S. Mizumaki

A thin superconducting solenoid magnet for particle astrophysics

An extremely thin superconducting solenoid magnet is being developed to investigate cosmic-ray antiparticles in the Universe. The uniform solenoidal field is provided in a particle detector system to analyze the particle momentum. The solenoid coil is wound with advanced aluminum stabilized superconductor recently developed by using micro-alloying with Ni, followed by cold-work mechanical hardening. It is designed with a central magnetic field of 1.2 T in a volume of 0.9 m in diameter and 1.4 m in length. The radiation thickness of the coil is to be 0.056 X/sub 0/ with a physical coil thickness of 3.4 mm. This paper describes the conceptual design and progress of basic development work.

Stability of cable-in-conduit superconductors for Large Helical Device

The stability of cable-in-conduit superconductors has been experimentally investigated as part of a poloidal field coil program for the Large Helical Device (LHD) project. A new conductor was designed and fabricated, focusing on the stability. As a result of a zero-dimensional stability analysis, it was found that the conductor had a high stability, 5*10/sup 5/ J/m/sup 3/, at the design condition of 20.8 kA and 6.5 T. Current transfer performance after partial quenching has been investigated by using a short sample of the conductor for the poloidal field coil. The effects of the current transfer among the strands on the conductor stability are discussed.<<ETX>>

Fabrication and mechanical performance of the ATLAS central solenoid

Fabrication of the central solenoid for ATLAS detector in the CERN-LHC project was completed, and the performance test has been successfully carried out in Japan. The solenoid has arrived at CERN to be assembled with the LAr calorimeter. This paper describes the fabrication and mechanical, performance of the ATLAS central solenoid.

Experimental results of the R&D forced-flow poloidal coil (TOKI-PF)

Abstract As research and development (R&D) of poloidal-field coils for the Large Helical Device (LHD), a forced-flow cooled cable-in-conduit-type NbTi superconducting coil (TOKI-PF) has been tested. The success of excitations assured us that the NbTi cable-in-conduit conductor can be adopted for the LHD poloidal coils. During cool-down, mainly the hydraulic characteristics were measured. The friction factor could be expressed by using an empirical formula. In the DC operations, training behavior was observed, like in a pool-cooled coil. The friction factor was also affected by the number of excitations, which may be related to strand movement. The stability margin and propagation velocity were also measured using an inductive heater. It became evident that the stability margin had a lower value when the operation current was higher than 15 kA. This current seems to correspond to the limiting current.

Development of the Magnetically Floating Superconducting Dipole in the RT-1 Plasma Device

A high-temperature superconducting dipole floating in the magnetic field of a normal conducting coil has been developed for the Ring Trap (RT)-1 plasma confinement apparatus at the University of Tokyo. The RT-1 device consists of the floating superconducting dipole, a levitation coil made of normal conductor, a vacuum vessel for plasma confinement and detachable services for the floating dipole. This paper describes the design concept and operating scenario of the floating dipole as well as the required services such as a HTS persistent current switch necessary to realize this scenario

First Experiment on Levitation and Plasma With HTS Magnet in the RT-1 Plasma Device

The high temperature superconducting (HTS) floating magnet of the ring trap 1 (RT-1) reached the first experiment on levitation and plasma. The magnet using an HTS coil was levitated stably by levitation coil, and plasma was produced around the ring-shaped HTS magnet by electron cyclotron heating with 8.2 GHz microwave. This novel plasma device was constructed at the University of Tokyo to explore means of achieving the advanced-fuel fusion. The plasma confinement mechanism is based on the concept of high-beta relaxed state that is self-organized within flowing plasma. The HTS magnet is operated in a persistent-current mode and magnetically levitated in a plasma vacuum chamber. The weight of the HTS magnet is about 110 kg. Initially the HTS coil is cooled below 20 K by an external cooling system with detachable transfer tubes. After the transfer tubes are detached, an experiment of levitation and plasma is conducted while the HTS coil temperature remains within the range of 20 K-32 K without cooling. This paper describes the HTS coil design and test results of the HTS magnet as follows; an initial cooling, a persistent-current operation without cooling and the first levitation and the first plasma experiment.

Development of a superconducting joint technique between CIC conductors for poloidal coil of large helical device (LHD)

A solid state bonding technique been developed for the large superconducting joint of LHD poloidal coils. Low electrical resistance, high superconducting stability and compactness are required for the joints between pancake coils. All NbTi strands of cable-in-conduit (CIC) conductors were jointed directly and at one time by the proposed technique. From the critical current test with the real scale joint model, it is shown that quench current of this joint is about 1/3 times of the conductor critical current. This paper describes the main points in manufacturing the joint and evaluation of the quench current.<<ETX>>

Fabrication of the R&D forced-flow poloidal coil (TOKI-PF)

Abstract A forced-flow NbTi superconducting poloidal coil (TOKI-PF) using a cable-in-conduit conductor (CICC) was fabricated as an R&D project for the LHD coils. The main objective of TOKI-PF is to gather engineering data for the superconducting poloidal field coil. The major parameters are as follows: inner and outer radii 0.6 and 0.82 m, respectively, operating current 25.6 kA, stored energy 1.04 MJ, conductor NbTi CICC sized 10.0 × 22.5 mm. The mechanical coil configuration and nominal current of 25.6 kA simulate those of the LHD poloidal coils. Useful technical data were obtained and the feasibility of fabricating the LHD poloidal coils was confirmed. In this paper, preliminary test results will also be described.

Performance of a proximity cryogenic system for the ATLAS central solenoid magnet

The ATLAS central solenoid magnet has been designed and constructed as a collaborative work between KEK and CERN for the ATLAS experiment in the LHC project. The solenoid provides an axial magnetic field of 2 Tesla at the center of the tracking volume of the ATLAS detector. The solenoid is installed in a common cryostat of a liquid-argon calorimeter in order to minimize the mass of the cryostat wall. The coil is cooled indirectly by using two-phase helium flow in a pair of serpentine cooling line. The cryogen is supplied by the ATLAS cryogenic plant, which also supplies helium to the Toroid magnet systems. The proximity cryogenic system for the solenoid has two major components: a control dewar and a valve unit. In addition, a programmable logic controller, PLC, was prepared for the automatic operation and solenoid test in Japan. This paper describes the design of the proximity cryogenic system and results of the performance test.

Experimental Rigidity Evaluation of Conduit Pack for Forced-Flow Superconducting Coil

The compressive rigidity tests of the conduit pack were carried out in liquid helium for evaluating the coil rigidity, and the rigidity of the conduit was investigated by FEM analysis of the plane strain problem. Also, the conventional method for the estimation of the coil rigidity was proposed on the basis of the curved-beam theory, and the apparent rigidity of the conduit pack was calculated.