Showing papers in "IEEE Transactions on Applied Superconductivity in 2001"

The use of pressurized bladders for stress control of superconducting magnets

Abstract: LBNL is using pressurized bladders in its high field superconducting magnet program Magnet RD3; a 14 T race track dipole, has been assembled and pre-stressed using such a system. The bladder, placed between the coil pack and the iron yoke, can provide 70 MPa of pressure while compressing the coil pack and tensioning a 40 mm thick structural aluminum shell. Interference keys replace the bladder's functionality as they are deflated and removed leaving the shell in 140 MPa of tension. During cool down, stress in the shell increases to 250 MPa as a result of the difference in thermal expansion between the aluminum shell and the inner iron yoke. A number of strain gauges mounted onto the shell were used to monitor its strain during assembly, cool-down and testing. This technique ensures that the final and maximum stress in the shell is reached before the magnet is ever energized. The use of a structural shell and pressurized bladders has simplified magnet assembly considerably. In this paper we describe the bladder system and its use in the assembly of a 14 T Nb/sub 3/Sn magnet.

Reduction of non-periodic environmental magnetic noise in MEG measurement by continuously adjusted least squares method

Abstract: We developed a signal processing method named CALM (Continuously Adjusted Least squares Method) to reduce the non-periodical low-frequency noise during magnetoencephalography (MEG) measurements. With this method, we have successfully measured motor related cortical fields (MRCF) under daytime heavy urban noise.

Atomic-layer engineering of superconducting oxides: yesterday, today, tomorrow

Abstract: In the last decade, great progress has been made in atomic-layer synthesis of high-temperature superconductors (HTS) and related oxides. Achievements include growth of single-crystal films of various HTS phases, precise multilayers and superlattices, the first artificial HTS compounds, and superconductor-normal metal-superconductor (SNS) trilayer Josephson junctions with good characteristics and uniformity. Today, we are trying to integrate atomic-layer engineering, combinatorial molecular beam epitaxy (MBE) synthesis, and state-of-the-art analytical tools for surface science. In future. I expect the technique to be improved further and scaled up to manufacturing. This will trigger progress in basic physics, materials science, and electronics. A variety of novel devices, combining different oxide functionality, will be built. Large-scale integration will be achieved. Eventually, one can envision multi-functional all-oxide electronics-sensors, processing, and memory devices, all monolithically integrated within a single chip.

FLUX chip: design of a 20-GHz 16-bit ultrapipelined RSFQ processor prototype based on 1.75-/spl mu/m LTS technology

Abstract: We describe the design and implementation of a single-chip microprocessor based on LTS Rapid Single-Flux-Quantum (RSFQ) technology. Two such chips are to be used in a dual-processor module, being developed by a SUNY-TRW collaboration as a spin-off of the HTMT project. Each FLUX chip represents a simple 16-bit 2-way long-instruction-word (LIW) microprocessor with a pipelined instruction memory of 30-bit instructions, decode and issue units, 8 integer ALUs interlaced with 8 registers, and input/output ports through which two FLUX chips can communicate with each other at a 7-GHz communication rate over a multi-layer MCM. The FLUX instruction set consists of /spl sim/25 instructions. High performance is reached with a scalable design featuring (1) a very high clock rate, (2) localized, regular and ultrapipelined processing in registers with very short wires, (3) instruction-level parallelism utilization with bit-level resolution of data hazards. A 16-bit implementation of FLUX processor consists of /spl sim/90,000 Josephson junctions on a /spl sim/10 mm/spl times/15 mm chip area. Our estimates show that the processor will be able to operate at clock frequencies up to 20 GHz when implemented using TRW's 4 kA/cm/sup 2/, 1.75-/spl mu/m Nb-trilayer technology.

