101 research outputs found
Optical modeling and polarization calibration for CMB measurements with ACTPol and Advanced ACTPol
The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization
sensitive upgrade to the Atacama Cosmology Telescope. Located at an elevation
of 5190 m, ACTPol measures the Cosmic Microwave Background (CMB) temperature
and polarization with arcminute-scale angular resolution. Calibration of the
detector angles is a critical step in producing maps of the CMB polarization.
Polarization angle offsets in the detector calibration can cause leakage in
polarization from E to B modes and induce a spurious signal in the EB and TB
cross correlations, which eliminates our ability to measure potential
cosmological sources of EB and TB signals, such as cosmic birefringence. We
present our optical modeling and measurements associated with calibrating the
detector angles in ACTPol.Comment: 12 pages, 8 figures, conference proceedings submitted to Proceedings
of SPIE; added reference in section 2 and merged repeated referenc
Mechanical design and development of TES bolometer detector arrays for the Advanced ACTPol experiment
The next generation Advanced ACTPol (AdvACT) experiment is currently underway
and will consist of four Transition Edge Sensor (TES) bolometer arrays, with
three operating together, totaling ~5800 detectors on the sky. Building on
experience gained with the ACTPol detector arrays, AdvACT will utilize various
new technologies, including 150mm detector wafers equipped with multichroic
pixels, allowing for a more densely packed focal plane. Each set of detectors
includes a feedhorn array of stacked silicon wafers which form a spline profile
leading to each pixel. This is then followed by a waveguide interface plate,
detector wafer, back short cavity plate, and backshort cap. Each array is
housed in a custom designed structure manufactured from high purity copper and
then gold plated. In addition to the detector array assembly, the array package
also encloses cryogenic readout electronics. We present the full mechanical
design of the AdvACT high frequency (HF) detector array package along with a
detailed look at the detector array stack assemblies. This experiment will also
make use of extensive hardware and software previously developed for ACT, which
will be modified to incorporate the new AdvACT instruments. Therefore, we
discuss the integration of all AdvACT arrays with pre-existing ACTPol
infrastructure.Comment: 9 pages, 5 figures, SPIE Astronomical Telescopes and Instrumentation
conference proceeding
Comparing complex impedance and bias step measurements of Simons Observatory transition edge sensors
The Simons Observatory (SO) will perform ground-based observations of the
cosmic microwave background (CMB) with several small and large aperture
telescopes, each outfitted with thousands to tens of thousands of
superconducting aluminum manganese (AlMn) transition-edge sensor bolometers
(TESs). In-situ characterization of TES responsivities and effective time
constants will be required multiple times each observing-day for calibrating
time-streams during CMB map-making. Effective time constants are typically
estimated in the field by briefly applying small amplitude square-waves on top
of the TES DC biases, and fitting exponential decays in the bolometer response.
These so-called "bias step" measurements can be rapidly implemented across
entire arrays and therefore are attractive because they take up little
observing time. However, individual detector complex impedance measurements,
while too slow to implement during observations, can provide a fuller picture
of the TES model and a better understanding of its temporal response. Here, we
present the results of dark TES characterization of many prototype SO
bolometers and compare the effective thermal time constants measured via bias
steps to those derived from complex impedance data.Comment: 10 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation
2020, Paper Number: 11453-18
The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters
We present the temperature and polarization angular power spectra measured by
the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time
data collected during 2013-14 using two detector arrays at 149 GHz, from 548
deg of sky on the celestial equator. We use these spectra, and the spectra
measured with the MBAC camera on ACT from 2008-10, in combination with Planck
and WMAP data to estimate cosmological parameters from the temperature,
polarization, and temperature-polarization cross-correlations. We find the new
ACTPol data to be consistent with the LCDM model. The ACTPol
temperature-polarization cross-spectrum now provides stronger constraints on
multiple parameters than the ACTPol temperature spectrum, including the baryon
density, the acoustic peak angular scale, and the derived Hubble constant.
Adding the new data to planck temperature data tightens the limits on damping
tail parameters, for example reducing the joint uncertainty on the number of
neutrino species and the primordial helium fraction by 20%.Comment: 23 pages, 25 figure
The Simons Observatory: Magnetic Sensitivity Measurements of Microwave SQUID Multiplexers
The Simons Observatory (SO) will be a cosmic microwave background (CMB)
survey experiment with three small-aperture telescopes and one large-aperture
telescope, which will observe from the Atacama Desert in Chile. In total, SO
will field 70,000 transition-edge sensor (TES) bolometers in six spectral
bands centered between 27 and 280 GHz in order to achieve the sensitivity
necessary to measure or constrain numerous cosmological quantities. The SO
Universal Focal Plane Modules (UFMs) each contain a 150 mm diameter TES
detector array, horn or lenslet optical coupling, cold readout components, and
magnetic shielding. SO will use a microwave SQUID multiplexing (MUX)
readout at an initial multiplexing factor of 1000; the cold (100 mK)
readout components are packaged in a MUX readout module, which is part of
the UFM, and can also be characterized independently. The 100 mK stage TES
bolometer arrays and microwave SQUIDs are sensitive to magnetic fields, and
their measured response will vary with the degree to which they are
magnetically shielded. We present measurements of the magnetic pickup of test
microwave SQUID multiplexers as a study of various shielding configurations for
the Simons Observatory. We discuss how these measurements motivated the
material choice and design of the UFM magnetic shielding.Comment: 5 pages, 6 figures, conference proceedings submitted to IEEE
Transactions on Applied Superconductivit
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