25 research outputs found
Optimization of transition edge sensor arrays for cosmic microwave background observations with the South Pole Telescope
In this paper, we describe the optimization of transition-edge-sensor (TES) detector arrays for the third-generation camera for the South Pole Telescope. The camera, which contains ~16 000 detectors, will make high-angular-resolution maps of the temperature and polarization of the cosmic microwave background. Our key results are scatter in the transition temperature of Ti/Au TESs is reduced by fabricating the TESs on a thin Ti(5 nm)/Au(5 nm) buffer layer and the thermal conductivity of the legs that support our detector islands is dominated by the SiOx dielectric in the microstrip transmission lines that run along the legs
Performance of Al-Mn Transition-Edge Sensor Bolometers in SPT-3G
SPT-3G is a polarization-sensitive receiver, installed on the South Pole
Telescope, that measures the anisotropy of the cosmic microwave background
(CMB) from degree to arcminute scales. The receiver consists of ten
150~mm-diameter detector wafers, containing a total of 16,000 transition-edge
sensor (TES) bolometers observing at 95, 150, and 220 GHz. During the 2018-2019
austral summer, one of these detector wafers was replaced by a new wafer
fabricated with Al-Mn TESs instead of the Ti/Au design originally deployed for
SPT-3G. We present the results of in-lab characterization and on-sky
performance of this Al-Mn wafer, including electrical and thermal properties,
optical efficiency measurements, and noise-equivalent temperature. In addition,
we discuss and account for several calibration-related systematic errors that
affect measurements made using frequency-domain multiplexing readout
electronics.Comment: 9 pages, 5 figures, submitted to the Journal of Low Temperature
Physics: LTD18 Special Editio
Performance and characterization of the SPT-3G digital frequency-domain multiplexed readout system using an improved noise and crosstalk model
The third generation South Pole Telescope camera (SPT-3G) improves upon its predecessor (SPTpol) by an order of magnitude increase in detectors on the focal plane. The technology used to read out and control these detectors, digital frequency-domain multiplexing (DfMUX), is conceptually the same as used for SPTpol, but extended to accommodate more detectors. A nearly 5x expansion in the readout operating bandwidth has enabled the use of this large focal plane, and SPT-3G performance meets the forecasting targets relevant to its science objectives. However, the electrical dynamics of the higher-bandwidth readout differ from predictions based on models of the SPTpol system. To address this, we present an updated derivation for electrical crosstalk in higher-bandwidth DfMUX systems, and identify two previously uncharacterized contributions to readout noise. The updated crosstalk and noise models successfully describe the measured crosstalk and readout noise performance of SPT-3G, and suggest improvements to the readout system for future experiments using DfMUX, such as the LiteBIRD space telescope
Constraints on CDM Extensions from the SPT-3G 2018 and Power Spectra
We present constraints on extensions to the CDM cosmological model
from measurements of the -mode polarization auto-power spectrum and the
temperature--mode cross-power spectrum of the cosmic microwave background
(CMB) made using 2018 SPT-3G data. The extensions considered vary the
primordial helium abundance, the effective number of relativistic degrees of
freedom, the sum of neutrino masses, the relativistic energy density and mass
of a sterile neutrino, and the mean spatial curvature. We do not find clear
evidence for any of these extensions, from either the SPT-3G 2018 dataset alone
or in combination with baryon acoustic oscillation and \textit{Planck} data.
None of these model extensions significantly relax the tension between
Hubble-constant, , constraints from the CMB and from distance-ladder
measurements using Cepheids and supernovae. The addition of the SPT-3G 2018
data to \textit{Planck} reduces the square-root of the determinants of the
parameter covariance matrices by factors of across these models,
signaling a substantial reduction in the allowed parameter volume. We also
explore CMB-based constraints on from combined SPT, \textit{Planck}, and
ACT DR4 datasets. While individual experiments see some indications of
different values between the , , and spectra, the combined
constraints are consistent between the three spectra. For the full
combined datasets, we report , which is the tightest constraint on
from CMB power spectra to date and in tension with the most
precise distance-ladder-based measurement of . The SPT-3G survey is
planned to continue through at least 2023, with existing maps of combined 2019
and 2020 data already having lower noise than the maps used in
this analysis.Comment: Submitted to PRD; 19 pages, 7 figure
The Design and Integrated Performance of SPT-3G
SPT-3G is the third survey receiver operating on the South Pole Telescope
dedicated to high-resolution observations of the cosmic microwave background
(CMB). Sensitive measurements of the temperature and polarization anisotropies
of the CMB provide a powerful dataset for constraining cosmology. Additionally,
CMB surveys with arcminute-scale resolution are capable of detecting galaxy
clusters, millimeter-wave bright galaxies, and a variety of transient
phenomena. The SPT-3G instrument provides a significant improvement in mapping
speed over its predecessors, SPT-SZ and SPTpol. The broadband optics design of
the instrument achieves a 430 mm diameter image plane across observing bands of
95 GHz, 150 GHz, and 220 GHz, with 1.2 arcmin FWHM beam response at 150 GHz. In
the receiver, this image plane is populated with 2690 dual-polarization,
tri-chroic pixels (~16000 detectors) read out using a 68X digital
frequency-domain multiplexing readout system. In 2018, SPT-3G began a multiyear
survey of 1500 deg of the southern sky. We summarize the unique optical,
cryogenic, detector, and readout technologies employed in SPT-3G, and we report
on the integrated performance of the instrument.Comment: 25 pages, 11 figures. Submitted to ApJ
Broadband, millimeter-wave antireflection coatings for large-format, cryogenic aluminum oxide optics
We present two prescriptions for broadband (ā¼77ā252GHz), millimeter-wave antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide optics: one for large-format (700 mm diameter) planar and planoāconvex elements, the other for densely packed arrays of quasi-optical elementsāin our case, 5 mm diameter half-spheres (called ālensletsā). The coatings comprise three layers of commercially available, polytetrafluoroethylene-based, dielectric sheet material. The lenslet coating is molded to fit the 150 mm diameter arrays directly, while the large-diameter lenses are coated using a tiled approach. We review the fabrication processes for both prescriptions, then discuss laboratory measurements of their transmittance and reflectance. In addition, we present the inferred refractive indices and loss tangents for the coating materials and the aluminum oxide substrate. We find that at 150 GHz and 300 K the large-format coating sample achieves (97Ā±2)% transmittance, and the lenslet coating sample achieves (94Ā±3)% transmittance
On-sky performance of the SPT-3G frequency-domain multiplexed readout
Frequency-domain multiplexing (fMux) is an established technique for the readout of large arrays of transition-edge sensor (TES) bolometers. Each TES in a multiplexing module has a unique AC voltage bias that is selected by a resonant filter. This scheme enables the operation and readout of multiple bolometers on a single pair of wires, reducing thermal loading onto sub-Kelvin stages. The current receiver on the South Pole Telescope, SPT-3G, uses a 68x fMux system to operate its large-format camera of ā¼
ā¼
16,000 TES bolometers. We present here the successful implementation and performance of the SPT-3G readout as measured on-sky. Characterization of the noise reveals a median pair-differenced 1/f knee frequency of 33 mHz, indicating that low-frequency noise in the readout will not limit SPT-3Gās measurements of sky power on large angular scales. Measurements also show that the median readout white noise level in each of the SPT-3G observing bands is below the expectation for photon noise, demonstrating that SPT-3G is operating in the photon-noise-dominated regime