Mamoru Ishihara

(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.

Properties of Ag-Sheathed Bi-Pb-Sr-Ca-Cu-O Superconducting Tapes Prepared by the Intermediate Pressing Process

The influence of an intermediate pressing process on the superconducting properties of Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting tapes has been investigated. The critical current density (Jc) was improved by the effect of the uniaxial pressing and by a sintering process after the initial sintering. The maximum transport Jc at 77.3 K under zero magnetic field was indicated as 2.36×104 A/cm2, and that at 4.2 K under zero magnetic field was indicated as 1.5×105 A/cm2. The magnetic field dependence on the Jc at 4.2 K was summarized as follows: 5×104 A/cm2 (I⊥H, C-axis⊥H, 10 T) and 3×104 A/cm2 (I⊥H, C-axis//H, 10 T).

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.

Thermal transport and scattering mechanisms in BPSCCO high-Tc superconductors

Abstract The thermal conductivity (ϰ) for BPSCCO superconductors has been measured between 10 K and 200 K at various stages of the annealing process. Decrease of charge carrier densities due to annealing in vacuum operates as suppressing a clear enhancement of ϰ in the vicinity of T c . The scattering mechanisms in thermal transport have been discussed, applying a relaxation time approximation to phonon transport and Kadanoffs theory to electron transport. The analysis based on the d-wave state reproduces the present experimental result better than that on the s-wave state.

Characteristics of high temperature operation in a conduction cooled (Nb,Ti)3Sn superconducting magnet

Intense investigations aiming at application workable at liquid nitrogen temperature have been performed, since the discovery of high temperature superconductors with the critical temperature Tc in excess of 77.3 K. Realization of practical superconductors at high temperature like 77.3 K is expected to significantly promote industrial development. The most important superconducting properties for application are the large critical current Ic and the high critical current density Jc. Especially, the large transport current in fields is a key parameter for power application. However, there exist many crucial issues in the Jc properties of high-Tc oxide superconductors. The flux creep behavior1 is one of the difficult problems to be solved out for application at 77.3 K. Although the flux creep has been already understood through the model proposed by Anderson and Kim2 in conventional low-Tc superconductors, it did not practically influence the usage at liquid helium temperature of 4.2 K for low-Tc superconductors, because of the negligibly small effect at 4.2 K. On the contrary, the extremely large flux creep phenomenon is observed at high temperature like 77.3 K in high-Tc superconductors. Therefore, the satisfactory solution of the flux creep is inevitable to realize a superconducting magnet employing high-Tc superconducting wires, which will be operated at 77.3 K, for instance.

Cryogen-Free Split-Pair Superconducting Magnet with a φ 50 mm × 10 mm Room Temperature Gap

A cryocooler-cooled split-pair superconducting magnet which will be a new functional system combined with important studies such as X-ray diffraction, neutron diffraction, and magneto-optics or opto-magnetism has been constructed. The split-pair NbTi superconducting magnet has a vertical clear bore of φ 68 mm and a horizontal gap of 58 mm, and is operated in a vacuum below 6 K using a GM-cryocooler with magnetic regenerator material ErNi0.9Co0.1. This magnet system is designed to generate a magnetic field of 5.0 T at the center of an experimental bore, and the maximum field is estimated to be 6.7 T at the coil winding.

Thermal conductivity of the c-axis aligned (Bi,Pb)2Sr2Ca2Cu3Oy in the superconducting and mixed states

Abstract The thermal conductivity of a c-axis aligned BPSCCO polycrystal in the superconducting and mixed states has been studied as a function of temperature and magnetic field up to 14T along the c-axis. Comparing the κ data of a semiconducting sample with those of a metallic sample, an observed anomaly in κ below Tc is attributed to the electronic thermal conductivity κe and seems to be explained by the electronelectron interaction model based on a strong suppression of the quasiparticle scattering rate in the superconducting state. A peak value in κ decreases and its position shifts to higher temperatures with increasing field strength. This behaviour in κ(T) is roughly described by the Kadanoff-Martin expression in κse taking into account quasiparticle scattering by quasiparticles in the normal core at several fixed fields. The K-M expression extended to the mixed state qualitatively explains an observed nonlinear field dependence of κ(H) at several fixed temperatures.

Cryocooler-cooled high field superconducting magnet

A high field NbTi/Nb3Sn superconducting magnet with no use of liquid helium was developed by adopting high-Tc Bi2Sr2Ca2Cu3O10 current leads and 4 K GM-cryocoolers. The initial cooldown from room temperature to 4.1 K for the coil was attained within 40 hours by conductively cooling in vacuum. The cryocooler-cooled superconducting magnet successfully achieved to generate a central field of 10.7 T in a 52 mm room temperature experimental bore, and to hold a field at 10.5 T for 24 hours.