Stray fields evolution near the gaps in a toroidal device

The magnetic field distribution near the shell gaps has been theoretically investigated in the case of a perfectly conducting wall; this ideal schematization can be well applied when the observation time is much less than the diffusion time. If the previous condition is not fulfilled, field diffusion across the shields must be taken into account. The space distributions of the measured field perturbations are presented and compared with those obtained by numerical integration of the Laplace's law; the dependence of the flux amplitude on the gap width is also shown. Finally the measured decay times of the magnetic fields are presented and compared with the theoretical diffusion time