Successful completion of quench protection circuit procurement for JT-60SA

Work on JT-60SAis rapidly moving forward: the final acceptance tests of the quench protection circuit (QPC) for the superconducting coils have been successfully completed.

The quench protection circuit has an important safety function in the JT-60SA machine: superconducting coils are needed to confine the fusion plasma, but if, for whatever reason, the coils stop being superconducting, it is necessary to immediately discharge them to avoid damage from overheating. This protective function is performed in JT-60SA by the 13 QPC units that, when operated, allow rapidly dissipating the huge magnetic energy stored in the coils (>2.3 GJ in total) into a set of discharge resistors. The quench protection system applies an innovative hybrid mechanical-static circuit breaker technology to interrupt dc currents of more than 25 kA withstanding reapplied voltages of about 4.2 kV. Large design margin was taken to improve reliability and to further increase it an explosively actuated circuit breaker is included as back-up protection.

The QPC are procured by the Italian Research Council (CNR) acting through Consorzio RFX in Padua, Italy, in the frame of an “Agreement of Collaboration” with F4E. It is the first time such advanced hybrid circuit breaker technology has been used in industrial application for this high current and voltage ratings, and for this reason a dedicated R&D activity has been performed since 2007 in Padua.

In 2010, the contract for the QPC procurement (including design, manufacturing, testing, transportation, installation, commissioning and final test) was entrusted by Consorzio RFX to the Italian supplier Nidec ASI, which endorsed the innovative solution and lunched an intense qualification process with the manufacturing and testing of two complete prototypes before starting the series production of the 13 QPC units in 2013.

The QPC installation in Japan started in December 2014, representing the first occasion of activities directly performed by European personnel at Naka Site for JT-60SA: a special VISA dedicated to Broader Approach Activities has been issued by Japanese government for the European personnel involved in the QPC installation.

After the completion of commissioning activities, the final acceptance tests were successfully performed in June 2015, allowing the closure of the QPC procurement activities on 31 July 2015, according to the original schedule.