Research on accelerator tunnel network adjustment method based on minimum constraints

Abstract In the establishment of control networks for large-scale scientific facilities, this study focuses on the high energy photon source tunnel network, currently the largest light source in China. We explored the impact of ‘2 + 1’ dimensional (2 + 1D) and three-dimensional (3D) adjustment methods on the structure of control networks using two minimal constraint methods: fixed parameter and centroid datum. Firstly, the method of a posteriori variance component estimation (VCE) was adopted to address the impact of observed value weighting and approximate coordinates on the adjustment results, ensuring the reliability and uniqueness of these results. Secondly, through the adjustment analysis of the entire facility, as well as closed and non-closed loop networks, it was found that the deviation of the results in the horizontal between 2 + 1D adjustment and 3D adjustment is only 0.1 mm, demonstrating good consistency. However, in height, the 3D adjustment exhibits larger distortion, particularly in areas connected through small sight holes, where the distortion accumulates towards the distal end at each station. For the slender accelerator tunnel network, which is established through a free station setting and multi-station overlap, it is advisable to use 3D adjustment cautiously in the presence of structural weaknesses in the network shape.