Magnetic flux loss of the permanent magnets used for the wigglers of FELs by the irradiation with high-energy electrons or X-rays

Study was made on the irradiation effects of the permanent magnets used for the wigglers of FELs with high-energy electrons and X-rays. Four kinds of Nd–Fe–B and one kind of Sm–Co samples were irradiated with 17 MeV electron beams or 60Co γ-rays. The magnetic flux loss of one kind of Nd–Fe–B samples irradiated with electrons at doses below 2.1×10−3 C/cm2 increased with the irradiation dose. For the electron irradiation at doses of about 1.4×10−3 C/cm2, magnetic flux loss was apparent for two kinds of Nd–Fe–B samples. No flux loss was observed for γ-rays at absorbed doses higher than that of the electrons. The influence of the irradiation of electrons on the magnets of a wiggler in FEL experiments is discussed.