Predictive nonlinear MHD simulations of quiescent H-mode plasma in the HL-3 tokamak

In this article, we investigate the edge localized mode (ELM)-free quiescent H (QH)-mode regime in the HL-3 tokamak via nonlinear MHD simulations. HL-3 (previously known as HL-2M) aims at high β plasmas and recently achieved its first H-mode operation. Large ELMs in H-mode discharges challenge the tolerance of plasma facing components in reactor-relevant tokamaks and small/no-ELM regimes become attractive options for existing and future fusion devices. A naturally ELM-free regime, QH-mode, is explored in this work with nonlinear extended MHD modeling for the HL-3 device. The simulation is conducted based on a realistic lower single null divertor configuration, and successfully produces a QH-mode plasma. Toroidal modes n=0,…,12 are simulated and the QH-mode plasma is dominated by a saturated n = 2 kink-peeling mode. After entering QH-mode, the plasma thermal energy becomes nearly stationary and the plasma pedestal is kept at a stable level. The saturated peeling instability produces an ergodized edge magnetic field region and some E×B convective cells, which enhance radial transport. The edge harmonic oscillation (EHO) as a characteristic feature of QH-mode plasmas is detected in the pedestal with a fundamental frequency (for the n = 1 mode) of 7.5 kHz. The EHO structures on the high-field side (HFS) and low-field side (LFS) are observed to be asymmetric. The EHO is dominated by the n = 2 mode with a frequency of 15 kHz on the HFS, while the n = 3 mode becomes dominant at the vicinity of ψnorm=0.95 on the LFS. It is also found that density and temperature profiles show different responses to the EHO in the simulation. The dependence on the safety factor for accessing QH-mode is demonstrated with the QH-mode being lost when q95 is reduced from 2.5 to 2.3. The EHO is absent in this scenario and a bursting ELM-like activity is observed instead.