Development of a focusing wiggler magnet with parabolic pole faces

Abstract A focusing wiggler magnet which consists of permanent magnets with parabolic pole faces has been developed. A magnet with parabolic pole faces gives an additional sextupole contribution to the conventional wiggler field, and generates a focusing force in both directions on an electron beam. Furthermore, it can give the FEL resonance properties as well as a helical wiggler. The shape of the magnet pole faces has been optimized using the TOSCA code. The alloy NdFeB was chosen as the magnetic material for a peak field of more than 0.43 T with a gap of 23 mm on the wiggler axis. Magnetic field errors could be substantially reduced using thin iron shimming plates attached to the permanent magnets. The results of the magnetic field measurements are in good agreement with the values obtained by TOSCA. Numerical simulation of the electron trajectory using a measured magnetic field is performed and it verified that the wiggler with parabolic pole faces has enough focusing force in the x direction in addition to the y direction.