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Nine toroidal field (TF) coils have been developed in Japan for the international thermonuclear experimental reactor (ITER). The joint resistance of TF coil should satisfy the requirement of smaller than 3 nano-ohm at 2 T of external magnetic field and 68 kA of transport current. Full-size joint sample (FSJS) tests were performed for joint development and for TF coil manufacture, as part of the process control. 11 FSJS tests are conducted in total. FSJS tests were conducted with assistance from a test faculty in the National Institute for Fusion Science as reported in a previous paper. All FSJS tests successfully satisfied the requirement of resistance less than 3 nΩ at 2 T. Additionally, the TF coil joints are subjected to cyclic electromagnetic force and warm-up/cool-down during the ITER operation. The authors investigated the joint performance for the abovementioned influence. The results showed no degradation in the joint resistance. Thus, the TF joint developed in Japan was qualified successfully. [ABSTRACT FROM AUTHOR]

An unusual negative lightning flash was recorded at the Säntis Tower on June 15, 2012. The flash did not contain an initial continuous current typical of upward negative lightning, which is the most common type of event at the Säntis Tower. The flash contained four strokes, the last three of which were normal while the current associated with the first stroke resembled a Gaussian pulse with an unusually high peak value of 102.3 kA, a long risetime of 28.4 μs, and a pulsewidth of 53.8 μs, which was followed by an opposite polarity overshoot with a peak value of 8.5 kA. Our current records suggest the involvement of a long upward connecting positive leader in response to the approaching downward negative leader in the formation of this flash. Lightning location system (LLS) data indicate that a positive cloud-to-ground stroke occurred 1 ms prior to the first stroke of the flash. In this paper, we present a detailed description of the data associated with this event. Moreover, both a return stroke model and an M-component model are used to reproduce the far-field waveform of this bipolar stroke. The simulations result in a radiated electric field waveform that is similar to those of large bipolar events (LBEs) observed in winter thunderstorms in Japan. A sensitivity analysis of the used simulation models reveals that, by proper selection of the input parameters, all field waveform characteristics, except for the positive half-cycle width, can be made to fall in the range of LBE field characteristics reported in Japan. [ABSTRACT FROM AUTHOR]

Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. We developed and installed a pair of Rogowski coils at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower in Japan (35.71°N, 139.81°E), and have conducted direct observation of lightning flashes striking the tower. As of November 2018, 70 lightning flashes striking the tower, 26 downward and 44 upward, have been observed since the end of February 2012. In this paper, we focus on the downward negative flashes that occurred at the tower for seven years from 2012 to 2018 and report on the observed results of typical waveform parameters of lightning stroke currents in comparison with other observed results on downward negative flashes. [ABSTRACT FROM AUTHOR]

JAEA has conducted qualification and rationalization activities in Japan since March 2009 in order to rationalize manufacturing procedure of ITER toroidal field coil (TFC) structures. These following activities has been performed: qualification of structural materials and qualification and development of welding procedure according to the JSME code constituted for fusion devices, demonstration of the manufacturing method and procedures through manufacture of 1 m mock-ups and full-scale segments of TFC structure. From results of these activities, JAEA confirmed quality of materials and weld joints of gas tungsten arc welding and gas metal arc welding. In addition, JAEA obtained knowledge of welding deformation of actual TFC structures. This paper describes results of these qualification and development activities for ITER TFC structure. [ABSTRACT FROM PUBLISHER]

This paper describes the detailed design of the quench protection circuits (QPCs) for the superconducting toroidal field (TF) and poloidal field (PF) magnets of the satellite tokamak JT-60SA, which will be installed in Naka, Japan. The nominal currents to be interrupted and the maximum reapplied voltages are 25.7 kA and 2.8 kV for the TF QPCs and 20 kA and 5 kV for the PF QPCs. The innovative solution proposed in the QPC design is based on a hybrid circuit breaker (CB) composed of a mechanical bypass switch for conducting the continuous current, in parallel to a static CB for current interruption. The main choices of the final design are presented and discussed, either to confirm or to update and complete the study performed at the conceptual design level. [ABSTRACT FROM PUBLISHER]