Effects of Eddy Current and Permeability of Vacuum Chamber on Magnetic Field in Booster Synchrotron of Siam Photon Source II

Abstract Siam Photon Source II (SPS-II), the second synchrotron light source in Thailand, has been designed and it is planned to open for users in 2034. Vacuum chamber for the SPS-II booster synchrotron will be made of thin-wall 316LN stainless steel tube to minimize the Eddy current while maintaining a good vacuum and mechanical performance. Magnetic permeability of the vacuum chamber needs to be kept small to reduce any effects on the magnetic field. In this work, Opera-3D is used for modelling of magnets and vacuum chamber for the booster synchrotron and for calculation of magnetic field. Effects of Eddy current due to ramping magnetic field, magnetic permeability and thickness of the vacuum chamber are studied. It was found that the maximum allowable relative permeability of the vacuum chamber is 1.02 with the chamber thickness of 0.75 mm, in order to keep the higher-order multipole field components below 1x10-4 in the combined dipole magnet. Eddy current, together with the magnetic property of the vacuum chamber, alters the sextupole component in the combined dipole magnet up to 10%. This will be compensated by the individual sextupole magnets in the booster synchrotron.