Study on the transverse gradient magnetic field properties and related issues of the elliptical polarized adjustable phase undulator

Hao-Wen Luo^1*, Ting-Yi Chung², Ching-Shiang Hwang², Chih-Hao Lee³

¹The Graduate Program in Science and Technology of Synchrotron Light source Department of Engineering and System Science, National Tsing Hua University, Hsinchu City, Taiwan
²Magnet Group, National Synchrotron Radiation Research Center, Hsinchu City, Taiwan
³Department of Engineering and System Science, National Tsing Hua University, Hsinchu City, Taiwan

* Presenter:Hao-Wen Luo, email:luo.hw@nsrrc.org.tw

An adjustable phase undulator (APU) is an undulator that tuning the resonance photon energy by adjusting the relative longitudinal position of the magnet arrays without changing the gap. For the elliptical polarized undulators that can produce linear polarized light in arbitrary angle, the adjustable longitudinal position is an inherent function. So the mechanical design and cost of the APU are simpler and cheaper than that of the adjustable gap undulator (AGU) respectively. But there exists unavoidable transverse gradient of magnetic field as well as the longitudinal magnetic field. These unwanted magnetic field component can cause many unwilling effects such as bending of trajectory, betatron tune shift and degrading of the performance of the synchrotron radiation. This presentation covers the topics including the origin of transverse gradient field, the coupling of gradient field and the trajectory, the properties of synchrotron radiation of an APU and some related issues such as the shifting of resonance photon in circular polarized mode.

Keywords: adjustable phase undulator, transverse gradient of magnetic field, dynamic field integral, synchrotron radiation