Jun Fujikami

A novel scaling of magnetic field dependencies of critical currents for Ag-sheathed Bi-2223 superconducting tape

Abstract Certain characteristics in magnetic field dependences of critical current densities (Jc) for the Ag-sheathed Bi-2223 superconducting tape have been found. One property regards the direction of the magnetic field applied to the tape. Both Jc values in the field, applied parallel and perpendicular to the tape surface, are on an identical curve when the magnitude of field (B), applied parallel to the tape surface, is multiplied by a characteristic coefficient, which relates to the grain alignment of each tape. Another concerns the relationship between Jc and the magnitude of the field. The Jc is expressed by a simple logarithmic function of B (log(B)) from a very low field to a high field. This relation is applicable within a wide temperature range.

Bismuth superconducting wires and their applications

Abstract The combination of a bismuth high T c phase ( T c = 110 K) and powder-in-tube processing technology enables the fabrication of superconducting wires with high critical current density, mass producibility and flexibility. The maximum critical current density in liquid nitrogen reached 53 700 A cm −2 in zero magnetic field, 42 300 A cm −2 at 0.1 T and 12 000 A cm −2 at 1 T. J c and J c − B enhancements were obtained with finely dispersed non-superconducting phases and clean grain boundaries. Various prototypes were made to clarify their feasibility, such as 114 m long wires ( J c ≈ 10 000 A cm −2 at 77.3 K), large current conductors ( I c = 2300 A at 77.3 K), a 0.21 T coil at 77.3 K, a 20.35 T coil at 20.3 K and a 23.37 T coil at 4.2 K.

Transport Current AC Losses of High-Tc Superconducting Tapes Exposed to AC Magnetic Field

A new measurement method is developed to properly measure transport current AC losses of high-Tc superconducting tapes which are subject to external magnetic field generated by adjacent tapes in multiple tapes assembled conductor. It has been pointed out that to correctly measure the AC losses of the tape, the voltage measurement loop should include the magnetic flux over a distance much larger than the tape width. However, this wide voltage loop needs wide space and picks up spurious loss caused by adjacent tapes when multiple tapes are assembled. In our arrangement, the leads from voltage taps on the tape are wound on a cylindrical surface enclosing the tape. This method can save space for voltage leads and avoid spurious loss component caused by the magnetic field of the other tape. In the paper, details of our measurement arrangement are explained and the validity of our method is investigated by theoretical and numerical analyses and an experiment. It is demonstrated that our method is effective.

Electrical and Mechanical Properties of DI-BSCCO Type HT Reinforced With Metallic Sheathes

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.

HTS large scale application using BSCCO conductor

The basic property of high-Tc superconducting cables (HTS cables) using Bi-2223-based Ag-sheathed multifilamentary wire (Ag-sheathed wire) have been investigated for the realization of large-scale and compact cables, these being replaceable with conventional cables in existing ducts or tunnels. The AC performance of multi-layer HTS conductors, and three-phase HTS cables with coaxial superconducting magnetic shielding structure was evaluated. The characteristics of the HTS conductor and cable models of long length was investigated on a 50 m scale.

High field generation using silver-sheathed BSCCO conductor

Abstract A J c (77 K) of a 1200 m long silver-sheathed bismuth-based superconducting wire has reached 10 900 A/cm 2 . The performance of application prototypes has also got a great deal of progress. For example, a 60 mm bore BSCCO magnet generated 4 T at 4.2 K, 3 T at 21 K, and stably generated 2.5 T at 21 K for over 150 h when cooled with GM refrigerator. This magnet has a practical-sized winding bore of 60 mm, and a 40 mm RT bore cryostat was installed for actual application. Also. high magnetic field properties of another BSCCO magnet having a 40 mm winding bore were evaluated with a backup field up to 22.54 T at 4.2 and 27 K. The maximum fields generated by a backup hybrid magnet and BSCCO coil was 24.0 and 23.4 T at 4.2 and 27 K, respectively.

