Commissioning Results of the KSTAR Superconducting Magnet System for the First Plasma Operation

The KSTAR device is a tokamak with a fully superconducting (SC) magnet system, which enables an advanced quasi-steady-state operation. Initial operation of the KSTAR SC magnet system has been accomplished for the first plasma discharge operation. The SC magnet system consists of 16 toroidal field (TF) coils and 14 PF coils, magnetic structures, SC buslines, current leads, and monitoring and protection system. One of the uniqueness of the KSTAR device is using the Nb3Sn superconductor both in 16 TF coils and in 10 PF coils except 4 PF coils made of NbTi. The objectives of the commissioning of the superconducting magnet are to verify the engineering reliability of all the superconducting magnets at the operating conditions and to develop the operational controllability for the successful plasma startup. The target parameters of the initial operation are TF coil current of 15 kA, PF coil current up to 4 kA and PF blip and feedback control using plasma control system (PCS). All the superconducting magnets were operated reliable without any severe failure to preventing the first plasma operational target. The TF magnet was operated reliably up to 15 kA for 8 hours and the temperature rising of TF magnet is less than 0.1 K. There was no quench during operation including slow and fast discharges. As the PF commissioning, the controllability of each power supply has been tested by using dummy copper load and each SC PF coil. After the individual test of the PF coil and power supply, integrated control was accomplished for the field null formation and for loop voltage generation to meet the first plasma discharge. The ac losses of the several PF coils have been measured by applying the single trapezoidal current and dc biased sinusoidal current with various ramp rate. The hysteresis loss of PF1 coil was less than 180 mJ/cc and the time constant of the coupling loss was less than 50 ms after 500 pulse operations. The field distortion by the Incoloy908 material in the superconductor was measured and modification in the PF coil current scenario has been adopted also. By the feedback control of the plasma current and position, the plasma current could be sustained up to 860 ms under the limited volt second of 1.1 Wb. FIG. 1. Configuration of the KSTAR superconducting magnet system FIG. 2. Bird eye view of the KSTAR superconducting magnet system