When relativistic electron which moving near the speed of light do curve movement and change direction under the magnetic field, its energy loss will emit along the tangential direction in the form of electromagnetic radiation. This radiation was firstly discovered by synchrotron of GM on 1947 and named synchrotron radiation. Scientists found synchrotron light has many excellent performances which conventional light source cannot be compared, includes the wide spectrum, high brightness and polarization. These performances bring the broad prospect for scientific and application research. Almost all high energy electron accelerators have constructed synchrotron radiation station and experimental apparatus. As a core component, undulator magnets were also participated in the development process of synchrotron radiation.
Undulator is one of the key equipment of the third-generation synchrotron light source and free electron laser device. Permanent magnet vacuum undulator occupies a fairly large proportion in numerous permanent magnet undulators. Undulator magnets are regarded as the heart of vacuum undulator. Its comprehensive magnetic characteristics have significant influence on the peak value, distribution and stability of the magnetic field. Both Samarium Cobalt magnets and Neodymium magnets are utilized as the undulator magnets. In order to adapt strong electromagnetic radiation environment, Samarium Cobalt magnet was the top choice in the early undulator, then high-performance Neodymium magnet dramatically enhanced the peak value and quality of vacuum undulator. Cryogenic permanent magnet undulator has become the research focus of international synchrotron radiation area, thus Praseodymium magnet substitute Neodymium magnet which has a spin reorientation transition under low temperature.