31 research outputs found
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
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
A Measurement of Gravitational Lensing of the Cosmic Microwave Background Using SPT-3G 2018 Data
We present a measurement of gravitational lensing over 1500 deg of the
Southern sky using SPT-3G temperature data at 95 and 150 GHz taken in 2018. The
lensing amplitude relative to a fiducial Planck 2018 CDM cosmology is
found to be , excluding instrumental and astrophysical
systematic uncertainties. We conduct extensive systematic and null tests to
check the robustness of the lensing measurements, and report a minimum-variance
combined lensing power spectrum over angular multipoles of , which
we use to constrain cosmological models. When analyzed alone and jointly with
primary cosmic microwave background (CMB) spectra within the CDM
model, our lensing amplitude measurements are consistent with measurements from
SPT-SZ, SPTpol, ACT, and Planck. Incorporating loose priors on the baryon
density and other parameters including uncertainties on a foreground bias
template, we obtain a constraint on using the SPT-3G 2018 lensing data alone, where
is a common measure of the amplitude of structure today and
is the matter density parameter. Combining SPT-3G 2018 lensing
measurements with baryon acoustic oscillation (BAO) data, we derive parameter
constraints of , , and Hubble constant
km s Mpc. Using CMB anisotropy and lensing measurements from
SPT-3G only, we provide independent constraints on the spatial curvature of
(95% C.L.) and the dark energy density
of (68% C.L.). When combining SPT-3G
lensing data with SPT-3G CMB anisotropy and BAO data, we find an upper limit on
the sum of the neutrino masses of eV (95% C.L.)
Design and assembly of SPT-3G cold readout hardware
The third-generation upgrade to the receiver on the South Pole Telescope, SPT-3G, was installed at the South Pole during the 2016–2017 austral summer to measure the polarization of the cosmic microwave background. Increasing the number of detectors by a factor of 10 to ∼16,000
∼16,000
required the multiplexing factor to increase to 68 and the bandwidth of the frequency-division readout electronics to span 1.6–5.2 MHz. This increase necessitates low-thermal conductance, low-inductance cryogenic wiring. Our cold readout system consists of planar thin-film aluminum inductive–capacitive resonators, wired in series with the detectors, summed together, and connected to 4K SQUIDs by 10−μm
10−μm
-thick niobium–titanium (NbTi) broadside-coupled striplines. Here, we present an overview of the cold readout electronics for SPT-3G, including assembly details and characterization of electrical and thermal properties of the system. We report, for the NbTi striplines, values of R≤10 −4 Ω
R≤10−4Ω
, L=21±1 nH
L=21±1 nH
, and C=1.47±.02 nF
C=1.47±.02 nF
. Additionally, the striplines’ thermal conductivity is described by kA=6.0±0.3 T 0.92±0.04 μW mm K −1
kA=6.0±0.3 T0.92±0.04 μW mm K−1
. Finally, we provide projections for cross talk induced by parasitic impedances from the stripline and find that the median value of percentage cross talk from leakage current is 0.22 and 0.09%
0.09%
from wiring impedance