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内容記述 |
A superconducting tokamak fusion test machine, JT-60SA, was constructed in 2020 as a satellite Tokamak project in a Broader Approach Program between Japan and EU. In the JT-60SA integrated commissioning test, when the equilibrium magnetic field coil EF1 was energized with high voltage (~6kV), the EF1 power supply current surged suddenly, and the overcurrent interlock of the power supply operated, cutting off the current output at 5 kA. At the same time, A cryostat vacuum deteriorated, the pressure in the magnet cooling loops increased, and rupture discs burst. As a result of visual inspection after a warm-up of the system, it was found that discharges occurred on both the positive and negative terminal joints of EF1. Several holes, molten by electrical short and considered a leak location of helium to the cryostat, were found in the cylindrical metal part of the joint. The measurement data at the time of the event was analyzed, and it was found that the discharge first occurred between the positive terminal joint and the support bracket that is the ground potential, and immediately after that, another discharge occurred between the neighboring negative terminal joint and the support bracket. These two discharges formed a short-circuited loop. The energy consumed at the short circuit is estimated to be about 60 kJ, which is enough to melt 75 g of metal.
In the presentation, the cause and measure of EF1 incidents are introduced. |
