Fabrication of Cryogenic Readout Circuits with n-type GaAs-JFETs for Low Temperature Detectors

We present the design and fabrication of cryogenic readout integrated circuits (ROICs) for Superconducting Tunneling Junctions using the SONY n-type GaAs-JFETs, which have good current-voltage characteristics and low noise performance even at <1 K. In order to fabricate the ROICs, we have designed simple GaAs-JFET amplifiers based on the measurement results of the GaAs-JFETs at <4.2 K: source follower amplifier, common source amplifier, and two types of cascode amplifiers. The obtainable gain of the cascode active load amplifiers is >100. These amplifiers were fabricated with the other circuit elements as an integrated circuit. We also show initial test results of the cascode active load amplifier.     

Superconducting NbN Thin-Film Nanowire Detectors for Time-of-Flight Mass Spectrometry

Superconducting nanowire detectors (SND) have been applied for time-of-flight mass spectrometry (TOF-MS) for the first time. In this study, we used the SND, which consists of a very thin niobium nitride (NbN) film having a nanowire meander pattern with a thickness of 6.8 nm and a width of 200 nm on a MgO substrate. The experiments were carried out for Angiotensin I and bovine serum albumin (BSA). These biomolecules were ionized by laser radiation with matrix-assisted laser desorption ionization (MALDI). The ions were accelerated by a static high voltage of 17.5 kV, and incident on the NbN meander, which is dc-biased below a superconducting critical current (I _c). It was found that the output pulses have a rise time of about 640 ps, which is extremely faster than superconducting tunnel junction (STJ) detectors, and a fall time of about 50 ns. Moreover, we investigated the bias current dependence of output pulses, and confirmed that molecules can be detected even for bias currents of about 50% of I _c.      

Detector Development for the Next Phases of the Cryogenic Dark Matter Search: Results from 1 Inch Ge and Si Detectors

The Cryogenic Dark Matter Search (CDMS) experiment is searching for Weakly Interacting Massive Particles (WIMPs) using detectors with the ability to discriminate between candidate (nuclear recoil) and background (electron recoil) events by measuring both phonon and ionization signals from recoils in the detector crystals. As CDMS scales up to greater WIMP sensitivity, it is necessary to increase the detector mass and further improve background discrimination. CDMS is engaged in ongoing fabrication and development of new detector designs in order to meet these criteria for the proposed SuperCDMS experiment. Thicker detector prototypes have been produced with new photolithographic masks. These masks have greater surface coverage of the quasi particle trap and transition edge sensor system to provide superior athermal phonon collection. Results from continuing laboratory tests are presented which already indicate improvement in discrimination parameters.      

Realization of Submillimeter-Wave Imaging Array with Superconducting Direct Detectors

Using nine element superconducting direct detectors, or SIS photon detectors, we have fabricated a submillimeter-wave astronomical imaging array for a ground-based submillimeter-wave telescope in Atacama Desert in Chile. We call the observing system SISCAM-9, the superconductive imaging submillimeter-wave camera with nine detector elements. SISCAM-9 is the first astronomical instrument using superconducting direct detectors successfully operated on submillimeter-wave telescope.      

Recent Activities of TIPC on Cryogenic Systems Used for Superconducting Accelerators in China

With the requirement of higher beam energy and luminosity, the cryogenic technologies are applied more and more widely in accelerator facilities. As a main research entity on cryogenics in China, Technical Institute of Physics and Chemistry (TIPC) makes significant contributions to the construction of cryogenic systems for several superconducting accelerators in China, i.e. the upgrade of the Beijing Electron-Positron Collider (BEPCII), the Shanghai Synchrotron Radiation Facility (SSRF) and the Peking University Free-Electron Laser Facility (PKU-FEL). In this paper the cryogenic systems for BEPCII, SSRF and PKU-FEL are introduced briefly, and our recent activities for these accelerators are described.     

Fabrication of a Thermally Isolated and Pre-Amplified Transistor Module with Polyimide Micro-Wires for Cryogenic Detectors

We report a pre-amplifying junction field effect transistor (JFET) module on a chip for cryogenic applications such as bolometer and X-ray microcalorimeter. In order to maintain the optimum performance of the JFETs at 130 K, the module has built-in aluminum micro-heaters while the JFETs are thermally isolated from a heat sink. The thermal isolation is achieved by suspending a micromachined silicon support platform (6 μm thick) with polyimide wires. A layer of aluminum electrodes is patterned on top of the polyimide wires for electrical contacts and on top of the silicon platform for the heaters. This process involves reactive-ion-etching (RIE) of silicon and polyimide, patterning of aluminum electrodes over the polyimide, back side deep-reactive-ion-etching (DRIE) of silicon, and releasing of the modules. In this paper, we describe a micromachining process of the JFET modules on silicon-on-insulator (SOI) wafers.      