AC coupling technique for Josephson waveform synthesis

Abstract: We demonstrate a new bias technique that uses low-pass and high-pass filters to separate the current paths of the sampling and signal frequencies in a Josephson waveform synthesizer. This technique enables the output voltage of the array to be directly grounded by removing the low-frequency common mode signal that previously prevented direct measurement of the array voltage with low-impedance instruments. We directly measure the harmonic spectra of 1 kHz and 50 kHz synthesized sine waves. We also use a thermal transfer standard to compare the rms voltages of synthesized sine waves at frequencies from 1 kHz to 50 kHz. Finally, we describe a new circuit that should enable a significant increase in output voltage by allowing several distributed arrays to be biased in parallel at high frequency, while combining their low frequency output voltages in series.

Large area YBCO-coated stainless steel tapes with high critical currents

Abstract: Recent progress in developing large area HTS-coated stainless steel tapes is reported. YBCO films have been grown on IBAD-YSZ buffered 0.1 mm-thick steel tapes using a high-rate pulsed-laser-deposition technique which allows a deposition rate up to 70 nm /spl middot/ m/sup 2//h. The coated conductors (CC) are provided with an optimized shunt layer and current contacts which reduce the generation of Joule's heat. An advanced technique for critical current I/sub c/ measurements was developed. The effects of self-field and time relaxation of current in helically wound tapes are analyzed. In long tapes of 10 m /spl times/ 4 mm, the highest I/sub c/ of 78 A at 77 K was observed. Critical currents of 67-75 A were reproducibly achieved in (8-10) m /spl times/ 4 mm coated tapes. For shorter tapes with a length of 0.2-1 m, critical currents of 317-391 A/cm width of the tape were observed. Fifteen wider CC tapes of 0.6 m /spl times/ 43 mm with I/sub c/ = 700 A have been manufactured and employed in newly developed fault current limiters with a nominal current of 3 kA. Critical current densities J/sub c/ = (1.3-2.5) MA/cm/sup 2/ at 77 K were observed in YBCO films. The CC tapes exhibit favorable behavior under axial stress and sufficiently small ac losses.

Fabrication and properties of an ultrafast NbN hot-electron single-photon detector

Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film's supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.

Long length manufacturing of high performance BSCCO-2223 tape for the Detroit Edison Power Cable Project

Abstract: American Superconductor has manufactured the BSCCO-2223 tapes for the Detroit Edison Power Cable Project. Pirelli Cables and Systems, along with Detroit Edison, Lotepro, EPRI, and Los Alamos National Lab, are developing, manufacturing, and installing the world's first HTS cable system in an electric utility network. Partially funded by the DOE-SPI program, the project goal is to fabricate, install, and test a 3-phase, 120-meter long, 100 MVA HTS cable system rated at 2400 A and 24 kV in Detroit Edison's Frisbie Station. Significant advances in HTS tape technology have been made in the past year, with average engineering critical current performance above 115 A at 77 K. We discuss the distribution of critical current as well as mechanical and environmental tests of more than 25 km of BSCCO tape manufactured for the Detroit Edison project. The environmental tests have been designed to simulate the behavior of HTS tapes under the actual operating conditions for an underground power cable.

AC loss properties of a 1 MVA single-phase HTS power transformer

Abstract: We designed and built a single-phase 1 MVA-22/6.9 kV HTS transformer with the multi-layered cylindrical windings composed of Bi2223 parallel conductors. In advance of the design, the AC loss induced in the windings was estimated on the basis of the observed results in a strand. A subcooled liquid nitrogen cryogenic system with the corresponding cooling capacity was developed and attached to the transformer. The actual AC loss was measured by an electrical method. It was a great part of the total heat load and dominated the temperature rise of subcooled liquid nitrogen. We discussed the validity of the present estimation procedure of the AC loss in the windings as compared with the observed results.

