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The design and development for a compact 1 GHz (23.5 T)-class NMR magnet are presented. The magnet uses inner coils wound with Ni alloy-reinforced Bi-2223 conductors in combination with LTS outer coils. The series-connected coils are operated in a power supply-driven mode. The total magnet size is very compact, and is comparable to that of a currently commercialized 600-MHz (14.1 T) NMR magnet. This owes to a high current density operation of the Bi-2223 inner coils, which contribute as much as 53% of the total magnetic field. This paper investigated the following properties of the Bi-2223 inner coils: First, joint resistance under external magnetic fields; second, tensile stress tolerances of the Bi-2223 conductor under bending condition; third, high compressive stress on Bi-2223 coils; fourth, the effect of screening current-induced magnetic field on the field homogeneity and stability; and fifth, the maximum permissible Joule heating to avoid a thermal runaway. Two Bi-2223 inner coils for the magnet were built and tested in liquid nitrogen, which provided important knowledge for the magnet excitation.

We are developing a cryocooled (RE)Ba2Cu3O7 (REBCO; RE = rare earth) persistent-mode superconducting magnet system that generates 1 T with multiple superconducting joints. In parallel to the design of the system, we have investigated transport characteristics of the REBCO superconducting joints. Critical currents (Ic) were measured as a function of magnetic field and temperature. Two joint samples with Ic of 107 and 53 A at 77 K, self-field were measured. The first one showed Ic of 357 A at 50 K and 0.1 T (magnetic field is perpendicular to the tape surface). Ic of the REBCO joint samples showed remarkable hysteresis. The anisotropy of Ic changed with temperature. Ic at B perpendicular to the tape were higher than those at B parallel to the tape at temperatures below 20 K. The random pinning is possibly the dominant pinning mechanism in the whole temperatures for the REBCO superconducting joints in magnetic fields perpendicular to c-axis.

The technological development for a 3-T high-temperature superconducting (HTS) magnetic resonance imaging (MRI) magnet is underway. The 3-T HTS MRI magnet is imaged such that RE(= Rare Earth)Ba 2 Cu 3 O 7-δ (REBCO) coils are installed and cooled using a cryocooler between 30 and 50 K without liquid helium refrigerant. REBCO MRI magnets are expected to maintain the magnetic field with stability better than 0.1 ppm/h with superconducting joints for a persistent-current mode. The resistance in a joint must be suppressed less than 1 × 10 -12 Ω to achieve the expected stability. The resistance of REBCO joint was estimated measuring the decay rate of trapped magnetic field in a REBCO single-turn loop including a joint. An external magnetic field of up to 1 T was applied to the joint in the STL at temperatures of 35 K and 50 K. The order of resistance in the REBCO joint was less than 1 × 10 -13 Ω.

Recent development in the superconducting REBCO joints is an encouraging prospect for realizing an HTS magnet in persistent current mode operation. In our ongoing project, we are developing a cryocooled 1 T REBCO magnet system with joints to demonstrate the joint performance in an operating condition expected, for example, for an MRI. Preliminarily, the small test coils have been fabricated to verify the winding method. Additionally, we have designed and manufactured the new leads structures for feeding the conductor from the winding to the joints.

A 1.02-GHz nuclear magnetic resonance (NMR) system was successfully operated in a driven-mode over a half year. A main coil of the 1.02-GHz NMR magnet consists of a Bi-2223 high-temperature superconducting (HTS) innermost coil and low-temperature s-uperconducting outer coils. The magnet including the HTS coil was designed to operate in the driven mode using highly stabilized dc power supply. The power supply should be operated continuously without interruption. Failure in the power supply due to a power outage is unacceptable. The equipment for a power outage, which consists of an emergency generator, a momentary voltage drop compensator, and a safety switch, was prepared. A malfunction of overcurrent occurred in the momentary voltage drop compensator at the power outage. Due to the equipment for the power outage, the dc power supply was successfully recovered without a quenching of the magnet.

This paper presents the results of a high field generation test for layer-wound HTS coils in a background magnetic field. The test revealed new types of degradation for a REBCO coil caused by an electromagnetic force. A series-connected REBCO coil and a Bi-2223 coil were charged at 4.2 K in a background magnetic field of 17.2 T to generate a central magnetic field of 28.2 T (nuclear-magnetic-resonace frequency of 1.2 GHz). However, a premature normal voltage appeared on the REBCO coil, and the charging was stopped at 25 T. Unwinding the REBCO coil after the experiment found: 1) delamination, due to a cleavage and peeling, of the conductor in a soldered joint inside the winding; and 2) axial movement and edgewise bend deformation of the REBCO conductor at the outermost layer. The keyword of the present degradation is stress concentration, which is also the origin of the more widely known thermal stress-induced degradation.

We had successfully operated the 1020-MHz (24.0 T) nuclear magnetic resonance (NMR) spectrometer for 8 months, including the cooling down, shimming, and the 6-month operation for NMR measurements. The NMR superconducting magnet, which had consisted of NbTi and Nb3Sn coils, was upgraded by replacing the innermost Nb3Sn coil with a (Bi,Pb)2Sr2Ca2Cu3O10 (Bi-2223) one. The Bi-2223 innermost coil was connected in series with Nb3Sn and NbTi coils. The magnet was cooled with pressurized superfluid helium (He II). The steady-state operating temperature was 1.72 K. The magnet was power-supply driven, i.e., the transport current was always supplied by a power supply. A small normal transition and a power outage occurred during the 8-month operation; however, the magnet quench was avoided.

