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Register a new userSub-Kelvin cooling for two kilopixel bolometer arrays in the PIPER receiver
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The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne telescope mission to search for inflationary gravitational waves from the early universe. PIPER employs two 32x40 arrays of superconducting transition-edge sensors, which operate at 100 mK. An open bucket dewar of liquid helium maintains the receiver and telescope optics at 1.7 K. We describe the thermal design of the receiver and sub-kelvin cooling with a continuous adiabatic demagnetization refrigerator (CADR). The CADR operates between 70-130 mK and provides ~10 uW cooling power at 100 mK, nearly five times the loading of the two detector assemblies. We describe electronics and software to robustly control the CADR, overall CADR performance in flight-like integrated receiver testing, and practical considerations for implementation in the balloon float environment.
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In the field of astrophysics, the faint signal from distant galaxies and other dim cosmological sources at millimeter and submillimeter wavelengths require the use of high-sensitivity experiments. Cryogenics and the use of low-temperature detectors are essential to the accomplishment of the scientific objectives, allowing lower detector noise levels and improved instrument stability. Bolometric detectors are usually cooled to temperatures below 1K, and the constraints on the instrument are stringent, whether the experiment is a space-based platform or a ground-based telescope. The latter are usually deployed in remote and harsh environments such as the South Pole, where maintenance needs to be kept minimal. CEA-SBT has acquired a strong heritage in the development of vibration-free multistage helium-sorption coolers, which can provide cooling down to 200 mK when mounted on a cold stage at temperatures <5K. In this paper, we focus on the development of a three-stage cooler dedicated to the BICEP Array project led by Caltech/JPL, which aims to study the birth of the Universe and specifically the unique B-mode pattern imprinted by primordial gravitational waves on the polarization of the Cosmic Microwave Background. Several cryogenic receivers are being developed, each featuring one such helium-sorption cooler operated from a 4K stage cooled by a Cryomech pulse-tube with heat lifts of >1.35W at 4.2K and >36W at 45K. The major challenge of this project is the large masses to be cooled to sub-kelvin temperatures (26 kg at 250mK) and the resulting long cool-down time, which in this novel cooler design is kept to a minimum with the implementation of passive and active thermal links between different temperature stages. A first unit has been sized to provide 230, 70 and 2{mu}W of net heat lifts at the maximum temperatures of 2.8K, 340 and 250mK, respectively, for a minimum duration of 48 hours.
Advanced ACTPol is an instrument upgrade for the six-meter Atacama Cosmology Telescope (ACT) designed to measure the cosmic microwave background (CMB) temperature and polarization with arcminute-scale angular resolution. To achieve its science goals, Advanced ACTPol utilizes a larger readout multiplexing factor than any previous CMB experiment to measure detector arrays with approximately two thousand transition-edge sensor (TES) bolometers in each 150 mm detector wafer. We present the implementation and testing of the Advanced ACTPol time-division multiplexing readout architecture with a 64-row multiplexing factor. This includes testing of individual multichroic detector pixels and superconducting quantum interference device (SQUID) multiplexing chips as well as testing and optimizing of the integrated readout electronics. In particular, we describe the new automated multiplexing SQUID tuning procedure developed to select and optimize the thousands of SQUID parameters required to readout each Advanced ACTPol array. The multichroic detector pixels in each array use separate channels for each polarization and each of the two frequencies, such that four TESes must be read out per pixel. Challenges addressed include doubling the number of detectors per multiplexed readout channel compared to ACTPol and optimizing the Nyquist inductance to minimize detector and SQUID noise aliasing.
The next generation of cosmology space missions will be sensitive to parasitic signals arising from cosmic rays. Using a composite bolometer, we have investigated pulses produced by $alpha$ particles in order to understand the movement of energy produced by ionising radiation. Using a series of measurements at 100 mK, we have compared the typical fitting algorithm (a mathematical model) with a second method of pulse interpretation by convolving the detectors thermal response function with a starting profile of thermalised athermal phonons, taking into account the effects of heat propagation. Using this new fitting method, we have eliminated the need for a non-physical quadratic nonlinearity factor produced using more common methods, and we find a pulse form in good agreement with known aspects of thermal physics. This work is carried forward in the effort to produce a physical model for energy deposition in this detector. The modelling is motivated by the reproduction of statistical features in the experimental dataset, and the new interpretation of $alpha$ pulse shapes represents an improvement in the current understanding of the energy propagation mechanisms in this detector.
We describe the design and performance of polarization selective antenna-coupled TES arrays that will be used in several upcoming Cosmic Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully lithographic polarimeter arrays utilize planar phased-antennas for collimation (F/4 beam) and microstrip filters for band definition (25% bandwidth). These devices demonstrate high optical efficiency, excellent beam shapes, and well-defined spectral bands. The dual-polarization antennas provide well-matched beams and low cross polarization response, both important for high-fidelity polarization measurements. These devices have so far been developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave atmospheric windows for CMB observations. In the near future, the flexible microstrip-coupled architecture can provide photon noise-limited detection for the entire frequency range of the CMBPOL mission. This paper is a summary of the progress we have made since the 2006 SPIE meeting in Orlando, FL.
A new concept of bolometer arrays is used for the imager of PACS, one of the three instruments aboard the future Herschel space observatory. Within the framework of PACS photometer characterization, irradiation tests were performed on a dedicated bolometer array in order to study long-term and short-term radiation effects. The main objective was to study particles impacts on the detectors applicable to future observations in orbit and possible hard and/or soft curing to restore its performances. Cobalt-60 gamma ray irradiations did not show significant degradation, so we mainly focused on single events effects (SEE). Protons and alphas irradiations were then performed at the Van de Graaf tandem accelerator at the Institut de Physique Nucleaire (IPN, Orsay, France), respectively at 20MeV and 30MeV. Observation showed that the shape of signal perturbations clearly depends on the location of the impacts either on the detector itself or the read-out circuit. Software curing has then to be anticipated in order to deglitch the signal. This test gives also a unique opportunity to measure some parameters of the detector: electrical crosstalk and thermo- electrical time constant. However a detailed bolometer model is necessary to understand the contribution of the thermal response in relation with the electrical response. It will be the second step of our study. Finally the complete radiation evaluation proved that this detector can be used in spatial experiments.
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