Author: Hara, T.
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TUA04 Suppression of the CSR Effects at a Dogleg Beam Transport Using DBA Lattice 216
  • T. Hara, T. Inagaki, C. Kondo, H. Maesaka, Y. Otake, H. Tanaka, K. Togawa
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • K. Fukami
    JASRI/SPring-8, Hyogo, Japan
  • T. Hasegawa, O. Morimoto, S. Nakazawa, M. Yoshioka
    SES, Hyogo-pref., Japan
  Multi-beamline, multi-user operation is an important issue of linac-based XFELs to improve usability and efficiency of facilities. At SACLA, the multi-beamline operation had been tested since 2015 using two beamlines (BL2 and BL3). But the CSR effects at a 3-degree dogleg beam transport of BL2 caused a projected emittance growth and instability of the beam orbit due to a high peak current of 10 kA and a short bunch duration of SACLA. Consequently, stable lasing was obtained only for elongated electron bunches with low peak currents below 3 kA. To mitigate the CSR effects, the beam optics of the dogleg was rearranged. The new beam optics are based on two DBA (double bend achromatic) structures and the transverse effects of CSR are cancelled between four bending magnets. To avoid the bunch length change, the electron beam passes an off-center orbit at the quadrupole magnets of DBA. Under the new beam optics, stable lasing has been successfully obtained with 10 kA electron bunches, and the parallel operation of the two beamlines will be started in September 2017 for user experiments.  
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Radiation-Induced Magnetization Reversal Causing a Large Flux Loss in Undulator Permanent Magnets  
  • R. Kinjo, Y. Asano, T. Hara, T. Hasegawa, Y. Kida, T. Tanaka
    RIKEN SPring-8 Center, Hyogo, Japan
  • T. Bizen, T. Itoga, A. Kagamihata, T. Seike, T. Watanabe
    JASRI/SPring-8, Hyogo, Japan
  A large degradation of undulator field up to 35 percent was observed at the entrance of the in-vacuum undulators in SACLA; although this may be because of the radiation-induced demagnetization, it is much larger than what is expected from the former irradiation experiments. From the measurement of the surface field profile of individual permanent magnets (PMs) and the numerical calculations, we found that not the demagnetization but the magnetization reversal in small areas of the magnets is the reason of the large degradation of the undulator field. Numerical and experimental studies suggest that the magnetization reversal is a highly nonlinear process with respect to the reverse field in the PM, which is applied to the PM in the hybrid array. The experimental study also shows that a 10-cm stainless steel block placed just in front of the PMs significantly impedes the progress of the magnetization reversal, which suggests a simple and effective method to improve the lifetime of in-vacuum undulators.*
* T. Bizen et al., Scientific Reports 6, 37937 (2016).
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