41 research outputs found
The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module
The Simons Observatory (SO) includes four telescopes that will measure the
temperature and polarization of the cosmic microwave background using over
60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES
bolometers are read out by a microwave RF SQUID multiplexing system with a
multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to
magnetic field pickup and that it is hard to predict how they will respond to
such fields, it is important to characterize the magnetic response of these
systems empirically. This information can then be used to limit spurious
signals by informing magnetic shielding designs for the detectors and readout.
This paper focuses on measurements of magnetic pickup with different magnetic
shielding configurations for the SO universal multiplexing module (UMM), which
contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic
pickup of a prototype UMM was tested under three shielding configurations: no
shielding (copper packaging), aluminum packaging for the UMM, and a
tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold
stage. The measurements show that the aluminum packaging outperforms the copper
packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K
shield further increases the relative shielding factor in the aluminum
configuration by 1-2 orders of magnitude.Comment: 7 pages, 4 figure, conference proceedings submitted to the Journal of
Low Temperature Physic
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: Detection of mm-wave transient sources
We report on the serendipitous discovery of three transient mm-wave sources
using data from the Atacama Cosmology Telescope. The first, detected at RA =
273.8138, dec = -49.4628 at total, brightened from less than 5
mJy to at least 1100 mJy at 150 GHz with an unknown rise time shorter than
thirteen days, during which the increase from 250 mJy to 1100 mJy took only 8
minutes. Maximum flux was observed on 2019-11-8. The source's spectral index in
flux between 90 and 150 GHz was positive, . The second,
detected at RA = 105.1584, dec = -11.2434 at total, brightened
from less than 20 mJy to at least 300 mJy at 150 GHz with an unknown rise time
shorter than eight days. Maximum flux was observed on 2019-12-15. Its spectral
index was also positive, . The third, detected at RA =
301.9952, dec = 16.1652 at total, brightened from less than 8
mJy to at least 300 mJy at 150 GHz over a day or less but decayed over a few
days. Maximum flux was observed on 2018-9-11. Its spectrum was approximately
flat, with a spectral index of . None of the sources were
polarized to the limits of these measurements. The two rising-spectrum sources
are coincident in position with M and K stars, while the third is coincident
with a G star.Comment: 8 pages, 4 figures, 1 tabl
The Atacama Cosmology Telescope: Microwave Intensity and Polarization Maps of the Galactic Center
We present arcminute-resolution intensity and polarization maps of the
Galactic center made with the Atacama Cosmology Telescope (ACT). The maps cover
a 32 deg field at 98, 150, and 224 GHz with ,
. We combine these data with Planck observations at
similar frequencies to create coadded maps with increased sensitivity at large
angular scales. With the coadded maps, we are able to resolve many known
features of the Central Molecular Zone (CMZ) in both total intensity and
polarization. We map the orientation of the plane-of-sky component of the
Galactic magnetic field inferred from the polarization angle in the CMZ,
finding significant changes in morphology in the three frequency bands as the
underlying dominant emission mechanism changes from synchrotron to dust
emission. Selected Galactic center sources, including Sgr A*, the Brick
molecular cloud (G0.253+0.016), the Mouse pulsar wind nebula (G359.23-0.82),
and the Tornado supernova remnant candidate (G357.7-0.1), are examined in
detail. These data illustrate the potential for leveraging ground-based Cosmic
Microwave Background polarization experiments for Galactic science.Comment: 26 pages, 14 figures, accepted for publication in Ap
The Simons Observatory Large Aperture Telescope Receiver
The Simons Observatory (SO) Large Aperture Telescope Receiver (LATR) will be
coupled to the Large Aperture Telescope located at an elevation of 5,200 m on
Cerro Toco in Chile. The resulting instrument will produce arcminute-resolution
millimeter-wave maps of half the sky with unprecedented precision. The LATR is
the largest cryogenic millimeter-wave camera built to date with a diameter of
2.4 m and a length of 2.6 m. It cools 1200 kg of material to 4 K and 200 kg to
100 mk, the operating temperature of the bolometric detectors with bands
centered around 27, 39, 93, 145, 225, and 280 GHz. Ultimately, the LATR will
accommodate 13 40 cm diameter optics tubes, each with three detector wafers and
a total of 62,000 detectors. The LATR design must simultaneously maintain the
optical alignment of the system, control stray light, provide cryogenic
isolation, limit thermal gradients, and minimize the time to cool the system
from room temperature to 100 mK. The interplay between these competing factors
poses unique challenges. We discuss the trade studies involved with the design,
the final optimization, the construction, and ultimate performance of the
system