Search

Recent advances in the development of cryogenic particle detectors such as magnetic microcalorimeters allow the fabrication of sensor arrays with an increasing number of pixels. Since these detectors must be operated at the lowest temperatures, the readout of large detector arrays is still quite challenging. This is especially true for the ECHo experiment, which presently aims to simultaneously run 6,000 two pixel detectors to investigate the electron neutrino mass. For this reason, we developed a readout system based on a microwave SQUID multiplexer (μ MUX) that is operated by a custom software-defined radio (SDR) at room-temperature. The SDR readout electronics consist of three distinct hardware units: a data processing board with a Xilinx ZynqUS+ MPSoC; a converter board that features DACs, ADCs, and a coherent clock distribution network; and a radio frequency front-end board to translate the signals between the baseband and the microwave domains. Here, we describe the characteristics of the full-scale SDR system. First, the generated frequency comb for driving the μ MUX was evaluated. Subsequently, by operating the SDR in direct loopback, the crosstalk of the individual channels after frequency demultiplexing was investigated. Finally, the system was used with a 16-channel μ MUX to evaluate the linearity of the SDR, and the noise contributed to the overall readout setup. [ABSTRACT FROM AUTHOR]

Cryogenic microcalorimeters are key tools for high-resolution X-ray spectroscopy due to their excellent energy resolution and quantum efficiency close to 100%. Multiple types of microcalorimeters exist, some of which have already proven outstanding performance. Nevertheless, they cannot yet compete with cutting-edge grating or crystal spectrometers. For this reason, novel microcalorimeter concepts are continuously developed. One such concept is based on the strong temperature dependence of the magnetic penetration depth of a superconductor operated close to its transition temperature. This so-called λ -SQUID provides an in-situ tunable gain and promises to reach sub-eV energy resolution. Here, we present some design considerations with respect to the optimization of such a detector that are derived by analytic means. We particularly show that for this detector concept the heat capacity of the sensor should match the heat capacity of the absorber. [ABSTRACT FROM AUTHOR]

We present the calibration and data analysis of BULLKID, a cryogenic, low threshold particle detector for searches of low mass dark matter candidates and coherent neutrino on nucleus scattering (CE ν NS) events. The BULLKID detector is an array of 60 cubic particle absorbers made out of 0.34 g of silicon per cube, each one sensed by a kinetic inductance detector (KID). This paper describes the energy calibration of the detector as well as an evaluation of the background rate of the device when operated in an above-ground unshielded environment. By performing coincidence cuts on a cluster of 3x3 dice, the background rejection power of the design is demonstrated, allowing reach to a flat background down to a threshold of 160 eV. [ABSTRACT FROM AUTHOR]

Metallic magnetic calorimeters (MMC) are low-temperature particle detectors based on calorimetry. They typically operate at temperatures below 100 mK. They utilize a metallic paramagnetic temperature sensor to convert the temperature rise of an absorber, during the absorption of energetic particles, into a change in magnetic flux sensed by a superconducting quantum interference device (SQUID). Since the SQUID has a high sensitivity to magnetic signals, the MMC system is very sensitive to external magnetic field interference. The magnetic shielding effect of the MMC directly affects its detection capability. Therefore, the design of the MMC magnetic shield system is particularly important. In this study, a set of MMC magnetic shields is designed based on the principle of magnetic shielding. The design is optimized using the COMSOL magnetic field simulation module by varying relevant parameters, such as the thickness and height of the shields as well as the diameter of the radioactive source hole, which determines the magnetic shielding effect. Through the simulation, the optimized magnetic shielding device can reduce the magnetic field interference of 2–0.0264 nT. The value can be further reduced by one order of magnitude if a high-permeability material with superior performance is used. This research is instructive for the design of MMC magnetic shielding devices in subsequent experiments. [ABSTRACT FROM AUTHOR]

We are developing the Cryogenic AntiCoincidence detector (CryoAC) of the ATHENA X-IFU spectrometer. It is a TES-based particle detector aimed to reduce the background of the instrument. Here, we present the result obtained with the last CryoAC single-pixel prototype. It is based on a 1 cm2 silicon absorber sensed by a single 2 mm × 1 mm Ir/Au TES, featuring an on-chip heater for calibration and diagnostic purposes. We have illuminated the sample with 55Fe (6 keV line) and 241Am (60 keV line) radioactive sources, thus studying the detector response and the heater calibration accuracy at low energy. Furthermore, we have operated the sample in combination with a past-generation CryoAC prototype. Here, by analyzing the coincident detections between the two detectors, we have been able to characterize the background spectrum of the laboratory environment and disentangle the primary (i.e. cosmic muons) and secondaries (mostly secondary photons and electrons) signatures in the spectral shape. [ABSTRACT FROM AUTHOR]

The experimental detection of the CE ν NS allows the investigation of neutrinos and neutrino sources with all-flavor sensitivity. Given its large content in neutrons and stability, Pb is a very appealing choice as target element. The presence of the radioisotope 210 Pb (T 1 / 2 ∼ 22 yrs) makes natural Pb unsuitable for low-background, low-energy event searches. This limitation can be overcome employing Pb of archaeological origin, where several half-lives of 210 Pb have gone by. We present results of a cryogenic measurement of a 15 g PbWO 4 crystal, grown with archaeological Pb (older than ∼ 2000 yrs) that achieved a sub-keV nuclear recoil detection threshold. A ton-scale experiment employing such material, with a detection threshold for nuclear recoils of just 1 keV would probe the entire Milky Way for SuperNovae, with equal sensitivity for all neutrino flavors, allowing the study of the core of such exceptional events. [ABSTRACT FROM AUTHOR]

