TSC simulation of ITER plasma termination scenario with stable H-L mode transition and avoidance of radiation collapse

Nakamura, Yukiharu*; Miyamoto, Seiji; Toshimitsu, Shinichi; Sugie, Tatsuo; Kusama, Yoshinori; Yoshino, Ryuji

The ITER termination scenario from 15 MA to 1.5 MA (500 s t 700 s) was reviewed by self-consistent simulations with the TSC code, comprised of newly developed D-T fuelling and pumping-out system. At 600 s, when the plasma current decreased to 10 MA, auxiliary NB heating was switched off to cease fusion -heating. Simultaneously, the energy confinement switches H to L mode by intentionally removing the H mode pedestal of edge transport barrier. The H to L mode transition dynamics, reduction in the plasma density while building-up of in-vessel neutral gas, disappearance of the edge BS current and consequent jump in the internal inductance , were investigated to assess performance of the ITER pump-out system. It was newly shown that the forced H to L mode transition may trigger a radiation collapse, consequently terminating the discharge. It was also demonstrated that EC heating with 170 GHz O-mode wave after the H to L mode transition provides an effective control means to hedge risk of the radiation collapse.