The Bicep/Keck Array experiment is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background polarization from the South Pole in search of a primordial B-mode signature. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We use high-fidelity, in-situ measurements of the beam response to estimate the temperature-to-polarization (T → P) leakage in our latest data including observations from 2016 through 2018. This includes three years of Bicep3 observing at 95 GHz, and multifrequency data from Keck Array. Here we present band-averaged far-field beam maps, differential beam mismatch, and residual beam power (after filtering out the leading difference modes via deprojection) for these receivers. We show preliminary results of "beam map simulations," which use these beam maps to observe a simulated temperature (no Q/U) sky to estimate T → P leakage in our real data.
BICEP3 is a 520 mm aperture on-axis refracting telescope at the South Pole, which observes the polarization of the cosmic microwave background (CMB) at 95 GHz to search for the B-mode signal from inflationary gravitational waves. In addition to this main target, we have developed a low-elevation observation strategy to extend coverage of the Southern sky at the South Pole, where BICEP3 can quickly achieve degree-scale E-mode measurements over a large area. An interesting E-mode measurement is probing a potential polarization anomaly around the CMB Cold Spot. During the austral summer seasons of 2018-19 and 2019-20, BICEP3 observed the sky with a flat mirror to redirect the beams to various low elevation ranges. The preliminary data analysis shows degree-scale E-modes measured with high signal-to-noise ratio.
The BICEP3 CMB Polarimeter is a small-aperture refracting telescope located at the South Pole and is specifically designed to search for the possible signature of inflationary gravitational waves in the Cosmic Microwave Background (CMB). The experiment measures polarization on the sky by differencing the signal of co-located, orthogonally polarized antennas coupled to Transition Edge Sensor (TES) detectors. We present precise measurements of the absolute polarization response angles and polarization efficiencies for nearly all of BICEP3's ~800 functioning polarization-sensitive detector pairs from calibration data taken in January 2018. Using a Rotating Polarized Source (RPS), we mapped polarization response for each detector over a full 360 degrees of source rotation and at multiple telescope boresight rotations from which per-pair polarization properties were estimated. In future work, these results will be used to constrain signals predicted by exotic physical models such as Cosmic Birefringence.
The Baryon Mapping eXperiment (BMX) is an interferometric array designed as a pathfinder for a future post-reionization 21 cm intensity mapping survey. It consists of four 4-meter parabolic reflectors each having offset pyramidal horn feed, quad-ridge orthomode transducer, temperature-stabilized RF amplification and filtering, and pulsed noise injection diode. An undersampling readout scheme uses 8-bit digitizers running at 1.1 Gsamples/ sec to provide access to signals from 1.1 - 1.55 GHz (third Nyquist zone), corresponding to HI emission from sources at redshift 0 < z < 0:3. An FX correlator is implemented in GPU and generates 28 GB/day of time-ordered visibility data. About 7,000 hours of data were collected from Jan. 2019 - May 2020, and we will present results on system performance including sensitivity, beam mapping studies, observations of bright celestial targets, and system electronics upgrades. BMX is a pathfinder for the proposed PUMA intensity mapping survey in the 2030s.
BICEP Array is a degree-scale Cosmic Microwave Background (CMB) experiment that will search for primordial B-mode polarization while constraining Galactic foregrounds. BICEP Array will be comprised of four receivers to cover a broad frequency range with channels at 30/40, 95, 150 and 220/270 GHz. The first low-frequency receiver will map synchrotron emission at 30 and 40 GHz and will deploy to the South Pole at the end of 2019. In this paper, we give an overview of the BICEP Array science and instrument, with a focus on the detector module. We designed corrugations in the metal frame of the module to suppress unwanted interactions with the antenna-coupled detectors that would otherwise deform the beams of edge pixels. This design reduces the residual beam systematics and temperature-to-polarization leakage due to beam steering and shape mismatch between polarized beam pairs. We report on the simulated performance of single- and wide-band corrugations designed to minimize these effects. Our optimized design alleviates beam differential ellipticity caused by the metal frame to about 7% over 57% bandwidth (25 to 45 GHz), which is close to the level due the bare antenna itself without a metal frame. Initial laboratory measurements are also presented.