Nuclear physics has long played a central role in our efforts to better understand the natural world. Several experiments are currently well positioned to improve limits in searches for physics Beyond the Standard Model (BSM). Many experiments in nuclear physics have traditionally used semiconductor or scintillation detectors for particle detection, yet these face fundamental performance limitations that greatly restrict the sensitivity achievable. A new detector paradigm for charged particle detection could potentially open up orders of magnitude improvement in sensitivity in searches for BSM physics. We are working to achieve this by adapting Thermal Kinetic Inductance Detectors (TKIDs) for external charged particle detection. These cryogenic detectors are used in X-ray and gamma spectroscopy as well as dark matter searches and have been shown to have photon energy resolutions on the order of tens of eV. They can be multiplexed to create large area detectors. Thus far, however, TKIDs have not yet been developed for external (non-embedded) charged particle detection. Creating a TKID with a sensitivity of 100s of eV or better suitable for external charged particle detection would significantly impact the next generation of nuclear experiments, allowing orders of magnitude improvements in sensitivity. [ABSTRACT FROM AUTHOR]

Metallic magnetic calorimeters (MMCs) are particle detectors that combine ultra-high energy resolution with a predictable and smooth response based on the physics of paramagnetism. For best energy resolution, MMCs are read out with dc SQUID preamplifiers. Since the ac Josephson effect also makes dc SQUIDs broadband RF sources in the 1–100 GHz range, the SQUID can potentially excite RF modes of the MMC sensor, with negative consequences. The importance of this possibility is magnified in direct-coupled MMCs, where the MMC sensor is part of the SQUID loop to maximize performance. For these reasons, the RF behavior of MMC sensors must be investigated. In this report, we present the results of exploratory RF simulations of MMC sensor modes and damping, and we assess three approaches to damp the parallel-meander direct-coupled MMC without excessive noise increase. [ABSTRACT FROM AUTHOR]

Phonon-mediated Kinetic Inductance Detectors (KIDs) on silicon substrates have demonstrated both O (10) eV energy resolution and mm position resolution when used as particle detectors, making them strong candidates for instrumenting next-generation rare event experiments such as in looking for dark matter. Previous work has demonstrated the performance of an 80-KID array on a Si wafer; however, current energy resolution measurements show a ∼ 25 × difference between otherwise identical KIDs—between 5 and 125 eV on energy absorbed by the KID. Here, we use a first principles approach and attempt to identify the drivers behind the variation. In particular, we analyze a subset of 8 KIDs using the unique approach of pulsing neighboring KIDs to generate signals in the target. We tentatively identify differences in quality factor as the likely culprit for the observed differences. [ABSTRACT FROM AUTHOR]

BULLKID is an R&D project on a cryogenic particle detector to search for rare low-energy processes such as low-mass dark matter and neutrino coherent scattering off nuclei. The detector unit we are designing consists in an array of ~ 100 silicon absorbers sensed by phonon-mediated, microwave-multiplexed kinetic inductance detectors, with energy threshold below 100 eV and total target mass around 30 g. The single detector unit will be engineered to ensure a straightforward scalability to a future kg-scale experiment. [ABSTRACT FROM AUTHOR]

This Special Issue of the Journal of Low Temperature Physics contains original contributions to the I 18th International Workshop on Low Temperature Particle Detectors (LTD i I 18) i . The conference was co-hosted by Università di Milano-Bicocca and Istituto Nazionale di Fisica Nucleare (INFN) and took place from July 22, 2019, to July 26, 2019, in Milano, at Palazzo Lombardia (headquarters of the Lombardia region) in the Directional Center of Milano. The LTD-18 Local Organizing Committee is grateful to Università di Milano-Bicocca, INFN, Regione Lombardia, to the members of the LTD-18 Scientific Advisory Committee for their support to the workshop, and to our students for their enthusiastic help during the entire duration of the workshop. [Extracted from the article]

The ATHENA observatory is the second large class ESA mission to be launched on 2031 at L2 orbit. One of the two onboard instruments is X-IFU, a TES-based kilo-pixel array able to perform simultaneous high-grade energy spectroscopy (FWHM 2.5 eV@7 keV) and imaging over the 5′ field of view. The X-IFU sensitivity is degraded by primary particle background of both solar and galactic cosmic ray (GCR) origins, and by secondary electrons produced by primaries, interacting with the materials surrounding the detector: These particles cannot be distinguished by the scientific photons, thus degrading the instrument performance. Results from studies regarding the GCR component performed by Geant4 simulations address the necessity to use background reduction techniques to enable the study of several key science topics. This is feasible by combining an active Cryogenic AntiCoincidence detector (CryoAC) and a passive electron shielding to reach the required residual particle background of 0.005 cts/cm2/s/keV inside the 2–10 keV scientific energy band. The CryoAC is a four-pixel detector made of Si-suspended absorbers sensed by a network of IrAu TESes and placed at a distance < 1 mm below the TES array. Here we will provide an overview of the CryoAC program, starting with some details on the background assessment having impacts on the CryoAC design; then, we continue with its design concept including electronics and the Demonstration Model results, to conclude with programmatic aspects. [ABSTRACT FROM AUTHOR]

