Junji Sakuraba

(Nb, Ti)3Sn Superconducting Magnet Operated at 11 K in Vacuum Using High-Tc (Bi, Pb)2Sr2Ca2Cu3O10 Current Leads

A conduction-cooled superconducting magnet using high-Tc oxide current leads was successfully demonstrated. We succeeded in constructing the (Nb, Ti)3Sn multifilamentary superconducting magnet system without liquid helium, which is operated at 11 K in vacuum using a cryocooler and generates a magnetic field of 4.6 T in a 50 mm bore (38 mm room temperature bore). Use of (Bi, Pb)2Sr2Ca2Cu3O10 current leads effectively contributed to realization of the compact cryostat with large current leads of 500 A.

11 T liquid helium-free superconducting magnet

Abstract An 11 T liquid helium-free superconducting magnet designed at 6 K in vacuum using high temperature superconducting current leads was developed. The NbTi Nb 3 Sn coil was conductively cooled down from room temperature to 4.1 K in 40 h by two 4 K GM-cryocoolers. In a performance test, the coil temperature rose to 6.8 K for the inner Nb3Sn coil and 5.9 K for the outer NbTi coil, while sweeping the field at 5 A min−1. A central field of 10.7 T in a 52 mm room temperature bore was generated at an operating current of 149 A. Holding the field at 10.5 T was achieved continuously for 24 h at a constant coil temperature of 4.8 K.

15 T Cryocooled Nb3Sn Superconducting Magnet with a 52 mm Room Temperature Bore

We succeeded in demonstrating a 15.1 T cryocooled Nb3Sn superconducting magnet with a 52 mm room temperature bore. Two operating currents of 157 A and 90 A for the divided section coils were utilized for the first time in a cryocooled superconducting magnet system. It is found that the current leads are no longer the dominant heat loads because of the use of high-temperature superconductors. In order to realize a high-field cryocooled superconducting magnet comparable to the usual superconducting magnet immersed in liquid helium at 4.2 K, we maintained the coil temperature at a value below 5.0 K during the field sweep in a high magnetic field region.

Performance of a Cryogen-Free 30 T-Class Hybrid Magnet

The worlds first cryogen-free hybrid magnet, which was developed at the High Field Laboratory for Superconducting Materials in order to realize an easy-operational magnet system with no use of liquid helium and nitrogen, has achieved 22.7 T in a 52 mm room temperature bore. After this success, we started to construct a new cryogen-free 30 T-class hybrid magnet, consisting of an outer wide-bore cryogen-free 11 T superconducting magnet and an inner water-cooled 19 T resistive magnet. Up to now, the NbTi outer section coil and the Nb3Sn inner one of a wide-bore cryogen-free superconducting magnet has generated individual central fields of 5.3 T at 350 A and 5.8 T at 303 A, respectively in a 360 mm room temperature bore. The wide-bore cryogen-free superconducting magnet was energized up to 9.5 T as a total background field. In hybrid magnet mode the system was operated up to an 8.5 T background field form the cryogen-free superconducting magnet, because a cooling problem was encountered with the innermost coil bobbin during ramping the Bitter magnet. As a result, the cryogen-free hybrid magnet generated 27.5 T in a 32 mm room temperature bore

Advances in the first cryogen-free hybrid magnet

In order to solve problems of a large amount of liquid helium supply for a wide bore superconducting magnet of a hybrid magnet, we intended to construct the first cryogen-free 23 T hybrid magnet, consisting of an outer wide bore cryogen-free superconducting magnet and an inner water-cooled resistive magnet. Up to now, the wide bore cryogen-free superconducting magnet was tested to generate a total central field 6.0 T in a 360 mm room temperature bore. The worlds first cryogen-free hybrid magnet achieved 21.5 T in a 52 mm room temperature bore, combining with 15.5 T water-cooled Bitter magnet. As the result, the cryogen-free hybrid magnet no longer needs a troublesome handling time for liquid helium transfer, and the machine time is extremely enlarged. The improvement of the maximum magnetic field generation toward our design value of 23 T is being carried out continuously. Furthermore, we have started a new construction project of a cryogen-free 30 T hybrid magnet. Since the magnetic force field BdB/dz of 2274 T/sup 2//m is obtained at 21.5 T, the cryogen-free hybrid magnet can provide a large magnetic force field enough to levitate diamagnetic materials. For new processing of materials development, a YAG laser furnace was installed into the cryogen-free 23 T hybrid magnet. A container-less melting for paraffin was examined by controlling a thermocapillary convection. We succeeded in fabricating a magnetic field oriented ball in magnetic levitation.

