Closed orbit correction of the HIMM synchrotron

In this paper the closed orbit correction of the Heavy Ion Medical Machine (HIMM) synchrotron is described. Results of simulations and measurements are presented. Consistently with simulations, it is possible to correct the maximum closed orbit distortion of the HIMM synchrotron down to 2.4mm in the horizontal direction and 0.7mm in the vertical one. The errors of dipole magnets, especially the longitudinal alignment errors (Δs), have large impact on the horizontal correction results. A Singular Value Decomposition (SVD) algorithm is adopted for computing the correction. The residual orbits and the effects of reducing the number of singular values are analytically expressed and simulated. In addition, the influences of BPM reading errors as well as corrector setting errors are analyzed. For further optimization, the method to estimate the dipole errors is studied. In the commissioning, the maximum closed orbits at BPMs can also be well corrected to within 1mm through SVD algorithm.