We present a status update on the development of a phonon-mediated particle detector using kinetic inductance detector (KID). The design is intended for O(1) kg substrate, using O(102) KIDs on a single readout line, to image the athermal phonon distribution at < 1 mm position resolution and O(10) eV energy resolution. The design specification is set by the need to improve position reconstruction fidelity while maintaining low energy threshold for future rare-event searches such as for low-mass dark matter. We report on the design, which shows negligible crosstalk and > 95% inductor current uniformity, using the coplanar waveguide feedline, ground shield, and a new class of KIDs with symmetric coplanar stripline (sCPS) inductor. The multiplexing is designed upon the frequency-geometry relation we develop for the sCPS KIDs. We introduce the fabrications of the Nb RF assessment prototypes and the high phonon collection efficiency Al-Nb devices. We achieve ≲ 0.07% frequency displacement on a 80-KID RF assessment prototype, and the result indicates that we may place more than 180 resonances in our 0.4 GHz readout band with minimal frequency misordering. The coupling quality factors are ∼ 105 as designed. Finally, we update our work in progress in fabricating the O(102) KID, bi-material, O(1) kg detectors, and the expected position and energy resolutions. [ABSTRACT FROM AUTHOR]

The ATHENA observatory is the second large-class ESA mission, in the context of the Cosmic Vision 2015-2025, scheduled to be launched on 2028 at L2 orbit. One of the two planned focal plane instruments is the X-ray Integral Field Unit (X-IFU), which will be able to perform simultaneous high-grade energy spectroscopy and imaging over the 5 arcmin FoV by means of a kilo-pixel array of transition-edge sensor (TES) microcalorimeters, coupled to a high-quality X-ray optics. The X-IFU sensitivity is degraded by the particle background, induced by primary protons of both solar and cosmic rays' origin and secondary electrons. A Cryogenic AntiCoincidence (CryoAC) TES-based detector, located $$<$$ 1 mm below the TES array, will allow the mission to reach the background level that enables its scientific goals. The CryoAC is a 4-pixel detector made of Silicon absorbers sensed by Iridium TESs. We currently achieve a TRL $$=$$ 3-4 at the single-pixel level. We have designed and developed two further prototypes in order to reach TRL $$=$$ 4. The design of the CryoAC has been also optimized using the Geant4 simulation tool. Here we will describe some results from the Geant4 simulations performed to optimize the design and preliminary test results from the first of the two detectors, 1 cm $$^{2}$$ area, made of 65 Ir TESs. [ABSTRACT FROM AUTHOR]

The HOLMES experiment will provide an important step forward in direct neutrino mass measurements with a calorimetric approach as an alternative to spectrometry. HOLMES will perform a calorimetric measurement of the energy released in the decay of $$^{163}$$ Ho and will deploy a large array of transition-edge sensor microcalorimeters with implanted $$^{163}$$ Ho nuclei. The resulting mass sensitivity could be as low as 0.4 eV, and it will also establish the potential of this approach to extend the sensitivity down to 0.1 eV and lower. [ABSTRACT FROM AUTHOR]

Calorimetric decay energy spectroscopy of electron-capture-decaying isotopes is a promising method to achieve the sensitivity required for electron neutrino mass measurement. The very low total nuclear decay energy $$(Q_\mathrm{EC}$$ $$<$$ 3 keV) and short half-life (4570 years) of $$^{163}$$ Ho make it attractive for high-precision electron-capture spectroscopy (ECS) near the kinematic endpoint, where the neutrino momentum goes to zero. In the ECS approach, an electron-capture-decaying isotope is embedded inside a microcalorimeter designed to capture and measure the energy of all the decay radiation except that of the escaping neutrino. We have developed a complete process for proton irradiation-based isotope production, isolation, and purification of $$^{163}$$ Ho. We have developed transition-edge sensors for this measurement and methods for incorporating $$^{163}$$ Ho into high-resolution microcalorimeters, and have measured the electron-capture spectrum of $$^{163}$$ Ho. We present our work in these areas and discuss the measured spectrum and its comparison to current theory. [ABSTRACT FROM AUTHOR]

Dome A in Antarctica, located at an altitude of 4093 m and with very low temperature in winter down to $$-$$ 83 $$^{\circ }$$ C, is an exceptionally dry site. Measurements of the atmospheric transmission in the range of 0.75-15 THz by a Far-infrared/THz Fourier transform spectrometer (FTS) strongly suggest that Dome A is a unique site for ground-based THz observations, especially for the 200- and 350-micron windows. A 5-m THz telescope (DATE5) is therefore proposed for Chinese Antarctic Kunlun Observatory. We are currently developing a THz superconducting imaging array (TeSIA) for the DATE5. The TeSIA will be working at the 350- $$\upmu $$ m window, with a pixel number of $$32 \times 32$$ and a sensitivity (NEP) of $$\sim $$ 10 $$^{-16}$$ W/Hz $$^{0.5}$$ . Ti transition-edge sensors with time-domain multiplexing and TiN microwave kinetic inductance detectors with frequency-domain multiplexing are both developed for the TeSIA. In this paper, detailed system designs and some measurement results will be presented. [ABSTRACT FROM AUTHOR]

We are developing a series of close-packed modular detector arrays for TIME-Pilot, a new mm-wavelength grating spectrometer array that will map the intensity fluctuations of the redshifted 157.7 $$\upmu $$ m emission line of singly ionized carbon ([CII]) from redshift $$z \sim 5$$ to 9. TIME-Pilot's two banks of 16 parallel-plate waveguide spectrometers (one bank per polarization) will have a spectral range of 183-326 GHz and a resolving power of $$R \sim 100$$ . The spectrometers use a curved diffraction grating to disperse and focus the light on a series of output arcs, each sampled by 60 transition edge sensor (TES) bolometers with gold micro-mesh absorbers. These low-noise detectors will be operated from a 250 mK base temperature and are designed to have a background-limited NEP of $${\sim }10^{-17}~ \mathrm {W}/\mathrm {Hz}^{1/2}$$ . This proceeding presents an overview of the detector design in the context of the TIME-Pilot instrument. Additionally, a prototype detector module produced at the Microdevices Laboratory at JPL is shown. [ABSTRACT FROM AUTHOR]

