Speaker
Description
Opening and reassembly are required in some accelerator magnet units during vacuum chamber installation, maintenance, or internal component adjustment. The reassembly state is commonly evaluated using high-precision top targets measured by laser tracker systems. This procedure provides a reliable engineering criterion for the recovery of the top-target region, but the targets are mainly distributed on the upper part of the magnet. Therefore, the relative geometric state between the upper and lower magnet halves, especially in side regions away from the top targets, cannot be directly described by the top-target residuals alone.
This study investigates a photogrammetric auxiliary measurement method for evaluating accelerator magnet opening and reassembly. Side supplemental targets are introduced around the magnet unit to provide additional geometric information beyond the top-target region, while the top targets are still used as common points for coordinate transformation and existing acceptance evaluation. A preliminary simulation is first conducted to analyze the limitation of using only top-target constraints. The results indicate that samples satisfying the top-target RMSE criterion may still show measurable geometric changes in side regions.
A photogrammetric error propagation model is then developed based on the collinearity equations, self-calibrating bundle adjustment, full point-coordinate covariance, and coordinate transformation through common top targets. Monte Carlo simulations are performed with fixed magnet geometry, simulated camera stations, image measurement noise, and interior-orientation/distortion parameter perturbations. The internal precision predicted by the full-covariance model is compared with external error statistics obtained from known simulation truth. The results are analyzed with respect to side-point height, extrapolation degree, magnet position, and coordinate constraint mode.
The proposed method provides a low-intrusion auxiliary measurement strategy for magnet opening and reassembly evaluation. It extends the available geometric information to side regions and supports a more comprehensive assessment of the reassembly state of accelerator magnet units.