Cryocooler Cooled Superconducting Magnets and Their Applications

Various types of cryocooler cooled superconducting magnets have been constructed and already used for some applications. An 11 T-52 mm room temperature bore magnet is used for a high-field heat treatment equipment, a 6 T-220 mm room temperature bore magnet is used for a new experiment on the electrochemical reaction in high fields, and a 5 T-50 mm bore with 10 mm gap split type magnet has been combined with an X-ray diffraction apparatus.

Critical current measurement unit utilizing Bi-based oxide superconducting current leads and cryocoolers

A measurement unit has been developed to investigate the dependence on temperature and magnetic field of superconducting cable critical current without the use liquid helium or liquid nitrogen. A test specimen, which is tested using the four probe method, is cooled by a Gifford-McMahon (GM) type cryocooler to a temperature of 20 K to 90 K in a vacuum vessel. Transporting direct current, up to 500 A, is supplied to the specimen through the Bi-based oxide superconducting current leads. The advantages of utilizing oxide superconducting current leads are that the leads have low thermal conductivity, and also that the leads create no Joule heating effect, so the heat input to the sample is minimized. The external magnetic field of up to 3 T, which is applied to the specimen, is generated by a superconducting magnet which also uses Bi-based oxide superconducting current leads and is also cooled by a GM cryocooler. Detail design of the unit, the results of operating test and an example of the measurement result on the Bi-based oxide bulk specimen are presented in the paper.<<ETX>>

High-Tc Oxide Current Leads and Superconducting Magnet Using No Liquid Helium

We applied Bi-based oxide superconducting bulk for use as current leads in a cryocoolercooled superconducting magnet that does not use liquid helium. The bulk has a composition of (Bi + Pb):Sr:Ca:Cu = 2:2:2:3 and is utilized in the form of thin-walled sintered cylindrical tubes. The critical current and the critical current density of the bulk under a self-magnetic field at 77 K are 1100 A and 1200 A/cm2, respectively.

Construction of the cryogen-free 23 T hybrid magnet

In order to settle problems requiring a large amount of liquid helium and limiting the operation time for a wide bore superconducting magnet of a hybrid magnet, a cryogen-free 23 T hybrid magnet is being constructed at the High Field Laboratory for Superconducting Materials for the first time. An outer compact superconducting magnet is wound with highly strengthened CuNb/Nb/sub 3/Sn multifilamentary wires and is refrigerated conductively by GM-cryocoolers. The maximum stress value of 210 MPa was designed for the CuNb/Nb/sub 3/Sn coil. The cryogen-free superconducting magnet will be operated using dual power supplies independently, and has potential to generate central fields of 4.59 T at 198 A for the outer section NbTi coil and 3.41 T at 145 A for the inner section CuNb/Nb/sub 3/Sn coil. When the cryogen-free 7.5 T superconducting magnet with a 360 mm room temperature bore is combined with an inner 15.5 T water-cooled resistive magnet, a cryogen-free hybrid magnet will achieve 23.0 T in a 52 mm room temperature experimental bore.

Design of a cryocooler-cooled large bore superconducting magnet for a 30T hybrid magnet

We are now developing a 30 T hybrid magnet utilizing a cryocooler-cooled superconducting magnet wound with highly strengthened (Nb, Ti)/sub 3/Sn. Diameter of the room temperature bore of the superconducting magnet is 360 mm and it generates 11.1 T. Water cooled resistive insert magnet generates 18.9 T, thus the hybrid magnet generates a central field of 30.0 T. The (Nb, Ti)/sub 3/Sn multifilamentary wires are strengthened by Cu/NbTi composite which volume ratio in conductor is about 35%. The reinforcing Cu/NbTi composite changes to CuTi intermetallic compounds during heat treatment for reaction of (Nb, Ti)/sub 3/Sn phase formation. The (Nb, Ti)/sub 3/Sn coil with inner diameter of 400 mm will be fabricated by wind and react method with Cu/NbTi reinforced (Nb, Ti)/sub 3/Sn wires. The innermost section of (Nb, Ti)/sub 3/Sn coil is wound with a wire which diameter is 1.85 mm and next second section is wound with a wire diameter of 1.8 mm. The (Nb, Ti)/sub 3/Sn coil is operated at 303 A and generates 5.8 T. The NbTi coil is wound with NbTi wires of 2.0 mm and 1.6 mm diameters. The NbTi coil generates 5.3 T at an operating current of 350 A. The maximum hoop stress is under 220 MPa for (Nb, Ti)/sub 3/Sn coil and 200 MPa for NbTi coil.