Researchers from Lawrence Livermore National Laboratory and their collaborators have conducted a comprehensive study on detachment physics in the Korean Superconducting Tokamak Advanced Research (KSTAR) device. The team, led by Menglong Zhao and including Xueqiao Xu, Ben Zhu, Thomas Rognlien, and others, has developed a large-scale database of two-dimensional UEDGE simulations to better understand and control plasma detachment, a critical process for managing heat and particle fluxes in fusion reactors.
The researchers generated nearly 70,000 steady-state solutions, systematically varying key parameters such as upstream density, input power, plasma current, impurity fraction, and anomalous transport coefficients. This extensive database allowed them to identify robust indicators of plasma detachment. They found that the strike-point electron temperature at the onset of detachment consistently falls within the range of 3-4 electron volts (eV), largely independent of upstream conditions. This finding provides a clear benchmark for detecting detachment in real-time control systems.
The study also revealed important scaling relations that differ from those predicted by one-dimensional models. Notably, the sensitivity to impurities was found to be weaker, and heat flux widths were shown to follow Eich’s scaling only under specific conditions of uniform, low particle and heat transport. Additionally, the simulations highlighted distinctive asymmetries between the inner and outer divertors in KSTAR, which differ qualitatively from those observed in the DIII-D tokamak. These insights are crucial for designing effective control strategies tailored to specific tokamak configurations.
Complementary time-dependent simulations were conducted to quantify the plasma response to gas puffing, a technique used to induce detachment. The simulations showed delays of 5-15 milliseconds at the outer strike point and approximately 40 milliseconds for the low-magnetic-field-side (LFS) radiation front. These dynamics were well captured by first-order-plus-dead-time (FOPDT) models, which are consistent with experimentally observed detachment-control behavior in KSTAR. The researchers plan to submit their findings to Plasma Phys. Control. Fusion (2025) for peer review and publication.
The practical applications of this research for the energy sector are significant. Understanding and controlling plasma detachment is essential for managing the extreme heat and particle fluxes in fusion reactors, which are key to developing sustainable and efficient fusion energy. The insights gained from this study can inform the design of real-time control systems, improving the reliability and performance of future fusion power plants. By providing a robust framework for detachment control, this research brings us one step closer to harnessing fusion energy as a clean and abundant power source.
This article is based on research available at arXiv.