Influence of the magnetic configuration on the high-field side scrape-off layer at ASDEX Upgrade and the role of the secondary separatrix

IF 2.1 2区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS Plasma Physics and Controlled Fusion Pub Date : 2024-04-12 DOI:10.1088/1361-6587/ad3a9f
D Hachmeister, C Silva, J Santos, G D Conway, L Gil, A Silva, U Stroth, J Vicente, E Wolfrum, R M McDermott, R Dux, D Brida, R Fischer, B Kurzan, the ASDEX Upgrade Team4, the EUROfusion MST1 Team5
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Abstract

In tokamaks, radial transport is ballooning, meaning it is enhanced at the low-field side (LFS). This work investigates the effect of the magnetic configuration on the high-field side (HFS) scrape-off layer. Our experiments involved L-mode and H-mode discharges at ASDEX Upgrade, in which we scanned the magnetic configuration from a lower to an upper single-null shape, thus varying the location of the secondary separatrix. We show that the secondary separatrix determines the width of the HFS scrape-off layer, meaning that the density is much lower in the region that is magnetically disconnected from the LFS scrape-off layer, outside the secondary separatrix. Furthermore, we observe that the large density often seen in the HFS divertor drastically decreases as the separation between the primary and secondary separatrices falls below a particular value. This value is different for L-mode and H-mode plasmas and closely matches the power decay length measured at the LFS midplane. We also show how the HFS scrape-off layer density is smaller in an upper single-null than in a lower single-null, when the ionic grad-B drift points down. This difference is likely caused by reversing the E×B drifts in the active divertor when switching the active X-point from the bottom to the top. We further observe that the neutral density in the lower divertor also correlates with the plasma shape and the high-density region in the HFS scrape-off layer. During the shape scans analyzed here, the HFS divertor remained partially detached throughout, with transitory reattachment modulated by ELM activity in H-mode. This work provides novel experimental data that can be leveraged to further the modeling capabilities and understanding of scrape-off layer physics in highly shaped plasmas.
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磁配置对 ASDEX 升级版高磁场侧刮除层的影响以及二次分离矩阵的作用
在托卡马克中,径向传输是气球式的,这意味着它在低场侧(LFS)得到增强。这项工作研究了磁配置对高场面(HFS)刮除层的影响。我们的实验涉及在 ASDEX Upgrade 进行的 L 模式和 H 模式放电,在实验中,我们将磁配置从下部单空形状扫描到上部单空形状,从而改变了二次分离矩阵的位置。我们发现二次分离矩阵决定了 HFS 刮离层的宽度,这意味着在二次分离矩阵之外与 LFS 刮离层磁性断开的区域,密度要低得多。此外,我们还观察到,当主分离矩阵和次级分离矩阵之间的间距低于某一特定值时,在 HFS 分流器中经常出现的大密度会急剧下降。这个值对于 L 模式和 H 模式等离子体是不同的,并且与在 LFS 中平面测量到的功率衰减长度非常吻合。我们还展示了当离子梯度-B 漂移指向下方时,上单空的 HFS 刮除层密度如何小于下单空。这种差异很可能是由于在将有源 X 点从底部切换到顶部时,有源分流器中的 E×B 漂移发生了逆转。我们进一步观察到,下部分流器中的中性密度也与等离子体形状和 HFS 刮除层中的高密度区域相关。在本文分析的形状扫描过程中,HFS分流器始终保持部分分离,并在H模式下通过ELM活动调制短暂的重新附着。这项工作提供了新颖的实验数据,可用于进一步提高建模能力和对高形状等离子体中刮离层物理学的理解。
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来源期刊
Plasma Physics and Controlled Fusion
Plasma Physics and Controlled Fusion 物理-物理:核物理
CiteScore
4.50
自引率
13.60%
发文量
224
审稿时长
4.5 months
期刊介绍: Plasma Physics and Controlled Fusion covers all aspects of the physics of hot, highly ionised plasmas. This includes results of current experimental and theoretical research on all aspects of the physics of high-temperature plasmas and of controlled nuclear fusion, including the basic phenomena in highly-ionised gases in the laboratory, in the ionosphere and in space, in magnetic-confinement and inertial-confinement fusion as well as related diagnostic methods. Papers with a technological emphasis, for example in such topics as plasma control, fusion technology and diagnostics, are welcomed when the plasma physics is an integral part of the paper or when the technology is unique to plasma applications or new to the field of plasma physics. Papers on dusty plasma physics are welcome when there is a clear relevance to fusion.
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