Analytical field calculation of helical magnets with an axially symmetric iron yoke

The magnetic field due to the current flowing in a helical conductor placed inside a cylindrical hole in iron is investigated. In order to calculate the contribution of an axially symmetric iron yoke on the inner field of helical magnets, a three-dimensional potential problem is solved. The obtained analytical expressions are applied for the helical dipole magnet for the Relativistic Heavy Ion Collider (RHIC), with good agreement.