The Simons Observatory (SO) will observe the temperature and polarization anisotropies of the cosmic microwave background (CMB) over a wide range of frequencies (27 to 270 GHz) and angular scales by using both small (∼0.5 m) and large (∼6 m) aperture telescopes. The SO small aperture telescopes will target degree angular scales where the primordial B-mode polarization signal is expected to peak. The incoming polarization signal of the small aperture telescopes will be modulated by a cryogenic, continuously-rotating half-wave plate (CRHWP) to mitigate systematic effects arising from slowly varying noise and detector pair-differencing. In this paper, we present an assessment of some systematic effects arising from using a CRHWP in the SO small aperture systems. We focus on systematic effects associated with structural properties of the HWP and effects arising when operating a HWP, including the amplitude of the HWP synchronous signal (HWPSS), and I → P (intensity to polarization) leakage that arises from detector non-linearity in the presence of a large HWPSS. We demonstrate our ability to simulate the impact of the aforementioned systematic effects in the time domain. This important step will inform mitigation strategies and design decisions to ensure that SO will meet its science goals.
The Next Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG) is a submillimeter mapping experiment planned for a 28 day long-duration balloon (LDB) flight from McMurdo Station, Antarctica during the 2018-2019 season. BLAST-TNG will detect submillimeter polarized interstellar dust emission, tracing magnetic fields in galactic molecular clouds. BLAST-TNG will be the first polarimeter with the sensitivity and resolution to probe the ∼0.1 parsec-scale features that are critical to understanding the origin of structures in the interstellar medium. With three detector arrays operating at 250, 350, and 500 μm (1200, 857, and 600 GHz), BLAST-TNG will obtain diffraction-limited resolution at each waveband of 30, 41, and 59 arcseconds respectively. To achieve the submillimeter resolution necessary for its science goals, the BLAST-TNG telescope features a 2.5 m aperture carbon fiber composite primary mirror, one of the largest mirrors flown on a balloon platform. Successful performance of such a large telescope on a balloon-borne platform requires stiff, lightweight optical components and mounting structures. Through a combination of optical metrology and finite element modeling of thermal and mechanical stresses on both the telescope optics and mounting structures, we expect diffractionlimited resolution at all our wavebands. We expect pointing errors due to deformation of the telescope mount to be negligible. We have developed a detailed thermal model of the sun shielding, gondola, and optical components to optimize our observing strategy and increase the stability of the telescope over the flight. We present preflight characterization of the telescope and its platform.
We present the results of a feasibility study, which examined deployment of a ground-based millimeter-wave polarimeter, tailored for observing the cosmic microwave background (CMB), to Isi Station in Greenland. The instrument for this study is based on lumped-element kinetic inductance detectors (LEKIDs) and an F/2.4 catoptric, crossed-Dragone telescope with a 500 mm aperture. The telescope is mounted inside the receiver and cooled to < 4 K by a closed-cycle 4He refrigerator to reduce background loading on the detectors. Linearly polarized signals from the sky are modulated with a metal-mesh half-wave plate that is rotated at the aperture stop of the telescope with a hollow-shaft motor based on a superconducting magnetic bearing. The modular detector array design includes at least 2300 LEKIDs, and it can be configured for spectral bands centered on 150 GHz or greater. Our study considered configurations for observing in spectral bands centered on 150, 210 and 267 GHz. The entire polarimeter is mounted on a commercial precision rotary air bearing, which allows fast azimuth scan speeds with negligible vibration and mechanical wear over time. A slip ring provides power to the instrument, enabling circular scans (360 degrees of continuous rotation). This mount, when combined with sky rotation and the latitude of the observation site, produces a hypotrochoid scan pattern, which yields excellent cross-linking and enables 34% of the sky to be observed using a range of constant elevation scans. This scan pattern and sky coverage combined with the beam size (15 arcmin at 150 GHz) makes the instrument sensitive to 5 < ` < 1000 in the angular power spectra.
EBEX is a balloon-borne telescope designed to measure the polarization of the cosmic microwave background radiation. During its eleven day science flight in the Austral Summer of 2012, it operated 955 spider-web transition edge sensor (TES) bolometers separated into bands at 150, 250 and 410 GHz. This is the first time that an array of TES bolometers has been used on a balloon platform to conduct science observations. Polarization sensitivity was provided by a wire grid and continuously rotating half-wave plate. The balloon implementation of the bolometer array and readout electronics presented unique development requirements. Here we present an outline of the readout system, the remote tuning of the bolometers and Superconducting QUantum Interference Device (SQUID) amplifiers, and preliminary current noise of the bolometer array and readout system.
The E and B Experiment (EBEX) is a balloon-borne telescope designed to probe polarization signals in the CMB resulting from primordial gravitational waves, gravitational lensing, and Galactic dust emission. EBEX completed an 11 day flight over Antarctica in January 2013 and data analysis is underway. EBEX employs two star cameras to achieve its real-time and post-flight pointing requirements. We wrote a software application called STARS to operate, command, and collect data from each of the star cameras, and to interface them with the main flight computer. We paid special attention to make the software robust against potential in-flight failures. We report on the implementation, testing, and successful in flight performance of STARS.