Generation of 24.0 T at 4.2 K and 23.4 T at 27 K with a high‐temperature superconductor coil in a 22.54 T background field

The 4.2 K and 27 K current‐carrying performance of a high‐temperature superconducting (HTS) coil was measured in background fields up to 22.54 T generated by a hybrid magnet (Hybrid III) at the MIT Francis Bitter National Magnet Laboratory. The coil, 40 mm winding i.d., 108 mm winding o.d., and 113 mm high, consists of 17 double pancakes, each wound with silver‐sheathed BSCCO‐2223 tapes. Each pancake is the product of a react‐and‐wind method. In total, the test coil contains ∼1200 m of BSCCO‐2223 conductor weighing ∼7 kg. Prior to the measurements in Hybrid III, the coil was tested in zero background field in the temperature range from 4.2 to 77 K. It was coupled to a Gifford–McMahon type cryocooler and at 15 K generated a peak field of 2.1 T; at 18 K, it generated 1.9 T, operating continuously for ∼50 h. In a 22.54 T background field of Hybrid III, the coil reached critical currents of 116.5 A ([Jc]sc, critical current density based on the BSCCO cross‐sectional area only, of 261 A/mm) at 4.2 K and 67 A (...

DI-BSCCO wires by Controlled over pressure sintering

Sumitomo Electric successfully developed drastically innovative Bi-2223 (DIBSCCO), namely, commercially produced Bi2223 long length wires using the controlled over pressure sintering (CT-OP) with unique properties quite different from conventional silver sheathed BSCCO wires. CT-OP prevented pores occurring in BSCCO cores, so it reformed conventional Bi2223 wires to DI-BSCCO with excellent properties of higher critical currents, stronger mechanical strength and better durability against temperature rise in cryogen such as pressurized liquid nitrogen. It enhanced the critical current by 50 percent conventional wires sintered in normal atmospheres. Critical tensile stress was also improved by more than 150 percent. Any ballooning defects and degradation of critical current, one of the critical problems for the conventional BSCCO wires, were not found in full length of several km long DI-BSCCO tapes after 24 hours immersion into 1MPa liquid nitrogen.

Drastic Improvement in Mechanical Properties of DI-BSCCO Wire With Novel Lamination Material

Ni-Cr alloys have been focused on as a new promising material for the reinforcement of DI-BSCCO wire. In addition to Ni-Cr alloy lamination, the thinner Type H wire and pretension have been employed. The fabricated Type H wires laminated with 35-μm-thick Ni-Cr alloys have shown no degradation in Ic properties and surpassed all the Type HT wires laminated with the thicker stainless-steel tapes in the tensile strength and double bending diameter. It was demonstrated that the wire could tolerate the practical extent of tensile load up to 10000 cycles. The in-field Ic performance has hardly been compromised with the moderate pretension. These results, along with the smaller cross-sectional size, have led to the compatibility between high Je and high mechanical strength. The Type HT wire with the thinner Type H wire and 30-μm-thick Ni-Cr tapes are currently developed.

Uniaxial strain dependence of the critical current of DI-BSCCO tapes

In order to explain the effect of uniaxial strain on the critical current of DI-BSCCO-Bi2223 tapes, we employed a springboard sample holder that can smoothly and continuously apply both tensile and compressive strains to tape samples. Over a narrow tensile strain region, the critical current in the tapes decreased linearly with increasing strain and returned reversibly with decreasing strain. When compressive strain was applied, the critical current first increased and then reached a weak maximum. Thereafter, it decreased monotonically with further increases in compressive strain. At room temperature, the local strain exerted on BSCCO filaments was measured by means of a quantum beam diffraction technique. Over the whole tensile strain region up to 0.2% and the small compressive strain range, the local strain changed linearly with applied strain. When the compressive strain was applied beyond the relaxation strain, the local strain (measured by diffraction) versus the applied strain (measured using a strain gauge) deviated from linearity, which is characteristic of strain relaxation and the onset of BSCCO filament fracture. Thus, the strain at the maximum critical current corresponds to a crossover point in strain, above which the critical current decreased linearly and reversibly with increasing applied strain, and below which the critical current decreased due to the BSCCO filament fracture. In this paper, we clearly characterize the reversible range terminated by both compressive and tensile strains, in which filaments do not fracture. Our analysis of the compressive regime beyond the relaxation strain suggests that although BSCCO filament fracture is the primary factor that leads to a decrease in critical current, the critical current in those regions of filaments that are not fractured increases linearly and reversibly with decreasing applied strain at compressive strains well beyond the reversible region for the tape.