Calibration System with Modulated Polarization Source for Superconducting Detectors at 0.1 K

We developed a calibration system with a modulated polarization source for superconducting detectors at the 0.1-K stage in a dilution cooler. Our target application for this system is detector calibration for observations of the cosmic microwave background polarization. For this application, the calibration system is required to generate a well-characterized polarization signal in a wide frequency range; e.g., 20–300 GHz. The calibration system is attached at the bottom of the 0.1-K stage. Radio absorbers, which are attached to the inner wall of a cylindrical metal shield, emit unpolarized black-body radiation (4.5 K). The radiation reflects off an aluminum mirror at 120 K, which induces a linearly polarized component because of the finite emissivity of the mirror; the magnitude of the polarization is 60 mK in this configuration. The axis of polarization can be varied by rotation of the mirror. Therefore, the detectors measure the modulated polarization; however, unpolarized radiation into the detector is maintained constant. We succeeded in cooling the system properly. The sample stage for setting the detector achieved a temperature below 0.1 K under the 5 K load condition (some of the radiation from the absorbers and the mirror emission, 0.5 K). High-frequency components of emission from the mirror are shielded by using two thermal filters: polytetrafluoroethylene and nylon 66.     

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.      

Properties of Superconducting Rhenium as an Absorber for Magnetic Calorimeters

A still puzzling problem in the development of low temperature micro-calorimeters for the measurement of the ¹⁸⁷rhenium β-spectrum is the understanding of the thermalization of energetic electrons in the superconducting rhenium absorber. We studied metallic magnetic calorimeters (MMC) with single crystal rhenium absorbers and paramagnetic Au:Er temperature sensors. The energy released into the detector leads to a change of magnetization of the paramagnetic sensor located in a weak magnetic field. A SQUID with meander shaped inductance is used to read out this change. This setup allows the study of several properties of the superconducting absorber. The transition to the superconducting state is studied by measuring the magnetic flux expelled by the rhenium sample. The resistivity of rhenium above T _c can be estimated from the measurement of the spectral power density of the Johnson noise. Furthermore the quasiparticle lifetime can be investigated through the analysis of the shape of detector signals caused by intrinsic β-decays and the absorption of X-rays. We present the data obtained in these experiments and discuss the physical quantities which can be derived from these.      

Development of Decay Energy Spectroscopy for Radionuclide Analysis Using Cryogenic 4π Measurements

We report the recent progress in the development of decay energy spectroscopy for radionuclide analysis using a metallic magnetic calorimeter. In the present analysis, sample radionuclides were completely enclosed by a 4π steradian absorber. The use of a 4π absorber composed of gold foil guarantees that the total energy associated with radioactive decay is converted into thermal energy in the absorber. A paramagnetic temperature sensor was attached to the absorber to accurately measure the temperature change due to radioactive decay. The plutonium isotopes ²³⁸Pu, ²³⁹Pu, and ²⁴⁰Pu were readily identified in the decay energy spectrum because each isotope creates a single peak at its characteristic Q value. Two clear peaks were observed for ²³⁹Pu and ²⁴⁰Pu, and a 6.3?keV FWHM was obtained. The energy resolution of the method was affected by the low-energy tail of the spectrum at the left-hand side of the peaks. A 4.1?keV FWHM of a Gaussian fit was obtained for the right-hand side of the peak. Slow heat release to the absorber due to heat flow mechanisms is discussed to explain the low-energy tailing effect.     

Development of Micro-SQUID Magnetometers for Investigation of Quantum Tunneling of Magnetization in Nanometer-Size Magnetic Materials

We report development of micro superconducting quantum interference device (μ-SQUID) magnetometers for investigation of quantum tunneling of magnetization in μm- and nm-size magnetic materials. Both high- and low-temperature superconductor (HTS and LTS) based μ-SQUID magnetometers were fabricated and a three dimensional magnetic coil system was constructed for this purpose. The HTS-μ-SQUIDs with a hole of 4×9 μm² work at temperatures between 4.2 and 70 K and in magnetic fields up to 120 mT. A magnetization measurement of a ferrimagnetic micro-crystal was carried out at 35 K with an accuracy of 10^?9 emu. The development of LTS-μ-SQUIDs has been started in order to study much smaller magnetic materials in a mK temperature range. We present a preliminary result on the LTS-μ-SQUID with a hole of 1×1 μm². The critical current as a function of applied magnetic field shows the SQUID modulation at 4.2 K and up to 30 mT. The heat release associated with the present measurement method is estimated to be on the order of several microwatts.     