We present the latest update and progress on the future Japanese X-ray satellite mission Diffuse Intergalactic Oxygen Surveyor (DIOS). DIOS is proposed to JAXA as a small satellite mission, and would be launched with an Epsilon rocket. DIOS would carry on the legacy of ASTRO-H, which carries semiconductor-based microcalorimeters and is scheduled to be launched in 2016, in high-resolution X-ray spectroscopy. A 400-pixel array of transition-edge sensors (TESs) would be employed, so DIOS would also provide valuable lessons for the next ESA X-ray mission ATHENA on TES operation and cryogen-free cooling in space. We have been sophisticating the entire design of the satellite to meet the requirement for the Epsilon payload for the next call. The primary goal of the mission is to search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy by detecting redshifted emission lines from OVII and OVIII ions. The results would have significant impacts on our understanding of the nature of 'dark baryons,' their total amount and spatial distribution, as well as their evolution over cosmological timescales. [ABSTRACT FROM AUTHOR]

Characterization of the minute cosmic microwave background polarization signature requires multi-frequency, high-throughput precision instrument systems. We have previously described the detector fabrication of a 40 GHz focal plane and now describe the fabrication of detector modules for measurement of the CMB at 90 GHz. The 90 GHz detectors are a scaled version of the 40 GHz architecture where, due to smaller size detectors, we have implemented a modular (wafer level) rather than the chip-level architecture. The new fabrication process utilizes the same design rules with the added challenge of increased wiring density to the 74 TES's as well as a new wafer level hybridization procedure. The hexagonally shaped modules are tile-able, and as such can be used to form the large focal planes required for a space-based CMB polarimeter. The detectors described here will be deployed in two focal planes with seven modules each in the Johns Hopkins University led ground-based Cosmology Large Angular Scale Surveyor (CLASS) telescope. [ABSTRACT FROM AUTHOR]

The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe $$\sim $$ 70 % of the sky. A variable-delay polarization modulator provides modulation of the polarization at $$\sim $$ 10 Hz to suppress the 1/ f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that spans both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously detect two orthogonal linear polarizations. The use of single-crystal silicon as the dielectric for the on-chip transmission lines enables both high efficiency and uniformity in fabrication. Integrated band definition has been implemented that both controls the bandpass of the single-mode transmission on the chip and prevents stray light from coupling to the detectors. [ABSTRACT FROM AUTHOR]

The Atacama B-Mode Search (ABS) instrument is a cryogenic ( $$\sim $$ 10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the cosmic microwave background (CMB) at large angular scales ( $$40<\ell <500$$ ) to limit the B-mode polarization spectrum around the primordial B-mode peak from inflationary gravity waves at $$\ell \sim 100$$ . The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers. They are coupled to orthogonal polarizations from a planar ortho-mode transducer and observe at 145 GHz. ABS employs an ambient-temperature, rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move the signal band away from atmospheric 1 / f noise, allowing for the recovery of large angular scales. We discuss how the signal at the second harmonic of the HWP rotation frequency can be used for data selection and for monitoring the detector responsivities. [ABSTRACT FROM AUTHOR]

We present an overview of the design and status of the Polarbear-2 and the Simons Array experiments. Polarbear-2 is a cosmic microwave background polarimetry experiment which aims to characterize the arc-minute angular scale B-mode signal from weak gravitational lensing and search for the degree angular scale B-mode signal from inflationary gravitational waves. The receiver has a 365 mm diameter focal plane cooled to 270 mK. The focal plane is filled with 7588 dichroic lenslet-antenna-coupled polarization sensitive transition edge sensor (TES) bolometric pixels that are sensitive to 95 and 150 GHz bands simultaneously. The TES bolometers are read-out by SQUIDs with 40 channel frequency domain multiplexing. Refractive optical elements are made with high-purity alumina to achieve high optical throughput. The receiver is designed to achieve noise equivalent temperature of 5.8 $$\upmu $$ K $$_\mathrm{CMB}\sqrt{s}$$ in each frequency band. Polarbear-2 will deploy in 2016 in the Atacama desert in Chile. The Simons Array is a project to further increase sensitivity by deploying three Polarbear-2 type receivers. The Simons Array will cover 95, 150, and 220 GHz frequency bands for foreground control. The Simons Array will be able to constrain tensor-to-scalar ratio and sum of neutrino masses to $$\sigma (r) = 6\times 10^{-3}$$ at $$r = 0.1$$ and $$\sum m_{\upnu } (\sigma =1)$$ to 40 meV. [ABSTRACT FROM AUTHOR]

In this paper, we explore the possibility of using transition edge sensor (TES) detectors in multi-mode configuration in the focal plane of the Short Wavelength Instrument for the Polarization Explorer (SWIPE) of the balloon-borne polarimeter Large-Scale Polarization Explorer (LSPE) for the Cosmic Microwave Background (CMB) polarization. This study is motivated by the fact that maximizing the sensitivity of TES bolometers, under the augmented background due to the multi-mode design, requires a non-trivial choice of detector parameters. We evaluate the best parameter combination taking into account scanning strategy, noise constraints, saturation power, and operating temperature of the cryostat during the flight. [ABSTRACT FROM AUTHOR]

