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.
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.
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
The E and B Experiment, EBEX, is a Cosmic Microwave Background polarization experiment designed to detect
or set upper limits on the signature of primordial gravity waves. Primordial gravity waves are predicted to be
produced by inflation, and a measurement of the power spectrum of these gravity waves is a measurement of
the energy scale of inflation. EBEX has sufficient sensitivity to detect or set an upper limit at 95% confidence
on the energy scale of inflation of < 1.4 × 1016 GeV. This article reviews our strategy for achieving our science
goals and discusses the implementation of the instrument.