Development of a 22 kV/6.9 kV single-phase model for a 3 MVA HTS power transformer

Abstract: We have developed a 22 kV/6.9 kV HTS single-phase transformer cooled by liquid nitrogen for field test, which is a practical model for the single-phase part of a 3 MVA HTS power transformer. First, we numerically simulated electromagnetic, mechanical and thermal conditions of the windings in accidental cases of short-circuit and lightning impulse, and considered the winding structure withstanding the severe loads. We constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed tapes and confirmed applicability of the design concept for the overcurrent and high-withstand-voltage tests. We designed and constructed a single-phase HTS transformer on the basis of the model-coil-test results. The primary and secondary windings are transposed parallel conductors of two and six Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS transformer as for usual oil-filled ones indicated the reliable operation and high performance. The field test in a distribution grid of Kyushu Electric Power Co. included in-rush-current test and long-term operation of the transformer cooled by a continuous supply system of subcooled liquid nitrogen with cryocoolers.

Installation and operation of the Southwire 30-meter high-temperature superconducting power cable

Abstract: Southwire Company has installed, tested and is operating the first real-world application of a high-temperature superconducting cable system at its headquarters in Carrollton, GA, USA. The cable is powering three Southwire manufacturing plants, marking the first time a company has successfully made the difficult transition front laboratory to practical field application of an HTS cable. The cables are rated at 12.4-kV, 1250-A, 60 Hz and are cooled with pressurized liquid nitrogen at temperatures from 70-80 K. Before placing the cables into service, extensive offline electrical testing was performed including voltage withstand, measurement of DC critical current, extended load current testing, rated voltage testing and partial discharge measurement. The cables were energized on Jan. 5, 2000 for online testing and operation, and by the end of August 2000, had provided 100% of the customer load for 2164 hours.

3D-MLSI: software package for inductance calculation in multilayer superconducting integrated circuits

Abstract: A new software package 3D-MLSI was developed for inductance calculation in multilayer superconducting integrated circuits. The key advantages of 3D-MLSI are: a new mathematical model that takes into account the 3D distribution of magnetic field, and a user interface compatible with the Cadence and ACAD design tools. The program is most applicable when both kinetic and magnetic inductances are important. A method of equivalent circuits inductance extraction is suggested.

SQUID magnetocardiography: status and perspectives

Abstract: Magnetocardiography (MCG), the magnetic equivalent to electrocardiography (ECG), is one of the most promising major applications of SQUID systems. Recent advances in SQUID-system technology such as improved noise suppression techniques, better field sensitivity (in particular for HTS SQUIDs), real time options, vector magnetometers and novel signal analysis approaches have appreciably reduced the technical constraints that hindered until recently the implementation of MCG into practical clinical use. Although MCG features several obvious advantages compared with ECG, it remains difficult to present convincing clinically attractive results to medical doctors that would initiate a commercial breakthrough for SQUID systems. Recent clinical MCG investigations have, however, revealed several areas of cardiology where MCG could play a significant role. This presentation will summarize the technical achievements and next steps necessary for system innovation, as well as the crucial clinical trials for the future commercial and clinical success of cardiac SQUID-systems.

Microfabricated transition-edge X-ray detectors

Abstract: We are developing high performance X-ray detectors based on superconducting transition-edge sensors (TES) for application in materials analysis and astronomy. Using our recently developed fully lithographic TES fabrication process, we have made devices with an energy resolution of 4.5/spl plusmn/0.1 eV for 5.9 keV X-rays, the best reported energy resolution for any energy dispersive detectors in this energy range. These detectors utilize micromachined thermal isolation structures and transition-edge sensors fabricated from Mo/Cu bilayers with normal-metal boundary conditions. We have found the normal-metal boundary conditions to be critical to stable and reproducible low noise operation. In this paper we present details of fabrication and performance of these devices.

