75 research outputs found
POLOCALC: a Novel Method to Measure the Absolute Polarization Orientation of the Cosmic Microwave Background
We describe a novel method to measure the absolute orientation of the
polarization plane of the CMB with arcsecond accuracy, enabling unprecedented
measurements for cosmology and fundamental physics. Existing and planned CMB
polarization instruments looking for primordial B-mode signals need an
independent, experimental method for systematics control on the absolute
polarization orientation. The lack of such a method limits the accuracy of the
detection of inflationary gravitational waves, the constraining power on the
neutrino sector through measurements of gravitational lensing of the CMB, the
possibility of detecting Cosmic Birefringence, and the ability to measure
primordial magnetic fields. Sky signals used for calibration and direct
measurements of the detector orientation cannot provide an accuracy better than
1 deg. Self-calibration methods provide better accuracy, but may be affected by
foreground signals and rely heavily on model assumptions. The POLarization
Orientation CALibrator for Cosmology, POLOCALC, will dramatically improve
instrumental accuracy by means of an artificial calibration source flying on
balloons and aerial drones. A balloon-borne calibrator will provide far-field
source for larger telescopes, while a drone will be used for tests and smaller
polarimeters. POLOCALC will also allow a unique method to measure the
telescopes' polarized beam. It will use microwave emitters between 40 and 150
GHz coupled to precise polarizing filters. The orientation of the source
polarization plane will be registered to sky coordinates by star cameras and
gyroscopes with arcsecond accuracy. This project can become a rung in the
calibration ladder for the field: any existing or future CMB polarization
experiment observing our polarization calibrator will enable measurements of
the polarization angle for each detector with respect to absolute sky
coordinates.Comment: 15 pages, 5 figures, Accepted by Journal of Astronomical
Instrumentatio
Design and characterization of the POLARBEAR-2b and POLARBEAR-2c cosmic microwave background cryogenic receivers
The POLARBEAR-2/Simons Array Cosmic Microwave Background (CMB) polarization
experiment is an upgrade and expansion of the existing POLARBEAR-1 (PB-1)
experiment, located in the Atacama desert in Chile. Along with the CMB
temperature and -mode polarization anisotropies, PB-1 and the Simons Array
study the CMB -mode polarization anisotropies produced at large angular
scales by inflationary gravitational waves, and at small angular scales by
gravitational lensing. These measurements provide constraints on various
cosmological and particle physics parameters, such as the tensor-to-scalar
ratio , and the sum of the neutrino masses. The Simons Array consists of
three 3.5 m diameter telescopes with upgraded POLARBEAR-2 (PB-2) cryogenic
receivers, named PB-2a, -2b, and -2c. PB-2a and -2b will observe the CMB over
multiple bands centered at 95 GHz and 150 GHz, while PB-2c will observe at 220
GHz and 270 GHz, which will enable enhanced foreground separation and
de-lensing. Each Simons Array receiver consists of two cryostats which share
the same vacuum space: an optics tube containing the cold reimaging lenses and
Lyot stop, infrared-blocking filters, and cryogenic half-wave plate; and a
backend which contains the focal plane detector array, cold readout components,
and millikelvin refrigerator. Each PB-2 focal plane array is comprised of 7,588
dual-polarization, multi-chroic, lenslet- and antenna-coupled, Transition Edge
Sensor (TES) bolometers which are cooled to 250 mK and read out using
Superconducting Quantum Interference Devices (SQUIDs) through a digital
frequency division multiplexing scheme with a multiplexing factor of 40. In
this work we describe progress towards commissioning the PB-2b and -2c
receivers including cryogenic design, characterization, and performance of both
the PB-2b and -2c backend cryostats.Comment: 20 page
The effects of inclination on a two stage pulse tube cryocooler for use with a ground based observatory
Abstract Ground-based observatories across a wide range of wavelengths implement cryogenic cooling techniques to increase the sensitivity of instruments and enable low temperature detector technologies. Commercial pulse tube cryocoolers (PTCs) are frequently used to provide 40 K and 4 K stages as thermal shells in scientific instruments. However, PTC operation is dependent on gravity, giving rise to changes in cooling capacity over the operational tilt range of pointed telescopes. We present a study of the performance of a two stage PTC with a cooling capacity of 1.8 W at 4.2 K and 50 W at 45 K (Cryomech PT420-RM) from 0 - 55 ° away from vertical to probe capacity as a function of angle over a set of realistic thermal loading conditions. Our study provides a method to extract temperature estimates given predicted thermal loading conditions across the angular range sampled. We then discuss the design implications for current and future tilted cryogenic systems
The Simons Observatory: Beam characterization for the Small Aperture Telescopes
We use time-domain simulations of Jupiter observations to test and develop a
beam reconstruction pipeline for the Simons Observatory Small Aperture
Telescopes. The method relies on a map maker that estimates and subtracts
correlated atmospheric noise and a beam fitting code designed to compensate for
the bias caused by the map maker. We test our reconstruction performance for
four different frequency bands against various algorithmic parameters,
atmospheric conditions and input beams. We additionally show the reconstruction
quality as function of the number of available observations and investigate how
different calibration strategies affect the beam uncertainty. For all of the
cases considered, we find good agreement between the fitted results and the
input beam model within a ~1.5% error for a multipole range l = 30 - 700.Comment: 22 pages, 21 figures, to be submitted to Ap
Constraints on axion-like polarization oscillations in the cosmic microwave background with POLARBEAR
Very light pseudoscalar fields, often referred to as axions, are compelling
dark matter candidates and can potentially be detected through their coupling
to the electromagnetic field. Recently a novel detection technique using the
cosmic microwave background (CMB) was proposed, which relies on the fact that
the axion field oscillates at a frequency equal to its mass in appropriate
units, leading to a time-dependent birefringence. For appropriate oscillation
periods this allows the axion field at the telescope to be detected via the
induced sinusoidal oscillation of the CMB linear polarization. We search for
this effect in two years of POLARBEAR data. We do not detect a signal, and
place a median upper limit of on the sinusoid amplitude
for oscillation frequencies between and
, which corresponds to axion masses between and . Under the
assumptions that 1) the axion constitutes all the dark matter and 2) the axion
field amplitude is a Rayleigh-distributed stochastic variable, this translates
to a limit on the axion-photon coupling .Comment: 17 pages, 5 figures, 2 tables. Published in Physical Review
- …