Abstract
We propose a new scheme to control the polarization state of undulator radiation, in which the helicity of circularly polarized radiation can be switched by translating the whole undulator along the horizontal direction. This is in contrast to the conventional method based on a phasing operation (longitudinal motion of magnetic arrays), which gives rise to a large variation of the three-dimensional magnetic force acting on the magnetic array. Because the mechanical design can be much simpler than conventional undulators equipped with a function for the phasing operation, the proposed scheme is well compatible with in-vacuum undulators. Numerical and experimental studies were carried out to reveal the performance and feasibility of the proposed scheme, showing its potential as an attractive option for the in-vacuum undulators.
Highlights
Polarization control is one of the key technologies in synchrotron radiation and x-ray free electron laser applications, and various schemes have been proposed and developed to date [1,2,3,4,5,6,7,8,9]
The polarization control of the APPLE undulator is based on a mechanical operation; the top and bottom magnetic arrays are horizontally split into two arrays that are mounted on two different girders, and a diagonal pair of girders is moved along the longitudinal direction to tune the polarization state of radiation, which is usually referred to as “phasing”
The most critical issue in designing the APPLE undulator is how to deal with the large magnetic force acting on the girders and magnetic arrays, especially during the phasing operation
Summary
Polarization control is one of the key technologies in synchrotron radiation and x-ray free electron laser applications, and various schemes have been proposed and developed to date [1,2,3,4,5,6,7,8,9]. In contrast to the magnetic-force variation during the gap operation in a conventional planar undulator, which is one dimensional (vertical) and monotonic (exponential), the force variation during the phasing operation is three dimensional and not monotonic. This imposes a stringent requirement on the mechanical specifications such as the stiffness of the girder and supporting frame, and the torque of the driving motor.
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