JT-60 Super Advanced (JT-60SA) is a full-superconducting tokamak constructed under JA-EU broader approach project. The magnet system of JT-60SA has 18 toroidal field (TF) coils, 4 modules of central solenoid (CS), and 6 coils of equilibrium field (EF) coils.
The TF coils are D-shaped coils, and CS and EF coils are circular coils put inside and outside of TF coils, respectively. The superconducting magnet system of JT-60SA have more than 8 m height, 10 m diameter, and the total weight of 700 tons. Maximum operating current and magnetic field are 25.7 kA -5.65 T for TF coils, 20 kA - 8.9 T for CS, 20 kA - 6.2 T for EF coils, respectively. TF coils were procured by European Union, and CS and EF coils were procured by Japan.
The first installation of the JT-60SA superconducting magnet was conducted in 2013 and the CS, which is the final installation magnet, was assembled in 2019. After that the piping of coolant for the superconducting magnet and closure of cryostat lid were conducted. The construction of JT-60SA was completed in March 2020. The first cool-down operation started in October 2020 for the integrated commissioning test, and the energization test started in January 2021. A nominal current of 25.7 kA operation was achieved for the TF coils, while only 5 kA, i.e. one fourth of the nominal current, were applied on the PF coils in the first phase of integrated commissioning. Due to an electrical insulation problem which resulted in an arc between the coil terminals in March 2021, integrated commissioning was stopped. It took two years to repair and reinforce parts of the electrical insulation.
The cool-down for the first plasma operation started in June 2023. The energization test of superconducting magnets started in August 2023. A nominal current of 25.7 kA operation was achieved for the TF coils, and 10 kA (CS1,2,4, EF1,3-6) or 5 kA (CS3, EF2) operation was achieved for the PF coils during individual energization test.
High voltage tests at cryogenic temperature and high vacuum insulation were limited to 2.2 kV for TF coils and 2.7 kV for PF coils to confirm the nominal operation of 25.7kA for the TF coils and limited current operation at 2.0 kV and 5 kA for the PF coils. All superconducting magnets were also energized simultaneously in the final step of energization test and the first plasma was achieved on 23rd October. The plasma pulse length and the plasma current were gradually increased and culminated in a maximum current of 1.2 MA.
The quench detection (QD) systems of the CS and EF coils adopt the pickup coil method to compensate inductive voltages during coil resistance measurements. Despite inductive voltages could be successfully cancelled, the operation of the PF coils was still limited by the large noise level of the QD circuit. The origin of the noise of QD system has been investigated to improve the QD performance for next operation. The measurement result showed that a large fraction of the noise originated from the RC low pass filter. Adjustment of a proper capacitor could reduce the noise. In addition, the analysis using a simple circuit model was able to explain this noise, and to estimate the required precision of capacitor adjustment.
In this presentation, the result of the first plasma operation, especially the superconducting coils, will be reported.
JT-60SA was jointly constructed and is jointly funded and exploited under the Broader Approach Agreement between Japan and EURATOM
Keywords: JT-60SA