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DIPOLE FRINGE FIELD EFFECTS IN THE ThomX RING∗

ThomX is a compact machine based on the Compton back-scattering, which is being built by LAL in France. The ThomX ring has a short circumference of 16.8 m and a low design energy of 50 MeV, and the dipole bending radius of 0.352 m. With such a short bending radius, the nonlinear effects due to the second order dipole fringe field in the ring become non-trivial. In this paper, we discuss the appropriate models of the dipole fringe field in the particle tracking, and then compare the vertical chromaticity of the ThomX ring calculated using four different codes: Tracy3, BETA, MADX and ELEGANT.