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Register a new userEBEX: A balloon-borne CMB polarization experiment
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Britt Reichborn-Kjennerud
Publication date
2010
fields
Physics
and research's language is
English
Authors
Britt Reichborn-Kjennerud
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EBEX is a NASA-funded balloon-borne experiment designed to measure the polarization of the cosmic microwave background (CMB). Observations will be made using 1432 transition edge sensor (TES) bolometric detectors read out with frequency multiplexed SQuIDs. EBEX will observe in three frequency bands centered at 150, 250, and 410 GHz, with 768, 384, and 280 detectors in each band, respectively. This broad frequency coverage is designed to provide valuable information about polarized foreground signals from dust. The polarized sky signals will be modulated with an achromatic half wave plate (AHWP) rotating on a superconducting magnetic bearing (SMB) and analyzed with a fixed wire grid polarizer. EBEX will observe a patch covering ~1% of the sky with 8 resolution, allowing for observation of the angular power spectrum from ell = 20 to 1000. This will allow EBEX to search for both the primordial B-mode signal predicted by inflation and the anticipated lensing B-mode signal. Calculations to predict EBEX constraints on r using expected noise levels show that, for a likelihood centered around zero and with negligible foregrounds, 99% of the area falls below r = 0.035. This value increases by a factor of 1.6 after a process of foreground subtraction. This estimate does not include systematic uncertainties. An engineering flight was launched in June, 2009, from Ft. Sumner, NM, and the long duration science flight in Antarctica is planned for 2011. These proceedings describe the EBEX instrument and the North American engineering flight.
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EBEX was a long-duration balloon-borne experiment to measure the polarization of the cosmic microwave background. The experiment had three frequency bands centered at 150, 250, and 410 GHz and was the first to use a kilo-pixel array of transition edge sensor (TES) bolometers aboard a balloon platform; shortly after reaching float we operated 504, 342, and 109 TESs at each of the bands, respectively. We describe the design and characterization of the array and the readout system. We give the distributions of measured thermal conductances, normal resistances, and transition temperatures. With the exception of the thermal conductance at 150 GHz. We measured median low-loop-gain time constants $tau_{0}=$ 88, 46, and 57 ms and compare them to predictions. Two measurements of bolometer absorption efficiency show high ($sim$0.9) efficiency at 150 GHz and medium ($sim$0.35, and $sim$0.25) at the two higher bands, respectively. We measure a median total optical load of 3.6, 5.3 and 5.0 pW absorbed at the three bands, respectively. EBEX pioneered the use of the digital version of the frequency domain multiplexing (FDM) system which multiplexed the bias and readout of 16 bolometers onto two wires. We present accounting of the measured noise equivalent power. The median per-detector noise equivalent temperatures referred to a black body with a temperature of 2.725 K are 400, 920, and 14500 $mu$K$sqrt{s}$ for the three bands, respectively. We compare these values to our pre-flight predictions and to a previous balloon payload, discuss the sources of excess noise, and the path for a future payload to make full use of the balloon environment.
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 experiments 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.
The E and B Experiment (EBEX) was a long-duration balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) radiation. EBEX was the first balloon-borne instrument to implement a kilo-pixel array of transition edge sensor (TES) bolometric detectors and the first CMB experiment to use the digital version of the frequency domain multiplexing system for readout of the TES array. The scan strategy relied on 40 s peak-to-peak constant velocity azimuthal scans. We discuss the unique demands on the design and operation of the payload that resulted from these new technologies and the scan strategy. We describe the solutions implemented including the development of a power system designed to provide a total of at least 2.3 kW, a cooling system to dissipate 590 W consumed by the detectors readout system, software to manage and handle the data of the kilo-pixel array, and specialized attitude reconstruction software. We present flight performance data showing faultless management of the TES array, adequate powering and cooling of the readout electronics, and constraint of attitude reconstruction errors such that the spurious B-modes they induced were less than 10% of CMB B-mode power spectrum with $r=0.05$.
We describe SPIDER, a balloon-borne instrument to map the polarization of the millimeter-wave sky with degree angular resolution. Spider consists of six monochromatic refracting telescopes, each illuminating a focal plane of large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting transition-edge sensors are distributed among three observing bands centered at 90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope modulates the polarization of incoming light to control systematics. Spiders first flight will be a 20-30-day Antarctic balloon campaign in December 2011. This flight will map sim8% of the sky to achieve unprecedented sensitivity to the polarization signature of the gravitational wave background predicted by inflationary cosmology. The Spider mission will also serve as a proving ground for these detector technologies in preparation for a future satellite mission.
Spider is a balloon-borne experiment that will measure the polarization of the Cosmic Microwave Background over a large fraction of a sky at 1 degree resolution. Six monochromatic refracting millimeter-wave telescopes with large arrays of antenna-coupled transition-edge superconducting bolometers will provide system sensitivities of 4.2 and 3.1 micro K_cmb rt s at 100 and 150 GHz, respectively. A rotating half-wave plate will modulate the polarization sensitivity of each telescope, controlling systematics. Bolometer arrays operating at 225 GHz and 275 GHz will allow removal of polarized galactic foregrounds. In a 2-6 day first flight from Alice Springs, Australia in 2010, Spider will map 50% of the sky to a depth necessary to improve our knowledge of the reionization optical depth by a large factor.
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