The Cosmic Microwave Background Stage Four Experiment (CMB-S4) is a planned DOE/NSF ground-based experiment that will probe the entire history of the cosmos by performing millimeter-wave sky surveys to produce multi-wavelength sky maps in both intensity and polarization of unprecedented quality. To meet its ambitious and transformative science goals within a reasonable survey duration, CMB-S4 employs a rigorous Systems Engineering approach to ensure tight control of instrumental sensitivity, systematic error, and instrument down-time. This disciplined Systems Engineering framework is essential for managing the instrumental configuration within the multi-institutional structure of the project. We present an overview of the project’s Systems Engineering approach, processes, tools, and status.
The search for the polarized imprint of primordial gravitational waves in the cosmic microwave background (CMB) as direct evidence of cosmic inflation requires exquisite sensitivity and control over systematics. The next-generation CMB-S4 project intends to improve upon current-generation experiments by deploying a significantly greater number of highly-sensitive detectors, combined with refined instrument components based on designs from field-proven instruments. The Precursor Small Aperture Telescope (PreSAT) is envisioned as an early step to this next generation, which will test prototype CMB-S4 components and technologies within an existing Bicep Array receiver, with the aim of enabling full-stack laboratory testing and early risk retirement, along with direct correlation of laboratory component-level performance measurements with deployed system performance. The instrument will utilize new 95/155 GHz dichroic dual-linear-polarization prototype detectors developed for CMB-S4, cooled to 100mK via the installation of an adiabatic demagnetization refrigerator, along with a prototype readout chain and prototype optics manufactured with wide-band anti-reflection coatings. The experience gained by integrating, deploying, and calibrating PreSAT will also help inform planning for CMB-S4 small aperture telescope commissioning, calibration, and operations well in advance of the fabrication of CMB-S4 production hardware.
Future millimeter wavelength experiments aim to both increase aperture diameters and broaden bandwidths to increase the sensitivity of the receivers. These changes produce a challenging anti-reflection (AR) design problem for refracting and transmissive optics. The higher frequency plastic optics require consistently thin polymer coats across a wide area, while wider bandwidths require multilayer designs. We present multilayer AR coats for plastic optics of the high frequency BICEP Array receiver (200-300 GHz) utilizing an expanded polytetrafluoroethylene (ePTFE) membrane, layered and compressively heat-bonded to itself. This process allows for a range of densities (from 0.3g/cc to 1g/cc) and thicknesses (>0.05mm) over a wide radius (33cm), opening the parameter space of potential AR coats in interesting directions. The layered ePTFE membrane has been combined with other polymer layers to produce band average reflections between 0.2% and 0.6% on high density polyethylene and a thin high modulus polyethylene window, respectively.
The BICEP3 Polarimeter is a small aperture, refracting telescope, dedicated to the observation of the Cosmic Microwave Background (CMB) at 95GHz. It is designed to target degree angular scale polarization patterns, in particular the very-much-sought-after primordial B-mode signal, which is a unique signature of cosmic inflation. The polarized signal from the sky is reconstructed by differencing co-localized, orthogonally polarized superconducting Transition Edge Sensor (TES) bolometers. In this work, we present absolute measurements of the polarization response of the detectors for more than approximately 800 functioning detector pairs of the BICEP3 experiment, out of a total of approximately 1000. We use a specifically designed Rotating Polarized Source (RPS) to measure the polarization response at multiple source and telescope boresight rotation angles, to fully map the response over 360 degrees. We present here polarization properties extracted from on-site calibration data taken in January 2022. A similar calibration campaign was performed in 2018, but we found that our constraint was dominated by systematics on the level of approximately 0.5° . After a number of improvements to the calibration set-up, we are now able to report a significantly lower level of systematic contamination. In the future, such precise measurements will be used to constrain physics beyond the standard cosmological model, namely cosmic birefringence.
Constraining the Galactic foregrounds with multi-frequency Cosmic Microwave Background (CMB) observations is an essential step towards ultimately reaching the sensitivity to measure primordial gravitational waves (PGWs), the sign of inflation after the Big-Bang that would be imprinted on the CMB. The BICEP Array is a set of multi-frequency cameras designed to constrain the energy scale of inflation through CMB B-mode searches while also controlling the polarized galactic foregrounds. The lowest frequency BICEP Array receiver (BA1) has been observing from the South Pole since 2020 and provides 30 GHz and 40 GHz data to characterize galactic synchrotron in our CMB maps. In this paper, we present the design of the BA1 detectors and the full optical characterization of the camera including the on-sky performance at the South Pole. The paper also introduces the design challenges during the first observing season including the effect of out-of-band photons on detectors performance. It also describes the tests done to diagnose that effect and the new upgrade to minimize these photons, as well as installing more dichroic detectors during the 2022 deployment season to improve the BA1 sensitivity. We finally report background noise measurements of the detectors with the goal of having photon-noise dominated detectors in both optical channels. BA1 achieves an improvement in mapping speed compared to the previous deployment season.
