Ugoletti M, Agostini M, La Matina M, Scarin P, Wang Y, Wüthrich C, Theiler C, Andrebe Y, Griener M, Zuin M
ISTP-CNR, Institute for Plasma Science and Technology, Corso Stati Uniti 4, 35127 Padova, Italy.
Consorzio RFX (CNR, ENEA, INFN, UNIPD, Acciaierie Venete SpA), Corso Stati Uniti 4, 35127 Padova, Italy.
Rev Sci Instrum. 2024 Aug 1;95(8). doi: 10.1063/5.0217220.
The Thermal Helium Beam (THB) is a diagnostic for simultaneously measuring the electron temperature and density profiles of the plasma edge and scrape off layer (SOL). It exploits the line ratio technique of selected He line intensities, emitted by He gas puffed inside the plasma, to locally estimate the plasma properties through a dedicated collisional radiative model (CRM). Standard THB diagnostics used in nuclear fusion devices measure three HeI emission lines: 667.8, 706.5, and 728.1 nm. For the RFP experiment RFX-mod2, a new THB is designed and tested for the first time at the TCV tokamak. It acquires an additional emission line at 501.6 nm, which is exploited to estimate the radiation re-absorption, which is not negligible in regions of large neutral He densities (leading to high re-absorption) and simultaneously low electron density and temperature (lack of other excitation channels). It affects the measurements most strongly at the far SOL, while the significance of re-absorption decreases as it approaches the separatrix. In this paper, plasma density and temperature profiles of the plasma edge at the outboard midplane of TCV, measured with this newly designed THB, are presented. For the first time, the effect of radiation re-absorption on the estimation of electron temperature and density profiles is experimentally measured in a tokamak using the 501 nm line emission intensity. Different CRMs are compared with and without radiation re-absorption, showing good agreement when re-absorption is included and demonstrating how it plays an important role in the far SOL, as expected.
热氦束（THB）是一种用于同时测量等离子体边缘和刮削层（SOL）的电子温度和密度分布的诊断方法。它利用等离子体内注入的氦气发射的选定氦线强度的线比技术，通过专用的碰撞辐射模型（CRM）来局部估计等离子体特性。核聚变装置中使用的标准THB诊断方法测量三条HeI发射线：667.8、706.5和728.1纳米。对于RFP实验RFX-mod2，首次在TCV托卡马克上设计并测试了一种新型THB。它获得了一条额外的501.6纳米发射线，用于估计辐射再吸收，在中性氦密度大（导致高再吸收）且电子密度和温度同时较低（缺乏其他激发通道）的区域，辐射再吸收不可忽略。它在远SOL处对测量影响最大，而随着接近磁分界面，再吸收的重要性降低。本文展示了用这种新设计的THB测量的TCV外侧中平面处等离子体边缘的等离子体密度和温度分布。首次在托卡马克中利用501纳米线发射强度通过实验测量了辐射再吸收对电子温度和密度分布估计的影响。比较了有无辐射再吸收的不同CRM，结果表明包含再吸收时两者吻合良好，正如预期的那样，这表明再吸收在远SOL中起着重要作用。