Strain effect in Bi-based oxide/Ag superconducting tapes

Abstract: The influence of mechanical strain on the critical current (I/sub c/) is investigated for (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/(Bi-2223)/ Ag-0.2wt%Mg-0.3wt%Sb superconducting tapes at 77 K. The tensile axial strain along tape length is successfully induced to the sample by using a U-shape holder. Continuous change of the axial strain can be obtained by changing the distance between both ends of the holder. The U-shape holders made of Ti, SUS304, or brass are used to examine the effect of thermal strain due to the contraction caused by the cooling. For example, the results for the samples glued to Ti or brass holder are as follows. Strain dependence of normalized I/sub c/ (I/sub c//I/sub c/(at as-cooled state)) is affected by holder material. A steep decrease of I/sub c/ occurs when we apply 0.1% and 0.3% strain for Ti and brass holder, respectively. The different thermal expansion (-0.15% for Ti and -0.37% for brass from 300 K to 77 K) explains it. All the results for normalized I/sub c/ vs. strain relation fall on a master curve with taking into account of the effect of the thermal strain. Thermal expansion of the tape from 300 K to 77 K is measured to be -0.35% by using a strain gage. The critical strain ( c) where a steep decrease of I/sub c/ occurs is evaluated to be 0.27% from self-contracted state of the tape.

Improvement of superconducting properties of Bi-2212 round wire and primary test results of large capacity Rutherford cable

Abstract: We have developed HTS cables using Bi-2212 round wires, which have high mechanical strength and an average J/sub c/ of 200 kA/cm/sup 2/ at 4.2 K in self-field. Four designs of cables were fabricated in this work and those tables could carry I/sub c/ values from 1 kA to 10 kA at 4.2 K and self-field depending on the number of strands. A 70m-long 20-strand Rutherford cable was successfully manufactured. Optimization of heat treatment conditions was effective to reduce I/sub c/ degradation observed in the case of heat treatment with a long length. I/sub c/ values of a Rutherford cable were measured under loading at 4.2 K in 4 T. The critical values of the stress on face loading and edge loading were 60 MPa and 100 MPa, respectively. We successfully obtained high J/sub c/ value of 500 kA/cm/sup 2/, which was almost double that of the conventional wires capitalize "Rutherford".

NbN hot electron bolometric mixers for terahertz receivers

Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.

DC SQUID series array amplifiers with 120 MHz bandwidth (corrected)

Abstract: We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 pm center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA//spl radic/Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.

Low cost Y-Ba-Cu-O coated conductors

Abstract: Solution-based techniques have been examined as potential low-cost processes for manufacturing YBCO coated conductors. YBCO films prepared from metal trifluoroacetate precursors have achieved performance levels equaling or exceeding that of vapor deposited films with the same thickness on CeO/sub 2//YSZ(sc) substrates. J/sub c/'s of 4.5 MA/cm/sup 2/ and 2 MA/cm/sup 2/ have been achieved in 0.4 /spl mu/m thick YBCO films on CeO/sub 2//YSZ(sc) and CeO/sub 2//YSZ/CeO/sub 2//Ni substrates, respectively. Textured Gd/sub 2/O/sub 3/ buffer layers have been deposited on deformation textured Ni substrates in a reel-to-reel process. The performance of YBCO films deposited on substrates containing the Gd/sub 2/O/sub 3/ seed layers is comparable in performance to YBCO films grown on all vacuum deposited buffer layers.

Finite element method simulation of AC loss in HTS tapes with B-dependent E-J power law

Abstract: The nonlinear behavior of high temperature superconductors (HTS) is often modeled by an E-J power law in order to describe their electromagnetic properties. This paper presents AC loss calculations in HTS tapes, performed by means of FEM commercial software using the A-V method. The implemented nonlinear model of the HTS tapes takes into account the B-dependence of the critical current density J/sub c/ and the power index n. The expressions for J/sub c/(B) and n(B) are obtained from electrical measurements of a Bi-2223 tape under applied DC magnetic field. Numerical simulations of HTS tapes under different experimental conditions have been performed, i.e. the application of a transport current and/or AC external perpendicular magnetic field at 59 Hz. A comparative analysis of AC loss is then presented where J/sub c/ and n are maintained either constant or B-dependent. The combined J/sub c/(B) and n(B) formulation leads to a better understanding of HTS electromagnetic behavior, especially when a perpendicular magnetic field is applied.