Using a Bi-2223 innermost coil, the world's first NMR magnet with a frequency beyond 1 GHz has been developed and operated at the National Institute for Materials Science during 2014-2015. The existing 920 MHz (21.6 T) NMR magnet was successfully upgraded to a 1030 MHz (24.2 T) magnet by replacing the Nb3Sn innermost coil with a Bi-2223 coil. After charging the magnet to 1020 MHz (24.0 T), a shimming operation was started to obtain the homogeneous magnetic field required for NMR measurements. However, a large magnetic field inhomogeneity appeared, which could not be compensated using conventional shimming methods, i.e., superconducting and room temperature shim coils. Therefore, a new ferromagnetic shimming technology was applied, which achieved powerful and fast-acting field compensation and performed comparably to active shimming. This enabled effective compensation of the magnetic field inhomogeneity, leading to a subsequently excellent NMR resolution test result of 0.7 ppb. This NMR resolution enables NMR measurements for a membrane protein sample.

We succeeded in upgrading the 920-MHz nuclear magnetic resonance (NMR) superconducting magnet (21.6 T) to 1020 MHz (24.0 T) by replacing the innermost Nb3Sn coil with a (Bi,Pb)2Sr2Ca2Cu3O10 (Bi-2223) coil. The 920-MHz NMR spectrometer had been installed in the National Institute for Materials Science, Tsukuba, Japan, in 2001. It has been operated in the persistent mode for six years. The upgrading project started in 2006. A Bi-2223 coil was developed as the innermost coil instead of the Nb3Sn one. The newly installed Bi-2223 innermost coil is connected to Nb3Sn and NbTi coils in series. The upgraded NMR magnet was seriously damaged by the Great East Japan Earthquake in March 2011. After more than two years of restoration and additional improvements of current leads and the power supply system, the magnet was cooled down to below 1.8 K in August 2014. The magnet successfully generated 24.0 T, corresponding to 1020 MHz, in October 2014. To achieve the required homogeneity and stability of the magnetic field, not only superconducting and room-temperature shim coils but also ferromagnetic shims were used. The 1020-MHz superconducting NMR magnet has been operated in a power-supply-driven mode for six months.

The use of REBCO coils is a promising approach to achieve super-high field NMR magnets. As the first step in this direction, we have started to develop an LTS/REBCO NMR magnet operated at 400-600 MHz (9.4-14.1 T). In this paper, based on numerical simulations, we describe a study of the thermal runaway of the REBCO innermost coil, which is one of the major problems of this type of magnet. Based on the simulation results, if an LTS coils quench occurs, the current in the REBCO coil continues to increase due to the electromagnetic induction and leads to a natural thermal runaway with a very high current density. The thermal runaway is limited to only the top and bottom ends of the REBCO coil, as the radial magnetic field is highest there and the quench propagation velocity is quite low. The current density for this type of thermal runaway is much higher than that of the operating current, resulting in the catastrophic overheating of the coil. This is the worst case scenario which must be prevented for the LTS/REBCO NMR magnet. An optimal size dump resistor for the REBCO coil can prevent the natural thermal runaway by suppressing the current increase due to electromagnetic induction.

Because of their high critical fields, high-Tc superconductors (HTS) are considered to be the only solution to dramatically increase the highest fields of NMR magnets. We have successfully demonstrated that a 500 MHz HTS/LTS NMR system with a Bi-2223 innermost coil could be used for solution NMR in a driven-mode operation. As the next step, the upgrade of the 920 MHz NMR system installed at the Tsukuba Magnet Laboratory is underway. The innermost Nb3Sn coil has been replaced by a Bi-2223 coil. The coil was fabricated as a layer-wound coil using five Bi-2223 conductors reinforced with bronze tapes. It was connected in series with the outer Nb3Sn and NbTi coils. The magnet is expected to generate a field of 24.2 T (1.03 GHz of 1H resonance frequency) at an operating current of 244.4 A. The test using the Bi-2223 coil and the outer Nb3Sn coils in combination was successfully carried out. The coil has been installed in the 1.03 GHz NMR magnet. Its cooling and operation are scheduled to take place within Fiscal Year 2010.

Shielding of magnetic fields (magnetic shielding) by rare earth-based REBCO coated conductors with a highly oriented superconducting layer was measured. The shielding of magnetic fields was measured using a Hall effect sensor installed between bundles consisting of commercial REBCO conductors 12 mm in width. Measurements of the shielding of magnetic fields by other commercial high-Tc superconductors were performed for comparison. The shielding of magnetic fields was found to depend on the number of conductors in the bundle and the route of the applied magnetic fields and was observed even for fields over 10 T. In steady magnetic fields, a temporal change in the shielding of magnetic fields, that is, a decay of shielding currents induced in conductors against applied magnetic fields, was measured. The temporal change of the shielding of magnetic fields exhibited the behavior typical of high-Tc superconductors, as explained by the flux creep model. Remanent magnetic fields measured in the experiments of the shielding of magnetic fields suggest that the bundle can be used as a magnet. A quasi-bulk magnet consisting of 100 Zr-doped Zr:REBCO conductors could hold over 3 T at 4.2 K.

