Fluctuation Characteristics of Non-ELM Crash Plasmas on KSTAR

The characteristics of two different non edge localized mode (ELM) crash plasmas have been investigated through the correlation analysis of 2-D fluctuation diagnostics: (1) Resonant Magnetic Perturbation (RMP)-driven ELM crash suppressed H-mode plasma, (2) natural ELM-less H-mode plasma. A reliable non-ELM crash plasma is essential for steady-state tokamak operation, so it is important to understand the underlying physics for future burning plasmas. The ELM crash suppression under RMP is characterized by the coexistence of the filamentary mode and small scale turbulent eddies at the pedestal region [1]. It is found that the filamentary mode structure is maintained with substantial fluctuations in amplitude without large scale collapse, which is distinguished from the ordinary ELMs with a quasiperiodic collapse of the pedestal. The cross-correlation technique on the 2-D electron cyclotron emission imaging (ECEI) [2] signals revealed that the RMP induces the turbulent fluctuations in the edge, which have a wide range of poloidal wave numbers and rotates in the electron diamagnetic direction. Bicoherence analysis of these fluctuations demonstrates that the coexisting filamentary mode and turbulent eddies nonlinearly interact with each other. Such nonlinear interaction suggests that the turbulent fluctuations induced by the RMP dissipate the free energy of the ELM growth by exchanging the energy between them.