Microstructure observations on butt joint composed of Nb3Sn CIC conductors

To precisely evaluate a butt joint technology for the JT-60SA CS coils, microstructure observations on the butt joint composed of Nb3Sn CIC conductors were conducted using a FE-SEM. As a sample for the observations, the butt joint sample utilized in the joint resistance measurement was used. During the sample fabrication, the butt joint sample was heated up to about 920 K from room temperature for diffusion bonding after heat treatment for Nb3Sn production. Then, the sample was subjected to the cycles of electromagnetic force in the joint measurement.The observation results indicated that Nb3Sn strands and a copper sheet were butted properly at the interface of the butt joint. In addition, there were hairline cracks in the Nb3Sn layers of the strands near the interface. To investigate a cause of the crack initiation, the stresses generated in the butt joint under same conditions were analyzed using a simple model. As a result, the cracks would occur with an axial compressive stress generated by the butt joint fabrication

The Far-Infrared Surveyor (FIS) for AKARI

The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcmin, and the pixel pitch is matches the diffraction limit of the telescope. Derived point spread functions (PSFs) from observations of asteroids are similar to the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and its performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the AKARI special issue of the Publications of the Astronomical Society of Japa

Conductor and joint test results of JT-60SA CS and EF coils using the NIFS test facility

In 2007, JAEA and NIFS launched the test project to evaluate the performance of cable-in-conduit (CIC) conductors and conductor joints for the JT-60SA CS and EF coils. In this project, conductor tests for four types of coil conductor and joint tests for seven types of conductor joint have been conducted for the past eight years using the NIFS test facility. As a result, the test project indicated that the CIC conductors and conductor joints fulfill the design requirement for the CS and EF coils. In addition, the NIFS test facility is expected to be utilized as the test facility for the development of a conductor and conductor joint for the purpose of the DEMO nuclear fusion power plant, provided that the required magnetic field strength is within 9 T

Overview of Construction and First Commissioning Results of JT-60SA Superconducting Magnets

JT-60SA (JT-60 Super Advanced) is a full-superconducting tokamak built in Ibaraki Japan. In 2012, the construction of JT-60SA started and the last superconducting magnet was assembled in 2019. Cooldown of magnet system stared in 2020 and the energization test was performed from January to March 2021. In this presentation, the overview of construction, the result of first commissioning and future commissioning plan will be reported.27th International Conference on Magnet Technology (MT-27

Investigation into quench detection for a mutli-stacked pancake coil wound with Nb3Sn CIC conductors

For a multi-stacked (MS) pancake coil wound with Nb3Sn CIC conductors,　quench detection methods using voltage measurements were investigated. In　this study, we utilized two methods: the balanced voltage between two coil windings and the balanced voltage between one coil winding and a disk-shaped pickup coil. During the energization of the MS pancake coil, voltage　measurements of the coil were conducted to compare the measurement results of the two quench detection methods. The measurement results indicate that the quench detection based on the balanced voltage between two coil windings is more reliable than the other.In the measurements, spike voltages were observed when there was a rapid change of a coil current. Magnetization of the MS pancake coil is considered one cause of the spikes. When determining criteria of quench detection, spike voltages should be taken into account to prevent malfunction of a quench detection system.28th International Toki Conference on Plasma and Fusion Research (ITC-28

Study on quench detection for a multi-stacked pancake coil wound with Nb3Sn cable-in-conduit conductors

To operate superconducting magnets stably and safety, quench protection for the magnets has to be conducted properly; otherwise superconducting magnets will suffer serious damage due to quench. In the quench protection, accurate detection of quench occurrence in superconducting magnets is essential. There are two types of the quench detection method which is used in the magnets for the fusion devices. One is quench detection based on the balanced voltage between either two coil windings or two segments into which one coil winding is divided. The other method is quench detection by using a pickup coil whose configuration is either a disk-shaped coil or a co-wound coil. In this method, the balanced voltage between a superconducting coil and a pickup coil is utilized to detect a quench. In this study, these two methods of quench detection are investigated experimentally by using a multi-stacked (MS) pancake coil wound with Nb3Sn cable-in-conduit (CIC) conductors, which is the JT-60SA CS1 module. The experiment with the MS pancake coil was carried out in the coil test facility at the National Institute for Fusion Science, as illustrated in Fig.1. This paper describes the measurements of the balanced voltage for the MS pancake coil by the two quench detection methods. And the quench detection methods are discussed based on the measurement results.the 10th Asian Conference on Applied Superconductivity and Cryogenics (ACASC

Investigation into Quench Detection for a Multi-Stacked Pancake Coil Wound with Nb3Sn CIC Conductors

For a multi-stacked (MS) pancake coil wound with Nb3Sn CIC conductors, quench detection methods using voltage measurements were investigated. In this study, we utilized two methods: the balanced voltage between two coil windings and the balanced voltage between one coil winding and a disk-shaped pickup coil. During the energization of the MS pancake coil, voltage measurements of the coil were conducted to compare the measurement results of the two quench detection methods. The measurement results indicate that the quench detection based on the balanced voltage between two coil windings is more reliable than the other. In the measurements, spike voltages were observed when there was a rapid change of a coil current. Magnetization of the MS pancake coil is considered one cause of the spikes. When determining criteria of quench detection, spike voltages should be taken into account to prevent malfunction of a quench detection system