Terry J L, von Stechow A, Baek S G, Ballinger S B, Grulke O, von Sehren C, Laube R, Killer C, Scharmer F, Brunner K J, Knauer J, Bois S
Massachusetts Institute of Technology - Plasma Science and Fusion Center, Cambridge, Massachusetts 02139, USA.
Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany.
Rev Sci Instrum. 2024 Sep 1;95(9). doi: 10.1063/5.0219336.
A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the "Gas-Puff Imaging" (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system's plasma-facing components. The system features a pair of "converging-diverging" nozzles for partially collimating the gas puffed locally ≈135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656 nm) and HeI (587 nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X.
已设计、建造、安装并运行了一个利用“喷气成像”（GPI）技术研究W7-X等离子体边界波动时空动力学的系统。该GPI系统解决了一些长脉冲超导装置（如W7-X）特有的挑战，包括等离子体与真空容器壁之间的长距离、等离子体与诊断端口之间的长距离、W7-X中不同磁配置下最后闭合磁通量表面（LCFS）位置的范围，以及系统面向等离子体部件上的热负荷管理。该系统具有一对“收敛-发散”喷嘴，用于局部准直在等离子体边界径向外侧约135毫米处喷出的气体，一个弹出式转向镜，用于从侧面观察喷气发射（它还用作再入式真空窗口的快门），以及一个高通量光学系统，该系统收集喷出气体与等离子体相互作用产生的可见发射，并将其沿水冷再入管直接导向快速相机的8×16像素探测器阵列。DEGAS 2中性代码用于模拟H₂和He特征性喷气在W7-X典型边缘等离子体剖面内激发时预期的Hα（656纳米）和HeI（587纳米）线发射，从而预测用于降低与系统灵敏度和视场位置相关风险的线亮度。在W7-X上运行GPI时，对于最小扰动的喷气，在视场内显示出优异的信噪比（2兆帧/秒时>100）。GPI系统提供了W7-X边缘和刮离层以及构成W7-X采用的岛偏滤器配置的LCFS外侧磁岛内外等离子体波动的二维（径向和极向）动力学的详细测量结果。
