Magnetostatic shielding design for electronic apparatus in fusion experiments

In controlled nuclear fusion research with magnetic confinement, experimental devices must produce high electromagnetic fields that can reach some tesla in the plasma zone. Therefore, a high stray magnetic field, slowly varying as a function of time, is present around the machines. For this reason, the numerous electronic apparatus and plasma diagnostics need an effective magnetostatic shield for their correct working condition. Many examples of magnetic shields for different apparatus have been analysed: video, various electronic instruments and plasma diagnostics. After a brief description of electromagnetic problems arising in the fusion plants, the paper provides two examples of applications: the shield for a standard rack instrument and the shield for a small photo-multiplier head. The shielding effect has been evaluated considering non-linear materials for the shields. Moreover the magnetic field distortion in the space, due to the presence of the ferromagnetic material, has been evaluated in order to estimate the effect of the shields on the plasma magnetic confinement.