Using high-Tc superconductors (HTS) is considered to be the only solution to dramatically increase the highest fields of NMR magnets because of their high critical fields. However, it is not easy to apply HTS to an NMR spectrometer (HTS-NMR) because a persistent-mode operation with HTS cannot satisfy the field stability of 0.01 ppm/h at present. To overcome this problem, we are now developing an HTS-NMR spectrometer in a driven-mode operation. As the first step, a layer-wound coil was fabricated with bronze-reinforced Bi-2223 conductors. Instead of the Nb3Sn coil, the Bi-2223 coil was installed as the innermost part of an existing NMR magnet. The magnet operated at a field of 11.7 T with a highly stabilized power supply. NMR measurements were carried out, and it was demonstrated that the quality of the multi-dimensional NMR spectra on the protein was equivalent to that obtained with a persistent-mode system. The next step will be to demonstrate its usefulness as a high-field NMR system. The upgrade of the 920 MHz NMR system installed at the Tsukuba Magnet Laboratory is underway. Its innermost coil is scheduled to be replaced by a Bi-2223 layer-wound coil for 2010. Its target field is 24.2 T (1.03 GHz).

Electrical and mechanical characteristics of Type HT tape, which is standard 4.2 mm wide DI-BSCCO tape reinforced with metallic tapes, have been evaluated. Longitudinal distributions of critical current and n-index in kilometer long Type HT tape has proved uniform from end to end just like the original insert tape, which is Type H tape. Type HT-CA reinforced with 50 mum thick heat-resistant copper alloy is highly balanced tape with high mechanical properties and low splice resistance. Type HT-SS reinforced with 20 mum thick stainless steel has the best mechanical properties, which has been demonstrated under the actual environment in high field magnet, namely the hoop stress load test energizing a one-turn coil in external high magnetic field and liquid helium.

Magnetic flux concentration is a very important technique for the effective generation of high magnetic fields. We propose the use of the diamagnetism of a high T c bulk superconductor (HTS bulk) instead of ferromagnetic materials such as Ho and Dy. We fabricated a magnetic field concentrator using Gd-Ba-Cu-O bulk. The essential point was slits to suppress the current along the circumference. The concentrator was cooled at the center of a superconducting magnet with liquid helium. By increasing the external field to 1.00 T, a magnetic flux density of 3.20 T was obtained at the center of the concentrator. At an external field of 2.00 T, a field of 5.65 T was also obtained. A magnetic lens using HTS bulk was successfully demonstrated. The experimental results were well explained by numerical analyses assuming HTS bulk as a perfect conductor.

In this study, we investigated in field properties of high-Tc superconductor (HTS) tapes electrically as well as mechanically. Metallic reinforced Bi-2223/Ag superconductor tapes were used in this work. The critical current (Ic), which is highly dependent on the magnetic field, was measured using fields applied parallel and perpendicular to the tape surface. The conductor was exposed to fields of up to 28 T at 4.2 K. In order to confirm the performance of tapes in practical NMR operation, Ic was also measured around 2 K. The conductor was wound on a large diameter bobbin and mechanical properties were then measured as the coil current was increased. Finally, we verified the conductor properties from coil Ic and maximum stress/strain of it.

The Tsukuba Magnet Laboratory (TML) and the High Field Laboratory for Superconducting Materials collaborated on the design study of a 50 T-class hybrid magnet. The highest fields of the hybrid magnet were examined with the existing 15 MW DC source at the TML used for the resistive insert magnet. The strength of the Cu-Ag wire exceeds 1400 MPa in ultimate tensile strength (UTS). Several upper-design stresses corresponding to the Cu-Ag wire strength were placed on Bitter disks to evaluate the resistive insert. The design was conducted with two inner radii, 29 mm and 19 mm. Resistive insert magnets are consist of three-layered coaxial Bitter coils operated with the 20 T outer superconducting magnet with a room temperature bore of 400 mm. In this hybrid magnet, a UTS of 1200 MPa is needed for the Bitter disks of the resistive insert to generate 46 T.

Although high-temperature superconductors (HTS) are very promising for high-field generation over 25 T, it is difficult to apply them to an NMR magnet because of their low index values and the difficulty caused by superconducting joints. The properties of HTS appear to cause poor magnetic field stability in the persistent-mode operation. Therefore, in this study, a high-field NMR magnet including HTS coils will be operated in the driven-mode. In order to evaluate the magnetic field stability in the driven-mode, we modified a 14 Tesla (600 MHz) vertical NMR magnet. With regard to the magnet, persistent switches for axial shim coils (z0, Z1, Z2) as well as the main coil were removed for constant operation with a power supply. In addition, a 1 W Gifford-McMahon (GM) cryocooler at 4 K and HTS current leads were installed in the cryostat to re-condense boiled helium gas. As a result, there was a long-term change of about 6 ppm in the magnetic field stability, but, in the short-term (a few hours), a change of about 2 ppm was observed. By the z0 shim control, in combination with the NMR field measurement, an averaged magnetic field drift of less than 0.0001 ppm/h was achieved.

