The E and B Experiment (EBEX) was a long-duration balloon-borne cosmic microwave background (CMB) polarimeter that flew over Antarctica in 2012. We describe the experiment's optical system, receiver, and polarimetric approach and report on their in-flight performance. EBEX had three frequency bands centered on 150, 250, and 410 GHz. To make efficient use of limited mass and space, we designed a 115 cm2 sr high-throughput optical system that had two ambient temperature mirrors and four antireflection-coated polyethylene lenses per focal plane. All frequency bands shared the same optical train. Polarimetry was achieved with a continuously rotating achromatic half-wave plate (AHWP) that was levitated with a superconducting magnetic bearing (SMB). This is the first use of an SMB in astrophysics. Rotation stability was 0.45% over a period of 10 hr, and angular position accuracy was 0.°01. The measured modulation efficiency was above 90% for all bands. To our knowledge the 109% fractional bandwidth of the AHWP was the broadest implemented to date. The receiver, composed of one lens and the AHWP at a temperature of 4 K, the polarizing grid and other lenses at 1 K, and the two focal planes at 0.25 K, performed according to specifications, giving focal plane temperature stability with a fluctuation power spectrum that had a 1/f knee at 2 mHz. EBEX was the first balloon-borne instrument to implement technologies characteristic of modern CMB polarimeters, including high-throughput optical systems, and large arrays of transition edge sensor bolometric detectors with multiplexed readouts.
|Original language||English (US)|
|Journal||Astrophysical Journal, Supplement Series|
|State||Published - Nov 2018|
Bibliographical noteFunding Information:
Support for the development and flight of the EBEX instrument was provided by NASA grants NNX12AD50G, NNX13AE49G, NNX08AG40G, and NNG05GE62G and by NSF grants AST-0705134 and ANT-0944513. We acknowledge support from the Italian INFN INDARK Initiative. P.A. and C.T. acknowledge the Science & Technology Facilities Council for its continued support of the underpinning technology for filter and wave plate development. We also acknowledge support by the Canada Space Agency, the Canada Research Chairs Program, the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, the Minnesota Supercomputing Institute, the National Energy Research Scientific Computing Center, the Minnesota and Rhode Island Space Grant Consortia, our collaborating institutions, and Sigma Xi, The Scientific Research Society. Baccigalupi acknowledges support from the RADIOFOREGROUNDS grant of the European Union’s Horizon 2020 research and innovation program (COMPET-05-2015, grant agreement no. 687312) and the INDARK INFN Initiative. J.D. acknowledges a NASA NESSF fellowship NNX11AL15H. B.R.-K. acknowledges an NSF Post-Doctoral Fellowship AST-1102774 and a NASA Graduate Student Research Fellowship. K.R. and K.Z. acknowledge support by the Minnesota Space Grant Consortium. We very much thank Danny Ball and his colleagues at the Columbia Scientific Balloon Facility for their dedicated support of the EBEX program. We are grateful for contributions to the fabrication of optical elements by Enzo Pascale and Lorenzo Moncelsi. Xin Zhi Tan’s and Chiou Yang Tan’s help with figures is acknowledged and much appreciated.
© 2018. The American Astronomical Society. All rights reserved.
- cosmic background radiation
- cosmology: observations
- instrumentation: polarimeters