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A cryogen-free 20 T superconducting magnet with a 52 mm room-temperature bore was developed and installed in Tohoku University in 2013. This magnet consists of a Bi2223 insert coil, which generates 4.5 T, and outer low-temperature superconducting (LTS) coils. Both coils were cooled by a GM/JT cryocooler with 4.2 W-class cooling capacity at 4.3 K. To generate a higher magnetic field, a new cryogen-free 25 T superconducting magnet using a REBCO insert coil, which generates 11.5 T, and new outer LTS coils is now under development. The magnetic field contribution of this REBCO insert coil is considerably higher than that of the previous Bi2223 insert coil, and the ac-loss of the insert coil during field ramping rises to approximately 9.7 W. The LTS coils have to operate at about 4 K, but the REBCO coil can operate at various temperatures above 4 K. In addition, the cooling capacity of a GM cryocooler is greater than that of a GM/JT cryocooler around 10 K. Thus, the REBCO insert coil is cooled to about 10 K by using two GM cryocoolers, independently of the LTS coils, which are cooled by two GM/JT cryocoolers. To protect the cryocoolers from the leakage field of the magnet, the two GM cryocoolers cool circulating helium gas through heat exchangers, and the gas is transported over a long distance to another heat exchanger provided for the REBCO insert coil. The maximum temperature of the REBCO insert coil was calculated under the most severe condition where an insert coil ac-loss of 9.7 W was generated continuously. And it was confirmed to be less than the target maximum temperature of 12 K. [ABSTRACT FROM PUBLISHER]

We have been developing high-strength Nb3 Sn strand cables to construct a high-field superconducting outsert for a 45 T hybrid magnet with a 25 T water-cooled resistive magnet. Evidence for cold work strengthening of repeated bending treatment (prebending effect) on Nb3 Sn strands internally reinforced with CuNb stabilizer, which exhibits significant enhancement of the critical current density, has been found in the superconducting magnet fabrication process using a react-and-wind method. The strand cables were designed by controlling the constituent number of CuNb/Nb3 Sn strands with the prebending effect and stainless steel strands, which are expected to have a stress limit 580 MPa at 0.4% strain. In order to design a compact superconducting outsert, high-strength strand cables are adopted in a magnetic field region below 14 T to maintain relatively large engineering current densities (Je). In a higher-field region above 14 T, YBa2Cu3O7 (Y123) coated conductors are employed for an insert coil. Using combination of V 123, Nb3 Sn and NbTi superconductors, a 20 T superconducting outsert with a room temperature bore of 400 mm consisting of three layers made of Y123, two layers of CuNb/Nb3 Sn and two layers of NbTi was designed. The coil parameters are 440 mm inner diameter, 1080 mm outer diameter and 1138 mm coil height. A very compact 20 T superconducting outsert with a stored magnetic energy 72 MJ at an operation current 903 A can be developed for a 45 T hybrid magnet. [ABSTRACT FROM AUTHOR]

The High Field Laboratory for Superconducting Materials (HFLSM) and the Tsukuba Magnet Laboratory (TML) conducted in collaboration a case study on development of a 50 T-class hybrid magnet. To construct a high magnetic field magnet with compact and energy-saving design as well as with easy operation and maintenance, one has to develop high-strength Nb3 Sn strand cables, with maximized superconducting characteristics and which can withstand a large electromagnetic force over 500 MPa. For this purpose, the HFLSM has proposed and investigated the effect of repeated bending treatment (prebending) on Nb3 Sn strands internally reinforced with CuNb stabilizer leading to significant enhancement of the critical current density. In this report we present our results on application of the prebending effect to the development of high-strength strand cables. The designed prebent-strand cables are composed of three CuNb/Nb3Sn strands (3 x Φ = 1.73 mm) and four stainless steel strands (4 x Φ = 1.73 mm). High-strength CuNb/Nb3Sn strand cables have shown a stress limit of 552 MPa at 0.4% strain, and a critical current of Ic = 1000 A at 18.5 T and 2.0 K. For such high-strength strand cables, a 20 T superconducting magnet with a room temperature bore (4 = 400 mm) consisting of five layers made of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are: inner diameter Φ = 440 mm, outer diameter Φ = 1332 mm, coil height 1321 mm, inductance 350 H and magnetic stored energy 144 MJ at 908 A of the operation current. Winding of the coil was experimentally successfully simulated using dummy 3 + 4 strands cable composed of three Cu strands and 4 stainless steel strands with a similar design to the 3 + 4 strands superconducting cable presented above. The 20 T superconducting coil will be used as a 20 T outsert for a 25 T water-cooled resistive insert to obtain a 45 T hybrid magnet. [ABSTRACT FROM AUTHOR]