An NMR spectrometer over 1 GHz requires the contribution of high-Tc superconductors(HTS). However, a persistent-mode operation with HTS cannot satisfy the field stability of 0.01 ppm/h at present. This is a great barrier for applying HTS to an NMR magnet. To overcome this problem, a new project was undertaken in Japan in October 2006. In the course of the project, we will develop a highly stabilized power supply, field-compensation methods, and measurement techniques that allow a certain field fluctuation. By integrating them, the feasibility of HTS to NMR will be demonstrated. We performed a long-term operation of a 600 MHz NMR magnet in the driven-mode. Allowable field fluctuation of the existing internal lock system for solution NMR was evaluated by a model experiment. As the next step, the innermost Nb3Sn coil of the 600 MHz NMR magnet will be replaced with a Bi-2223 coil, and the field homogeneity, as well as the field stability, will be evaluated. In the final step of the project, the replacement of the innermost coil of the existing 920 MHz NMR magnet will be planned. The targeting field is 24.7 T (1.05 GHz for 1H NMR resonance frequency). The solid-state NMR on 17O nuclei in a labeled peptide will be demonstrated using a magic angle spinning probe; the probe has a 1H decoupling frequency of 1.05 GHz.

High-temperature superconductors (HTS) are considered to be indispensable to realize NMR magnets that exceed 1 GHz owing to their high critical current densities even in high magnetic fields exceeding 20 T. Feasibility studies of the 1-GHz NMR magnet with the HTS inner coil have been reported. HTS conductors are brittle, and it is not easy to apply to superconducting coils such as the inner coils of the 1-GHz NMR magnet. Investigations into the mechanical properties of HTS coils are quite important. The hoop stress is an important factor in magnet design. Bi-2223 conductors are most promising because they are commercially available and can be obtained with lengths of more than 1,000 m. Double pancake coils with an inner diameter of 260 mm wound from Bi-2223/Ag conductors of the Sumitomo DI-BSCCO (high- type and high-strength type) were fabricated to evaluate the hoop stress dependence of the critical current of the coil. The double pancake coils were tested using the 14-T superconducting magnet with a room temperature bore of 400mm in diameter at the Tsukuba Magnet Laboratory (TML). The critical current of the high- test coil was 164 A, where the hoop stress was estimated at 323 MPa. The critical current decreased to 140 A after energizing the coil above a hoop stress of 300 MPa. The high-strength test coil burst at a hoop stress of approximately 200 MPa.

For the development of high magnetic field application using high temperature superconductor (HTS), Bi-2223/Ag tape is one of the promising materials because of its high current capacity and upper critical field. However, Bi-2223/Ag tape shows very strong anisotropy and significant deterioration of critical current in the magnetic field. To explore the possibility of HTS in high field applications, we evaluated the critical current and index value of Bi-2223/Ag conductor in high magnetic field. The Bi-2223/Ag tape was characterized as a function of increasing and decreasing field. The temperature dependence was also examined lower than 4.2 K. All measurements were carried out with hybrid magnet system up to 30 T and the experimental results are reported.

In order to obtain a large magnetic force environment using a commercially available superconducting magnet with a room-temperature bore, a new cryostat cooling a high-temperature superconductor (HTS) bulk cylinder with a G-M cryocooler down to approximately 20 K was developed. The cryostat was inserted so that the bulk cylinder might be located at the mid-plane of a 12-T cryocooler-cooled magnet. In the first experiment, the cylinder was cooled from room temperature to 21 K at 5.0 T. The backup field was then decreased to 0 T. A field of 4.9 T was maintained along the Z-axis inside the cylinder. The second experiment was carried out from a backup field of 11.5 T. The HTS bulk cylinder maintained the magnetic flux down to about a backup field of 7.6 T, at which point the superconducting state of the cylinder was lost in a brief period. The experimental data exhibit good accordance with the calculation results. In the calculation, the minimum BdB /dz of -1029 T2/m was estimated to be generated along the Z-axis. As that of the magnet is -564 T2/m at 12 T, the enhancement of the magnetic force with the HTS bulk cylinder was confirmed.

A workbench magnet that generates magnetic fields on a room-temperature (RT) plate was developed. The magnet did not have a RT bore. The improvement of accessibility to magnetic fields has made several types of processing and measurement easier. The magnet provides external fields, magnetic fields in the vicinity of the top of a winding, of a solenoid coil on the RT plate. The external fields depend strongly on the gap between the RT plate and the top of the winding. The magnet was a cryocooled superconducting magnet with a 1-W GM cryocooler at 4 K. The magnet successfully generated magnetic fields of over 3 T at the center of the RT plate. The magnet could generate magnetic fields more than twice the surface magnetic fields of permanent magnets with the same accessibility.

Although high-temperature superconductors (HTS) are very promising for high-field generation over 25 T, it is difficult to apply them to an NMR magnet because of their low index values and the difficulty caused by superconducting joints. We have developed a drift compensation technique to apply HTS to a high-resolution NMR using a 14 T (600 MHz) vertical NMR magnet. The magnet had a poor magnetic field stability of about -0.7 ppm/hour, so a drift compensation unit based upon a flux pump method was added. The unit consisted of nested inner (secondary) and outer (primary) coils. The inner coil was connected in series to the main coil circuits, and the outer coil was connected to the auxiliary power supply to sweep the output current very slowly. While the current of the outer coil was changed at an adequate sweep rate by the power supply, the current was induced by inductive coupling in the inner coil. The induced current canceled out the decay of the main coil current that caused the poor drift of the magnet. With the drift compensation unit, the magnetic field drift was improved to less than 0.0001 ppm/hour for 3 days at 14 T. This period was long enough for one NMR measurement.

