Design and Research of a Magnetic Shield for Turbo-Molecular Pump under Strong Stray Magnetic Field

Currently,a 230 MeV superconducting cyclotron is under development at China Institute of Atomic Energy. The superconducting main magnet of this cyclotron is optimized to be ultra-compact to be installed in the hospital,thus inevitably has larger magnetic leakage at the turbo pump installation ports,where the magnetic flux density reaches 1000 Gauss,which is 20 times larger than the turbo pump's safe operation limit(within 50 Gs).This may further cause the malfunction of the turbo pumps. To solve this problem,a sophisticated magnetic shielding is designed using a 3 D FEM model. Then a careful measurement of the magnetic flux density after shielding is performed,and the results show that the residual field within the shielding is limited below 50 Gauss. Further monitoring of the turbo pump operation parameters,like the driving current,the temperature of the turbo bearing,etc.,show a good agreement with the non-magnetic working condition.