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When a quench occurs in a superconducting magnet, excessive joule heating in normal region may damage the magnet. It is necessary to detect the quench as soon as possible and discharge magnetic energy stored in the magnet. The authors have presented a quench detection/protection system based on an active power method which detects the quench regardless of a self-inductive and mutual-inductive voltages and electromagnetic noise. In the conventional active power method, the inductive voltages are removed by cancel coils. In this paper, the authors propose a method to cancel an inductive voltage using a capacitor circuit. The quench detection/protection system becomes more precise and smaller than the conventional system through the capacitor circuit.

When a quench occurs in a superconducting magnet, excessive joule heating may damage the magnet. We have presented the quench protection system based on an active power method. Our previous quench protection tests have been carried out for small superconducting magnets whose self inductances are less than several hundred mH to verify principles of our proposed system. In this paper, we present experimental results of quench protection tests of a cryocooler cooled 6 T NbTi superconducting magnet (self inductance 15.5 H), which is a commercial size magnet made by Tamakawa Co., Ltd. We confirmed that our proposed system could inhibit the maximum temperature of the superconducting magnet (initial temperature 4.3 K) after the quench to less than about 44 K at operation magnetic field 5.5 T. Experimental results suggest that our proposed system is useful for practical used superconducting magnets.

When a quench occurs in a superconducting magnet, excessive joule heating may damage the magnet. The authors have presented a quench detection/protection system based on an activ e power method, which can detect the quench quickly and precisely by measuring an active power dissipated within the magnet after the quench. In this paper, the authors show usefulness of a softwa re quench detection/protection system for a cr yocooled NbTi superconducting magnet which is a commercial size magnet made by Tamakawa Co., Ltd.. Experimental results show that the proposed system is useful for the practical used superconducting magnet.

In high temperature superconductors, local and excessive temperature rise occurs after normal transition because normal zone propagation velocities are slow at high operation temperature and then the superconductors may be degraded or burned. Therefore, it is essential to detect the temperature rise in high temperature superconducting coils and protect them as soon as possible. The authors have presented a detection method based on time-frequency visualization of AE signals. In this paper, the authors discuss detection and frequency analysis of AE signals accompanying with epoxy cracks caused by thermal expansion in an HTS coil by using the method.

The normal zone propagation velocities in high T c superconductors are slow at high operation temperature and therefore local and excessive temperature rise generates at quench occurrence, and then the superconductors are degraded or burned. Therefore it is essential to detect the temperature rise in high T c superconducting (HTS) coils as soon as possible and protect them. The authors have presented a quench detection method for HTS coils by time–frequency visualization of AE signals and have shown its usefulness for a HTS coil with height and outer diameter of 40–50 mm. In this paper, the authors present a quench detection/protection system based on superior method in quench detection time to the previous method and show its usefulness for a larger HTS coil (height and outer diameter: 160–190 mm) than the previous coil.

When the quench occurs in the superconducting coil, the excessive joule heating in the normal region may damage the coil. It is necessary to detect the quench in the coil as soon as possible and discharge the magnetic energy stored in the coil. We have presented a quench protection system based on the active power method which detects a quench regardless of the self-inductive and mutual-inductive voltage for multi-layer superconducting coils. In this paper, the usefulness of the developed system is confirmed for two-layer superconducting coils wound with Bi2Sr2Ca2Cu3Ox HTS tapes.

High temperature superconducting (HTS) motors electromagnetically consist of a rotator wound with HTS wires and an armature with conventional copper wires like Litz wire. The HTS rotor windings, as field coils, consist of a straight part and an end-ring part. Because a major rotation torque is induced by an interaction between magnetic fields and current-carrying conductors in the straight part, most of mechanical stresses in the motor occur at the straight part. An end-ring is placed in the edge of the straight part and used to connect to each adjacent straight-part coils. The magnetic fields by coil currents concentrate on the end-ring part, therefore, it is expected that the critical current of the entire coil, straight and end-ring, can be determined by the magnitude of the field in the end-ring. This paper deals with the overall Jc degradation in the end-ring part by self-field generated from the coil. In addition to electromagnetic analyses, we have performed a numerical analysis in order to evaluate mechanical stresses in the straight part of field coil by armature reaction on steady-state operation. The analytical results will be presented in this paper.

