Design and Fabrication Highlights Enabling a 2 mm, 128 Element Bolometer Array for GISMO

The Backshort-Under-Grid (BUG) superconducting bolometer array architecture is intended to be highly versatile, operating over a large range of wavelengths and background conditions. To validate the basic array design and to demonstrate its applicability for future kilopixel arrays, we will demonstrate a 128-element bolometer array optimized for 2 mm wavelength using a new Goddard Space Flight Center instrument, GISMO (Goddard IRAM Superconducting 2-Millimeter Observer). The design considerations unique to GISMO and laboratory experimental results will be discussed.      

Antenna-Coupled Bolometer Arrays for Measurement of the Cosmic Microwave Background Polarization

We are building antenna-coupled Transition Edge Sensor bolometer arrays to measure the polarization of the cosmic microwave background. 217 GHz prototype pixels have previously been characterized and showed promising performance (Myers et al. in Appl. Phys. Lett. 86:114103, [2005]). Our design uses a double slot dipole antenna and an integrated microstrip band defining filter. New devices have been tested which include on-chip test structures to improve our understanding of detector performance and guide future development. In parallel with this, large arrays of bolometers based on the prototype pixel design have also been constructed. The array pixels are a heterogeneous mixture of single band pixels at 90 GHz, 150 GHz, and 220 GHz and now incorporate dual-polarization antennas (Chattopadhyay and Zmuidzinas in IEEE Trans. Antennas Propag. 46:736, [1998]). Preliminary results from optical testing of array pixels are presented. These bolometer arrays will be used in the upcoming CMB polarization experiment Polarbear.      

Design and Expected Performance of GISMO-2, a Two Color Millimeter Camera for the IRAM 30 m Telescope

We present the main design features for the GISMO-2 bolometer camera, which we build for background-limited operation at the IRAM 30 m telescope on Pico Veleta, Spain. GISMO-2 will operate simultaneously in the 1 and 2 mm atmospherical windows. The 1 mm channel uses a \(32 \times 40\) TES-based backshort under grid (BUG) bolometer array, the 2 mm channel operates with a \(16 \times 16\) BUG array. The camera utilizes almost the entire full field of view provided by the telescope. The optical design of GISMO-2 was strongly influenced by our experience with the GISMO 2 mm bolometer camera, which is successfully operating at the 30 m telescope. GISMO is accessible to the astronomical community through the regular IRAM call for proposals.     

Norton-Corrected Measurement of Complex Impedances of a Large Format Bolometer Array

We report on our efforts to measure simultaneously a well-calibrated complex impedance of a large number of detectors in a long wavelength bolometer array. The array is described in other presentations. A method for correcting the complex impedance measurements of bolometers and calorimeters has been presented by Lindeman et al. (Rev. Sci. Instrum. 78:043105, [2007]) using a Thévenin equivalent circuit to represent the bias network. We have built on this method for superconducting bolometers with a Norton equivalent circuit and have used it to improve our impedance data. We further describe our method for extracting a Norton-corrected complex impedance as a function of frequency from a stream of multiplexed time-ordered data. This method is well-suited to producing simultaneous complex impedance measurements for a large number of detectors.      

High-Magnetic-Field XMCD as a Novel Tool for the Study of Valence Fluctuation Phenomena—Application to Eu-based Intermetallic Compounds

X-ray magnetic circular dichroism (XMCD) in Eu-based valence fluctuating compounds, EuNi₂(Si_1?x Ge _x )₂ (x=0.82, 0.85) and EuNi₂P₂ are investigated at high magnetic fields up to 40 T. Distinct two XMCD peaks corresponding to different valence states, i.e., Eu²⁺ and Eu³⁺ states are observed in EuNi₂(Si_1?x Ge _x )₂ (x=0.82) and EuNi₂P₂ at the L absorption edges (2p→5d). This suggests that the Eu 5d electrons are magnetically polarized in the both valence states. Since Eu³⁺ state has nonmagnetic ground state J=0, where J is total angular momentum, finite XMCD of Eu³⁺ state can be closely related to the magnetic polarization of the conduction electrons that is induced by the local magnetic moments of Eu²⁺ (J=7/2) state through the strong hybridization.     

Empirical likelihood confidence intervals for the endpoint of a distribution function

Estimating the endpoint of a distribution function is of interest in product analysis and predicting the maximum lifetime of an item. In this paper, we propose an empirical likelihood method to construct a confidence interval for the endpoint. A simulation study shows the proposed confidence interval has better coverage accuracy than the normal approximation method, and bootstrap calibration improves the accuracy.     

Evidence of Two-Dimensional Weak Localization in Polycrystalline SnO2 Films by High Field Magnetoconductance Study

We focus in this article on high field magnetoconductance results obtained on SnO₂ polycrystalline (cassiterite) films. The high field magnetoconductance is found to be in agreement with the magnetoconductance universal behavior due to weak localization in two dimensions as suggested by Zduniak et al. (Phys. Rev. B 56: 1996, 1997).     

