Across the transition from QH to wide-pedestal QH, the pedestal electron pressure generally increases by 60% and widens by 50% and the plasma confinement (ITER Hy98y2) rises by 40%. It is referred more » to as ‘wide-pedestal QH-mode’ because the pedestal width exceeds the EPED kinetic ballooning mode (KBM) limit. The regime was originally found in conventional QH-mode when the counter-Ip neutral beam torque drops to ~2Nm in double null plasma shapes. A new QH-mode regime with enhanced pedestal has been discovered in DIII-D at reactor-relevant low torque and collisionality. The additional transport to maintain constant density and radiation is provided by the benign coherent edge harmonic oscillations mode (EHO) which is thought to be a kink/peeling mode. Quiescent H-mode (QH-mode) is a naturally ELM-stable high performance operation mode which has been obtained in DIII-D, ASDEX Upgrade, JET, and JT-60U. These findings reveal that the fundamental physics mechanism of the QH-mode may be shear flow and are significant for understanding the mechanism of EHO and QH-mode. The nonlinear mode interaction is enhanced during the mode amplitude saturation phase. At the meantime, the nonlinear simulations of the QH-mode indicate that the shear flow in both co- and counter directions of diamagnetic flow has some similar effects. The stronger shear flow shifts the most unstable mode to lower-n and narrows the mode spectrum. Adopting the much more general shape of E×B shear (ω E=E r/RB θ) profiles, the linear and nonlinear BOUT++ simulations show qualitative consistence with the experiments. Using the shifted circular cross-section equilibriums including bootstrap current, more » the results demonstrate that the E×B shear flow strongly destabilizes low-n peeling modes, which are mainly driven by the gradient of parallel current in peeling-dominant cases and are sensitive to the E r shear. Simulations about the effects of E×B shear flow on the quiescent H-mode (QH-mode) are carried out using the three-field two-fluid model in the field-aligned coordinate under the BOUT++ framework. It is crucial for the burning plasma devices such as ITER. Recently, the stationary high confinement operations with improved pedestal conditions have been achieved in DIII-D, accompanying the spontaneous transition from the coherent edge harmonic oscillation (EHO) to the broadband MHD turbulence state by reducing the neutral beam injection torque to zero. Our findings advance the physics basis for developing stationary ELM-free high-confinement operation at low rotation for future burning plasma where similar collisionality and rotation levels are expected. Improved transport in the outer core region (0.8≤ρ≤0.9) owing to increased ExB flow shear in that region and the enhanced pedestal boost the overall confinement by up to 45%. Even with the significantly enhanced pedestal pressure, the edge operating point is below the peeling ballooning mode stability boundary and thus without ELMs. We posit that the more » enhanced edge turbulence-driven transport, enabled by the lower edge ExB flow shear due to lower torque reduces the pedestal gradient and, combined with the high edge instability limit provided by the balanced double-null plasma shape, permits the development of a broader and thus higher pedestal that is turbulence-transport-limited. And at the transition, the coherent edge harmonic oscillations (EHO) that usually regulate the standard QH edge cease and broadband edge MHD modes appear along with a rapid increase in the pedestal pressure height (by ≤60%) and width (by ≤50%). As the injected neutral beam torque is ramped down and the edge ExB rotation shear reduces, the transition from standard QH to the wide pedestal QH-mode occurs. The observed minimum edge ExB shear required for the EHO decreases linearly with pedestal collisionality v$$*\atop,Ī stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D with reactor relevant edge parameters and no ELMs. New experimental studies and modelling of the coherent Edge Harmonic Oscillation (EHO), which regulates the conventional Quiescent H-mode (QH-mode) edge, validate the proposed hypothesis of edge rotational shear in destabilizing the low-n kink peeling mode as the additional drive mechanism for the EHO.
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