BICEP3 is a 520mm aperture on-axis refracting telescope observing the polarization of the cosmic microwave background (CMB) at 95GHz in search of the B-mode signal originating from in ationary gravitational waves. BICEP3's focal plane is populated with modularized tiles of antenna-coupled transition edge sensor (TES) bolometers. BICEP3 was deployed to the South Pole during 2014-15 austral summer and has been operational since. During the 2016-17 austral summer, we implemented changes to optical elements that lead to better noise performance. We discuss this upgrade and show the performance of BICEP3 at its full mapping speed from the 2017 and 2018 observing seasons. BICEP3 achieves an order-of-magnitude improvement in mapping speed compared to a Keck 95GHz receiver. We demonstrate 6.6μK√s noise performance of the BICEP3 receiver.
The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground based CMB observations and is the current location of the Bicep/Keck Array telescopes and the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.
Targeting faint polarization patterns arising from Primordial Gravitational Waves in the Cosmic Microwave Background requires excellent observational sensitivity. Optical elements in small aperture experiments such as Bicep3 and Keck Array are designed to optimize throughput and minimize losses from transmission, reflection and scattering at millimeter wavelengths. As aperture size increases, cryostat vacuum windows must withstand larger forces from atmospheric pressure and the solution has often led to a thicker window at the expense of larger transmission loss. We have identified a new candidate material for the fabrication of vacuum windows: with a tensile strength two orders of magnitude larger than previously used materials, woven high-modulus polyethylene could allow for dramatically thinner windows, and therefore significantly reduced losses and higher sensitivity. In these proceedings we investigate the suitability of high-modulus polyethylene windows for ground-based CMB experiments, such as current and future receivers in the Bicep/Keck Array program. This includes characterizing their optical transmission as well as their mechanical behavior under atmospheric pressure. We find that such ultra-thin materials are promising candidates to improve the performance of large-aperture instruments at millimeter wavelengths, and outline a plan for further tests ahead of a possible upcoming field deployment of such a science-grade window.
Bicep Array is a cosmic microwave background (CMB) polarization experiment that will begin observing at the South Pole in early 2019. This experiment replaces the five Bicep2 style receivers that compose the Keck Array with four larger Bicep3 style receivers observing at six frequencies from 30 to 270GHz. The 95GHz and 150GHz receivers will continue to push the already deep Bicep/Keck CMB maps while the 30/40GHz and 220/270GHz receivers will constrain the synchrotron and galactic dust foregrounds respectively. Here we report on the design and performance of the Bicep Array instruments focusing on the mount and cryostat systems.
Bicep Array is the newest multi-frequency instrument in the Bicep/Keck Array program. It is comprised of four 550mm aperture refractive telescopes observing the polarization of the cosmic microwave background (CMB) at 30/40, 95, 150 and 220/270 GHz with over 30,000 detectors. We present an overview of the receiver, detailing the optics, thermal, mechanical, and magnetic shielding design. Bicep Array follows Bicep3's modular focal plane concept, and upgrades to 6" wafer to reduce fabrication with higher detector count per module. The first receiver at 30/40GHz is expected to start observing at the South Pole during the 2019-20 season. By the end of the planned Bicep Array program, we project 0.002 ⪅ σ(r) ⪅ 0.006, assuming current modeling of polarized Galactic foreground and depending on the level of delensing that can be achieved with higher resolution maps from the South Pole Telescope.
H. Hui, P. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, J. Grayson, M. Halpern, S. Harrison, G. Hilton, V. Hristov, K. Irwin, J. Kang, K. Karkare, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, R. Schwarz, C. Sorensen, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, D. Wiebe, J. Willmert, W. L. Wu, K. W. Yoon
BICEP3, the latest telescope in the BICEP/Keck program, started science observations in March 2016. It is a 550mm aperture refractive telescope observing the polarization of the cosmic microwave background at 95 GHz. We show the focal plane design and detector performance, including spectral response, optical efficiency and preliminary sensitivity of the upgraded BICEP3. We demonstrate 9.72 μKCMB√s noise performance of the BICEP3 receiver.
