Toshio Uede

Design and testing of a pair of current leads using bismuth compound superconductor

The thermal behavior of current leads using an oxide superconductor for the low-temperature portion has been studied. Numerical calculations predict a reduction of the necessary coolant flow rate and refrigerator input power. A pair of current leads has been manufactured where the low-temperature portion consists of six sintered Bi compound cylindrical bars and the high-temperature portion consists of a Cu wire bundle. The lead, cooled by gaseous helium along its entire length, is 0.9 m long and designed to carry 1 kA. The leads have been tested in the same arrangement as practical applications. The helium flow rate necessary to hold thermal equilibrium was about 80% of that for conventional copper leads. The calculation shows that power consumption of the refrigerator needed to cool high-temperature superconductor current leads with an optimum cooling scheme will be about one-third of that for conventional current leads.<<ETX>>

Critical current measurements using 13-T split coils and 100-kA superconducting transformer (for FER)

A description is given of a large scale superconductor test facility composed of a 13-T magnetic field and a 100-kA sample current. A superconductor transformer with a 100-kA secondary conductor was fabricated as a current amplifier in order to supply the 100-kA sample current. Superconducting split coils with 100-mm clear bore diameter were fabricated, and a 13-T available field was generated by these coils. Both the 100-kA superconducting transformer and the 13-T superconducting split coils were installed in a 2-m-diameter FRP dewar for the purpose of testing large-scale superconductors. A description is given of the performance of the 100-kA superconducting transformer and the 13-T superconducting split coils as well as the results from critical current measurements of prototype conductors for toroidal coils.

Engineering design of the Mini-RT device

The plasma experiment apparatus S-RT (Superconducting Ring Trap) is planned for the purpose of high beta plasma confinement research in the University of Tokyo. As a preceding step, Mini-RT, which is the size reduction version of S-RT, has been constructed as a joint research of NIFS, the University of Tokyo, and Kyushu University. In this experiment a magnetic-levitation coil (floating coil) operated in persistent current mode has to levitate for 8 hours in the plasma vacuum vessel. The HTS floating coil wound with a Bi-2223 tape has a diameter of 300 mm and an electromotive force of 50 kA. Since any refrigerant cannot be fed to the coil during the plasma experiment, the coil is designed so that the temperature rise after 8 hours of levitation is less than 40 K with the specific heat of the coil and radiation shield. At the end of the daily plasma experiment, the coil will be drawn down to the maintenance location at the bottom of the plasma vacuum vessel, and it will be re-cooled to 20 K.

Superconducting current feeder system for the large helical device

A flexible superconducting (SC) busline was developed as a current feeder system for the fusion experimental device, LHD. An aluminum stabilized NbTi/Cu compacted strand cable was developed to satisfy the fully stabilized requirements at a rated current of 31.3 kA. A pair of SC cables was electrically insulated and installed in a cryogenic transfer line. Measured breakdown voltage in the 77 K helium gas is 8.33 kV. Nine sets of SC current feeders with 45-65 m lengths are installed for LHD. The total heat loads into 80 and 4.2 K levels are estimated to be 2.12 and 1.02 kW, respectively. The SC current feeder system is designed to maintain its rated capacities for 30 minutes, whenever the coolants supplied to the current feeder system are accidentally stopped.

Design of a 60-kA HTS current lead for fusion magnets and its R&D

A 60 kA HTS current lead has been designed for large fusion magnets such as the ITER magnet. The actual refrigeration input power required to cool the current lead is specified to be reduced to one third that of the conventional copper lead. The HTS part of the 60 kA lead consists of 48 units installed with cylindrical array into the outer surface of a stainless steel tube with a diameter of 146 mm. Each unit is composed of six Bi2223/Ag-10at%Au tapes, and its cross-sectional dimension is 6.5 mm/spl times/2.7 mm. The HTS part is cooled by conduction, and the warm and cold end temperature conditions of the HTS part are 50 K and 4.5 K, respectively. The copper part is cooled by helium gas, a flow rate of 3.9 g/s and the inlet temperature of 35 K. The 60-kA lead has been designed in consideration of safety under the long discharge time condition of ITER-TF coil with a detection time of 2 sec, and a discharge time constant of 15 sec. For the purpose of verifying the reliability of the design for the long discharge time, one unit sample has been fabricated and tested. The result indicates that the maximum temperature rise of the HTS part is less than 150 K for the ITER like-discharge from 1.25 kA corresponding to 60 kA of the full lead with 48 units.

Excitation test results of the HTS floating coil for the Mini-RT project

A magnetically levitated superconducting coil device, Mini-RT, is being developed using high temperature superconductors for the purpose of examining a new magnetic confinement scheme of high-beta plasmas. The floating coil has Bi-2223 Ag-sheathed tape conductors, which will be effectively used in the temperature range of 20-40 K. The fabrication of the coil has been completed, and excitation tests of the coil were carried out in a helium cryostat. The coil was successfully excited up to the nominal current with a proper PCS operation.

Engineering research and development of magnetically levitated high-temperature superconducting coil system for mini-RT project

A magnetically levitated superconducting coil system is being developed using high temperature superconductors for examining a new magnetic confinement of high-beta plasmas. A miniature double-pancake coil was fabricated with a Bi-2223 Ag-sheathed tape for the purpose of developing a floating control using laser displacement gauges. The coil was inductively excited with liquid nitrogen cooling and successfully levitated in the air. A persistent current switch is also being developed with a Bi-2223 Ag-0.3wt%Mn-sheathed tape, and a prototype model was successfully tested.

Development and tests of a flexible superconducting bus-line for the Large Helical Device

A flexible superconducting bus-line is proposed as an electrical feeder between the superconducting coils of the Large Helical Device (LHD) and the devices power supplies. The bus-line consists of superconducting cables and a cryogenic flexible transfer-line. A specially developed aluminum stabilized NbTi/Cu compacted strand cable satisfies requirements for large current capacity, high stability, high reliability and flexibility. A full-scale model with a length of 20 m was designed and constructed to investigate the feasibility and performance of the superconducting bus-line. Its fabrication, transportation, installation, cooling and excitation tests were successfully carried out. The bus-line was very stable and could be excited up to 40 kA (rated current is 30 kA) without a quench. The stability, current distribution and heat load were also measured. >

Experiments of the HTS floating coil system in the mini-RT project

A magnetically levitated superconducting coil device, Mini-RT, has been constructed using a high-temperature superconductor for the purpose of examining a new magnetic confinement scheme of high-beta plasmas. The floating coil is wound with Bi-2223 Ag-sheathed tapes, and it is operated in the temperature range 20-40 K. The excitation tests of the coil were carried out and the rated current was successfully achieved by overcoming many difficulties. The first magnetic levitation was realized for one hour and the plasma production was initiated.

Development of HTS current leads for 1 kWh/1 MW module type SMES system. I. Design study

We have been developing high-temperature superconducting (HTS) current leads for a 1 kWh/1 MW module-type SMEs. Each module of a module-type SMES requires a pair of current leads. Therefore, we employed bulk HTS in order to reduce the heat load of the current leads. It is important that HTS current leads for SMES be reliable. The HTS current leads described in this paper have been designed to minimize the heat load and to maintain a high level of reliability. The HTS current leads are designed to hold the heat load at the cold-end terminal to less than 0.1 W. They are also designed with safety leads to bypass current in the event the HTS is quenched and with metal superconductors to assure the continuation of SMES operation even if the HTS should fail or deteriorate in performance. This paper describes an optimal design and the results of a heat load evaluation of HTS current leads for SMES.