We present the design of MOCCA, a large-area particle detector that is developed for the position- and energy-resolving detection of neutral molecule fragments produced in electron-ion interactions at the Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg. The detector is based on metallic magnetic calorimeters and consists of 4096 particle absorbers covering a total detection area of $$44.8\,\mathrm {mm} \times 44.8\,\mathrm {mm}$$ . Groups of four absorbers are thermally coupled to a common paramagnetic temperature sensor where the strength of the thermal link is different for each absorber. This allows attributing a detector event within this group to the corresponding absorber by discriminating the signal rise times. A novel readout scheme further allows reading out all 1024 temperature sensors that are arranged in a $$32 \times 32$$ square array using only $$16+16$$ current-sensing superconducting quantum interference devices. Numerical calculations taking into account a simplified detector model predict an energy resolution of $$\Delta E_\mathrm {FWHM} \le 80\,\mathrm {eV}$$ for all pixels of this detector. [ABSTRACT FROM AUTHOR]

We have demonstrated in the laboratory multiple, fully functional, kilopixel, bolometer arrays for the upgraded instrument, the High-resolution airborne wideband camera plus (HAWC+), for the stratospheric observatory for infrared astronomy (SOFIA). Each kilopixel array consists of three individual components assembled into a single working unit: (1) a filled, Transition Edge Sensor (TES) bolometer array, (2) an infrared, back-termination, and (3) an integrated, two-dimensional superconducting quantum interference device (SQUID) multiplexer readout. Kilopixel TES arrays are directly indium-bump-bonded to a 32 $$\times $$ 40 SQUID multiplexer (MUX) circuit. In order to provide a fully superconducting pathway from the TES to the SQUID readout, numerous superconductor-to-superconductor interfaces must be made. This paper focuses on the fabrication techniques needed to create the superconducting path from the TES, out of the detector membrane, through the wafer, and to the SQUID readout. [ABSTRACT FROM AUTHOR]

We present results from laboratory detector characterizations of the first kilopixel BUG arrays for the High- resolution Wideband Camera Plus (HAWC+) which is the imaging far-infrared polarimeter camera for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our tests demonstrate that the array performance is consistent with the predicted properties. Here, we highlight results obtained for the thermal conductivity, noise performance, detector speed, and first optical results demonstrating the pixel yield of the arrays. [ABSTRACT FROM AUTHOR]

A performance evaluation of superconducting transition-edge sensors (TESs) in the environment of a pion beam line at a particle accelerator is presented. Averaged across the 209 functioning sensors in the array, the achieved energy resolution is 5.2 eV FWHM at Co $$K_{\alpha }$$ (6.9 keV) when the pion beam is off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of $$\pm $$ 0.04 eV is demonstrated for Fe $$K_{\alpha }$$ (6.4 keV) with in-situ energy calibration obtained from other nearby known X-ray lines. To achieve this small uncertainty, it is essential to consider the non-Gaussian energy response of the TESs and thermal cross-talk pile-up effects due to charged particle hits in the silicon substrate of the TES array. [ABSTRACT FROM AUTHOR]

The CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, whose second phase has been successfully finished in summer 2015, aims at the direct detection of dark matter particles. The intrinsic radiopurity of CaWO $$_4$$ crystals, the capability to reject recoil events from alpha-surface contamination, and the energy threshold were significantly improved compared to previous runs of the experiment. A moderate exposure of 29 kg-days acquired by one $$\sim $$ 250 g CaWO $$_4$$ detector provides competitive limits on the spin-independent dark matter particle-nucleon cross section and probes a new region of parameter space for dark matter particle masses below 3 GeV/c $$^2$$ . The potential for low-mass dark matter particle search can be further exploited by a new detector design planned for CRESST-III. We describe the experimental strategy for the near future and give projections for the sensitivity. [ABSTRACT FROM AUTHOR]

The determination of the neutrino mass is an open issue in modern particle physics and astrophysics. The direct mass measurement is the only theory-unrelated experimental tool capable to probe such quantity. The HOLMES experiment will measure the end-point energy of the electron capture decay of $$^{163}$$ Ho, aiming at a statistical sensitivity on the neutrino mass around 1 eV/c $$^2$$ . In order to acquire the large needed statistics by keeping the pile-up contribution as low as possible, 1000 transition edge sensors will be readout simultaneously with the frequency domain readout, a multiplexing technique where the multiplex factor is only limited by the bandwidth of the available commercial fast digitizers. We outline here the HOLMES project with its technical challenges, and its status and perspectives. [ABSTRACT FROM AUTHOR]

Superconducting/normal metal bilayers with tunable transition temperature are a critical ingredient to the fabrication of high-performance transition edge sensors. Popular material choices include Mo/Au and Mo/Cu, which exhibit good environmental stability and provide low resistivity films to achieve adequate thermal conductivity. The deposition of high-quality Mo films requires sufficient adatom mobility, which can be provided by energetic ions in sputter deposition or by heating the substrate in an e-beam evaporation process. The bilayer $$T_\mathrm{c}$$ depends sensitively on the exact deposition conditions of the Mo layer and the superconducting/normal metal interface. Because the individual contributions (strain, crystalline structure, contamination) are difficult to disentangle and control, reproducibility remains a challenge. Recently, we have demonstrated that low-energy ion-beam-assisted e-beam evaporation offers an alternative route to reliably produce high-quality Mo films without the use of substrate heating. The energy and momentum delivered by the ion beam provides an additional control knob to tune film properties such as resistivity and stress. In this report we describe modifications made to the commercial end-Hall ion source to avoid iron contamination allowing us to produce superconducting Mo films. We show that the ion beam is effective at enhancing the bilayer interface transparency and that bilayers can be further tuned towards reduced $$T_\mathrm{c}$$ and higher conductivity by vacuum annealing. [ABSTRACT FROM AUTHOR]

