Alignment of beam position monitors in cryomodule of CADS injector II

Significant temperature difference (300–77 K or even 4 K) can cause large deformations and displacements of the beam position monitors (BPMs), which affect BPMs measurement resolution or even cause their malfunction in cryogenic situations. In this paper, to check the offset from the mechanical to electrical center in low temperature (77 K), Fourier’s law and finite element method are used to simulate cryo-deformation. Laser tracker and micro-alignment telescope are employed in combined BPM calibration, installation and monitoring. The calibration error is <0.02 mm, and the installation and monitoring precision are 0.06 mm and 0.01 mm, respectively. The monitored cryo-deformation agrees well with the simulation results. These indicate that the combined alignment can improve performance of the BPM system. All these guaranteed the success of running the 9.55 MeV@2.14 mA cw protons.