141 research outputs found
The Simons Observatory: Antenna control software integration and implementation
The Simons Observatory (SO) is a ground-based cosmic microwave background
survey experiment that consists of three 0.5 m small-aperture telescopes and
one 6 m large-aperture telescope, sited at an elevation of 5200 m in the
Atacama Desert in Chile. SO will study the polarization and temperature
anisotropies of the Cosmic Microwave Background (CMB). The observatory will
require well-understood telescope pointing and scanning. Good antenna control
will allow us to execute the scan strategy devised to optimize sensitivity to
our scientific goals, calibrate the system with celestial targets, and make
maps. To achieve this, we integrate the data acquisition and control of the
telescopes' Antenna Control Units (ACUs) within the software framework of the
SO Observatory Control System (OCS). We present here the current status of the
software integration for the ACUs, as well as measurements of the Small
Aperture Telescope platforms' responsiveness to software commanding in the
factory, plans for in situ measurements, and prospects for implementation on
the Large Aperture Telescope.Comment: 20 pages, 8 figures, paper 12190-170 for "Proc. SPIE 12190
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for
Astronomy XI
Optimizing the Efficiency of Fabry-Perot Interferometers with Silicon-Substrate Mirrors
We present the novel design of microfabricated, silicon-substrate based
mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR
to sub-mm/mm wavelength regime. One side of the silicon substrate will have a
double-layer metamaterial anti-reflection coating (ARC) anisotropically etched
into it and the other side will be metalized with a reflective mesh pattern.
The double-layer ARC ensures a reflectance of less than 1% at the surface
substrate over the FPI bandwidth. This low reflectance is required to achieve
broadband capability and to mitigate contaminating resonances from the silicon
surface. Two silicon substrates with their metalized surfaces facing each other
and held parallel with an adjustable separation will compose the FPI. To create
an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination
of inductive and capacitive gold meshes evaporated onto the silicon substrate.
We also consider the use of niobium as a superconducting reflective mesh for
long wavelengths to eliminate ohmic losses at each reflection in the resonating
cavity of the FPI and thereby increase overall transmission. We develop these
silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g.
HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope
concept). Such FPIs are well suited for spectroscopic imaging with the upcoming
large IR/sub-mm/mm TES bolometer detector arrays. Here we present the
fabrication and performance of multi-layer, plasma-etched, silicon metamaterial
ARC, as well as models of the mirrors and FPIs.Comment: Presented at SPIE Advances in Optical and Mechanical Technologies for
Telescopes and Instrumentation III, June 14, 201
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
Anti-reflection coatings for submillimeter silicon lenses
Low-loss lenses are required for submillimeter astronomical applications, such as instrumentation for CCAT, a 25 m diameter telescope to be built at an elevation of 18,400 ft in Chile. Silicon is a leading candidate for dielectric lenses due to its low transmission loss and high index of refraction; however, the latter can lead to large reflection losses. Additionally, large diameter lenses (up to 40 cm), with substantial curvature present a challenge for fabrication of antireflection coatings. Three anti-reflection coatings are considered: a deposited dielectric coating of Parylene C, fine mesh structures cut with a dicing saw, and thin etched silicon layers (fabricated with deep reactive ion etching) for bonding to lenses. Modeling, laboratory measurements, and practicalities of fabrication for the three coatings are presented and compared. Measurements of the Parylene C anti-reflection coating were found to be consistent with previous studies and can be expected to result in a 6% transmission loss for each interface from 0.787 to 0.908 THz. The thin etched silicon layers and fine mesh structure anti-reflection coatings were designed and fabricated on test silicon wafers and found to have reflection losses less than 1% at each interface from 0.787 to 0.908 THz. The thin etched silicon layers are our preferred method because of high transmission efficiency while having an intrinsically faster fabrication time than fine structures cut with dicing saws, though much work remains to adapt the etched approach to curved surfaces and optics < 4" in diameter unlike the diced coatings
The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power Spectrum
We report a measurement of the power spectrum of cosmic microwave background
(CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter
(ACTPol) CMB data. The CMB lensing power spectrum is extracted from both
temperature and polarization data using quadratic estimators. We obtain results
that are consistent with the expectation from the best-fit Planck LCDM model
over a range of multipoles L=80-2100, with an amplitude of lensing A_lens =
1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of
the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054;
including baryon acoustic oscillation scale data, we constrain the amplitude of
density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update
constraints on the neutrino mass sum. We verify our lensing measurement with a
number of null tests and systematic checks, finding no evidence of significant
systematic errors. This measurement relies on a small fraction of the ACTPol
data already taken; more precise lensing results can therefore be expected from
the full ACTPol dataset.Comment: 17 pages, 11 figures, to be submitted to Physical Review
The optical design of the six-meter CCAT-prime and Simons Observatory telescopes
A common optical design for a coma-corrected, 6-meter aperture,
crossed-Dragone telescope has been adopted for the CCAT-prime telescope of CCAT
Observatory, Inc., and for the Large Aperture Telescope of the Simons
Observatory. Both are to be built in the high altitude Atacama Desert in Chile
for submillimeter and millimeter wavelength observations, respectively. The
design delivers a high throughput, relatively flat focal plane, with a field of
view 7.8 degrees in diameter for 3 mm wavelengths, and the ability to
illuminate >100k diffraction-limited beams for < 1 mm wavelengths. The optics
consist of offset reflecting primary and secondary surfaces arranged in such a
way as to satisfy the Mizuguchi-Dragone criterion, suppressing first-order
astigmatism and maintaining high polarization purity. The surface shapes are
perturbed from their standard conic forms in order to correct coma aberrations.
We discuss the optical design, performance, and tolerancing sensitivity. More
information about CCAT-prime can be found at ccatobservatory.org and about
Simons Observatory at simonsobservatory.org.Comment: Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 1070041 (2018
Investigation of Parameters Affecting Gypsum Dewatering Properties in a Wet Flue Gas Desulphurization Pilot Plant
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