The water-cooled insert magnet of the TML hybrid magnet successfully generated 37.9 T in a 32-mm room- temperature bore with a 14.02 T buckup field generated by a superconducting outsert magnet. At that magnetic field, the maximum electric power for the insert magnet was 13.35 MW. This Bitter-type insert magnet is divided into three coaxial coils, and the innermost coil consists of two coaxial coils. The inner coil is connected in series with the outer two coils connected in parallel. The Bitter plates for the outermost coil were made of GlidCop AL-25, and those for the other coils were made of hard-worked Cu-Ag plates. The thickness of the Cu-Ag plates was 0.40 mm, and the average 0.2% yield strength was about 810 MPa at 373 K

A magnet that allows horizontal as well as vertical access to the magnet center is suitable for industrial applications. We designed and fabricated a split-paired magnet cooled with two G-M refrigerators. The magnet has a vertical room-temperature bore of 400 mm in diameter and a horizontal room-temperature gap of 73 mm. Its design value of field uniformity around the magnet center is 0.53% in a space 200 mm in diameter and 50 mm in height. The magnet successfully operated up to 3 T. It was applied to produce anisotropic conductive sheets. Anisotropic conductive materials that are composed of dispersed contacts in polymer film are indispensable for electrical connections in multimedia devices. The magnet was combined with a sheet-forming machine that could press a mold up to 5 tons and 473 K. By using the mold with finely arranged ferromagnetic pins, the production of anisotropic conductive sheets with highly dense contacts and high reliability was successfully achieved

A new 52-mm warm-bore resistive insert for a hybrid magnet was designed and constructed at the Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science (NIMS). This magnet successfully generated a peak magnetic flux density of 35.5 T at the operating current of 34.88 kA and 367.5 V with a background field of 14.05 T. To supply the high magnetic fields for more time in the 52-mm warm bore, an axially cooled three-coaxial-coil structure and a staggered layout of the elongated cooling holes were adopted for Bitter disks after a parameter survey that was conducted to consider a reduction in the operating electric power. Disks were stacked in a modified Weggel scheme on a turntable with a rotating angle controlled by the stacking data of each coil. The innermost coil was connected electrically in series with the two outer coils connected in parallel. The Bitter disks used in the coils were made from two kinds of Cu-Ag plates. The magnet is now in operation for users

We developed an apparatus for the measurement of thermal expansion using double extensometers between 290 K and 5 K. The sample was set vertically in a variable temperature cryostat and its expansion or contraction was measured using the extensometers directly attached to the sample. The temperatures of the samples were controlled with He gas from the cryostat and a heater wounded around the sample chamber. In order to ensure the validity of this system, we measured the thermal expansion of Ag plates with different thicknesses. As a result, the measured thermal expansion curves were confirmed to show good agreement with each other for Ag plates with thickness of 3 mm, 1 mm and 0.2 mm. Good agreement was also ensured for the curves measured during both the cooling and warming processes. These results suggest that our system will be applicable for superconducting composites with a cross-section as small as 1 mm 2 .

A 920-MHz high-resolution NMR spectrometer has been operating at the Tsukuba Magnet Laboratory (TML) since April 2002. It has proved its effectiveness by determining the 3-D structures of protein molecules. To accelerate studies in structural biology and solid-state NMR, a second high-field NMR magnet was developed and installed at TML. Although its basic design was the same as that of the first magnet, some improvements were made. For the innermost coil, a 16%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor was employed. The increase in the critical current density above that of a 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor made it possible to reduce the conductor size from 3.5 mm /spl times/ 1.75 mm in the first magnet to 2.80 mm /spl times/ 1.83 mm in the second. At the same operating current of the first magnet, the second magnet is expected to operate at 930 MHz. The liquid helium reservoir and the superfluid helium cooler, which were separated in the first system, were united in the same chamber in the new magnet. The latter magnet was energized up to 21.9 T without quenching in March 2004 and has operated in a persistent-mode at that field. It will be utilized mainly for solid-state NMR measurements.

A direct measurement has been carried out of the upper critical magnetic field (B/sub c2/) of bronze-processed Nb/sub 3/Sn wires with and without the addition of various third-elements to the Cu-Sn matrix using a hybrid-magnet at the Tsukuba Magnet Laboratory at fields up to 30 T. The B/sub c2/ of pure Nb/sub 3/Sn rose with increasing heat treatment temperature up to 880/spl deg/C (B/sub c2/=24.7 T at 4.2 K), above which point it decreased rapidly. Its value was independent of the Sn content in the bronze. In the Ti addition samples, the optimum value of B/sub c2/ (=26 T at 4.2 K) depended on both Ti content and heat treatment temperature. When Sb was added, B/sub c2/ showed a sharp fall below a heat treatment of 700/spl deg/C due to the replacement at the Sn site by a Sb atom.

The performance of a flux concentrator using an YBCO oxide superconductor was tested to raise the steady state magnetic field generated by the existing magnet. This concentrator was composed of an outside hollow cylinder and a pair of half cylinders that goes in and out in the outside cylinder. This flux concentrator generated additional magnetic field more than 1.6 T for an applied magnetic field 28 T.

