Development of wavelength calibration techniques for high-resolution x-ray imaging crystal spectrometers on the EAST tokamak

Newly developed large-area pixelated two-dimensional detector and two-crystal assemblies were deployed for the first time on tokamaks to enable time-resolved Bragg-diffracted x-ray imaging with good framing rate and water-cooling capabilities for in-vacuum long-pulse operations. High-quality helium-like (He-like) and hydrogen-like (H-like) argon spectra have been observed simultaneously for the first time on a single detector for a wide range of plasma parameters to infer both ion temperature and rotation profiles and support studies on spontaneous rotation, impurity transport, and RF physics. Since tokamak plasmas rotate in both the poloidal (theta) and toroidal (phi) directions, a reliable wavelength calibration is needed to account for the correct Doppler shift as well as to compute the spectrometer's instrumental function. Ly(alpha) lines emitted from Cd x-ray tubes are proposed to be used as "markers" to provide an in situ calibration of the EAST's X-ray imaging crystal spectrometer systems measuring He-and H-like argon spectra. The first lab test indicated that the X-ray tube can excite strong Ly(alpha) lines at 15 kV voltage and 1 mA current when the crystal is shined for 10 min. Other indirect calibration methods using locked-mode discharge scenarios were also studied as complementary methods.

本研究首次将新研发的大面积像素化二维探测器与双晶体组件部署于托卡马克（tokamak）装置，以实现兼具优异帧频与水冷性能的时间分辨布拉格衍射X射线成像，可满足真空环境下长脉冲运行的需求。本研究首次在单台探测器上，针对宽泛范围的等离子体参数同时观测到高质量的类氦（helium-like）与类氢（hydrogen-like）氩光谱，可同时反演离子温度与旋转剖面，为自发旋转、杂质输运与射频（RF）物理相关研究提供支撑。由于托卡马克等离子体同时沿极向（poloidal，θ）与环向（toroidal，φ）方向旋转，因此需要开展可靠的波长校准，以准确修正多普勒频移，并计算光谱仪的仪器响应函数。研究提议将镉（Cd）X射线管辐射出的莱曼α（Ly-α）谱线作为"标定标记"，用于对EAST装置的类氦与类氢氩光谱X射线成像晶体光谱仪系统开展原位校准。首次实验室测试结果表明，当晶体受辐照10分钟时，该X射线管可在15千伏电压、1毫安电流条件下激发出强度优异的莱曼α谱线。研究团队同时探索了利用锁模放电场景的其他间接校准方法作为补充方案。