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In this paper we show that changing from an ion temperature gradient (ITG) to a trapped electron mode (TEM) dominant turbulence regime (based on linear gyrokinetic simulations) results experimentally in a strong density pump-out (defined as a reduction in line-averaged density) in low collisionality, low power H-mode plasmas. We vary the turbulence drive by changing the heating from predominantly ion heated using neutral beam injection to electron heated using electron cyclotron heating, which changes the ratio and the temperature gradients. Perturbed gas puff experiments show an increase in transport outside , through a strong increase in the perturbed diffusion coefficient and a decrease in the inward pinch. Linear gyrokinetic simulations with TGLF show an increase in the particle flux outside the mid-radius. In conjunction an increase in intermediate-scale length density fluctuations is observed, which indicates an increase in turbulence intensity at typical TEM wavelengths. However, although the experimental changes in particle transport agree with a change from ITG to TEM turbulence regimes, we do not observe a reduction in the core rotation at mid-radius, nor a rotation reversal.

Excellent reproducibility of KSTAR resonant magnetic perturbation (RMP)-driven, edge-localized mode (ELM)-crash suppression enables us to construct a database reliably for the study of ELM-crash suppression conditions. To establish a high-fidelity database, we have selected one of the frequently used RMP configurations in KSTAR, n = 1, +90° phasing RMP-coil configuration. A series of fitting curves based on edge profile diagnostics data is used for normalized electron collisionality (ν∗e) and plasma toroidal rotation (Vtor) at pedestal top. Since ITER is expected to employ slowly rotating, low-collisionality, high-density plasmas whose conditions are not readily accessible in the existing devices, the exploration and understanding of these two parameters would be important not only for RMP-driven, ELM-crash-suppression physics but also for the success of ITER. The data points for the ELM-crash suppression phase are in the range of 0.2 < ν∗e,ped< 1.1 with Zeff = 2 assumption and Vtor,ped> 40 km/s. Suppression thresholds or boundaries in ν∗e,ped or Vtor,ped are not confirmed in the investigated parameter ranges so far. The KSTAR database still needs additional experimental datasets in ITER-relevant conditions (ν∗e,ped ∼ 0.1 and low-torque low-rotation) to confirm the boundary of the ELM-crash suppression window in KSTAR and reduce the uncertainties of the RMP ELM-crash control technique in ITER. In both ν∗e,ped and Vtor,ped parameters, the phase-space distribution of the ELM-crash suppression has no clear distinction from that of the ELM-crash mitigation. Linear discriminant analysis provides a linear combination of parameters relevant to ELM-crash suppression, best separating two data categories. Recursive feature elimination indicates that ne,ped and IRMP, as well as ν∗e,ped and Vtor,ped, are critical variables in the separation of the data groups. [ABSTRACT FROM AUTHOR]

Toroidal rotation and ion temperature validation studies utilizing an X-ray imaging crystal spectrometer (XICS) and charge exchange spectroscopy (CES) are continuously investigated from previous experiments as part of an International Tokamak Physics Activity Diagnostics Working Group Joint Experimental Activity. Core toroidal rotation and ion temperature measurements of different impurity species from XICS and CES diagnostics have shown good agreement again with various plasma discharges from KSTAR. The experimental results from the XICS diagnostic show detailed toroidal rotation behavior due to improved time resolution. [ABSTRACT FROM AUTHOR]