Accuracy index selection during optimization of particle accelerator ring tunnel network design based on Monte Carlo method

With advancements in science and technology, more countries are investing in fourth-generation light sources. The scale of these sources continues to expand, and the requirements for alignment accuracy are also higher. With the increasing requirements of particle accelerators for alignment accuracy, the optimal design of tunnel control networks has become a core research issue. This study focuses on the 480 m storage ring of the Hefei Advanced Light Facility (HALF). We systematically analyze the impact of laser tracker measurement distance and network density on the overall measurement accuracy of the control network based on the principles of three-dimensional measurement and network adjustment with software SpatialAnalyzer. Using Monte Carlo simulation, three kinds of control network accuracy evaluation indexes (true value deviation, uncertainty, error) are compared. When using uncertainty and true value deviation as accuracy indicators, it is recommended to prioritize widening the laser tracker measurement range to optimize the layout of high-precision three-dimensional tunnel control networks and further refine network density. The results indicate that as the number of repeated measurements at control points increases, both deviation and uncertainty metrics improve, initially at a rapid rate that then gradually slows. Notably, the improvement in uncertainty is more pronounced than in deviation. After optimization, the HALF storage ring control network achieves a mean true value deviation of 66 mu m and a mean uncertainty of 236 mu m. The maximum deviation from the true value and uncertainty can reach 118 mu m and 453 mu m. This study provides a methodological framework for optimizing control networks in future particle accelerators and large-scale precision metrology applications.