Parameter dependences of small edge localized modes (ELMs)
Parameter dependences of small edge localized modes (ELMs)
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DOI：
10.1088/1741-4326/aad757
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发表时间：
2018-09
期刊：
影响因子：
3.3
通讯作者：
G. Harrer;E. Wolfrum;M. Dunne;P. Manz;M. Cavedon;P. Lang;B. Kurzan;T. Eich;B. Labit;J. Stober;H. Meyer;M. Bernert;F. Laggner;F. Aumayr
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文献类型：
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作者：
G. Harrer;E. Wolfrum;M. Dunne;P. Manz;M. Cavedon;P. Lang;B. Kurzan;T. Eich;B. Labit;J. Stober;H. Meyer;M. Bernert;F. Laggner;F. Aumayr
小边缘局域模式（ELM）场景的发展对于减少等离子体表面元件的应变具有重要意义。在ASDEX Upgrade中，可以在高密度、高形状、接近双零等离子体的情况下找到这样的一种情况，显示出频率为Hz且功耗低的小型elm。从气体燃料到颗粒燃料的变化导致了基座顶部与分离矩阵碰撞解耦的边缘轮廓。当基顶值保持不变时，只有低分离矩阵和刮脱层（SOL）密度的相显示出大的elm，中间是小的elm。在高分离矩阵密度的相中，小的elm振幅增加，而大的elm不出现。同样，等离子体垂直位置仅向下变化约2厘米，恒定地减小小elm的尺寸，而大elm则显得更加强烈。对这种行为的一种可能的解释可能是靠近分离矩阵的模态的驱动和稳定的影响。当这些小的ELM模引起足够的输运时，它们使分离矩阵周围的梯度区域变平，从而使有效基座宽度变窄。由于较窄的基座对全局PB模态更稳定，稳定性边界向更高的压力梯度移动，因此不会发生i型elm。结果表明，较高的局部磁切变增大了小elm的振幅，与基本的气胀模理论一致，较高的局部磁切变减小了小elm的振幅。
The development of small edge localized mode (ELM) scenarios is important in order to reduce the strain on plasma facing components. One such scenario can be found at high densities, in highly shaped, close to double-null plasmas in ASDEX Upgrade, showing small ELMs characterized by a frequency Hz and a low power loss. Changing from gas fuelling to pellet fuelling results in edge profiles in which the collisionality of pedestal top and separatrix are decoupled. While the pedestal top values remain unchanged, only the phases with low separatrix and scrape-off layer (SOL) density show large ELMs with small ELMs in between. In phases with high separatrix density the small ELMs increase in amplitude and large ELMs do not occur. Similarly, a change in vertical plasma position by only ∼2 cm downwards, at constant reduces the size of small ELMs while the large ELMs appear more intense. A possible explanation of this behaviour could be the influence of the drive and the stabilization of modes positioned close to the separatrix. When these small ELM modes cause enough transport, they flatten the gradient region around the separatrix and thereby consequently narrow the effective pedestal width. Because a narrower pedestal is more stable against global PB modes, the stability boundary is shifted towards higher pressure gradients and type-I ELMs do not occur. It is shown that a higher increases the amplitude of small ELMs and, in agreement with basic ballooning mode theory, a higher local magnetic shear reduces their amplitude.