Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
复制标题
具有类似 ITER 壁的低三角度 JET 托卡马克放电中的基座演化物理
DOI：
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
A. Wynn
中科院分区：
文献类型：
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作者：
C. Bowman;D. Dickinson;L. Horvath;A. Lunniss;H. Wilson;I. Cziegler;L. Frassinetti;K. Gibson;A. Kirk;B. Lipschultz;C. Maggi;C. Roach;S. Saarelma;P. Snyder;A. Thornton;A. Wynn
托卡马克等离子体边缘的高约束基座区域的压力梯度在等离子体喷发期间迅速坍塌，称为边缘局域模式(ELM)，然后在下一次ELM之前的较长时间尺度上重建。对控制ELMS之间喷流基座演变的物理因素进行了分析，其中包括1.4MA、1.7T、低三角度、δ = 0.2与热核实验堆样壁的放电，发现压力梯度通常跟踪理想的磁流体动力气球极限，与动力学气球模式的作用一致。此外，基座宽度经常受到气球模式二次稳定的等离子体区域的影响，这可以解释ELM之间有时复杂的演化。对第二个稳定通量面的局地回转动力学分析揭示了动力气球模式的稳定性；全球效应有望提供一种破坏稳定的机制，需要在这种第二个稳定情况下保持。除了电子尺度的电子温度梯度模式，与该通量表面相关的离子尺度不稳定性还包括一个电磁捕获电子分支和两个沿离子方向传播的静电分支，其中一个具有高的径向波数。在这第二种稳定情况下，ELM是由剥离-气球模式触发的；否则，在ELM开始时，基座略低于剥离-气球模式的边缘稳定边界。在后一种情况下，有证据表明，高频榆树是通过等离子体的振荡来调整速度的，在到达剥离-气球边界之前，导致基座崩溃。提出了一个模型，在该模型中，振荡与热等离子体丝有关，热等离子体丝被气球模式推向等离子体边缘，将它们的自由能量排入那里较冷的等离子体中，然后松弛回来重复这一过程。结果表明，避免振荡并最大化具有二次稳定通道的等离子体区域将导致最高的基座高度，从而获得最佳限制--这是优化JET和未来托卡马克(如ITER)聚变性能的关键结果。
The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, δ = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electron-scale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement—a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.
影响因子：
8.6
作者：
C. Ham;S. Cowley;G. Brochard;H. R. Wilson-H. R.-Wilson-2253514205
通讯作者：
C. Ham;S. Cowley;G. Brochard;H. R. Wilson-H. R.-Wilson-2253514205