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

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. A time duration required for the current ramp-up without CS flux consumption becomes as long as 150 s in the scenario we have examined. In order to achieve a 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 used in this early phase with a low central electron density (~2 × 1019 m−3) due to large shine through loss, while it can be effectively used 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, plasma beta (the ratio of the plasma pressure to the magnetic pressure) becomes high. Ideal MHD instabilities of such high beta plasmas have been investigated using a linear ideal MHD stability analysis code (MARG2D). External kink modes which might affect the core plasma can be stabilized 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 with the H-mode pedestal and the internal transport barrier.