A new lambertson magnet for the FNAL 400 MeV LINAC

A new Lambertson magnet has been constructed for use at the downstream end of the Fermilab 400 MeV Linac. To reduce costs, the core is composed of laminations left over from the Main Injector dipoles with a round hole through one pole face. In contrast with more conventional Lambertson designs, the magnet is excited by two coils located above and below the field region. The integrated transverse fringe field at the end of the field-free region is minimized using a pole piece extension with 75% packing factor followed by a thick flux return plate. The relatively low packing factor prevents saturation of the extension by the return flux while preserving the odd longitudinal symmetry of the transverse flux distribution. Measurements show better than an order of magnitude reduction of the integrated transverse field, in good agreement with simulations.