The stability and the protection of superconducting applications are very important issues. High temperature superconductor (HTS) is stable than low temperature superconductor (LTS). However, due to the high stability of HTS, HTS coils have complicate behaviors of normal transition – such as a recovery into the superconducting state or thermal runaway – which is determined by the magnitude of disturbance, coil size, the structure of winding wire and cooling condition. In this paper, we propose the quench protection system based on the active power method which can detect the quench by measuring the generating instantaneous active power in HTS coils. And the quench detection circuit adopted a software circuit by LabVIEW which was added a new quench protection technique to the circuit in order to improve its detection performance. Furthermore, it can monitor interior states of HTS coils with acquiring the only coil voltages in real time. To confirm the validity of the suggested technique, the experiments were performed with the hardware circuit for quench detection simultaneously. The experimental results are presented and discussed in this paper.

To understand the effects of the hot pressing on the pinning behavior for the SiC doped MgB2 tape wire, magnetic field and temperature dependences on a critical current density Jc and the pinning force have been studied. The MgB2 tapes were fabricated using an in situ powder-in-tube (PIT) method, the hot pressing process with nano-SiC powders and the carbon steel sheath. Jc of the hot pressing processed wire is enhanced especially at low field compared with that of the no hot-pressed wire. It is suggested that the enhancement of Jc is caused by the improvement of the MgB2 grain connectivity came from the hot pressing. The pinning analysis using the pinning models of a surface pinning and a normal point pinning lead to that the scaled curve of the pinning force for the SiC-doped MgB2 tape with the hot pressing process showed anisotropy in a lower field. This result suggests that the pinning center of the hot pressing processed MgB2 wire forms into inequi-axial shape, which is different from that in the tape without the hot pressing having the equi-axial pinning center in our previous report. It was also found that the scaled pinning force of the SiC-doped MgB2 tape with the hot pressing is larger than the surface pinning model in a higher field. This suggests that the pinning force was enhanced by the hot pressing in a higher field.

The resistive type fault current limiter based on YBCO thin film with high critical current density was proposed and developed because of its fast recovery characteristics. We have been developing a magnetic field measurement system with hall sensor to study the critical current density distribution or magnetic properties of high-Tc superconductors such as thin film, tape conductor and coated conductors. In this study, the transport current distribution in straight line and U-corner region of meander type resistive fault current limiter using YBCO thin film was investigated experimentally. The both axial and radial self-magnetic field components according to the direct (DC) and alternating (AC) transport currents were measured by two-axis hall probe to estimate the current distribution. And also, the self-magnetic field at the corner of bispiral type fault current limiter was measured by two-axis hall probe with a high spatial resolution to compare with the meander type fault current limiter.

When the quenching occurs in a superconducting coil, excessive joule heating in normal area may damage the coil. It is necessary to detect quenching in the coil as soon as possible and discharge the magnetic energy stored in the coil. Therefore, we propose a superconducting coil protection system based on an active power method. The system is highly resistant to the noise and does not require cancel voltage taps, so it is useful for both AC and DC coils. We have presented the effectiveness of the system using some test coils cooled in LN 2 or LHe. However, we have not discussed the effectiveness of the proposed system for helium-free cryocooled magnets, in which a larger temperature rise occurs after quenching than in liquid-cooled magnets. In this paper, we verify the effectiveness and practicality of the proposed system through coil protection tests for a cryocooled Nb 3 Al LTS coil.

We have been developing a 3D superconducting actuator with HTS (high temperature superconducting) bulk and two-dimensionally arranged multiple electromagnets. The application of HTS bulk enables stable levitation and suspension due to its strong pinning force. The performance of the actuator is determined mainly by the spatial distribution of the generated magnetic field of the electromagnets. For the sake of improving the levitation force, we proposed to attach a sliced iron sheet (we called this cap core) on the top surface of the core in each electromagnet. The proposed cap core was expected to lead to an intensive concentration and abrupt gradient increase of the perpendicular component in the magnetic field through the HTS bulk of the electromagnets. We experimentally confirmed and measured the effect of the cap core. For the optimized design of the cap core, we calculated the spatial distribution of the magnetic field on the surface of the electromagnet using 3D FEM analysis for several cap cores and estimated the levitation force of the HTS bulk using the calculated result.

