53 research outputs found
DETECTORS FOR THE COSMOLOGY LARGE ANGULAR SCALE SURVEYOR (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) observes the cosmic microwave background (CMB) polarization over large angular scales with the aim of detecting and characterizing the inflationary gravitational waves and measuring the optical depth to reionization. CLASS is a ground-based, multi-frequency microwave polarimeter that surveys 70% of the microwave sky every day from the Atacama Desert. CLASS consists of four telescopes: a 40 GHz receiver probing the polarized synchrotron emission, a 150/220 GHz dichroic receiver mapping the polarized dust, and two 90 GHz receivers optimized for CMB observation near the minimum of polarized Galactic emission. The high sensitivity CMB polarization measurement for CLASS is made possible by its background-limited detector arrays. The detector arrays for all CLASS telescopes contain smooth-walled feedhorns that couple to transition-edge sensor (TES) bolometers through symmetric planar orthomode transducers (OMTs). This thesis begins by introducing the inflationary paradigm and its observational signature in the CMB polarization. In the second chapter, I describe the CLASS science goals, and discuss the instrument design and survey strategy implemented to achieve these goals. The third chapter introduces the CLASS detectors optimized for high sensitivity and control over systematics required for precise measurement of the CMB polarization over large angular scales. The fourth and fifth chapters focus on the design, assembly, and in-lab characterization of the 90 and the 150/220 GHz detector arrays, respectively. Finally, I present the on-sky performance of the CLASS detectors in the sixth chapter
The Cosmology Large Angular Scale Surveyor
The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array
designed to characterize relic primordial gravitational waves from inflation
and the optical depth to reionization through a measurement of the polarized
cosmic microwave background (CMB) on the largest angular scales. The
frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one
dichroic system at 145/217 GHz, are chosen to avoid spectral regions of high
atmospheric emission and span the minimum of the polarized Galactic
foregrounds: synchrotron emission at lower frequencies and dust emission at
higher frequencies. Low-noise transition edge sensor detectors and a rapid
front-end polarization modulator provide a unique combination of high
sensitivity, stability, and control of systematics. The CLASS site, at 5200 m
in the Chilean Atacama desert, allows for daily mapping of up to 70\% of the
sky and enables the characterization of CMB polarization at the largest angular
scales. Using this combination of a broad frequency range, large sky coverage,
control over systematics, and high sensitivity, CLASS will observe the
reionization and recombination peaks of the CMB E- and B-mode power spectra.
CLASS will make a cosmic variance limited measurement of the optical depth to
reionization and will measure or place upper limits on the tensor-to-scalar
ratio, , down to a level of 0.01 (95\% C.L.)
Testing CMB Anomalies in E-mode Polarization with Current and Future Data
In this paper, we explore the power of the cosmic microwave background (CMB)
polarization (E-mode) data to corroborate four potential anomalies in CMB
temperature data: the lack of large angular-scale correlations, the alignment
of the quadrupole and octupole (Q-O), the point-parity asymmetry, and the
hemispherical power asymmetry. We use CMB simulations with noise representative
of three experiments -- the Planck satellite, the Cosmology Large Angular Scale
Surveyor (CLASS), and the LiteBIRD satellite -- to test how current and future
data constrain the anomalies. We find the correlation coefficients
between temperature and E-mode estimators to be less than , except for the
point-parity asymmetry ( for cosmic-variance-limited simulations),
confirming that E-modes provide a check on the anomalies that is largely
independent of temperature data. Compared to Planck component-separated CMB
data (SMICA), the putative LiteBIRD survey would reduce errors on E-mode
anomaly estimators by factors of for hemispherical power asymmetry and
point-parity asymmetry, and by for lack of large-scale correlation.
The improvement in Q-O alignment is not obvious due to large cosmic variance,
but we found the ability to pin down the estimator value will be improved by a
factor . Improvements with CLASS are intermediate to these.Comment: 23 pages, 15 figures, 6 table
Control and systems software for the Cosmology Large Angular Scale Surveyor (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) is an array of
polarization-sensitive millimeter wave telescopes that observes ~70% of the sky
at frequency bands centered near 40GHz, 90GHz, 150GHz, and 220GHz from the
Atacama desert of northern Chile. Here, we describe the architecture of the
software used to control the telescopes, acquire data from the various
instruments, schedule observations, monitor the status of the instruments and
observations, create archival data packages, and transfer data packages to
North America for analysis. The computer and network architecture of the CLASS
observing site is also briefly discussed. This software and architecture has
been in use since 2016, operating the telescopes day and night throughout the
year, and has proven successful in fulfilling its design goals.Comment: 19 pages, 8 figures, to appear in Proc. SPI
On-sky performance of new 90 GHz detectors for the Cosmology Large Angular Scale Surveyor (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) is a
polarization-sensitive telescope array located at an altitude of 5,200 m in the
Chilean Atacama Desert and designed to measure the polarized Cosmic Microwave
Background (CMB) over large angular scales. The CLASS array is currently
observing with three telescopes covering four frequency bands: one at 40 GHz
(Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (HF). During
the austral winter of 2022, we upgraded the first 90 GHz telescope (W1) by
replacing four of the seven focal plane modules. These new modules contain
detector wafers with an updated design, aimed at improving the optical
efficiency and detector stability. We present a description of the design
changes and measurements of on-sky optical efficiencies derived from
observations of Jupiter.Comment: 5 pages, 3 figures, to appear in the IEEE Transactions on Applied
Superconductivity. arXiv admin note: text overlap with arXiv:2208.0500
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