Simulation research on effect of neutrals and carbon impurities on divertor detachment in HL-3 tokamak

<sec>Divertor detachment is a critical technique for managing the thermal load on the divertor of the HL-3 tokamak, an important device in magnetic confinement fusion research. However, existing studies on detachment have largely overlooked the complex multi-species particle dynamics in the scrape-off layer (SOL) and divertor regions, particularly the interactions involving hydrogen isotopes (e.g, deuterium), externally injected impurities (e.g, neon), and intrinsic impurities (e.g, carbon). This study aims to address this problem by employing the newly developed multi-species particle transport code SD1D to investigate the effects of carbon impurities and neutral particles on two detachment scenarios in HL-3: plasma density ramp-up and neon injection into the divertor.</sec><sec>The SD1D code models the transport, collision, and radiation processes of various particles, including deuterium ions, atoms, and molecules, as well as carbon and neon impurities, along the magnetic field lines from the SOL upstream to the divertor target. The study focuses on understanding how carbon impurities and neutral particles affect the detachment mechanisms under different conditions.</sec><sec>The results reveal that carbon impurities generated in the divertor significantly enhance the detachment in the density ramp-up scenario by increasing the density of deuterium atoms, molecules, and ions near the target plate, thereby increasing the total radiation power. This effect lowers the density threshold required for detachment and reduces the peak current on the target plate. However, carbon impurities have a minimal influence on detachment achieved through neon injection, as they do not significantly change the density of deuterium species or the total radiation power in this scenario.</sec><sec>Furthermore, this study highlights the distinct roles of neutral particles in the two detachment mechanisms. In the density ramp-up scenario, the increased plasma density promotes the recycling process in the divertor, generating a substantial population of neutral particles. The energy loss and momentum loss resulting from plasma-neutral interactions are crucial for achieving detachment. In contrast, neon injection directly reduces the saturation current on the target plate, suppressing the recycling process and diminishing the importance of neutral particles.</sec><sec>In conclusion, this work demonstrates that carbon impurities play a significant role in facilitating detachment during plasma density ramp-up but have limited influence on detachment via neon injection. The findings underscore the importance of considering multi-species particle dynamics, including neutral particles and impurities, in understanding and optimizing divertor detachment strategies. Future work will involve validating the SD1D model based on experimental data from HL-3 to further refine its predictiveness.</sec>