K. Karkare, P. A. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, J. Grayson, M. Halpern, S. Harrison, G. Hilton, V. Hristov, H. Hui, K. Irwin, J. Kang, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. T. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, M. St. Germaine, R. Schwarz, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, J. Willmert, C. L. Wong, W. L. Wu, K. W. Yoon
BICEP3 is a small-aperture refracting cosmic microwave background (CMB) telescope designed to make sensitive polarization maps in pursuit of a potential B-mode signal from inflationary gravitational waves. It is the latest in the Bicep/Keck Array series of CMB experiments located at the South Pole, which has provided the most stringent constraints on inflation to date. For the 2016 observing season, BICEP3 was outfitted with a full suite of 2400 optically coupled detectors operating at 95 GHz. In these proceedings we report on the far field beam performance using calibration data taken during the 2015-2016 summer deployment season in situ with a thermal chopped source. We generate high-fidelity per-detector beam maps, show the array-averaged beam profile, and characterize the differential beam response between co-located, orthogonally polarized detectors which contributes to the leading instrumental systematic in pair differencing experiments. We find that the levels of differential pointing, beamwidth, and ellipticity are similar to or lower than those measured for Bicep2 and Keck Array. The magnitude and distribution of Bicep3’s differential beam mismatch – and the level to which temperature-to-polarization leakage may be marginalized over or subtracted in analysis - will inform the design of next-generation CMB experiments with many thousands of detectors.
J. Grayson, P. A. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, M. Halpern, S. Harrison, G. Hilton, V. Hristov, H. Hui, K. Irwin, J. Kang, K. Karkare, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, R. Schwarz, C. Sorenson, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, D. Wiebe, J. Willmert, W. L. Wu, K. W. Yoon
Bicep3 is a 520mm aperture, compact two-lens refractor designed to observe the polarization of the cosmic microwave background (CMB) at 95 GHz. Its focal plane consists of modularized tiles of antenna-coupled transition edge sensors (TESs), similar to those used in Bicep2 and the Keck Array. The increased per-receiver optical throughput compared to Bicep2/Keck Array, due to both its faster f=1:7 optics and the larger aperture, more than doubles the combined mapping speed of the Bicep/Keck program. The Bicep3 receiver was recently upgraded to a full complement of 20 tiles of detectors (2560 TESs) and is now beginning its second year of observation (and first science season) at the South Pole. We report on its current performance and observing plans. Given its high per-receiver throughput while maintaining the advantages of a compact design, Bicep3- class receivers are ideally suited as building blocks for a 3rd-generation CMB experiment, consisting of multiple receivers spanning 35 GHz to 270 GHz with total detector count in the tens of thousands. We present plans for such an array, the new "BICEP Array" that will replace the Keck Array at the South Pole, including design optimization, frequency coverage, and deployment/observing strategies.
The inflationary paradigm of the early universe predicts a stochastic background of gravitational waves which would generate a B-mode polarization pattern in the cosmic microwave background (CMB) at degree angular scales. Precise measurement of B-modes is one of the most compelling observational goals in modern cosmology. Since 2011, the Keck Array has deployed over 2500 transition edge sensor (TES) bolometer detectors at 100 and 150 GHz to the South Pole in pursuit of degree-scale B-modes, and Bicep3 will follow in 2015 with 2500 more at 100 GHz. Characterizing the spectral response of these detectors is important for controlling systematic effects that could lead to leakage from the temperature to polarization signal, and for understanding potential coupling to atmospheric and astrophysical emission lines. We present complete spectral characterization of the Keck Array detectors, made with a Martin-Puplett Fourier Transform Spectrometer at the South Pole, and preliminary spectra of Bicep3 detectors taken in lab. We show band centers and effective bandwidths for both Keck Array bands, and use models of the atmosphere at the South Pole to cross check our absolute calibration. Our procedure for obtaining interferograms in the field with automated 4-axis coupling to the focal plane represents an important step towards efficient and complete spectral characterization of next-generation instruments more than 10000 detectors.
Searching for evidence of inflation by measuring B-modes in the cosmic microwave background (CMB) polarization at degree angular scales remains one of the most compelling experimental challenges in cosmology. BICEP2 and the Keck Array are part of a program of experiments at the South Pole whose main goal is to achieve the sensitivity and systematic control necessary for measurements of the tensor-to-scalar ratio at σ(r) ~0:01. Beam imperfections that are not sufficiently accounted for are a potential source of spurious polarization that could interfere with that goal. The strategy of BICEP2 and the Keck Array is to completely characterize their telescopes' polarized beam response with a combination of in-lab, pre-deployment, and on-site calibrations. We Sereport the status of these experiments, focusing on continued improved understanding of their beams. Far-field measurements of the BICEP2 beam with a chopped thermal source, combined with analysis improvements, show that the level of residual beam-induced systematic errors is acceptable for the goal of σ(r) ~ 0:01 measurements. Beam measurements of the Keck Array side lobes helped identify a way to reduce optical loading with interior cold baffles, which we installed in late 2013. These baffles reduced total optical loading, leading to a ~ 10% increase in mapping speed for the 2014 observing season. The sensitivity of the Keck Array continues to improve: for the 2013 season it was 9:5 μK _/s noise equivalent temperature (NET). In 2014 we converted two of the 150-GHz cameras to 100 GHz for foreground separation capability. We have shown that the BICEP2 and the Keck Array telescope technology is sufficient for the goal of σ(r) ~ 0:01 measurements. Furthermore, the program is continuing with BICEP3, a 100-GHz telescope with 2560 detectors.