We have proposed new applications of bulk high-temperature superconductors in high magnetic fields. High-temperature superconductors, such as BSCCO or YBCO, maintain their superconductivity over 30 T at 4.2 K. A field-cooled superconducting hollow cylinder traps the magnetic flux inside itself. A field-cooled superconducting solid cylinder traps in the interior of it. An increase of the applied magnetic field induces shielding current in the interior of the cylinder to maintain the magnetic flux constant. By suitably arranging the cylinders, we can concentrate the magnetic flux and enhance the gradient of the magnetic field. In order to confirm these concepts, we performed experiments using bulk YBCO cylinders. The cylinders are made of YBa/sub 2/Cu/sub 3/O/sub 7-x/ quasisingle crystals containing Y/sub 2/BaCuO/sub 5/ particles. Hollow and solid cylinders were employed to concentrate the magnetic flux. Using three hollow cylinders, the concentrated magnetic field of 0.49 T was observed in the applied magnetic field of 10.14 T. The concentrated magnetic field of 0.64 T was observed for the solid cylinders in the applied magnetic field of 10.24 T. The magnetic flux concentration was observed even in the high magnetic field over 20 T.

Magnetic field direction often greatly influences material properties, such as critical current densities of tape-shaped superconductors. To determine the influence of this parameter, an object is usually rotated in a fixed magnetic field, which is not always effective. We are developing a variable-field-direction superconducting magnet that can change its field direction continuously in a 2D plane. Two sets of split-pair coils are placed perpendicular to each other, and the perpendicular magnetic fields generated by each split-pair coil are superimposed. By independently controlling the operating current of each split-pair coil, we can continuously change the direction of the superimposed magnetic field. Four solenoid coils were wound with Nb-Ti conductors. This magnet is designed to rotate a field of 1 T. The field homogeneity is estimated to be less than 1% in a 10 mm-diameter sphere volume. This is a conduction-cooled superconducting magnet employing 4K-GM refrigerators. We constructed a cryostat with two types of room-temperature bores and conducted a cooling test without solenoid coils and supporting structures was conducted.

The first 920 MHz high-resolution NMR (nuclear magnetic resonance) magnet was successfully installed at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. A persistent operation at 21.6 T has continued since April 2002 without any problems. Excellent field stability of 0.31 Hz/h was observed from December 2002 to January 2003. Since July 2002, the magnet was used as an essential part of the only 920 MHz high-resolution NMR spectrometer in the world. The signal-to-noise ratio of 0.1% ethylbenzene using a proton-selective probe was as high as 2981. An HCN triple-resonance probe is now attached to the spectrometer to contribute to the National Project on Protein Structural and Functional Analysis in Japan. The completion of the second 920 MHz-class NMR spectrometer is scheduled for spring 2004.

The Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science has been producing epoch-making achievements in the history of high-field magnets. TML is also known as one of the largest high magnetic field facilities in the world and opened to domestic and international users. As a milestone in the 1-GHz NMR project, a 920-MHz high-resolution NMR magnet using Nb 3 Sn innermost coil was developed in order to accelerate studies to obtain stereoscopic protein structures. Measurements for analyzing the stereoscopic structure of protein molecules using 920 MHz NMR magnet have been performed since July 2002.

In this paper, we propose new applications of bulk high-temperature superconductors in high magnetic fields. High-temperature superconductors, such as Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+d/ (BSCCO) or YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO), maintain their superconductivity over 30 T at 4.2 K. A field-cooled superconducting hollow cylinder traps the magnetic flux inside it. An increase of the applied magnetic field induces shielding current in the interior of the cylinder to maintain the magnetic flux constant. By suitably arranging the cylinders, we can concentrate the magnetic flux and enhance the gradient of the magnetic field. In order to confirm these concepts, we performed experiments using bulk YBCO hollow cylinders. The cylinders are made of YBa/sub 2/Cu/sub 3/O/sub 7-x/ quasi single-crystals containing Y/sub 2/BaCuO/sub 5/ particles. They have an inner diameter of 5 mm, an outer diameter of 10 mm, and a height of 10 mm. Using three hollow cylinders, a magnetic concentration of 0.49 T was observed in an applied magnetic field of 10.14 T. The energized hollow cylinder with a shielding current modify surrounding magnetic fields and magnetic force fields. A magnetic force field enhanced by using a hollow cylinder was calculated numerically for an applied magnetic field of 10 T and estimated to exceed 6000 T/sup 2//m.

A rapid heating and quenching (RHQ) operation along a long-length of jellyroll Nb/Al precursor over 300 m has been established. The J/sub c/ varies sensitively with the joule-heating current (I/sub RHQ/) that determines the temperature from which a precursor wire is quenched, excluding the "plateau" region where the bcc supersaturated-solid solution (Nb(Al)/sub ss/) only forms. The RHQ operation using such a plateau condition can suppress a scatter of J/sub c/ from point to tail of a long-length of wire. The standard deviation of J/sub c/ (4.2 K) at 21 T along a long-length of wire was about 5%, which was less than the variation of J/sub c/ with I/sub RHQ/ in the plateau region (/spl plusmn/7%). The mechanical deformation process needed when incorporating the Cu stabilizer also plays an important role in ensuring uniform heat treatment of the coil that is wound with a long-length of wire and, hence, large heat capacity. Although a temperature ramp-up rate might differ from place to place in the coil, the deformation processing makes such a ramp-up rate insensitive to these critical parameters. The coils using 300.5 m and 254 m lengths of Cu-clad RHQT JR Nb/sub 3/Al conductor generated additional 2.3 T and 3.2 T in bores of 90.2 mm/spl phi/ and 64.6 mm/spl phi/, respectively, indicating that a long-length of RHQT JR Nb/sub 3/Al conductor can be trustworthy for practical coil applications.

