The EBEX Balloon-borne Experiment-Optics, Receiver, and Polarimetry
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 b...
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Published in | The Astrophysical journal. Supplement series Vol. 239; no. 1; pp. 7 - 31 |
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Main Authors | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Saskatoon
The American Astronomical Society
01.11.2018
IOP Publishing American Astronomical Society/IOP |
Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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Bibliography: | AAS05863 Instrumentation, Software, Laboratory Astrophysics, and Data National Aeronautics and Space Administration (NASA) USDOE National Science Foundation (NSF) |
ISSN: | 0067-0049 1538-4365 1538-4365 |
DOI: | 10.3847/1538-4365/aae434 |