An Electromagnetic THz Wiggler at SXFEL

SXFEL intends to use a frequency beating laser-modulated electron beam scheme to simultaneously generate X-rays and high pulse energy tunable frequency coherent terahertz (THz) radiation, which is generated by an electromagnetic wiggler. The wiggler consists of 16 periods, each with a length of 280 mm, and it has an effective magnetic peak strength of up to 1.75 T. By manipulating the energy of the electron beam and the magnetic field of the wiggler, the radiation frequency can be adjusted within a range of 5 to tens of THz. In addition, the wiggler has the capability to modify the coil combination, thereby altering the period to 560 mm. This adjustment leads to a significant increase in the K value. This, in turn, will further reduce the radiation frequency. The results of the magnetic measurement indicate that the wiggler's magnetic field quality meets the requirements of the physical experiment. The wiggler was installed on the SXFEL SASE undulator line in September 2023. This paper presents an overview of the simulation calculations, mechanical design, magnetic measurement scheme, and the final magnetic measurement results of the wiggler.