Self-compensation of the residual field gradient in double-shell open-ended cylindrical axial magnetic shields

An important and not-obvious demonstration made in this work is that replac ing a closed double-shell axial cylindrical shield with a similar but open- ended shield can lead to an increasing in not only the axial shielding fact or, but in the residual magnetic field uniformity as well. It is shown that a self-compensation of the residual field gradient and a significant impro vement of the total residual field uniformity are potentially possible by c ombining two open-ended cylindrical shells having different length-to-diame ter ratios and providing opposite signs and appropriate magnitudes of the r esidual field gradients. A numerical example confirms the applicability of the method. It is shown that an similar to 6-fold reduction of the residual field gradient along the axial direction and an similar to 2-fold reductio n of that along the radial direction over a relatively wide area inside a d ouble-shell cylindrical axial shield are possible if its both ends are open .