Modeling of neutrals for the analysis of the L-H/H-L transition effect on ITER operation scenario

Miyamoto, Seiji; Hayashi, Nobuhiko; Oyama, Naoyuki; Takenaga, Hidenobu; Toshimitsu, Shinichi; Sugie, Tatsuo; Kusama, Yoshinori; Yoshino, Ryuji

In the operation of ITER, transition from the high confinement (H) mode to the low confinement (L) mode (H-L transition) is serious disturbance to control system, and therefore it is an important issue in operation scenario development to model the plasma behavior during the transition. Especially, the analysis must include neutral particles in plasma behavior. In the ITER current ramp-down scenario, the plasma is kept in H-mode, and thereby in low internal inductance, to leave a control margin. Then the plasma goes to L-mode at the final stage of the discharge. When the plasma particles emitted at the H-L transition flow back to the plasma as neutrals, the discharge may lead to a radiation collapse if the pumping capacity is too low. It is therefore required to perform a simulation including a model of fueling and pumping system. We did not take into account the scrape-off-layer (SOL) and divertor models previously. However, these models influence the plasma particle behavior through neutralization of ions in front of the divertor target and re-ionization of neutrals in the SOL. In the presentation, we describe the implementation of the SOL and divertor models in the tokamak simulation code (TSC) and the effect on the plasma and neutral behavior.