The intermediate oscillatory phase during the L–H transition, termed the I-phase, is studied in the EAST superconducting tokamak using a newly developed dual gas puff imaging (GPI) system near the L–H transition power threshold. The experimental observations suggest that the oscillatory behaviour appearing at the L–H transition could be induced by the synergistic effect of the two components of the sheared m, n = 0 E × B flow, i.e. the turbulence-driven zonal flow (ZF) and the equilibrium flow. The latter arises from the equilibrium, and is, to leading order, balanced by the ion diamagnetic term in the radial force balance equation. A slow increase in the poloidal flow and its shear at the plasma edge are observed tens of milliseconds prior to the I-phase. During the I-phase, the turbulence recovery appears to originate from the vicinity of the separatrix with clear wave fronts propagating both outwards into the far scrape-off layer (SOL) and inwards into the core plasma. The turbulence Reynolds stress is directly measured using the GPI system during the I-phase, providing direct evidence of kinetic energy transfer from turbulence to ZFs at the plasma edge. The GPI observations strongly suggest that the SOL transport physics and the evolution of pressure gradient near the separatrix play an important role in the L–I–H transition dynamics. To highlight these new physics, the previous predator–prey model is extended to include a new equation for the SOL physics. The model successfully reproduces the L–I–H transition process with several features comparing favourably with GPI observations.
EAST超导托卡马克中，利用新开发的双气体成像（GPI）系统，在L–H转换功率阈值附近研究了L–H转换期间的中间振荡相（I相）。实验观测表明，L–H转换期间出现的振荡行为可能由剪切m, n = 0 E × B流的两个分量的协同效应引起，即湍流驱动的带状流（ZF）和平衡流。后者源于平衡，并在径向力平衡方程中至最低阶由离子抗磁项平衡。在I相之前数十毫秒，观察到等离子体边缘极向流及其剪切缓慢增加。在I相期间，湍流恢复似乎起源于分界线附近，具有清晰的波前，分别向外传播到刮削层（SOL）和向内传播到芯部等离子体。利用GPI系统在I相期间直接测量了湍流雷诺应力，提供了从湍流到带状流（ZF）在等离子体边缘动能传递的直接证据。GPI观测强烈表明，刮削层（SOL）输运物理和分界线附近压力梯度的演化在L–I–H转换动力学中起重要作用。为突出这些新物理，将先前的捕食者–猎物模型扩展，加入一个描述刮削层（SOL）物理的新方程。该模型成功再现了L–I–H转换过程，其若干特征与GPI观测结果吻合良好。