We present experimental observations suggesting that the non-diffusive avalanche-like events are a prevalent and universal process of the electron turbulent heat transport in tokamak core plasmas. They are observed in the low confinement mode and the weak internal transport barrier tokamak plasmas in the absence of magnetohydrodynamic instabilities. In addition, the electron temperature profile corrugation, which indicates the existence of the E × B shear flow layers, is clearly demonstrated as well as their dynamical interaction with the avalanche-like events. The measured width of the profile corrugation is around 45ρ i , which implies the mesoscale nature of the structure. a)

Time-dependent nonlinear simulation using the BOUT++ 3-field model is performed for a study of edge localized mode (ELM) dynamics in KSTAR H-mode plasmas. The simulated results of the ELM evolution are directly compared with the 2D ELM structures, measured by electron cyclotron emission imaging systems, from the initial growth to crash phase. The simulation results are qualitatively in good agreement with the observations. Specifically, it is notable in simulation and experiment that higher-n modes in a quasi-steady state phase evolve into lower-n modes close to the ELM-crash in time. It suggests that lower-n modes may be responsible for the onset of the crash. A postanalysis supports that nonlinear mode coupling between toroidal harmonics may drive the lower-n mode.

The integrated resonant magnetic perturbation (RMP)-based ELM-crash-control process aims to enhance the plasma performance during the RMP-driven ELM crash suppression, where the RMP induces an unwanted confinement degradation. In this study, the normalized beta (βN) is introduced as a metric for plasma performance. The integrated process incorporates the latest achievements in the RMP technique to enhance βN efficiently. The integrated process triggers the n = 1 edge-localized RMP (ERMP) at the L-H transition timing using the real-time machine learning (ML) classifier. The pre-emptive RMP onset can reduce the required external heating power for achieving the same βN by over 10 % compared to the conventional RMP onset. During the RMP phase, the adaptive feedback RMP ELM controller, demonstrating its performance in previous experiments, plays a crucial role in maximizing βN during the suppression phase and sustaining the βN-enhanced suppression state by optimizing the RMP strength. The integrated process achieves βN up to ~2.65 during the suppression phase, which is ~10 % higher than the previous KSTAR record but ~6 % lower than the target of the K-DEMO first phase (βN = 2.8), and maintains the suppression phase above the lower limit of target βN (= 2.4) for ~4 s (~60 τE). In addition to βN enhancement, the integrated process demonstrates quicker restoration of the suppression phase and recovery of βN compared to the adaptive control with the n = 1 conventional RMP (CRMP). The post-analysis of the experiment shows the localized effect of the ERMP spectrum in radial and the close relationship between the evolution of βN and the electron temperature.

The EPEC code is employed to model the q95 windows for n = 2 and n = 1 resonant magnetic perturbation (RMP)-induced edge localized mode (ELM) suppression in typical KSTAR H-mode discharges. The plasma equilibria used in the study are derived by rescaling the experimental plasma equilibrium in KSTAR discharge #18594 measured at time t = 6450 ms. The n = 2 and n = 1 ELM suppression windows predicted by EPEC are comparatively narrow in q95 (i.e., Δq95≃0.1) and are such that (assuming a relative pedestal pressure reduction of 15% is required to trigger ELM suppression), even in the middle of the windows, there is a threshold RMP coil current of about 1–3 kA/turn that must be exceeded before ELM suppression occurs. The n = 2 and n = 1 ELM suppression windows calculated by the EPEC code are consistent with the experimental observations and are also broadly similar to those recently calculated by the TM1 code [Hu et al., Phys. Plasmas 28, 052505 (2021)].