Simulation of plasma current ramp-up with reduced magnetic flux consumption in JT-60SA

JT-60SAにおける磁束消費を抑えたプラズマ電流立ち上げのシミュレーション

若月 琢馬; 鈴木 隆博; 林 伸彦; 白石 淳也; 井手 俊介; 高瀬 雄一*

Wakatsuki, Takuma; Suzuki, Takahiro; Hayashi, Nobuhiko; Shiraishi, Junya; Ide, Shunsuke; Takase, Yuichi*

Current ramp-up with reduced central solenoid (CS) flux consumption in JT-60SA has been investigated using an integrated modeling code suite (TOPICS) with a turbulent model (CDBM). The plasma current can be ramped-up from 0.6 MA to 2.1 MA with no additional CS flux consumption if the plasma current is overdriven by neutral-beam-driven and bootstrap current. The time duration required for the current ramp-up without CS flux consumption becomes as long as 150s. In order to achieve the current overdrive condition from 0.6 MA, the current drive by a lower energy neutral beam (85 keV) is effective. A higher energy neutral beam (500 keV) cannot be utilized in this early phase due to large shine through loss, while it can be effectively utilized in the later phase. Therefore, the main current driver should be switched from the lower energy neutral beam to the higher energy neutral beam during the current ramp-up phase. As a result of an intensive auxiliary heating needed to overdrive the plasma current, plasma beta becomes high. Ideal MHD stabilities of such high beta plasmas have been investigated using a linear ideal MHD stability analysis code (MARG2D). External kink modes can be stabilized in most of the time during the current ramp-up if there is a perfectly conducting wall at the location of the stabilizing plate and the vacuum vessel of JT-60SA and the plasma has a broader pressure profile.