Flux Concentrator Optimization of PMG for High-Temperature Superconducting Maglev Vehicle System

The permanent magnetic guideway (PMG) composed of permanent magnet (PM) and steel is developed under flux concentration principle, which is the crucial component of high-temperature superconducting (HTS) maglev vehicle system. Optimum PMG design is an effective way to increase levitation force and associated stiffness for improving the load capability of HTS maglev vehicle. In order to realize higher vertical field component B _z in upper surface, three PMG demonstrators with three different forms of flux concentrator are fabricated with same volume of magnet. The levitation performances of onboard HTS bulks array over them are studied. The experimental results indicate that the PMG with a permanent magnet as the flux concentrator would produce biggest levitation force, levitation stiffness and trapped flux when interacting with HTS superconductor.     

Superconducting MgB2 Thin Film Detector for Neutrons

The superconducting neutron detector using high-quality ¹⁰B-enriched MgB₂ thin films at higher operating temperatures has been proposed, where a resistance change induced by the nuclear reaction of neutron and ¹⁰B in MgB₂ is used to detect a neutron. Cold neutrons from a nuclear research reactor irradiated the MgB₂ detector, and the output voltage was clearly observed through a low-noise amplifier by using a digital oscilloscope. The out-of-equilibrium thermodynamics was investigated by means of the time-dependent Ginzburg-Landau equations by using the Earth Simulator.      

Development of Ultra-Low Noise HEMTs for Cryoelectronics at ≤4.2 K

We report on DC and noise characteristics at 4.2 K of High Electron Mobility Transistors (HEMTs) which have been realized at LPN/CNRS. This work is aimed to develop high performance, low-power, low-frequency noise and low-temperature field-effect transistors for the future cryoelectronics. A high quality two-dimensional electron gas (2DEG) based on AlGaAs/GaAs heterostructure has been used to realize appropriately designed HEMTs with different gate configurations. With these transistors, we have obtained, for example, a transconductance of about 100 mS and a voltage gain of 26 with a power dissipation of less than 100 μW at 4.2 K; and a corresponded equivalent input voltage noise of 1.2 nV/Hz^1/2 at 1 kHz and as low as 0.12 nV/Hz^1/2 at 100 kHz.     

Development of a Digital Signal Readout System for Large TES Arrays

We are developing a digital signal readout system for arrays of high-resolution gamma and fast-neutron detectors based on superconducting transition edge sensors (TESs). The readout system allows for real time data acquisition and analysis at count rates exceeding 100 Hz for pulses with several ∼ms decay times with minimal loss of energy resolution compared to optimum filtering. This digital signal processing system had originally been developed for gamma-ray analysis with HPGe detectors, and we have modified the hardware and firmware to accommodate the slower TES signals. Parameters of the filtering algorithm have been optimized to maximize either resolution or throughput. Here we present a summary of the digital signal processing hardware and discuss its initial performance.      

Development and Characterization of Microcalorimeters for a Next Generation 187Re Beta-Decay Experiment

It has been demonstrated in the past that observing the β-decay spectrum of ¹⁸⁷Re with microbolometers provides a suitable method to determine the mass of the electron anti-neutrino from β-endpoint measurements. In a first step, with the experiment MIBETA a sensitivity of m _νe≤15 eV/c² was achieved. To compete with the sensitivity of m _νe≤2.2 eV/c² established by the Mainz/Troitsk tritium β-decay experiment and the limit of m _νe≤0.2 eV/c² aimed at with KATRIN, a new experiment MARE has been initiated. As a first stage (MARE-1), 300 detectors consisting of silicon implanted thermistors, produced by NASA/GSFC, and absorbers of AgReO₄ crystals will be mounted. To optimize the experimental setup, a test array was equipped with 10 AgReO₄ crystals of various size and shape. The influence of the crystal quality as well as of different types of resin on rise time and energy resolution was investigated.      

Superconducting YBa2Cu3O7?δ Thin Film Detectors for Picosecond THz Pulses

Ultra-fast THz detectors from superconducting YBa₂Cu₃O_7?δ (YBCO) thin films were developed to monitor picosecond THz pulses. YBCO thin films were optimized by the introduction of CeO₂ and PrBaCuO buffer layers. The transition temperature of 10 nm thick films reaches 79 K. A 15 nm thick YBCO microbridge (transition temperature—83 K, critical current density at 77 K—2.4 MA/cm²) embedded in a planar log-spiral antenna was used to detect pulsed THz radiation of the ANKA storage ring. First time resolved measurements of the multi-bunch filling pattern are presented.     

Heat Capacity Setup for Superconducting Bolometer Absorbers below 400 mK

A calorimeter set up with very low heat capacity ( $\sim $ 20 nJ/K at 100 mK) has been designed using commercial Carbon based resistors. This calorimeter is used to determine the heat capacity of small samples of superconducting bolometer absorbers. In particular, we present heat capacity studies of Tin, a bolometer candidate for Neutrinoless Double Beta Decay in $^{124}$ Sn, in the temperature range of 60–400 mK.