Development of a diagnostic system for atomic processes in the whole divertor region of HL-3.

The atomic processes are important for understanding the mechanisms of divertor detachment physics. The developed diagnostic system for atomic processes aims to present the atomic process distributions of ionization and recombination in the whole divertor region of HL-3, which is equipped with the multi-channel visible imaging optics, two SCMOS cameras having identical parameters, and bandpass filters. This configuration enables high spatiotemporal resolution measurements of Balmer lines across the entire divertor region. The maximum frequency of the cameras is 400 fps (512 pixel × 512 pixel), and the field of view covers the entire 1100 × 650 cm2 area of the divertor with the spatial resolution of 1 × 1 cm2. The intensity ratio of experimental measurements of Balmer lines can be used to assess the leading region of ionization, transition from ionization to recombination, and recombination from the Atomic Data and Analysis Structure database. The preliminary results show that ionization is primarily distributed near the last closed flux surface (LCFS), while the transition from ionization to recombination and recombination predominate within a limited region distant from the LCFS. Through the corresponding S/XB, the numbers of ionization and recombination per unit time within the divertor region are obtained. With the evolution of time, the electron density gradually increases, and the ionization region and ionization rate gradually increase. This holds immense significance in advancing our comprehension of the detachment mechanism, facilitating real-time control of divertor detachment and steady-state control technology of heat load in the future.