EX/P9-5 Comprehensive Control of Resistive Wall Modes in DIII-D Advanced Tokamak Plasmas

The resistive wall mode (RWM) and neoclassical tearing mode (NTM) have been simultaneously suppressed in the DIII-D for durations over 2 seconds at beta values 20% above the no-wall limit with modest electron cyclotron current drive (ECCD) and low plasma rotation. The critical plasma rotation was significantly lower than reported at the IAEA FEC in 2006. However, even in this stabilized regime, stable steady-state operation is not unconditionally guaranteed. Various localized MHD activities such as edge localized modes (ELMs) and fishbones begin to couple to the RWM branch near the no-wall limit. Feedback is useful to improve the stability. Simultaneous operation of slow dynamic error field correction and fast feedback suppressed the ELM-induced RWM at high normalized beta. The result implies that successful feedback operation requires careful control of residual RWMs. The effectiveness of feedback operation was demonstrated using a reproducible current-driven RWM. The present findings are extremely useful in the challenge of control of RWM and NTM in the unexplored physics territory of burning plasmas in ITER.