Akira Ninomiya

Test of the ITER central solenoid model coil and CS insert

The Central Solenoid Model Coil (CSMC) was designed and built from 1993 to 1999 by an ITER collaboration between the U.S. and Japan, with contributions from the European Union and the Russian Federation. The main goal of the project was to establish the superconducting magnet technology necessary for a large-scale fusion experimental reactor. Three heavily instrumented insert coils were built to cover a wide operational space for testing. The CS Insert, built by Japan, was tested in April-August of 2000. The TF Insert, built by Russian Federation, will be tested in the fall of 2001. The NbAl Insert, built by Japan, will be tested in 2002. The testing takes place in the CSMC Test Facility at the Japan Atomic Energy Research Institute, Naka, Japan. The CSMC was charged successfully without training to its design current of 46 kA to produce 13 T in the magnet bore. The stored energy at 46 kA was 640 MJ. This paper presents the main results of the CSMC and the CS Insert testing-magnet critical parameters, ac losses, joint performance, quench characteristics and some results of the post-test analysis.

Test of the ITER TF insert and Central Solenoid Model Coil

The Central Solenoid Model Coil (CSMC) was designed and built by ITER collaboration between the European Union, Japan, Russian Federation and the United States in 1993-2001. Three heavily instrumented insert coils have been also built for testing in the background field of the CSMC to cover a wide operational space. The TF Insert was designed and built by the Russian Federation to simulate the conductor performance under the ITER TF coil conditions. The TF Insert Coil was tested in the CSMC Test Facility at the Japan Atomic Energy Research Institute, Naka, Japan in September-October 2001. Some measurements were performed also on the CSMC to study effects of electromagnetic and cooldown cycles. The TF Insert coil was charged successfully, without training, in the background field of the CSMC to the design current of 46 kA at 13 T peak field. The TF Insert met or exceeded all design objectives, however some interesting results require thorough analyses. This paper presents the overview of main results of the testing - magnet critical parameters, joint performance, effect of cycles on performance, quench and some results of the post-test analysis.

Recent Progress of Experiment on DC Superconducting Power Transmission Line in Chubu University

A test stand of a DC superconducting power transmission cable was finished to construct in October 2006 in Chubu University, Japan, and three cooling cycles were carried out to measure the properties of the cable. Critical current of HTS tapes in the cable was measured at every cooling cycle and shows the similar temperature dependence; conclusively, the HTS tapes suffered no damage after cooling and heating process between the each cycle. Peltier current leads were partly installed in the test stand, and it was measured that the temperatures of the feedthrough near to the liquid nitrogen were decreased in spite of a current feeding.

Test of the NbAl insert and ITER central solenoid model coil

The Central Solenoid Model Coil (CSMC) was designed and built by an ITER collaboration in 1993-2001. Three heavily instrumented Inserts have been also built for testing in the background field of the CSMC. The Nb/sub 3/Al Insert was designed and built by Japan to explore the feasibility of an alternative to Nb/sub 3/Sn superconductor for fusion magnets. The Nb/sub 3/Al Insert coil was tested in the CSMC Test Facility at the Japan Atomic Energy Research Institute, Naka, Japan in March-May 2002. It was the third Insert tested in this facility under this program. The Nb/sub 3/Al Insert coil was charged successfully without training in the background field of the CSMC to the design current of 46 kA at 13 T peak field and later was successfully charged up to 60 kA in 12.5 T field. This paper presents the test results overview.

AE measurement of the LHD helical coils

The authors have measured AE signals from the helical coils of the LHD (Large Helical Device) system at NIFS (National Institute of Fusion Science, Gifu, Japan) in order to monitor the state of the superconducting coils. Four AE sensors are attached on the surface of the vessel containing the helical coils, and preamplifiers are installed close to the sensors in the area with a leakage magnetic field of about 0.02 T. The measuring system is remotely controlled by PCs via a LAN system. The AE signals are recorded and analyzed. Their relation with the balance voltage signal of the coil has been investigated. The obtained experimental result shows that (1) the AE signals have been successfully recorded despite the leakage magnetic field on preamplifier, (2) the AE signal shows a good correlation with the balance voltages, (3) the AE signal is observed only when the excitation current is changing, (4) the pattern of the observed AE signal is stable for each excitation pattern.

Cryogenic System for DC Superconducting Power Transmission Line

Due to the recent developments of the electric power devices and the HTS power cables, DC superconducting power transmission system is considered to be practical. As one of the R & D issues of the DC superconducting power transmission system, we measured the radiation heat of the thermally-isolated stainless steel pipes with different surfaces. As the result, one sheet of aluminum foil pasted on the inner pipe surface reduced the heat radiation to 1.98 m/W between LN2 and the room temperature of 300 K.

Equivalent circuit and leakage reactances of superconducting 3-phase fault current limiter

The authors have been studying a novel type of superconducting fault current limiting reactor (SCFCLR). The SCFCLR is a reactor which has three superconducting windings with the same numbers of turns wound on a single iron core. An equivalent circuit is proposed for the SCFCLR. Using this equivalent circuit, the leakage reactances of the SCFCLR were calculated, and they agree well with the experimental data. Ground fault tests in a model power system were carried out. When the SCFCLR was inserted in the model transmission line, a ground fault was not observed.<<ETX>>

RADIATION HEAT MEASUREMENT ON THERMALLY-ISOLATED DOUBLE-PIPE FOR DC SUPERCONDUCTING POWER TRANSMISSION

Multilayer insulator (MLI) is a strong tool for use as a radiation heat shield, though the use of MLI has disadvantages in construction and evacuation for a long superconducting power cable. We have proposed the “MLI-free” radiation heat shielding for DC superconducting power cable and have measured the radiation heat transfer for thermally-isolated double-pipes with different surfaces. Here, Zn coating, MLI, and Al-foil sheet were tested. Consequently, from the radiation heat of 9.7 W/m for bare stainless-steel pipe, Zn-coated stainless-steel surface reduced to 2.6 W/m, whereas the use of MLI reduced to 0.2 W/m. It is expected that the simultaneous use of Zn coating and MLI can reduce the number of total MLI sheets to reduce the evacuation time.

Measurement of joint resistance of Bi-2223/Ag tapes using one-turn shorted coil

Considering the application of high T/sub c/ superconductor to power cables, the loss at conductor joint would be very important. Therefore, we have carried out a measurement of joint resistance of Bi-2223/Ag tapes at 77 K. A one-turn coil was wound by Bi-2223/Ag tape. Both ends of the tapes were overlapped and soldered to each other. The samples have different overlap-lengths. DC current is induced in the one-turn HTS shorted coil by energizing the excitation coil wound by copper wire closely located to the HTS coil. The magnetic flux density in the HTS coils was measured by a Hall element. From these data, we estimated the current induced in the HTS shorted coil. The decay of the persistent current in the coil was measured and the joint resistance was calculated. We examined the effect of the lapped part length on the joint resistance.

Flux Trapping Characteristics of YBCO Bulks using Pulse Magnetization

We have been studying magnetization characteristics of plural HTS bulks arranged in array. Previously, we presented experimental results using field-cool method in copper coils [1],a superconducting coil [2]. This time, we have carried out a pulse magnetization experiment using a capacitor bank and a pulse coil wound by copper wire. Plural HTS bulks are arranged in array in the magnetization coil. The trapped magnetic flux densities of the bulks are measured 2-dimensionally using Hall probe.