Fast dynamics of type I ELMs and transport of the ELM pulse in JT-60U
Fast dynamics of type I ELMs and transport of the ELM pulse in JT-60U
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DOI：
10.1088/0029-5515/44/5/002
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发表时间：
2004-05
期刊：
影响因子：
3.3
通讯作者：
N. Oyama;N. Asakura;A. Chankin;T. Oikawa;M. Sugihara;H. Takenaga;K. Itami;Y. Miura;Y. Kamada-Y.-Kamad
中科院分区：
文献类型：
--
作者：
N. Oyama;N. Asakura;A. Chankin;T. Oikawa;M. Sugihara;H. Takenaga;K. Itami;Y. Miura;Y. Kamada-Y.-Kamad
使用反射计、干涉仪、Dα强度和磁探针同时进行的快速ELM测量揭示了I型ELM的详细特征。从反射仪指示截止层径向运动的位相信号可以观察到ELM事件中的四个不同阶段，即前驱阶段、坍塌阶段、恢复阶段和松弛阶段。在坍塌阶段，密度底座的径向塌陷程度达到底座宽度的两倍。观察到水平干涉仪信号的快速下降，而高场边沿等离子体上的垂直干涉仪信号只有很小的延迟下降。ELMS引起的等离子体响应的这些特征可能表明密度基座在极向方向上的不均匀坍塌，位于低场侧(LFS)中面附近。用刮离层马赫探头测量了LFS中板的出射粒子，用快速红外电视摄像机测量了偏滤器靶的热流密度。峰值热负荷的时间常数与朝向偏滤器目标的等离子体流增强的时间常数相当。JT-60U基座储能的归一化榆木能量损失小于基座储能的10%。它对基座参数，如电子碰撞、平行离子损失时间和基座密度与Greenwald密度极限的比值表现出弱的依赖性。
Simultaneous fast ELM measurements using a reflectometer, interferometers, Dα intensity and a magnetic probe reveal the detailed characteristics of type I ELMs. From the phase signal of the reflectometer indicating the radial movement of the cut-off layer, four different phases in the ELM event, i.e. a precursor phase, collapse phase, recovery phase and a relaxation phase, were observed. In the collapse phase, the radial extent of the collapse of the density pedestal reached up to twice the pedestal width. A fast drop of the horizontal interferometer signal was observed, while the vertical interferometer on the high-field side edge plasma only exhibited a small and delayed reduction. These features of the plasma response due to ELMs might indicate a non-uniform collapse of the density pedestal in the poloidal direction, localized near the low-field side (LFS) midplane. Expelled particles from the LFS midplane were measured by using scrape-off layer Mach probes, and the heat flux to the divertor target was measured using a fast infrared TV camera. The time constant of the peak heat load was comparable to that of the enhancement of the plasma flow towards the divertor target. The normalized ELM energy loss by pedestal stored energy in JT-60U was found to be less than 10% of the pedestal stored energy. It shows weak dependence on the pedestal parameters such as electron collisionality, parallel ion loss time and the ratio of the pedestal density to the Greenwald density limit.