Micro-X is a NASA funded, rocket borne X-ray imaging spectrometer that uses transition edge sensors (TESs) to do high-resolution microcalorimetry. The TESs are cooled by an adiabatic demagnetization refrigerator, whose salt pill functions as a heat sink for the detectors. We have made a thermal model of the cryostat with SPICE for the purposes of understanding its behavior at low temperatures. Implementing modifications based on this model has further allowed us to cool the system down to a lower temperature than had previously been accessible and to improve its low-temperature hold time. These modifications include a variety of schemes for power through heat sinks and tweaking the conductance between the cold baths and the refrigerated hardware. We present an overview of the model and its constituent parameters, information about thermal modifications, and a summary of results from thermal tests of the entire system. [ABSTRACT FROM AUTHOR]

As part of the Q&U Bolometric Interferometer for Cosmology instrument targeting the cosmic microwave background primordial B-modes, two kilo-pixel focal planes have been designed for a NEP of $$\sim $$ $$3 \times 10^{-17}$$ W $$\sqrt{\mathrm {Hz}}$$ adapted for ground-based observations. Those pixels are transition edge sensors (TESs) made of voltage-biased NbSi thin films with a critical temperature $$T_\mathrm{c}$$ $$\sim $$ 400 mK and TiV absorbing grids. The TESs are coupled to a time-domain multiplexed electronics based on superconducting quantum interference devices and an additional SiGe cryogenic integrated circuit which provides a second multiplexing stage. In this paper, we briefly discuss the instrumental context of a quarter of focal plane (a 256-TES sub-array). Then, we present its typical manufacturing process and first test results at cryogenic temperature. [ABSTRACT FROM AUTHOR]

The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive receiver for the 6-m Atacama Cosmology Telescope (ACT) and measures the small angular scale polarization anisotropies in the cosmic microwave background (CMB). The full focal plane is composed of three detector arrays, containing over 3000 transition edge sensors (TES detectors) in total. The first two detector arrays, observing at 146 GHz, were deployed in 2013 and 2014, respectively. The third and final array is composed of multichroic pixels sensitive to both 90 and 146 GHz and saw first light in February 2015. Fabricated at NIST, this dichroic array consists of 255 pixels, with a total of 1020 polarization sensitive bolometers and is coupled to the telescope with a monolithic array of broad-band silicon feedhorns. The detectors are read out using time-division SQUID multiplexing and cooled by a dilution refrigerator at 110 mK. We present an overview of the assembly and characterization of this multichroic array in the lab, and the initial detector performance in Chile. The detector array has a TES detector electrical yield of 85 %, a total array sensitivity of less than 10 $$\upmu $$ K $$\sqrt{\text {s}}$$ , and detector time constants and saturation powers suitable for ACT CMB observations. [ABSTRACT FROM AUTHOR]

Micro-X is a NASA-funded sounding rocket-borne X-ray imaging spectrometer designed to enable high precision measurements of extended astrophysical systems. To perform high energy resolution measurements and capture unprecedented spectra of supernova remnants and galaxy clusters, Micro-X must maintain tight temperature control. One of the biggest challenges in payload design is to prevent heating of the detectors due to the vibrational loads on the rocket skin during launch. Several stages of vibration damping systems are implemented to prevent energy transmission from the rocket skin to the detector stage, each stage more rigid than the last. We describe recent redesign efforts to improve this vibration isolation by tuning the resonant frequencies of the various stages to minimize heating prior to the projected launch in 2016. [ABSTRACT FROM AUTHOR]

Kinetic inductance detectors (KIDs) are a promising technology for astronomical observations over a wide range of wavelengths in the mm and sub-mm regime. Simple fabrication, in as little as one lithographic layer, and passive frequency-domain multiplexing, with readout of up to $$\sim $$ 1000 pixels on a single line with a single cold amplifier, make KIDs an attractive solution for high-pixel-count detector arrays. We are developing an array that optimizes KIDs for optical frequencies near 100 GHz to expand their usefulness in mm-wave applications, with a particular focus on CMB B-mode measurement efforts in association with the QUBIC telescope. We have designed, fabricated, and tested a 20-pixel prototype array using a simple quasi-lumped microstrip design and pulsed DC reactive magnetron-sputtered TiN/Ti/TiN trilayer resonators, optimized for detecting 100 GHz (3 mm) signals. Here we present a discussion of design considerations for the array, as well as preliminary detector characterization measurements and results from a study of TiN trilayer properties. [ABSTRACT FROM AUTHOR]

Metallic magnetic calorimeters (MMCs) are low-temperature particle detectors that are typically read out by using superconducting quantum interference devices (SQUIDs). But since MMCs are sensitive to the input circuitry and the noise performance of the SQUID, the energy resolution of MMCs have not yet reached their fundamental limit. A possible solution to overcome present limits is to maximize the flux coupling by minimizing parasitic inductance in the input circuit. To show the suitability of this approach, we realized a 64 pixel MMC detector array with integrated dc-SQUID readout, i.e., detector and SQUID are on the same chip. We observed an influence of the power dissipation of the SQUID on the detector temperature. We achieved a baseline energy resolution of $$\Delta E_\mathrm {FWHM} = 25\,\mathrm {eV}$$ and $$\Delta E_\mathrm {FWHM} = 30\,\mathrm {eV}$$ for X-rays with energies up to $$6\,\mathrm {keV}$$ . [ABSTRACT FROM AUTHOR]

