Unique features in magnet designs for R&D Energy Recovery Linac at BNL

In this paper we describe the unique features and analysis techniques used on the magnets for a R&D Energy Recovery Linac (ERL) [1] under construction at the Collider Accelerator Department at BNL. The R&D ERL serves as a test-bed for future BNL ERLs, such as an electron-cooler-ERL at RHIC [2] and a future 20 GeV ERL electron-hadron at eRHIC [3]. Here we present select designs of various dipole and quadrupole magnets which are used in Z-bend merging systems [4] and the returning loop, 3-D simulations of the fields in aforementioned magnets, particle tracking analysis, and the magnet's influence on beam parameters. We discuss an unconventional method of setting requirements on the quality of magnetic field and transferring them into measurable parameters as well as into manufacturing tolerances. We compare selected simulation with results of magnetic measurements.