The EBEX Balloon Borne Experiment - Optics, Receiver, and Polarimetry

• Published in: arXiv.org
• Main Authors: The EBEX Collaboration, Aboobaker, Asad M, Ade, Peter, Araujo, Derek, Aubin, François, Baccigalupi, Carlo, Bao, Chaoyun, Chapman, Daniel, Didier, Joy, Dobbs, Matt, Geach, Christopher, Grainger, Will, Hanany, Shaul, Helson, Kyle, Hillbrand, Seth, Hubmayr, Johannes, Jaffe, Andrew, Johnson, Bradley, Jones, Terry, Klein, Jeff, Korotkov, Andrei, Lee, Adrian, Levinson, Lorne, Limon, Michele, MacDermid, Kevin, Matsumura, Tomotake, Miller, Amber D, Milligan, Michael, Raach, Kate, Britt Reichborn-Kjennerud, Sagiv, Ilan, Savini, Giorgio, Locke, Spencer, Tucker, Carole, Tucker, Gregory S, Westbrook, Ben, Young, Karl, Zilic, Kyle
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 30.05.2017
• Subjects: Ambient temperature; Angular position; Astrophysics; Big Bang theory; Bolometers; Cosmic microwave background; Experiments; Flight characteristics; Focal plane; Frequencies; Knee; Magnetic bearings; Magnetic lenses; Physics - Instrumentation and Methods for Astrophysics; Polarimeters; Polarimetry; Polyethylenes; Sensor arrays; Stability; Variations; Wave plates
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1703.03847

The E and B Experiment (EBEX) was a long-duration balloon-borne cosmic microwave background polarimeter that flew over Antarctica in 2013. 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 cm\(^{2}\)sr high throughput optical system that had two ambient temperature mirrors and four anti-reflection 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). Rotation stability was 0.45 % over a period of 10 hours, and angular position accuracy was 0.01 degrees. This is the first use of a SMB in astrophysics. 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 that contained 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 fluctuation power spectrum that had \(1/f\) 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 mutiplexed readouts.