We present the design and measured performance of the superconducting magnetic bearing (SMB) that was used successfully as the rotation mechanism in the half-wave plate polarimeter of the E and B Experiment (EBEX) during its North American test flight. EBEX is a NASA-supported balloon-borne experiment that is designed to measure the polarization of the cosmic microwave background. In this implementation the half-wave plate is mounted to the rotor of an SMB that is operating at the sink temperature of 4 K. We demonstrate robust, remote operation on a balloon-borne payload, with angular encoding accuracy of 0.01°. We find rotational speed variation to be 0.2% RMS. We measure vibrational modes and find them to be consistent with a simple SMB model. We search for but do not find magnetic field interference in the detectors and readout. We set an upper limit of 3% of the receiver noise level after 5 minutes of integration on such interference. At 2 Hz rotation we measure a power dissipation of 56 mW. If this power dissipation is reduced, such an SMB implementation is a candidate for low-noise space applications because of the absence of stick-slip friction and low wear.
We present the hardware and software systems implementing autonomous operation, distributed real-time monitoring,
and control for the EBEX instrument. EBEX is a NASA-funded balloon-borne microwave polarimeter
designed for a 14 day Antarctic flight that circumnavigates the pole.
To meet its science goals the EBEX instrument autonomously executes several tasks in parallel: it collects
attitude data and maintains pointing control in order to adhere to an observing schedule; tunes and operates
up to 1920 TES bolometers and 120 SQUID amplifiers controlled by as many as 30 embedded computers;
coordinates and dispatches jobs across an onboard computer network to manage this detector readout system;
logs over 3 GiB/hour of science and housekeeping data to an onboard disk storage array; responds to a variety
of commands and exogenous events; and downlinks multiple heterogeneous data streams representing a selected
subset of the total logged data. Most of the systems implementing these functions have been tested during a
recent engineering flight of the payload, and have proven to meet the target requirements.
The EBEX ground segment couples uplink and downlink hardware to a client-server software stack, enabling
real-time monitoring and command responsibility to be distributed across the public internet or other standard
computer networks. Using the emerging dirfile standard as a uniform intermediate data format, a variety of
front end programs provide access to different components and views of the downlinked data products. This
distributed architecture was demonstrated operating across multiple widely dispersed sites prior to and during
the EBEX engineering flight.
Britt Reichborn-Kjennerud, Asad Aboobaker, Peter Ade, François Aubin, Carlo Baccigalupi, Chaoyun Bao, Julian Borrill, Christopher Cantalupo, Daniel Chapman, Joy Didier, Matt Dobbs, Julien Grain, William Grainger, Shaul Hanany, Seth Hillbrand, Johannes Hubmayr, Andrew Jaffe, Bradley Johnson, Terry Jones, Theodore Kisner, Jeff Klein, Andrei Korotkov, Sam Leach, Adrian Lee, Lorne Levinson, Michele Limon, Kevin MacDermid, Tomotake Matsumura, Xiaofan Meng, Amber Miller, Michael Milligan, Enzo Pascale, Daniel Polsgrove, Nicolas Ponthieu, Kate Raach, Ilan Sagiv, Graeme Smecher, Federico Stivoli, Radek Stompor, Huan Tran, Matthieu Tristram, Gregory Tucker, Yury Vinokurov, Amit Yadav, Matias Zaldarriaga, Kyle Zilic
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 l = 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.
François Aubin, Asad Aboobaker, Peter Ade, Carlo Baccigalupi, Chaoyun Bao, Julian Borrill, Christopher Cantalupo, Daniel Chapman, Joy Didier, Matt Dobbs, Will Grainger, Shaul Hanany, Johannes Hubmayr, Peter Hyland, Seth Hillbrand, Andrew Jaffe, Bradley Johnson, Terry Jones, Theodore Kisner, Jeff Klein, Andrei Korotkov, Sam Leach, Adrian Lee, Michele Limon, Kevin MacDermid, Tomotake Matsumura, Xiaofan Meng, Amber Miller, Michael Milligan, Daniel Polsgrove, Nicolas Ponthieu, Kate Raach, Britt Reichborn-Kjennerud, Ilan Sagiv, Graeme Smecher, Huan Tran, Gregory Tucker, Yury Vinokurov, Amit Yadav, Matias Zaldarriaga, Kyle Zilic
EBEX (the E and B EXperiment) is a balloon-borne telescope designed to measure the polarisation of the
cosmic microwave background radiation. During a two week long duration science flight over Antarctica, EBEX
will operate 768, 384 and 280 spider-web transition edge sensor (TES) bolometers at 150, 250 and 410 GHz,
respectively. The 10-hour EBEX engineering flight in June 2009 over New Mexico and Arizona provided the first
usage of both a large array of TES bolometers and a Superconducting QUantum Interference Device (SQUID)
based multiplexed readout in a space-like environment. This successful demonstration increases the technology
readiness level of these bolometers and the associated readout system for future space missions. A total of 82,
49 and 82 TES detectors were operated during the engineering flight at 150, 250 and 410 GHz. The sensors
were read out with a new SQUID-based digital frequency domain multiplexed readout system that was designed
to meet the low power consumption and robust autonomous operation requirements presented by a balloon
experiment. Here we describe the system and the remote, automated tuning of the bolometers and SQUIDs. We
compare results from tuning at float to ground, and discuss bolometer performance during flight.
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