Magnetic measurement of the pi bend dipole magnets for the IR-FEL at the Thomas Jefferson National Accelerator Facility

A family of large bending dipoles has been successfully magnetically measured, installed and is operational in the high power IR-FEL. These magnets are unique in that they bend the beam 180 degrees on a 1 meter radius. The optics requirements for the magnets include low fields, large horizontal apertures, tight field homogeneity, high repeatability of core field and integrated field, and control of the horizontal and vertical focusing terms that are designed into the magnets. Quantifying the optics requirements proved to be a difficult task, due to the magnet´s mechanical construction and sharp bending radius. The process involved in measuring and achieving the results are discussed