Design and Test of Magnetic Shields for Turbomolecular Pumps

The use of turbomolecular pumps in plasma experiments with magnetic field confinement set troublesome problems because of the presence of the static magnetic fields. The utmost consequence of this interaction could be very dangerous: the rupture of the turbomolecular pump. In order to protect these pumps against the applied magnetic field, different magnetic shield layouts have been tested: simple cylindrical tube, tube with partial enclosures, and tube with enclosure plus a reinforced collar. All these shields have been made by cheap and easy to find material as iron Fe-37. This work presents the preliminary study of the expected shielding performance carried out by finite elements calculation and in-situ measure to validate the shielding structure analysis. The principal aim of the present work is to indicate a possible approach to the problem and how to obtain a practical solution. The general guidelines described in this work can be applied also for vacuum devices exposed to the stray magnetic field of large tokamaks as ITER.