Large-Scale Simulation of Magnetization Process of HTS Undulator for X-Ray FEL Based on ${T}$ -Method

In a development of the next-generation light source such as X-ray free-electron laser (FEL), it is necessary to achieve very intense undulator magnetic field with compact magnets. For this purpose, the pure-type high-Tc superconductor (HTS) undulator was proposed. In general, it is very difficult to adjust the magnetic field distribution after the HTSs are magnetized all together in a cryostat; therefore, a very careful design of the undulator magnets using a numerical analysis is required. The authors have been working on a development of the numerical simulation code of the magnetization process of the HTS undulator by using the current vector potential method (T-method). In this paper, the previously developed numerical code is modified to be used for much larger scale simulations by using a method of a multipole expansion for calculations of magnetic field aiming a practical FEL undulator design.