As a milestone in the 1-GHz NMR magnet project that is being carried out at the Tsukuba Magnet Laboratory (TML), a 920-MHz high-resolution NMR magnet was successfully manufactured. It is made of 15%Sn-bronze-processed (Nb, Ti)/sub 3/Sn, Ta-reinforced (Nb, Ti)/sub 3/Sn, and NbTi conductors. The room-temperature bore of the cryostat is 54 mm in diameter. All the coils are cooled with pressurized superfluid helium at 1.55 K. The magnet was moved to a new building of the TML in December 2001. A persistent operation at 920 MHz started in April 2002. The field homogeneity after correcting with superconducting shim coils was less than 0.1 ppm in a sample volume. Field decay decreased to below 1.3 Hz/h at the beginning of July. NMR measurements using this magnet started in July.

The field stability of high-field resistive magnets is generally inferior to that of superconducting magnets. The main reason for this is the low inductance of resistive magnets. High-precision measurements, such as those conducted using nuclear magnetic resonance, are very difficult by using high-field resistive magnets due to lack of field stability and ripples in the magnetic fields. However, recent progress in the area of high-temperature bulk superconductors indicates that it is possible to drastically improve these measurements. We used a YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) bulk cylinder made by the Nippon Steel Corporation. Its dimensions were 5 mm (inner diameter)/spl times/10 mm (outer diameter)/spl times/10 mm (height). A pickup coil was inserted into the center of the cylinder to measure ripples in the magnetic field. The bulk cylinder with the pickup coil was then inserted into a resistive magnet of the Tsukuba Magnet Laboratory. At a certain field, the bulk superconductor was cooled down from room temperature to the superconducting state. The signals of the pickup coil before and after transition to the superconducting state were compared.

Development of a high-field NMR magnet has been underway at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. The magnet succeeded in a persistent-mode operation at 21.17 T in December 1999. A 283-day long-term operation was carried out from October 2000 to August 2001. It included a persistent operation at 21.6 T (920 MHz) for 108 days. This was the highest field that the superconducting magnets have ever achieved in a persistent operation. Field decay was less than 2 Hz/h. Field homogeneity after correcting with superconducting shim coils were less than 0.1 ppm in a sample volume. These results confirmed that this magnet had been successfully developed as a high-resolution NMR magnet.

The critical currents of the innermost coil mainly limit the highest field of the present superconducting solenoids. For this reason, the insert coils in high-field solenoids are often wound with newly developed superconductors to increase their highest fields. This is a good demonstration of the high-field performance of the newly developed conductors. Design issues of high-field superconducting inserts are overviewed. Representative examples that have been carried out and are now in progress are introduced.

Magnetic force is one of the most promising tools to realize a virtual microgravity environment on Earth. It has been found that the growth of protein crystals might be affected by microgravity. The reason for this influence appears to be the suppression of the convectional flow. We are developing superconducting magnets to generate spatially uniform and high magnetic force fields that will suppress the convectional flow. We have completed a design for a superconducting magnet that is composed of Nb/sub 3/Sn and NbTi conductors. This magnet is designed to generate spatially uniform magnetic force fields up to 860 T/sup 2//m. The design was carried out using a method of nonlinear programming. The error of the axial component of the magnetic force fields is less than 1%, and the error of the radial ones is less than 2%. The central magnetic field of this magnet is 17 T at the operating current. We identified this magnet as Prototype II because the Prototype I, which had been constructed in 1998, was constructed with only NbTi conductors. Furthermore, it generates a magnetic force field of 240 T/sup 2//m and has a central magnetic field of 9 T, had been constructed in 1998. Prototype II will be cooled down below 4.5 K by two GM cryocoolers.

Persistent-mode operations of a cryocooler-cooled HTS magnet were carried out. The closed circuit of the magnet consisted of a Bi-2212 solenoid coil and a NbTi/CuNi persistent-current switch (PCS). Thermal conductance between the PCS and the cooling stage was designed not to heat up the coil. The temperature increase was maintained within 0.1 K during the normal state of the PCS. The transition times of the PCS between a superconducting and a normal state were sufficiently short for practical use. The magnet started a persistent-mode operation from an initial magnetic field of 2.1 T. Decay behaviors during persistent-mode operations were successfully observed over 90 hours. Except for the initial period, field decay was limited by resistance of the joint. A method to compensate the field decay was performed by installing a NbTi cylinder in the coil bore.

The magnetic lens, a new device for concentrating magnetic flux using the diamagnetism of superconductors, has been experimentally confirmed by employing HTS bulk. In this paper, a new magnetic lens made of NbTi/Cu rings is introduced. The rings, which have identical outer diameters and increasing inner diameters, were stacked to form a hollow cone. Each ring has a slit to suppress the circumference current. The slits were placed in the same position to form a leakage path. The lens was assembled in an existing cryostat system with a NbTi magnet, and the magnetic properties were measured. The concentrated magnetic flux density rose to 0.618 T when the background field reached 0.339 T at the tip of the lens. The concentration ratio was 1.82. These experimental results agree well with the numerical results.

