Quadrupoles design and measurement for a compact THz FEL

The THz source based on free-electron laser (FEL) has many remarkable performance, such as tunability, high power, high efficiency and flexible picosecond-pulse time structure of coherent radiation. A low-cost, compact FEL facility can also be built on THz region to provide monochromatic, tunable, high power and high quality radiation. Due to the space limitation, the quadrupole magnets on the FEL should reduce their size as much as possible while meeting the performance requirement. The size of the magnetic yokes aperture and length are 64 mm100 mm for two quadrupoles, and 45 mm100 mm for the other three. The quadrupole magnets magnetic field gradient can reach 0.6-1.9 Tm-1. The Poisson codes and Opera-3D codes have been used to calculate the magnetic field. This paper presents the design, analysis and measurement procedure of the magnets.