The magnetic chromatograph (MC) system is one of the promising methods for ion separation because of its strong magnetic field gradients. We have been developing the MC system to separate the fine particles and ions, and have also developed the numerical analysis computer code based on fluid dynamics and electromagnetism to investigate the separating characteristics and optimization of MC system. We investigated MC technology for magnetic particles separation using superconducting magnet and micro-scale magnetic column with ferromagnetic wires experimentally. A channel height of magnetic column for ion separation was optimized by the developed computer code.

Recently, HTS coils have been developed for electric power apparatuses. In superconducting coils, local and excessive joule heating may give damage to the superconducting windings when a quench occurs and therefore it is essential that the quench is detected quickly and precisely so that the coils can be safely discharged. Resistive voltage measurement method is universally used for the quench detection, however, it is vulnerable to an electromagnetic noise which causes insufficient quench detection and at least needs a central voltage tap in windings. In a large superconducting coil, a lead-wire from the central voltage tap may cause a short-circuit when high voltage will be applied. In this paper, we present a quench protection system based on the active power method which detects a quench by measuring the instantaneous active power generated in a superconducting coil. The protection system based on this method is very strong against to the noise and no more needs a central voltage tap. The performance of system developed by us is confirmed by using test coil wound with Bi-2223 HTS tapes.

The new in situ MgB 2 tapes with/without SiC addition and the hot pressing process have been fabricated using the carbon steel sheath. The critical temperature ( T c ), critical current density ( J c ) and the AC transport current loss of those tapes have been studied and discussed in various conditions. The MgB 2 tapes with the carbon steel sheath that improved the core hardness and homogeneity, resulting in high J c , and the SiC addition, and the hot pressing brought narrow T c transition width. As the carbon steel has ferromagnetism, it affected the loss of the MgB 2 tape. The large losses that were two to three orders of magnitude higher than Norris’ theoretical curve were obtained. It was clarified that the main loss of the MgB 2 tape was the hysteresis loss of the carbon steel sheath.

We have been developing a three-dimensional (3-D) superconducting actuator with HTS bulk and electromagnets. Proposed 3-D superconducting actuator consists of the stator constructed by two-dimensional arranged electromagnets and HTS bulk superconductor as a mover. To realize the 3-D superconducting actuator with high performance, we have to investigate the shape-dependences of electromagnets and HTS bulk on levitating characteristics. In this study, we fabricated the individually controlled eight-polarities electromagnets and the two kinds of bolted joints cap cores to improve the control ability and levitation characteristics. And also, we prepared the disk-shaped and ring-shaped (with 20 mm inner diameter) HTS bulk with 60 mm diameter, and evaluated how magnetic field distribution influences the levitating characteristics as functions of levitation force and height.

We have been developing a magnetic field measurement system with two-axis hall-probes to study the critical current density distribution or magnetic properties of high- T c superconductors. In this study, the current distributions at corners of the meander type resistive fault current limiters were measured by hall probe with high spatial resolution. The both of axial and radial magnetic field components ( B x and B z ) according to the direct (DC) and alternating (AC) transport currents were measured by hall probe to estimate the current density distribution with high accuracy. And, it is confirmed that the measured radial components are very useful to estimate the current distribution.

Reducing AC loss in a superconducting apparatus is one of the most important issues, and the precise measurement and estimation of AC losses are essential to reduce them. The four-terminal method is universally used as an electric measurement method of AC losses for superconducting tapes and wires. In this method, noise and inductive voltage superposed on the terminal voltage of the superconductor are eliminated by a lock-in amplifier and cancel coil, respectively, and then measurement of very small resistive voltage is achieved. However, using this conventional method, a plurality of measuring instruments and apparatuses are needed, and therefore the measuring system becomes complicated and much time is consumed in the calibration process. In this paper, we present a simple and precise measurement system based on an active power detection method, which is proposed as a quench detection method. The proposed system consists of a small number of instruments and apparatus and is less susceptible to noise. Its usefulness is verified by comparing the proposed method and the conventional four-terminal method in measuring the AC transport current loss of a Bi2223/Ag tape.

