Optimization of Plasma Initiation Scenarios in JT-60SA

Stable plasma initiation is very important in nuclear fusion devices especially in superconducting tokamaks, because available electric field at breakdown will be limited to the range of 0.3~0.5 V/m for suppressing large AC losses in the superconducting magnet. However, induced current in passive structures such as vacuum vessel and stabilizing plate will increase to the comparable level of plasma current of several hundred kA even in the case of breakdown assisted by Electron Cyclotron Heating (ECH), and it will enhance the strength of error field. Therefore, optimization of the voltage waveforms of poloidal field coil is necessary to realize the stable plasma initiation. In this paper, magnetic field control method for the stable plasma initiation and cost effectively designed magnet power supply system in JT-60SA are presented.