CMB-S4 will map the cosmic microwave background to unprecedented precision, while simultaneously surveying the millimeter-wave time-domain sky, in order to advance our understanding of cosmology and the universe. CMB-S4 will observe from two sites, the South Pole and the Atacama Desert of Chile. A combination of small- and large-aperture telescopes with hundreds of thousands of polarization-sensitive detectors will observe in several frequency bands from 20–300 GHz, surveying more than 50% of the sky to arcminute resolution with unprecedented sensitivity. CMB-S4 seeks to make a dramatic leap in sensitivity while observing across a broad range of largely unprotected spectrum which is increasingly being utilized for terrestrial and satellite transmissions. Fundamental aspects of CMB instrument technology leave them vulnerable to radio frequency interference (RFI) across a wide range of frequencies, including frequencies outside of their observing bands. Ground-based CMB instruments achieve their extraordinary sensitivities by deploying large focal planes of superconducting bolometers to extremely dry, high-altitude sites, with large fractional bandwidths, wide fields of view, and years of integration time. Suitable observing sites have historically offered significant protection from RFI, both naturally through their extremely remote locations as well as through restrictions on local emissions. Since the coupling mechanisms are complex, “safe” levels or frequencies of emission that would not interfere with CMB measurements cannot always be determined through straightforward calculations. We discuss models of interference for various types of RFI relevant to CMB-S4, mitigation strategies, and the potential impacts on survey sensitivity.
Observations of the Cosmic Microwave Background rely on cryogenic instrumentation with cold detectors, readout, and optics providing the low noise performance and instrumental stability required to make more sensitive measurements. It is therefore critical to optimize all aspects of the cryogenic design to achieve the necessary performance, with low temperature components and acceptable system cooling requirements. In particular, we will focus on our use of thermal filters and cold optics, which reduce the thermal load passed along to the cryogenic stages. To test their performance, we have made a series of in situ measurements while integrating the third receiver for the BICEP Array telescope. In addition to characterizing the behavior of this receiver, these measurements continue to refine the models that are being used to inform design choices being made for future instruments.
We present the conceptual design of the modular detector and readout system for the Cosmic Microwave Background – Stage four (CMB-S4) ground-based survey experiment. CMB-S4 will map the cosmic microwave background (CMB) and the millimeter-wave sky to unprecedented sensitivity, using 500,000 superconducting detectors observing from Chile and Antarctica to map over 60% of the sky. The fundamental building block of the detector and readout system is a detector module package operated at 100 mK, which is connected to a readout and amplification chain that carries signals out to room temperature. It uses arrays of feedhorn-coupled orthomode transducers (OMT) that collect optical power from the sky onto dc-voltage-biased transition-edge sensor (TES) bolometers. The resulting current signal in the TESs is then amplified by a two-stage cryogenic Superconducting Quantum Interference Device (SQUID) system with a time-division multiplexer to reduce wire count, and matching room-temperature electronics to condition and transmit signals to the data acquisition system. Sensitivity and systematics requirements are being developed for the detector and readout system over wide range of observing bands (20 to 300 GHz) and optical powers to accomplish CMB-S4’s science goals. While the design incorporates the successes of previous generations of CMB instruments, CMB-S4 requires an order of magnitude more detectors than any prior experiment. This requires fabrication of complex superconducting circuits on over 10 m2 of silicon, as well as significant amounts of precision wiring, assembly and cryogenic testing
New experiments that target the B-mode polarization signals in the Cosmic Microwave Background require more sensitivity, more detectors, and thus larger-aperture millimeter-wavelength telescopes, than previous experiments. These larger apertures require ever larger vacuum windows to house cryogenic optics. Scaling up conventional vacuum windows, such as those made of High Density Polyethylene (HDPE), require a corresponding increase in the thickness of the window material to handle the extra force from the atmospheric pressure. Thicker windows cause more transmission loss at ambient temperatures, increasing optical loading and decreasing sensitivity. We have developed the use of woven High Modulus Polyethylene (HMPE), a material 100 times stronger than HDPE, to manufacture stronger, thinner windows using a pressurized hot lamination process. We discuss the development of a specialty autoclave for generating thin laminate vacuum windows and the optical and mechanical characterization of full scale science grade windows, with the goal of developing a new window suitable for BICEP Array cryostats and for future CMB applications.
