Magnetic Field Produced by a Single Current Line near or within a Ferromagnetic Cylinder or Tube

In this paper, we carry out an analytical computation of the vector potential produced in the whole space by a current line located near or within a ferromagnetic cylinder or tube. Whenever possible, we determine the image currents that can be used to derive directly the contribution from the ferromagnetic material. Most of these cases are relevant to the determination of the magnetic field produced by accelerator magnets, and we give the expressions of the corresponding multipole field coefficients.