

POLARBEAR : Polarization of Background Radiation. Huan T. Tran. Huan T. Tran UC Berkeley. POLARBEAR Collaboration. University of California at Berkeley Kam Arnold Daniel Flannigan Wlliam Holzapfel Jacob Howard Zigmund Kermish Adrian Lee P.I.

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Huan T. Tran UC Berkeley

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  1. POLARBEAR: Polarization of Background Radiation Huan T. Tran Huan T. Tran UC Berkeley

  2. POLARBEAR Collaboration University of California at Berkeley Kam Arnold Daniel Flannigan Wlliam Holzapfel Jacob Howard Zigmund Kermish Adrian Lee P.I. Marius Lungu Mike Myers Roger O'Brient Erin Quealy Christian Reichardt Paul Richards Chase Shimmin Bryan Steinbach Huan Tran P.M. Oliver Zahn Lawrence Berkeley National Lab Julian Borrill Christopher Cantalupo Theodore Kisner Eric Linder Helmuth Spieler University of Colorado at Boulder Aubra Anthony Nils Halverson 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 KEK Masashi Hasumi Haruki Nishino Takayuki Tomaru McGill University Peter Hyland Matt Dobbs Cardiff University Peter Ade Carole Tucker

  3. 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 • Stringent Ground Shielding/monolithic primary • Located in Chile for Sky Rotation Eric Chauvin-General Dynamics (Vertex) Test phase in California- Cedar Flat

  4. 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 • Flat-telecentric focal plane • Cold Lyot Stop Cold Reimaging Optics

  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 • now demonstrated with APEX/SPT 2m

  7. POLARBEAR Array • 7 Hexagonal wafers in Chile • 2 Wafers at Cedar Flat • 637 Pixels/1274 bolometers @ 150 GHz Antenna Filter Bolometer Pixel pair Si Wafer Si Lenslet

  8. POLARBEAR Detector performance Receiver Spectrum Polarization Purity Beam map E-Plane

  9. POLARBEAR DfMUX Readout capacitors inductors NIST squids Bolometer wafer FPGA-based Oscillator-Demodulators

  10. POLARBEAR HWP rotation mechanism Idler Drive • Single plate Sapphire (not shown) • AR coated with TMM • ~70K 28cm • Designed for both continuous and stepped rotation • Ball bearing • Belt driven / stepper motor • Optical encoder readout • ~Arcsec repeatability (stepped) Tooth Pawl

  11. POLARBEAR Groundshielding • Goal: Ground must be suppressed by ~109 • Cylindrically symmetric • Curved panels • Extra tall to shield mountains

  12. Systematic errors Atmosphere Foregrounds HWPSS Polarization Calibration Array Temp stability Band mismatch Scan Strategy Ghost reflections HWP Ground/sidelobes Small beam size Telescope flexure Beam Measurement Beam Distortions

  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 non-uniformity polarization coverage f2 : dipole and oct-pole non-uniformity

  15. POLARBEAR Parameter Tolerances Instrumental leakage Suppression due to modulation Diff Pointing Diff Ellipticity Diff FWHM Diff Gain Diff Rotation

  16. Beam effect Suppression Differential gain Beam constrained 10-3 lensing Diff Ellipticity Suppression With sky rot Suppression w/ stepped HWP Diff Rotation Diff Beam Width small beams => Peak in leakage at high-l Diff Pointing

  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

  20. POLARBEAR Deployment Polarbear concept • Testing phase at Cedar Flat • Telescope assembly underway • First light in months • Test stepped vs continuous HWP • Test for atmospheric removal

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