This conference presentation was prepared for the Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
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.
A detection of curl-type (B-mode) polarization of the primary CMB would be direct evidence for the inflationary paradigm of the origin of the Universe. The Bicep/Keck Array (BK) program targets the degree angular scales, where the power from primordial B-mode polarization is expected to peak, with ever-increasing sensitivity and has published the most stringent constraints on inflation to date. Bicep Array (BA) is the Stage-3 instrument of the BK program and will comprise four Bicep3-class receivers observing at 30/40, 95, 150 and 220/270 GHz with a combined 32,000+ detectors; such wide frequency coverage is necessary for control of the Galactic foregrounds, which also produce degree-scale B-mode signal. The 30/40 GHz receiver is designed to constrain the synchrotron foreground and has begun observing at the South Pole in early 2020. By the end of a 3-year observing campaign, the full Bicep Array instrument is projected to reach σr between 0.002 and 0.004, depending on foreground complexity and degree of removal of B-modes due to gravitational lensing (delensing). This paper presents an overview of the design, measured on-sky performance and calibration of the first BA receiver. We also give a preview of the added complexity in the time-domain multiplexed readout of the 7,776-detector 150 GHz receiver.
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.
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.
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.
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.
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.
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.
Bicep3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of Bicep1, Bicep2 and the Keck Array experiments | it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, Bicep3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5x larger than a Bicep2/Keck Array receiver and faster optics (f=1:6 vs. f=2:4). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, Bicep3 will have survey speed comparable to Keck Array 150 GHz (2013), and will signifcantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the Bicep2 observation patch
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.
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 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.
A. Orlando, R. Aikin, M. Amiri, J. Bock, J. Bonetti, J. Brevik, B. Burger, G. Chattopadthyay, P. Day, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, K. Irwin, M. Kenyon, J. Kovac, C. L. Kuo, A. Lange, H. LeDuc, N. Llombart, H. Nguyen, R. Ogburn, C. Reintsema, M. Runyan, Z. Staniszewski, R. Sudiwala, G. Teply, A. Trangsrud, A. Turner, P. Wilson
BICEP2/Keck and SPIDER are cosmic microwave background (CMB) polarimeters targeting the B-mode polarization
induced by primordial gravitational waves from inflation. They will be using planar arrays of polarization
sensitive antenna-coupled TES bolometers, operating at frequencies between 90 GHz and 220 GHz. At 150 GHz
each array consists of 64 polarimeters and four of these arrays are assembled together to make a focal plane, for a
total of 256 dual-polarization elements (512 TES sensors). The detector arrays are integrated with a time-domain
SQUID multiplexer developed at NIST and read out using the multi-channel electronics (MCE) developed at
the University of British Columbia. Following our progress in improving detector parameters uniformity across
the arrays and fabrication yield, our main effort has focused on improving detector arrays optical and noise
performances, in order to produce science grade focal planes achieving target sensitivities. We report on changes
in detector design implemented to optimize such performances and following focal plane arrays characterization.
BICEP2 has deployed a first 150 GHz science grade focal plane to the South Pole in December 2009.
We present a method of cross-calibrating the polarization angle of a polarimeter using Bicep Galactic observations.
Bicep was a ground based experiment using an array of 49 pairs of polarization sensitive bolometers
observing from the geographic South Pole at 100 and 150 GHz. The Bicep polarimeter is calibrated to ±0.01
in cross-polarization and less than ±0.7° in absolute polarization orientation. Bicep observed the temperature
and polarization of the Galactic plane (R.A = 100° ~ 270° and Dec. = -67° ~ -48°). We show that the
statistical error in the 100 GHz Bicep Galaxy map can constrain the polarization angle offset of Wmap W band
to 0.6° ± 1.4°. The expected 1σ errors on the polarization angle cross-calibration for Planck or EPIC are 1.3°
and 0.3° at 100 and 150 GHz, respectively. We also discuss the expected improvement of the Bicep Galactic
field observations with forthcoming Bicep2 and Keck observations.
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.
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.
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.
Bicep is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature
on the B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. Currently
in its third year of operation at the South Pole, Bicep is measuring the CMB polarization with unprecedented
sensitivity at 100 and 150 GHz in the cleanest available 2% of the sky, as well as deriving independent constraints
on the diffuse polarized foregrounds with select observations on and off the Galactic plane. Instrument
calibrations are discussed in the context of rigorous control of systematic errors, and the performance during the
first two years of the experiment is reviewed.
The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17° with angular resolution of 55' and 37' at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.
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