A Nb/sub 3/Al superconductor based on jelly-rolled (JR) Nb/Al composites of high performance can be fabricated by rapid-heating and quenching of a wire of such composites with subsequent transformation-annealing to form the Nb/sub 3/Al phase (RHQT process). Since the conductor thereby is heated up to 2000/spl deg/C, far above the melting point of Cu, the Cu stabilizer needs to be externally incorporated by a mechanical-cladding method between quenching and annealing. Such an appropriate deformation promotes the transformation from a disordered bcc phase, and thereby enhances the critical current density J/sub c/. A solenoid coil was fabricated by a wind-and-react method: the Cu-clad conductor (1.61/sup w//spl times/0.71/sup t/ mm/sup 2/) with Al/sub 2/O/sub 3/ yarn insulation was wound into a coil (19.7/40.8/sup /spl phi///spl times/49.7/sup H/ mm), transformed at 800/spl deg/C, and impregnated with beeswax. The resultant coil, while carrying a current of 179 A at 2.1 K in a superconducting back-up field of 21.2 T, generated an additional 1.3 T. The total magnetic field of 22.5 T is the highest record ever for a metallic superconducting coil.

As a milestone in the 1-GHz NMR magnet project being carried out at the Tsukuba Magnet Laboratory, a 900-MHz class NMR magnet was successfully manufactured and operated in December 1999. The developed magnet is made of 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn, Ta-reinforced (Nb,Ti)/sub 3/Sn, and NbTi conductors. The room temperature bore of the cryostat is 54 mm is diameter. All the coils are cooled with pressurized superfluid helium. The magnet generated a field of 21.20 T in a driven mode and then operated in a persistent mode at 21.17 T corresponding to a proton NMR frequency of 902 MHz. The field may be raised to the range of 21.6 T (920 MHz) in the near future.

Magnetic force is one of the most promising tools to realize a virtual microgravity environment on earth. It has been found that the growth of protein crystals might be affected by microgravity owing to the suppression of convectional flow. We started the development of superconducting magnets for the generation of uniform and high magnetic force fields to suppress convectional flow, as it was not clear what configuration of superconducting coils could generate most effectively high magnetic force fields, while they maintain their uniformity. For this purpose, we used a nonlinear programming method. The results obtained clarified that a magnet whose inner coil is longer than the outer one can generate more uniform and higher magnetic force fields in a long sample space. A superconducting magnet generating a magnetic force field of 240 T/sup 2//m has already been constructed with NbTi conductors at the Tsukuba Magnet Laboratory. We have also completed the design of a superconducting magnet composed of Nb/sub 3/Sn and NbTi conductors to generate uniform magnetic force fields up to 882 T/sup 2//m.

A resistive insert magnet consisting of Bitter-type coils was fabricated, incorporated into the 400-mm bore of the superconducting outsert, and tested under a backup field of 14.2 T. This hybrid magnet generated a total field of 37.3 T in the center of a 32-mm room-temperature bore. At this magnetic field, the operating current of the resistive insert magnet was 33.25 kA at a voltage of 431 V. This insert magnet is divided into three coaxial coils. The bitter plates of the two inner coils are made of hard-worked Cu–Ag plates, and those of the outermost coil are made of GlidCop AL-25. The thickness of the plates used in the two inner coils was 0.84 mm, and the 0.2% proof stress in the direction parallel to the roll work was about 800 MPa at 375 K. This temperature is designed to be the maximum of the innermost coil at 37.3 T. Elongated cooling channels were punched in a staggered formation in these plates. The flow rate of the cooling water was 0.141 m 3 /s at the maximum field. Regular operation up to 35 T started from June 2000 at the Tsukuba Magnet Laboratory.

The Tsukuba Magnet Laboratory (TML) of the National Research Institute for Metals has been producing epoch-making achievements in the history of high-field magnets. Its hybrid magnet is in operation, providing users with fields up to 30 T in a 52-mm∅ room-temperature bore. In September 1999, the hybrid magnet generated a field of 37.3 T in a 32-mm∅ room-temperature bore, which was the world record of the steady-state fields at that time. The superconducting magnet system operating at TML succeeded in generating 23.4 T using two Bi-2212 insert coils. As a milestone in the 1 GHz NMR magnet project carried at TML, a 900 MHz NMR magnet was successfully manufactured and operated in a persistent mode. A challenging program in which different types of superconducting magnets are developed to meet specific requirements is in operation. One example is a magnet designed to generate uniform magnetic force fields defined as B grad B in a sample space. TML is now a user facility open to domestic and international users. Efforts will be continued to improve its high-field facilities by developing magnet technology as well as materials for high-field magnets.

We have developed a novel superconducting joint method for Nb3Al conductors, which can be used for the innermost coil of a 1-GHz NMR magnet. First, we optimized the joint property; then, we prepared a closed circuit with an NbTi coil and a pair of Nb3Al-NbTi joints; finally, we determined the joint resistance by using the field decay of the persistent current. A joint resistance of 1.27 times 10-12 Omega was obtained, which is sufficiently low for high field NMR.