A superconducting actuator with multiple motions is proposed and experimentally investigated for the development of microelectrical machines. The disk-shaped YBCO bulk was located above the electromagnets and cooled down in the field-cooling method, which enabled the flux pinning. The YBCO bulk superconductor was driven in vertical, horizontal and/or self-rotation by PC-controlled coil currents using multiple electromagnets. The most suitable levitation stability was obtained when we used four electromagnets and NNSS trapped field type. It was confirmed that the levitation force and horizontal moving force strongly depended on the coil current and the air gap length, respectively.

The aim of this study is to determine the diagnostic value of cerebrospinal fluid (CSF) soluble CD27 (sCD27) as a tumor marker for primary central nervous system lymphoma (PCNSL). We examined sCD27 levels in CSF obtained from various types of brain tumor patients. Forty-two patients were studied (including 12 PCNSL patients) who had not received any therapy for their tumors. In all PCNSL cases, CSF sCD27 levels were more than 15 U/ml (median 84.5 U/ml, range 17–484 U/ml) and in other brain tumor cases, CSF sCD27 levels were all less than 15 U/ml. Our data suggest that CSF sCD27 levels are useful to distinguish PCNSL from other brain tumors.

We have already completed the fabrication, installation, cabling, and the piping of a 40 T class hybrid magnet system including a 15 MW DC power supply (430 V × 35 kA), 15 MW water-cooling system (inlet temperatures below 10°C, flow rates up to 800 t/h) helium liquefier/refrigerator, and a hybrid magnet composed of an outer superconducting magnet and an inner resistive magnet. Their test operations are progressing now. Except for the hybrid-mode test operations for the hybrid magnet system we have nearly completed all the other test operations. In this article we describe mainly the specifications of the hybrid magnet, the DC power supplies, total control system, water-cooling system, and the present situation of the test operation.

We are constructing a 40 T class hybrid magnet composed of a 25 T inner resistive partand a 15 T outer superconductive part. We have performed successfully the first test operation of the superconductive part.It took about 145 hr to cool down the superconductive part from room-temperature to 4.2 K by using a helium refrigerator of 200 W. The magnet could generate a central field up to 14.01 T in a 400 mm room-temperature bore without quenching, when the operation current was 13 84.5 A with helium evaporating rate of 18.8 1/hr. After detailed check on the magnet system the full operation at 15 T will be carried out at the end of 1994.

A case of a cervical cord compression by the vertebral artery within the spinal canal is reported in a 47-year-old man. The clinical presentation, radiologic features, and the operative treatment are summarized. The mechanism by which this lesion caused a severe cervical pain is discussed.

Recent improvements and developmental research on several high field superconducting wires are reviewed. High field characteristics of NbTiHf wires, wound in a 13.08 T superconducting magnet in a 1.8 K pressurized superfluid helium bath, have been studied in detail. Ti-alloyed Nb 3 Sn fm wires prepared by the Nb-tube method showed excellent high field J c -characteristics and were wound in a 16.7 T superconducting magnet. One of these wires was employed in the HOMER facility (a multipurpose superconducting magnet at KfK) and generated 20.15 T, recently. A new process called the clad chip extrusion (CCE) method has been developed for the preparation of superconducting Nb 3 Al wires. Short samples of the CCE processed Nb 3 Al wires showed J c higher than 10 4 A/cm 2 up to 18.8 T at 4.2 K. One of the in-situ processed V 3 Ga short sample wires prepared by an induction melting using a CaO crucible showed J c =10 4 A/cm 2 at 16.2 T and 4.2 K, which will be improved by further optimization of the process and the composition.

Tube processed (Nb, Ti)3Sn and NbTi conductors have been developed for a 15 T class superconducting magnet with a 400 mm clear bore of a 40 T class hybrid magnet. Prior to testing the actual conductor, the transverse compressive stress effects on the critical current (Ic) of the (Nb. Ti)3Sn conductors were studied using a 1 7 scale reduced conductor. The Ic of the samples with clearance of gap length of over 0.3 mm between Cu-housings and (Nb,Ti)3Sn monolith reached over 90% of unloaded Ic(Ic0) at 14 T and 60 MPa of the transverse compressive stress. Based on the above-mentioned results, a new structure for full-scale Cu-housing (Nb,Ti)3Sn conductors has been designed and fabricated. Fabricated (Nb, Ti)3Sn conductors flowed more than 3870 A at 15 T and had 300 M Pa of 0.2% proof stress. All these values exceeded the values in the specification with a good margin.