The Bicep2 and Keck Array experiments are designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 2-4 degrees (ℓ = 50–100). This is the region in which the B-mode signal, a signature prediction of cosmic inflation, is expected to peak. Bicep2 was deployed to the South Pole at the end of 2009 and is in the middle of its third year of observing with 500 polarization-sensitive detectors at 150 GHz. The Keck Array was deployed to the South Pole at the end of 2010, initially with three receivers—each similar to Bicep2. An additional two receivers have been added during the 2011-12 summer. We give an overview of the two experiments, report on substantial gains in the sensitivity of the two experiments after post-deployment optimization, and show preliminary maps of CMB polarization from Bicep2.
The Keck Array (SPUD) began observing the cosmic microwave background's polarization in the winter of 2011 at the South Pole. The Keck Array follows the success of the predecessor experiments BICEP and BICEP2, 1 using five on-axis refracting telescopes. These have a combined imaging array of 2500 antenna-coupled TES bolometers read with a SQUID- based time domain multiplexing system. We will discuss the detector noise and the optimization of the readout. The achieved sensitivity of the Keck Array is 11.5 μKCMB√s in the 2012 configuration.
Between the BICEP2 and Keck Array experiments, we have deployed over 1500 dual polarized antenna coupled bolometers
to map the Cosmic Microwave Background’s polarization. We have been able to rapidly deploy these detectors because
they are completely planar with an integrated phased-array antenna. Through our experience in these experiments, we
have learned of several challenges with this technology- specifically the beam synthesis in the antenna- and in this paper
we report on how we have modified our designs to mitigate these challenges. In particular, we discus differential steering
errors between the polarization pairs’ beam centroids due to microstrip cross talk and gradients of penetration depth in the
niobium thin films of our millimeter wave circuits. We also discuss how we have suppressed side lobe response with a
Gaussian taper of our antenna illumination pattern. These improvements will be used in Spider, Polar-1, and this season’s
retrofit of Keck Array.
The Keck Array (SPUD) is a set of microwave polarimeters that observes from the South Pole at degree angular scales in search of a signature of Inflation imprinted as B-mode polarization in the Cosmic Microwave Background (CMB). The first three Keck Array receivers were deployed during the 2010-2011 Austral summer, followed by two new receivers in the 2011-2012 summer season, completing the full five-receiver array. All five receivers are currently observing at 150 GHz. The Keck Array employs the field-proven BICEP/ BICEP2 strategy of using small, cold, on-axis refractive optics, providing excellent control of systematics while maintaining a large field of view. This design allows for full characterization of far-field optical performance using microwave sources on the ground. We describe our efforts to characterize the main beam shape and beam shape mismatch between co-located orthogonally-polarized detector pairs, and discuss the implications of measured differential beam parameters on temperature to polarization leakage in CMB analysis.
J. Brevik, R. Aikin, M. Amiri, S. Benton, J. Bock, J. Bonetti, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. L. Kuo, A. Lange, E. Leitch, C. Netterfield, H. Nguyen, R. Ogburn, A. Orlando, C. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, C. Sheehy, Z. Staniszewski, R. Sudiwala, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
We report on the preliminary detector performance of the Bicep2 mm-wave polarimeter, deployed in 2009 to
the South Pole. Bicep2 is currently imaging the polarization of the cosmic microwave background at 150 GHz
using an array of 512 antenna-coupled superconducting bolometers. The antennas, band-defining filters and
transition edge sensor (TES) bolometers are photolithographically fabricated on 4 silicon tiles. Each tile consists
of an 8×8 grid of ~7 mm spatial pixels, for a total of 256 detector pairs. A spatial pixel contains 2 sets of
orthogonal antenna slots summed in-phase, with each set coupled to a TES by a filtered microstrip. The detectors
are read out using time-domain multiplexed SQUIDs. The detector pair of each spatial pixel is differenced to
measure polarization. We report on the performance of the Bicep2 detectors in the field, including the focal
plane yield, detector and multiplexer optimization, detector noise and stability, and a preliminary estimate of
the improvement in mapping speed compared to Bicep1.