Andreev surface bound sates are known to exist on the boundaries of superfluid $$^3$$ He-B. However, the detailed nature of their interaction with bulk quasi-particles is not well known. In a manner similar to angle-resolved photo-emission spectroscopy, surface states can be probed by measuring the change in momentum of bulk quasi-particles scattered from the surface. In order to make such a measurement, we have designed a spatially resolved quasi-particle detector. The detector consists of an array of micro-machined resonators, which are sensitive to quasi-particle flux. The detector is based on previously developed micro-machined resonators, which have been successfully used to study superfluid $$^3$$ He-B and $$^4$$ He. Presented here is the design of the detector and the fabrication procedure. [ABSTRACT FROM AUTHOR]

Once that the focal plane of the HFI instrument of the Planck mission (launched in May 2009) has reached operational temperature, we have observed the thermal effect of cosmic ray interaction with the Planck satellite, located at Lagrangian point L2. When a particle hits a component of the bolometers (e.g.: thermometer, grid or wafer) composing the focal plane of HFI, a thermal spike (called glitch), due to deposited energy, is observed. Processing these data revealed another effect due to high energy cosmic ray particle showers: High Coincidence Events (HCE), composed of glitches occurring coincidentally in many detectors and with a temperature increase from nK to $$\upmu $$ K after the shower. A flux of about 100 HCE per hour has been calculated. Two types of HCE have been detected: fast and slow. For the first type, the untouched bolometers reach the same temperature as the touched ones in a few seconds which can be explained by a storage of the deposited energy in the stainless steel focal plane. The second type of HCE is not fully understood yet. These effects might be explained by extra conduction from the helium released from cryogenic surfaces, creating a temporary thermal link between the different stages of the HFI. [ABSTRACT FROM AUTHOR]

We are developing athermal-phonon mediated particle detectors that utilize microwave kinetic inductance detectors (MKIDs) as phonon sensors. MKIDs afford natural frequency domain multiplexing, which allows for massive substrates to be patterned with hundreds of sensors while keeping readout complexity to a minimum. Previously, our 2 cm $$\times $$ 2 cm $$\times $$ 1 mm proof-of-principle device utilized 20 MKIDs and, from the magnitude and timing of their response, we were able to reconstruct the position of a particle interaction to $$<$$ 1 mm. From this, we corrected for variations in detector response across the device and measured an energy resolution of $$\sigma _E = 0.55$$ keV at 30 keV. We have designed and fabricated a new 3-inch prototype device that utilizes 256 MKID sensors, and we present results from its initial testing. Applications include rare event searches, such as the direct detection of dark matter and neutrinoless double beta decay, as well as hard X-ray/soft $$\gamma $$ -ray astrophysics. [ABSTRACT FROM AUTHOR]

Following earlier presentations of arrays of high quality factor (Q $$>$$ 10.000) superconducting resonators in the MHz regime, we report on improvement of the packing density of resonance frequencies to 160 in the 1-3 MHz band. Spread in the spacing of resonances is found to be limited to 1 kHz (1 $$-$$ $$\sigma )$$ with the present fabrication procedure. The present packing density of frequencies and chip area approaches the requirements for the SAFARI instrument on the SPICA mission (in preparation). The a-Si:H dielectric layer in the planar S-I-S capacitors shows a presently unexplained apparent negative effective series resistance, depending on operating temperature and applied testing voltage. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search (CDMS) detectors measure ionization and athermal phonons in high purity germanium crystals to discriminate between nuclear recoils from dark matter candidates and radioactive backgrounds. In order to reach lower energy detection thresholds, the CDMSlite experiment operates the CDMS detectors with a larger voltage bias to increase the signal-to-noise ratio using the Neganov-Luke effect. Breakdown in those detectors was observed at fields of order 30 V/cm, but the reason for the breakdown is unknown. It is unclear if the breakdowns are due to surface leakage current, impact ionization in the bulk of the crystals, or some other effect due to the very low operating temperatures of the detectors. Germanium detectors used in gamma spectroscopy at 77 K are regularly operated with fields in excess of 1,000 V/cm. In order to understand the origin of breakdown in the CDMS detectors, a P-type Point Contact detector was equipped with transition edge phonon thermistors and operated at a base temperature of $$\sim $$ 30 mK. The linearity of the Neganov-Luke phonon amplification was studied and no sign of breakdown for biases up to 400 V was observed. This excludes impact ionization on neutral impurity states as the primary cause of the breakdown observed in the CDMSLite detectors. This demonstrates that the Neganov-Luke phonon amplification is a viable method for lowering the energy threshold in germanium detectors of masses of order 1 kg. [ABSTRACT FROM AUTHOR]

It has been recently demonstrated that superconducting transition edge-sensors behave as weak-links due to longitudinally induced superconductivity from the leads with higher $$T_c$$ . In this work we study the implication of this behaviour for transition-edge sensors (TES)-based bolometers and microcalorimeter under ac bias. The TESs are read-out at frequencies between 1 and $$5 \,\mathrm {MHz}$$ by a frequency domain multiplexer based on a linearised two-stage SQUID amplifier and high- $$Q$$ lithographically made superconducting $$LC$$ resonators. In particular, we focus on SRON TiAu TES bolometers with a measured dark noise equivalent power of $$3.2\times 10^{-19}\,{\mathrm{W}/\sqrt{\mathrm{Hz}}}$$ developed for the short wavelength band for the instrument SAFARI on the SPICA telescope. [ABSTRACT FROM AUTHOR]

