Chaoyun Bao

A cryogenic half-wave plate polarimeter using a superconducting magnetic bearing

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.

The impact of the spectral response of an achromatic half-wave plate on the measurement of the cosmic microwave background polarization

We study the impact of the spectral dependence of the linear polarization rotation induced by an achromatic half-wave plate on measurements of cosmic microwave background polarization in the presence of astrophysical foregrounds. We focus on the systematic effects induced on the measurement of inflationary gravitational waves by uncertainties in the polarization and spectral index of Galactic dust. We find that for the experimental configuration and noise levels of the balloon-borne EBEX experiment, which has three frequency bands centered at 150, 250, and 410 GHz, a crude dust subtraction process mitigates systematic effects to below detectable levels for 10% polarized dust and tensor-to-scalar ratio of as low as r = 0.01. We also study the impact of uncertainties in the spectral response of the instrument. With a top-hat model of the spectral response for each band, characterized by band center and bandwidth, and with the same crude dust subtraction process, we find that these parameters need to be determined to within 1 and 0.8 GHz at 150 GHz; 9 and 2.0 GHz at 250 GHz; and 20 and 14 GHz at 410 GHz, respectively. The approach presented in this paper is applicable to other optical elements that exhibit polarization rotation as a function of frequency.

The performance of the bolometer array and readout system during the 2012/2013 flight of the e and B experiment (EBEX)

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.

First implementation of TES bolometer arrays with SQUID-based multiplexed readout on a balloon-borne platform

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.

Temperature calibration of the E and B Experiment

The E and B Experiment (EBEX) is a balloon-borne polarimeter designed to measure the polarization of the cosmic microwave background radiation and to characterize the polarization of galactic dust. EBEX was launched December 29, 2012 and circumnavigated Antarctica observing

Software systems for operation, control, and monitoring of the EBEX instrument

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MAXIMUM LIKELIHOOD FOREGROUND CLEANING FOR COSMIC MICROWAVE BACKGROUND POLARIMETERS IN THE PRESENCE OF SYSTEMATIC EFFECTS

6,000 square degrees of sky during 11 days at three frequency bands centered around 150, 250 and 410 GHz. EBEX was the first experiment to operate a kilo-pixel array of transition-edge sensor bolometers and a continuously rotating achromatic half-wave plate aboard a balloon platform. It also pioneered the use of detector readout based on digital frequency domain multiplexing. We describe the temperature calibration of the experiment. The gain response of the experiment is calibrated using a two-step iterative process. We use signals measured on passes across the Galactic plane to convert from readout-system counts to power. The effective smoothing scale of the EBEX optics and the star camera-to-detector offset angles are determined through \c{hi}2 minimization using the compact HII region RCW 38. This two-step process is initially performed with parameters measured before the EBEX 2013 flight and then repeated until the calibration factor and parameters converge.

EBEX: A balloon-borne CMB polarization experiment

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.

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

We extend a general maximum likelihood foreground estimation for cosmic microwave background polarization data to include estimation of instrumental systematic effects. We focus on two particular effects: frequency band measurement uncertainty, and instrumentally induced frequency dependent polarization rotation. We assess the bias induced on the estimation of the

The EBEX Balloon Borne Experiment - Detectors and Readout

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