In order to obtain a high-intensity neutron beam for neutron scattering experiments, strong sextupole magnets with large apertures are useful as a focusing element. We have started the development of a Nb3Sn sextupole magnet for this purpose. The design field strength of the sextupole is 12780 T/m² and the aperture of the coil is 46 mm in diameter. As a first step of the development, three model coils have been made in order to learn about Nb3Sn technology and to evaluate the fabrication techniques. Single-pole tests of these coils have been performed to assess the conductor stability and training behavior of the Nb3Sn coils. This paper describes the design of the magnet, the fabrication of the model coils and the results of single-pole tests. [ABSTRACT FROM AUTHOR]

In order to study magnetic levitation easily, we develop a cryo-cooled large magnetic field gradient superconducting magnet as the insert magnet for a large bore (220 mm cylindrical room temperature bore) cryo-cooled superconducting magnet. The insert magnet consists of a modified cusp coil and generates large magnetic field gradient. Combined with the background magnet, this magnet system realizes the stable magnetic levitation for the diamagnetic materials. The magnet system is designed to generate 1400 T² /m for the magnetic levitation of water. As a result, this cryo-cooled magnet system quenched from the insert magnet, but could achieve nearly 1050 T² /m. As a performance test, a bismuth tip was levitated using the newly developed cryo-cooled superconducting magnet. [ABSTRACT FROM AUTHOR]

We have started a new project to develop a cryogen-free 19 T superconducting magnet with a 52-mm room temperature bore. The magnet is designed to be consisting of three sections, i.e., the innermost high-Tc superconducting coil section, the middle Nb3 Sn section and the outer NbTi section. The electromagnetic hoop stress is applied to the supercon- ducting wire due to the magnetic field generation. It is described to the products of magnetic field, transport current density, and winding radius. The maximum electromagnetic stress is estimated to exceed 200 MPa in the middle Nbc Sn section and 50 Pa in the high-Ta section. It is important to explore the mechanical characteristics to design the magnet. In this study, mechanical properties, i.e., stress-strain characteristics and stress dependence of the critical current, were investigated for oxide superconducting tapes. [ABSTRACT FROM AUTHOR]

MJ-class HTS SMES has been developed for bridging instantaneous voltage dips using newly-developed Bi-2212 cable. The developed Bi-2212 wire for SMES coils achieves high-performance conductive characteristics that do not deteriorate in high magnetic fields beyond 10 T, which enable compactly arranged SMES coils to be operated in a high magnetic field, and SMES coils of the Bi-2212 wire can be adequately insulated due to a high temperature margin. Therefore it is possible for the SMES coils to enhance dielectric strength and output power. The insulating, cooling and conductive characteristics of 4 unit coils (Outer Diameter: 700 mm, Height: 127 mm, Stored Energy: 90 kJ) were checked under a variety of conditions. Moreover, fundamental performance tests were done on bridging instantaneous voltage dips, using a 125 kW resistance and 50 kW motor as imitation loads. Testing showed that the HTS SMES operated reliably. Up to the present, 11 unit coils (Outer Diameter: 700 mm, Height: 390 mm, Stored Energy: 560 kJ) have been stacked and tested. [ABSTRACT FROM AUTHOR]

Abstract: We have successfully developed a cryocooled superconducting magnet which generates the world’s highest magnetic field of 18.1 T. This conduction-cooled superconducting magnet has a 52-mm room temperature bore. The magnet consists of three sections; a high- superconducting insert coil, four Nb3 Sn coils, and an outer NbTi coil. Each section was energized by an individual power supply. The superconducting coils are cooled conductively by a Gifford-McMahon–Joule-Thomson (GM–JT) cryocooler with a cooling capacity of 4.3 W at 4.3 K. The ramp-up time to 18 T is 60 min. The high- insert coil is composed of 25 double- pancake coils using Ag/(Bi,Pb)2 Sr2 Ca2 Cu3 O10 (Bi2223) high- superconducting tape with stainless steel tape reinforcement. The reinforcement co-winding reduces the effective hoop stress down to 48 MPa, and, hence, Bi2223 tape can be used. The innermost of the Nb3 Sn section is made of an internal-tin-processed Nb3 Sn wire because this wire can withstand high critical current density in high magnetic fields. Other three coils require high mechanical strength. They experience hoop stress of 230 MPa, and in this case, bronze-processed high-strength Nb3 Sn wires were used. The magnet has a distinctive feature, that is the high- insert coil is replaceable. It indicates that the magnet can be used as a 15.5 T back-up magnet for a new insert coil. A Y123 coil is a candidate for the replacement. [Copyright &y& Elsevier]