The low-to-high mode or L-H transition in tokamaks involves a sudden reduction in the edge turbulence level and a decrease in the edge plasma transport. The mechanism for the L-H transition is widely believed to be associated with changes in the poloidally averaged poloidal turbulence velocity. Using a gas puff imaging (GPI) diagnostic, the poloidally averaged poloidal turbulence velocity ⟨V_pol⟩_pol was measured for a set of 16 shots with L-H transitions in NSTX. These measurements were focused –2 cm inside the separatrix where the relative fluctuation level as seen in GPI decreases significantly and consistently at the transition. The magnitude of this poloidal velocity preceding the transition varied widely, ranging from |V_pol| ∼ 1–4 km/s during the last 1 ms before the transition, and the magnitude of the radial gradient also had a wide shot-to-shot range of |grad V_pol| ∼ 0.34 to 1.9 km/s cm during this same time. The frequency spectrum of ⟨V_pol⟩_pol during the 30 ms before the transition had a near-coherent peak at ∼2–5 kHz, but only in about half of these shots. In general, there were no clear and consistent changes in the poloidal velocity of the turbulence preceding the L-H transition in this database.

中文翻译：

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NSTX中LH过渡之前的边缘湍流速度

托卡马克中的从低到高模式或LH跃迁涉及边缘湍流水平的突然降低和边缘等离子体传输的降低。人们普遍认为，LH跃迁的机制与多倍体平均多倍体湍流速度的变化有关。使用气体抽吸成像（GPI）诊断中，极向场均极向紊流速度⟨ V _POL ⟩ _POL被用于一组16个投与NSTX LH转变进行测定。这些测量聚焦在分离线内部– 2 cm处，在GPI中观察到的相对波动水平在过渡时显着且一致地降低。过渡之前该极向速度的大小变化很大，范围为| |。V _POL| 在过渡前的最后1毫秒内约1-4 km / s，并且径向梯度的幅度也具有较宽的| grad V _pol |范围。在同一时间〜0.34至1.9 km / s cm。⟨的频谱V _POL ⟩ _POL转换前的30毫秒期间~2-5千赫有近相干峰值，但只有在这些镜头的一半。通常，在该数据库中，在LH跃迁之前，湍流的极点速度没有明显一致的变化。