Texture development in IBAD MgO films as a function of deposition thickness and rate

Abstract: We have examined the effect of film thickness on in-plane texture for ion-beam assisted deposition (IBAD) of MgO films. Plan-view dark-field transmission electron microscopy (TEM) has revealed that texture develops rapidly, reaching its best value at a critical thickness of/spl sim/10 nm. These results have been confirmed by quantifying the in-plane texture of these samples at each thickness with X-ray diffraction /spl phi/-scans. We have also examined the effects of variable deposition rate on texture formation. X-ray diffraction shows that the optimum in-plane texture is achieved at the critical thickness with a rate of 0.2 nm/s. However, TEM imaging has shown that the distribution of well-aligned grains decreases with an increase in rate. As such, deposition at 0.1 nm/s was found to be sufficient for achieving good in-plane distribution values and good surface coverage for subsequent depositions. By combining the results of both of these experiments, we were then able to optimize our deposition process and apply them to the growth of IBAD MgO on metal substrates.

HTS filter subsystems for wireless telecommunications

Abstract: After many years of research and development, HTS filter subsystems for telecommunications are finally being manufactured in volume. Nearly 1,000 HTS filter subsystems are currently deployed worldwide with millions of hours of cumulative operation. An overview of the worldwide effort to commercialize HTS filter subsystems is presented. The essential technology elements required to manufacture HTS filter subsystems are discussed i.e., filters, cryogenic low-noise amplifiers, advanced cryopackaging, cryocoolers and control electronics. Currently sales of HTS filter subsystems are limited to existing analog and digital telephony networks. Planned third generation (3G) systems for wireless telephony and data communications require higher receiver performance to maintain high data rates with even lower-power handsets. The deployment of HTS filter subsystems in these 3G networks may be an excellent opportunity to achieve greater market penetration. Selected results of field trials of HTS filter subsystems are also presented.

Investigation of high-Tc bulk material for its use in resistive superconducting fault current limiters

Abstract: Superconducting fault current limiters (SCFCL) offer an attractive means to limit short-circuit currents in power systems. Comparisons of available HTS material led to the derision to investigate melt cast processed (MCP) BSCCO and melt textured polycrystalline YBCO for use in resistive SCFCLs. As a great length of a superconductor per unit element is preferred, the BSCCO samples are shaped as bifilar coils prepared from tubes and the YBCO samples are manufactured in a meander shaped geometry. Test results concerning contact resistances, E-J curves, AC losses as well as the quench behaviour of the samples are presented. The experiments reveal the requirement of a high material homogeneity as the main challenge.

Application of resistor based superconducting fault current limiter to enhancement of power system transient stability

Abstract: This paper presents an application of a superconducting fault current limiter (SFCL) to enhance the power system transient stability. Resistance as the current limiting devices is used for damping the generator accelerating power. A method to evaluate an appropriate resistance is proposed. The SFCL is combined with the superconducting magnetic energy storage (SMES) for power system stabilization. As a result the capacity of SMES is significantly reduced.

DC SQUID series array amplifiers with 120 MHz bandwidth

Abstract: We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 /spl mu/m center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/ Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.

A stability criterion for cryocooler-cooled HTS coils

Abstract: The magnet technology of a high-temperature superconductor (HTS) with a conduction cooling system by a GM cryocooler has been advanced. It is very important to understand the thermal and electromagnetic phenomena in HTS tapes for HTS coil design. We have measured the quench characteristics of HTS tapes with a conduction cooling system of a GM cryocooler and developed a computer program based on the finite element method (FEM) to investigate the thermal and electromagnetic behaviors within HTS tapes. From these experimental and analytical results, the validity of the computer program has been confirmed. In this paper, we discuss a stability criterion for cryocooler-cooled HTS coils by using the computer program. The current at which "thermal runaway" occurs, which depends on the relationship between the cooling power of the GM cryocooler and the heat generation within HTS coils, is chosen as a stability criterion. We also investigate the transient thermal and electromagnetic behavior in HTS coils.

