Optimized design considerations for hybrid undulator
The hybrid undulator, is optimized in beam direction based on transverse optimization developed in ESRF. The thickness of the magnet and the pole is optimized at the ratio of 16∶9 for the maximized peak field. The analytical equations for designing the hybrid undulator are listed and discussed. One prototype hybrid undulator with 25mm period length is being constructed with NdFeB magnets and vanadium permendur poles by the optimized results. The magnet gap of the hybrid undulator can be tunable in 10～300mm. At 10mm magnetic gap, the undulator peak field can reach 0.648T with only the main magnet. It can be enhanced to 0.722T and 0.773T by further adding the side magnet and top magnet. The field resolution is better than 10~(-4)T with 1μm gap tuning system driven by servomotor. All optimization are based on 3-dimensional finite element electromagnetic computation, the Opera3d. The typical technical parameters of the hybrid undulator are listed. The computed induction field in the beam axis and in the middle plane of the hybrid undulator is respectively shown, which illustrates that the optimized configuration has more than 10mm good field region. The field distribution in the pole surface shows that it already reaches saturation with the present NdFeB magnets and vanadium permendur pole technology.