Design and Realization of the Control and Measurement System of the Wuhan Pulsed High Magnetic Field Facility

A user-friendly Control and Measurement System (CMS) is designed and realized at the Wuhan High Magnetic Field Center (WHMFC). Structure and functions of the CMS system are described in detail. Three kernel parts of CMS are discussed. The success of the comprehensive system test shows that the CMS is effective and reliable.     

Design of the Cryogen-Free Cryogenic System for the CUORE Experiment

We present here the final design of the cryogenic system where the CUORE detector will be installed in 2010. It is a large cryogen-free cryostat cooled by pulse tubes and by a high-power dilution refrigerator. To avoid radioactive background, about 15000 kg of lead will be cooled to below 1 K and only few construction materials are acceptable. The detector assembly will have a total mass of about 1500 kg and must be cooled to less than 10 mK in a vibration-free environment. We discuss the adopted technical solutions, the results of the preliminary thermal analysis of the system, and its expected performance.      

A Theoretical Study of the Pressure for Liquid Metal Infiltration of a Fiber Preform

A theoretical model has been established for calculating the infiltration pressure of metal melt into the preform of ceramic fibers according to the basic principle of hydromechanics. There are three forces acting on the infiltration process in the model, i.e. viscous friction, capillary force, and gravity The effects of the volume fraction of fibers (Vf) and infiltrating depth on the infiltration pressure are discussed. The results show that the infiltration pressure increases with the increase of fiber volume fraction and infiltration depth. There is a linear relationship between infiltration pressure and infiltiation depth. The effect of gravity on the infiltration pressure can be ignored     

An Asymmetrical Permanent Magnet Guideway Design for the High Temperature Superconducting Maglev Curve

An asymmetrical permanent magnet guideway (PMG) design is considered for the high temperature superconducting (HTS) Maglev during traveling on a curved path. This translationally asymmetrical PMG design can produce a better guidance performance, which cannot be provided by the common translationally symmetrical PMG design. The additional guidance improvement is attributed to its asymmetrical magnetic field distribution. The outside part of the asymmetrical PMG has more magnetic material than the inside part, so that the outside magnetic field density is enhanced or becomes a multi-pole distribution. These two effects result in a larger guidance force and a better curve negotiation ability. Above the asymmetrical curved PMG, the HTS Maglev vehicle system can overcome larger centrifugal forces and run with a smaller or even zero lateral displacement. Moreover, this asymmetrical PMG design is helpful to realize the “straight line to curve to straight line” running environment. The improvement effect and running feasibility of the asymmetrical PMG is calculated and proven for future use in HTS Maglev curves.     

Application of Acoustic Emission to the Study on Cathodic Polarization and SCC for High Strength Steels

The ambiguous effect of cathodic polarization onSCC of two high strength steels in 0.1 M Na_2HPO_4 and0.1 M NaNO_3 has been investigated by means of meas-uring electric resistance(R)and recording acoustic emis-sion(AE)signals simultaneously.Results showed that AEsensitivity strongly depends on K value in different solu-tions.Both anodic and cathodic polarization can acceler-ate crack growth rate at high K values,but it appears thatthere are only subtle differences in their AEcharacteristics.AE signals only reflect the macroprocessesof crack growth rather than the elementary ones and cannot be used for identification of the micro-mechanisms ofSCC.     

Electrical and Thermal Characterization of Membrane-Isolated, Antenna-Coupled, TES Bolometers for the SPIDER Experiment

We have fabricated and measured the thermal and DC electrical properties of transition-edge sensing (TES) bolometers to be employed on the SPIDER experiment, a balloon-based observatory for studying the polarization of the cosmic microwave background (CMB). The bolometers consist of Al and Ti thermistors in series and a termination resistor which couples to an on-chip, polarization sensitive, 150 GHz slot-array antenna through a superconducting microstrip transmission line. Several important parameters were measured. Transition temperature measurements were performed by measuring the Johnson noise in the Ti thermistor. Current-voltage characteristic measurements were performed at various temperatures allowing for the deduction of the thermal conductance and the temperature coefficient of resistance. Electrical noise equivalent power was measured to sub-Hertz frequencies. Finally, the time constant of the bolometers was measured within the Al and Ti transitions where electrothermal feedback speeds up the bolometer response compared with the natural time constant measured just above the Ti transition temperature. The results of these measurements are within the design specifications for SPIDER.      

