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Einstein Polarization Interferometer for Cosmology ( EPIC )

The Einstein Polarization Interferometer for Cosmology (EPIC) aims to measure cosmic microwave background (CMB) polarization to detect gravitational waves from inflation and gravitational lensing signatures. This ambitious project utilizes advanced interferometric techniques that enhance angular resolution and directly measure Stokes parameters. The mission will deploy multiple interferometric arrays across various frequency bands to optimize foreground removal and allows for instantaneous differencing of sky signals, improving sensitivity in challenging atmospheric conditions.

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Einstein Polarization Interferometer for Cosmology ( EPIC )

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  1. Einstein Polarization Interferometer for Cosmology(EPIC) Peter Timbie University of Wisconsin - Madison Beyond Einstein SLAC May 12-14 2004

  2. EPIC Mission Concept Study Team

  3. CMB Power Spectrum

  4. C Farese et al.(2003) C POLAR Upper Limit Zre ~ 30 Reionization Peak Josh Gundersen,

  5. CMB Polarization Detections! WMAP TT/10 WMAP TE DASI EE

  6. Experimental Challenges • Sensitivity • Angular resolution • Modulation - spatial “chop” - polarization (Q--U) • Atmosphere • Temperature stability • Instrumental polarization • Antenna sidelobes

  7. Sensitivity of CMB Detector Systems vs Epoch Dicke COBE WMAP Maxipol Planck Penzias & Wilson Inflation Probe

  8. Detectors micromachined Si legs • bolometers are capable of reaching background limit from CMB • cooled to < 100 mK • superconducting transition-edge thermistors (TES) • readout with SQUID multiplexers waveguide x-section Si frame at 100 mK Waveguide-coupled bolometer from MSAM balloon-borne telescope

  9. Angular Resolution PLANCK telescope DASI interferometer

  10. Why use an interferometer for CMB? Systematics! • simple optics – no reflectors, which can polarize light • correlation measurement is stable, measures Stokes U directly on a single detector (no differencing) • instantaneous differencing of sky signals without scanning • angular resolution ~ 2X better than filled dish of same dia • measures both Temp and Polarization anisotropy

  11. Consider rotations: y  x Example: for   /4 Stokes Parameters For a linearly polarized wave, where Stokes parameters are: -additive -coordinate-dependent

  12. The Spinning CorrelationPolarimeter CMB Ground Screens Ex Ey y N  OMT x E Gx Gy 0°, 180° Phase Shifter Multiplier TP-y TP-x

  13. Correlation Polarimeter

  14. Ryle’s Phase-switching Interferometer (1952) Correlation of signal from 2 antennas

  15. 3-Element Interferometer Angular Response Functions

  16. Examples of window functions for a 2-element interferometer. Window Functions 2-element interferometer baselines 64 diameter filled dish

  17. Polarized Foregrounds

  18. EPIC Overview • Goal 1: measure gravitational waves from inflation • Goal 2: measure gravitational lensing of CMB • 4-year mission, observe full sky 2X per year • > 6 frequency bands for foreground removal • Multiple interferometric arrays (>2) at each wavelength for l-space ranges covering l = 2 to >400 • Measures Stokes I, Q, U interferometrically for l > 40, directly for l < 40 • Bolometric (TES) detectors (> 2700) cooled to ~ 50 mK • Multiplexed SQUID readout

  19. The Millimeter-Wave Bolometric Interferometer (MBI) • 8 feedhorns (23 baselines) • 90 GHz (3 mm) • ~1o angular resolution – search for B-mode pol’n • 7o FOV • under construction, first light expected winter 2005 • White Mountain, CA (13,500 ft)

  20. Single-Baseline Test horn antennas beam combiner

  21. EPIC Mission Concept Study Tasks • Sensitivity analysis • Optimize l-space coverage of arrays • Optimize frequency coverage for foregrounds (WMAP, Planck, etc. results are key) • Beam combiner • Phase shifters • Data analysis/simulations of aperture synthesis • Cryogenics

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