Controlling the critical temperature ( $$T_{C}$$ ) of Ti/Au bilayers is vital in the development of practical TES detectors. Previously empirical studies have been done on aging effects in Ti/Au and other superconducting bilayers but no link with theory has been made. Here we attempt to explain the change in $$T_{C}$$ with a diffusion mechanism. The change in $$T_{C}$$ has been measured for a set of Ti/Au bilayer samples that have been given a variety of bake-out treatments, where we found a trend that can be partly explained by an inter-diffusion mechanism. With an empirical model based on diffusion a safe zone can be defined as a region of bake-out treatments, where the $$T_{C}$$ is not affected beyond the requirements. This will shine light on the bake-out and the storage condition boundaries of these detectors. [ABSTRACT FROM AUTHOR]

In this paper we present a new measurement setup, where a transition-edge sensor detector array is used to detect X-rays in particle induced X-ray emission (PIXE) measurements with a 2 MeV proton beam. Transition-edge sensors offer orders of magnitude improvement in energy resolution compared to conventional silicon or germanium detectors, making it possible to recognize spectral lines in materials analysis that have previously been impossible to resolve, and to get chemical information from the elements. Our sensors are cooled to the operation temperature ( $$\sim $$ 65 mK) with a cryogen-free adiabatic demagnetization refrigerator, which houses a specially designed X-ray snout that has a vacuum tight window to couple in the radiation. For the best pixel, the measured instrumental energy resolution was 3.06 eV full width at half maximum at 5.9 keV. We discuss the current status of the project, benefits of transition-edge sensors when used in PIXE spectroscopy, and the results from the first measurements. [ABSTRACT FROM AUTHOR]

We evaluated the current sensitivity of a quasi-one-junction SQUID (QOS) comparator with an input transformer at 4.2 K. A comparator based on a QOS is promising for constructing the single flux quantum (SFQ) readout circuits of an array system of multiple superconducting detectors.The QOS comparator is made of three Nb/AlO $$_x$$ /Nb Josephson junctions, senses an output signal of a superconductor detector, and generates the SFQ pulses.There are strong demands for enhancing the current sensitivity of the QOS comparator because an output current from superconducting detector typically remains at the magnitude of a few $$\upmu $$ A. We fabricated the QOS comparator with an input transformer using AIST Standard Process 2, where the critical current density of the Josephson junctions is chosen as high as 2.5 kA/cm $$^{2}$$ . We designed the input transformer to enhance the current sensitivity under the conditions of 200 $$\upmu $$ m $$\times $$ 200 $$\upmu $$ m in size and 20:1 in turn ratio. Consequently, we succeeded in reducing a gray zone width of the comparator, and achieved the current sensitivity of 400 nA at 4.2 K in the low frequency range. [ABSTRACT FROM AUTHOR]

We have fabricated multilayer readout wiring transition edge sensors (TES), which enable us to realize both large effective area and high-energy resolution for future X-ray astrophysical missions, such as diffuse intergalactic oxygen surveyor. By sandwiching a SiO $$_2$$ insulation layer between Al superconducting signal and return lines, self/mutual inductances and self fielding of bias leads are expected to be reduced. We fabricated $$4\times 4$$ and $$20\times 20$$ TES array on the multilayer wiring and tested their performance. Under the low temperature condition, several pixels in the TES array showed sharp superconducting transitions at around $$\sim $$ 300 mK. We also succeeded in detecting X-ray signals from the $$4\times 4$$ TES, contrary to the previous results of $$20\times 20$$ TES. We further investigated the reasons for the differences between the $$4\times 4$$ TES and the $$20\times 20$$ TES, and present future plans for improving the multilayer TES array fabrication. [ABSTRACT FROM AUTHOR]

Frequency division multiplexing (FDM) is a promising approach to read out a large format transition-edge sensor (TES) array for future astrophysical missions. We constructed a four channel FDM readout system using baseband feedback in the MHz band. We demonstrated the principle of our FDM method with an actual TES array, a multiplexing SQUID and LC band-pass filters under 100 mK. The resonant frequencies of LC filters were consistent with the design value with an accuracy of better than 3 %. We successfully obtained X-ray pulses from two TESs simultaneously but the energy resolution was degraded to about 100 eV at 5.9 keV and crosstalk effects were observed. The origin of the crosstalk effects is investigated by modified setups. Based on comparative experiments and numerical calculations, we conclude that the non-linearity of the SQUID is the cause of some of the crosstalk effects. Unlike the regular crosstalk effect from the adjoining channels, the crosstalk effect due to non-linearity observed in this paper occurs in all channels. Solving these problems will help us to obtain FDM readout with sufficient energy resolution. [ABSTRACT FROM AUTHOR]

We demonstrate a technique for creating high quality, large area tunnel junction barriers for normal-insulating-superconducting or superconducting-insulating-superconducting tunnel junctions. We use atomic layer deposition and an aluminum wetting layer to form a nanometer scale insulating barrier on gold films. Electronic transport measurements confirm that single-particle electron tunneling is the dominant transport mechanism, and the measured current-voltage curves demonstrate the viability of using these devices as self-calibrated, low temperature thermometers with a wide range of tunable parameters. This work represents a promising first step for superconducting technologies with deposited tunnel junction barriers. The potential for fabricating high performance junction refrigerators is also highlighted. [ABSTRACT FROM AUTHOR]

We describe a feasibility study of a frequency multiplexed read-out scheme for large number transition edge sensor arrays. The read-out makes use of frequency up- and down-conversion and RF-to-DC conversion with superconducting-isolator-superconducting tunnel junctions operating at GHz frequencies, in combination with an existing frequency multiplexed read-out at MHz frequencies. The read-out scheme can drastically reduce the wiring from room temperature to the cryogenic detectors, with a possibility to read-out and control as many as 30000 pixels over three coaxial lines within a bandwidth of 1 GHz. [ABSTRACT FROM AUTHOR]