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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 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.

The innermost coil of a new high-field NMR magnet such as a 1-GHz NMR magnet is designed by using a new superconductor. It is therefore important that a superconducting joint between the new superconductor and the NbTi conductor was developed. We have developed a new superconducting joint method for the Nb3Al conductor, which is expected to be used for the innermost coil of the 1-GHz NMR magnet. This joint method uses the Nb3Sn layer that is formed on the Nb matrix surface of the Nb3Al conductor. This Nb3Sn layer enables the soldering of the Nb3Al conductor; thus, it is possible to solder the Nb3Al conductor and NbTi conductor. The superconducting property of the Nb3Al-NbTi joint that is joined by the superconducting solder (for example, SnBiPb solder) showed good performance under a magnetic field of 0.1 T

This paper presents a long charging delay for a no-insulation (NI) REBCO layer-wound (LW) coil and an electromagnetic-induced thermal runaway, resulting in damages on the coil. A small NI REBCO LW coil with a self-inductance of 1.62 mH showed a charging delay time constant of ∼3000 s at 4.2 K. The coil was installed in the cold bore of a low-temperature superconducting (LTS) magnet, and the LTS outer coil was charged. Although the circuit of the NI REBCO LW coil was opened, the induced current inside the coil screened the magnetic field generated by the outer coils. Eventually, the NI REBCO LW coil showed a thermal runaway during charging the outer coils. After the experiment, we found burnouts of the REBCO conductor near the electrodes and buckling of the conductor for all the layers of the winding. The present results point out the technical problem and the worst case for a NI REBCO LW coil, which must be considered.

We have developed a protein crystal formation system, which can, on the ground, suppress convections, exerting magnetic forces on the solution including proteins. The protein formation system consists of a superconducting magnet system, protein crystallization cells, and observational equipment; the latter two devices are placed in the magnet bore. The superconducting magnet system includes two coil groups, each generating a magnetic field opposing in direction to each other. The product of magnetic flux density and its spatial gradient is proportional to the magnetic force and needs to be approximately 1400 T2/m in order to levitate water. The magnet is operated in persistent current mode. The crystallization cells are made of a transparent plastic on a plate. The experimental space and cells can be controlled between 4°C and 20°C. The observational equipment, which is a kind of periscope, enables in-situ observation of protein solution in high magnetic fields. In order to optimize experimental conditions, we have also carried out a simulation study based on a solution flow model.

In a measurement of the critical current of a rare-earth cuprate (RE-Ba-Cu-O) coated conductor in liquid helium, we found that the coated conductor delaminated under a magnetic field with angles of 10° and 20° relative to the tape surfaces. To explore causes of the delamination, strains in the direction of the tape widths were observed under an increase in the background magnetic field using two kinds of coated conductors: one had a copper stabilizer surrounding the superconducting layer, while the other had a copper stabilizer that was laminated on the tape surface. The former conductor did not delaminate, but the latter conductor delaminated by applying only a background magnetic field in liquid helium. For the above reason, we concluded that some mechanical support was required to prevent the latter coated conductor from delaminating. In fact, the delamination was preventable by a mechanical support born down to the tape surfaces. As a result, we succeeded to measure the critical current of the coated conductor in liquid helium under a background magnetic field. These results suggest that mechanical support for joints in REBCO coils needs careful consideration.

RE-Ba-Cu-O (REBCO) high-temperature superconducting conductors have the advantage of high critical current density in a magnetic field above 10 T as well as tolerance to high tensile stress. REBCO high-temperature superconducting coils are expected to be applied to superconducting magnets using cryocoolers. While epoxy-resin-impregnated superconducting coils are considered to be appropriate for superconducting magnets using cryocoolers because the impregnation provides sufficient thermal conductivity, the degradation of epoxy-resin-impregnated REBCO coils due to extremely low nominal cleavage strength is a serious problem. This problem is negligible for wax (paraffin)-impregnated REBCO coils. A wax-impregnated GdBCO layer-wound coil using cryocoolers was successfully operated at a current between $-$ 300 and 300 A.

We are developing a superconducting magnet system that can, on the ground, control gravitational force on protein crystal solutions through use of magnetic forces. Magnetic forces give rise to a variety of effects on motions of protein solutions. We proposed a dynamical model of fluid and material flow in solution under gravity and magnetic force in our previous works. The numerical calculation results showed that magnetic forces could suppress convections and lead to unexpected concentration distributions of solutes under some hypothetical conditions. In this paper, we present some simulation results under actual conditions in a superconducting magnet. The results show that inhomogeneity of magnetic force affects modifies concentration and convection distributions.

A nuclear magnetic resonance (NMR) system using a high-temperature superconducting (HTS) magnet and a probe with an HTS radio frequency coil is currently under development. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. RE-Ba-Cu-O-coated (REBCO-coated) conductors offer the advantages of a higher critical current density than low-temperature superconductors in magnetic fields above 10 T as well as tolerance to high tensile stress. Both of these factors are expected to lead to a reduction in the volume of the magnet. Four REBCO layer-wound test coils were fabricated in order to investigate their properties under electromagnetic forces in an external magnetic field of up to 17. 2 T. The REBCO coils with a practical inner diameter were successfully operated under electromagnetic forces of over 200 MPa in high magnetic fields.