Bicep2 deployed to the South Pole during the 2009-2010 austral summer, and is now mapping the polarization
of the cosmic microwave background (CMB), searching for evidence of inflationary cosmology. Bicep2 belongs
to a new class of telescopes including Keck (ground-based) and Spider (balloon-borne) that follow on Bicep's
strategy of employing small, cold, on-axis refracting optics. This common design provides key advantages ideal
for targeting the polarization signature from inflation, including: (i) A large field of view, allowing substantial
light collecting power despite the small aperture, while still resolving the degree-scale polarization of the CMB;
(ii) liquid helium-cooled optics and cold stop, allowing for low, stable instrument loading; (iii) the ability to
rotate the entire telescope about the boresight; (iv) a baffled primary aperture, reducing sidelobe pickup; and
(v) the ability to characterize the far field optical performance of the telescope using ground-based sources. We
describe the last of these advantages in detail, including our efforts to measure the main beam shape, beammatch
between orthogonally-polarized pairs, polarization efficiency and response angle, sidelobe pickup, and
ghost imaging. We do so with ground-based polarized microwave sources mounted in the far field as well as
with astronomical calibrators. Ultimately, Bicep2's sensitivity to CMB polarization from inflation will rely on
precise calibration of these beam features.
R. W. Ogburn, P. Ade, R. Aikin, M. Amiri, S. Benton, J. Bock, J. Bonetti, J. Brevik, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. Kuo, A. Lange, E. Leitch, C. Netterfield, H. Nguyen, A. Orlando, C. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, C. Sheehy, Z. Staniszewski, S. Stokes, R. Sudiwala, G. P. Teply, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
The Bicep2 telescope is designed to measure the polarization of the cosmic microwave background on angular
scales near 2-4 degrees, near the expected peak of the B-mode polarization signal induced by primordial gravitational
waves from inflation. Bicep2 follows the success of Bicep, which has set the most sensitive current limits
on B-modes on 2-4 degree scales. The experiment adopts a new detector design in which beam-defining slot antennas
are coupled to TES detectors photolithographically patterned in the same silicon wafer, with multiplexing
SQUID readout. Bicep2 takes advantage of this design's higher focal-plane packing density, ease of fabrication,
and multiplexing readout to field more detectors than Bicep1, improving mapping speed by nearly a factor of
10. Bicep2 was deployed to the South Pole in November 2009 with 500 polarization-sensitive detectors at 150
GHz, and is funded for two seasons of observation. The first months' data demonstrate the performance of the
Caltech/JPL antenna-coupled TES arrays, and two years of observation with Bicep2 will achieve unprecedented
sensitivity to B-modes on degree angular scales.
C. Sheehy, P. Ade, R. Aikin, M. Amiri, S. Benton, C. Bischoff, J. Bock, J. Bonetti, J. Brevik, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. L. Kuo, A. Lange, E. Leitch, M. Lueker, C. Netterfield, H. T. Nguyen, R. Ogburn, A. Orlando, C. L. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, Z. Staniszewski, S. Stokes, R. Sudiwala, G. Teply, K. Thompson, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
The Keck Array is a cosmic microwave background (CMB) polarimeter that will begin observing from the South
Pole in late 2010. The initial deployment will consist of three telescopes similar to BICEP2 housed in ultracompact,
pulse tube cooled cryostats. Two more receivers will be added the following year. In these proceedings
we report on the design and performance of the Keck cryostat. We also report some initial results on the
performance of antenna-coupled TES detectors operating in the presence of a pulse tube. We find that the
performance of the detectors is not seriously impacted by the replacement of BICEP2's liquid helium cryostat
with a pulse tube cooled cryostat.
BICEP2/SPUD is the new powerful upgrade of the existing BICEP1 experiment, a bolometric receiver to study the
polarization of the cosmic microwave background radiation, which has been in operation at the South Pole since January
2006. BICEP2 will provide an improvement up to 10 times mapping speed at 150 GHz compared to BICEP1, using the
same BICEP telescope mount. SPUD, a series of compact, mechanically-cooled receivers deployed on the DASI mount
at the Pole, will provide similar mapping speed in to BICEP2 in three bands, 100, 150, and 220 GHz. The new system
will use large TES focal plane arrays to provide unprecedented sensitivity and excellent control of foreground
contamination.
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