Reel to reel continuous formation of Y-123 coated conductors by IBAD and PLD method

Abstract: Continuous deposition of Y-123 tapes was performed by ion-beam-assisted deposition (IBAD) and pulsed laser deposition (PLD) method. YSZ template films were deposited by IBAD on Ni-based alloy tapes with tape shifting speeds of 0.1-0.3 m/h. They were uniformly coated with an in-plane mosaic spread of 12-13 degrees in 5 m length. In order to overcome the low deposition rate of the IBAD process, large area ion sources with inductively coupled discharge plasma were applied. Y-123 films were deposited by PLD on the YSZ templates with a tape shifting speed of 1.0 m/h. The degradation of Y-123 targets for the PLD process was effectively restricted by combined motion of rapid rotation and linear shifting. I/sub c/ of 84.0 A and J/sub c/ of 0.76MA/cm/sup 2/ were obtained at 77 K, 0 T in the length of 1.0 m when the in-plane mosaic spread for the Y-123 film was 7 degrees. I/sub c/ of 35.0 A and J/sub c/ of 0.25MA/cm/sup 2/ were obtained in a 4.6 m long sample at the length of 4.0 m, when the in-plane mosaic spread for the Y-123 film was 11 degrees.

Application of high T/sub c/ SQUID magnetometer to biological immunoassays

Abstract: A high T/sub c/ SQUID system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. Design and set up of the system is described. Minimum detectable amplitude of the magnetic flux is 0.6 m/spl Phi//sub 0/ for the measurement bandwidth from 0.2 Hz to 5 Hz when we use a magnetometer. The system noise does not increase when the magnetic field of 0.8 mT is applied in parallel to the SQUID. An experiment to measure the antigen-antibody reaction shows that the sensitivity of the present system is 10 times better than that of the conventional method using an optical marker. When a gradiometer is used, the system noise decreased by a factor of 5, compared to the case of the magnetometer. This improvement indicates the usefulness of the gradiometer to suppress the residual environmental noise in the present system. Magnetic markers that have remanent magnetic moment are also studied in order to increase the signal.

Low noise HTS dc-SQUID flip-chip magnetometers and gradiometers

Abstract: We have fabricated HTS dc-SQUID flip-chip sensors with a large area multilayer flux transformers. Different layouts of the flux transformers provide a large variety of magnetometers and planar gradiometers. For the magnetometers a resolution /spl sim/6 fT//spl radic/Hz and the planar gradiometers a resolution of about /spl sim/30 fT/cm./spl radic/Hz were routinely obtained at 77 K. The noise was nearly white down to frequencies of few Hz. The sensors were vacuum-tight encapsulated together with a heater and a feedback coil. This makes the handling of the sensors more reproducible and convenient. Production of the magnetometers and gradiometers in small series was proven.

Study on high temperature superconducting magnetic bearing for 10 kWh flywheel energy storage system

Abstract: Flywheel energy storage systems with high temperature superconducting magnetic bearings are expected for load leveling use. A 1 kWh flywheel of 600 mm diameter was developed and the maximum energy storage of 1.4 kWh at 20,000 RPM was attained. For the development of a large capacity flywheel system, it is necessary to sophisticate the cooling system and improve the performance of the HTS magnetic bearing. So, an advanced cooling system of the bearing with a cryogenic refrigerator has been developed, and also the bearing characteristics in several cooling conditions have been investigated. It has been confirmed that the repulsive force of the bearing at 50 K was 1.5 times of its value at 80 K, and the rotating loss of the bearing at 50 K was one third of its value at 80 K, but the lateral magnetic stiffness at 50 K became small in comparison to that of 80 K. On the basis of the above results, an HTS magnetic bearing for 12.5 kWh flywheel system is under development.