Dynamic Simulation of High Temperature Superconductors Above a Spinning Circular Permanent Magnetic Guideway

Before a high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle system can be fully applied and operational, the study of its dynamic characteristics is necessary. With the developed HTS Maglev dynamic measurement system (SCML-03), with a circular permanent magnet guideway (PMG) of 1.5 m in diameter, the vehicle’s translational motion above a PMG can be effectively simulated with the PMG allowed to rotate freely. Levitation force measurements of a high temperature superconductor (HTSC) array of seven YBa₂Cu₃O_7−x bulks were carried out above regular (linear) and a simulated (circular) PMG. The levitation force above a linear PMG segment and a circular PMG segment in the static state is found to be in good agreement with each other. The levitation force in the dynamic state is found to slowly attenuate since the presence of a rotating circular PMG below the HTS array is found to be analogous to the application of an AC external magnetic field.     

Determination of the Photon Impact Position within a DROID

Distributed read-out imaging detectors (DROIDs) combine a good energy resolution with a high position resolving power. Therefore they are promising candidates to build cameras with a huge detection area. A new method is proposed to determine the photon energy and impact position from the two signals of a one-dimensional DROID. For this purpose the diffusion equation was solved for asymmetric devices with arbitrarily trapping. The new method is then applied to fit the experimental data obtained from the illumination with soft X-ray of a 400 μm long Ta absorber strip with one Ta/Al read-out STJ at each end.      

Theoretical Analysis of Responsivity of a High Temperature Superconductor (HTSC)—Hot Electron Far Infrared Bolometer (HEFIB)

The use of hot electron phenomena is very attractive from the point of view of making fast, high performance infrared detectors for the giga hertz – tera hertz frequency range. Low temperature superconductors at present provide efficient materials in this area but with the constraint of using nano meter thin films and milli Kelvin operating temperatures. This paper explores the possibility of exploiting high temperature superconductor materials for the hot electron far infrared bolometer, using 77 K as the operating temperature and micron thick films. Two temperature (electron and phonon) time dependent heat transfer equations involving electron and phonon interactions within the sensor lattice and the heat exchange with the substrate are developed and solved. A detailed mathematical analytic expression for the responsivity is presented. Computational analysis of responsivity choosing various combinations of involved parameters is carried out. Some important results for a 1 thick sensor of 1 mm × 1 mm crosssectional area are presented.     

Positron Study of Origin of Thermoelastic MartensiteStabilization for a Cu-Zn-Al Alloy

A series of Cu-23Zn-10Al (at pct) alloy specimens subjected to different heat-treatment processes have been studied by means of Doppler broadening technique of positron annihilation combined with mechanical test. Results show that the mechanism of quenched-in vacancies, instead of the other suggested ones, plays a dominant role in thermoelastic martensite stabilization of Cubased shape memory alloy. Knowing the character of the movement of quenched-in vacancies and eliminating them as rapidly as possible are the basis for further optimizing heat-treatment process to obtain desired shape memory performance     

The Characteristics of the Superconducting and Magnetic Phases in the Polycrystalline Samples of Ruthenocuprates of Nominal Compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8−δ

The temperature dependencies of the resistivity for the superconducting ruthenocuprates of nominal compositions RuSr₂GdCu₂O₈, Ru_0.98Sr₂GdCu₂O₈ and Ru_0.5Sr₂GdCu_2.5O_8?δ were examined for the magnetic field dependent characteristics of the superconducting transitions. The effect of the insignificant diminishing of the Ru/Cu ratio in parent RuSr₂GdCu₂O₈ was confirmed as relevant for the stabilisation of the superconducting phase. Noted differences in the compared characteristics are interpreted for possible inhomogeneous nucleation of the superconducting phase in the parent ruthenocuprate. The phase anisotropy in RuSr₂GdCu₂O₈ and Ru_0.98Sr₂GdCu₂O₈, in presence of the compounds Ru magnetism, appears to be a cause of a significant softening of the H _c2(T) phase line. An anomalous lowering of the magnetoresistivity was observed in the approx. 10 K range above the onset of the superconducting transition, which may suggest the presence of enhanced superconducting fluctuations in the samples. The positive magnetic field shift of the temperatures, which limit the magnetoresistivity and the specific heat signatures of the magnetic ordered state of the Ru sublattice, suggests probing the influence of the ferromagnetic Ru interactions in an effective metallic-like conduction channel present in the samples. Superconducting characteristics of the Ru_0.5Sr₂GdCu_2.5O_8?δ reveal a significant contribution of the Gd paramagnetic signal at low temperatures, interpreted for the presence of a significant anisotropy of the superconducting phase. It is concluded that the Ru–Cu substituted phases of ruthenocuprates may present an opportunity to investigate the effectively anisotropic superconducting phase despite its comparatively high T _c in the compounds related to the 123-type cuprate superconductor.     

Development of High Count-Rate Digital Processing System with SpaceWire for TES-Calorimeter Array

A digital processing system for a TES microcalorimeter array is being developed based on “SpaceWire” interface. In this system, we introduced a trigger logic which can handle double-pulse events due to high count rate in future X-ray missions and several application on the ground experiments. The detailed design and performance of this system is described.