WEC —  Undulators, Photon Diagnostics, Beamline   (23-Aug-17   13:30—15:00)
Chair: S.V. Benson, JLab, Newport News, Virginia, USA
Paper Title Page
Photon Beam Transport and Diagnostics Systems at an EUV FEL Facility: General Considerations, and Specific Challenges, Solutions and Developments at the FERMI Seeded FEL  
  • M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  After the start of FLASH user operations in 2005, the possibility of performing user experiments at an EUV free electron laser source became reality. This kind of opportunity was extended in 2012 when the Italian FERMI seeded-FEL user facility started its user program. As a consequence, for such light sources new photon transport and diagnostic solutions were designed, developed, and implemented. A brief general overview about these issues will be introduced, together with a more detailed presentation of challenges faced and solutions found at the FERMI FEL. In particular, different instruments were developed in order to meet machine and endstation users' requirements concerning online non-invasive spectral content determination, pulse length and intensity characterization/control, active modification of the focusing properties, etc. Some examples and results will be presented, possibly comparing them to what was done elsewhere. Possible future implementations in photon-beam manipulation and characterisation will also be discussed.  
slides icon Slides WEC01 [10.857 MB]  
WEC02 Optimization of Superconducting Undulators for Low Repetition Rate FELs 1
  • J.A. Clarke, K.B. Marinov, B.J.A. Shepherd, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • V. Bayliss, T.W. Bradshaw, A.J. Brummitt, S.J. Canfer, M.J.D. Courthold, B. Green, D.S. Wilsher, J. Boehm, t. Hayler, p. Jeffery, c. Lockett
    STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
  • S. Milward, E.C.M. Rial
    DLS, Oxfordshire, United Kingdom
  Superconducting undulators (SCUs) optimized for storage rings and MHz-level FELs require an intermediate beam screen to intercept the power deposited by the electron beam, due to resistive wall wakefields, to prevent magnet quenching. This beam screen increases the magnet gap by around 2 mm which is a significant increase when compared to the typical electron beam aperture of around 5 mm. However, lower repetition rate FELs only deposit of the order of tens of mW/m and so the beam screen is no longer needed resulting in a significant reduction in undulator magnet gap. We have investigated the impact of this reduced magnet gap and found that the magnetic field level increases greatly. For example, an SCU with a 15 mm period and 5 mm aperture optimized for a low repetition rate FEL instead of a storage ring will generate a field of 2.1 T compared to 1.4 T. Such a major increase in undulator performance could have a significant impact on the optimization of FELs. This paper describes how an SCU optimized for application in a FEL will be able to generate magnetic field levels far beyond those currently foreseen for any other magnet technology.  
Wavefront Preserving Optics for the LCLS Photon Transport System  
  • D. Cocco, C.L. Hardin, D.S. Morton, P. Stefan
    SLAC, Menlo Park, California, USA
  • J. Nicolás
    ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
  The Linac Coherent Light Source (LCLS) is upgrading to a High Repetition Rate mode and to a higher quality of the wavefront. This poses extreme challenges to the optical components. A new approach to beamline design is needed, starting from a new way to assess the effect of slope and shape errors, to taking into account any potential source of distortion. Among the technical novelties the LCLS optics team is introducing, the most important are: a novel cooling scheme to maintain the mirror shape within 0.5 nm rms under heat load, the study of the effect of the cooling interface to the mirror surface, and new diagnostic systems. Ultra-flat mirrors with novel holder mechanisms have been recently installed. First results, showing the improvement of the beam quality, are expected in mid-June 2017. A controlled cleaning process to remove, in situ, carbonaceous contamination from carbon-based coatings will also be presented. It has been successfully implemented in the SXR mirrors. All the above tests and studies will be presented, as well as the effect seen on a six-year old mirror exposed to FEL for its entire lifetime.  
Progress of PAL-XFEL Undulator Program  
  • D.E. Kim, H.-S. Kang, K.-H. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
  • I.S. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  Pohang Accelerator Laboratory (PAL) recently commissioned and started early user service of 0.1 nm SASE-based FEL based on the 10 GeV S-band linear accelerator named PAL-XFEL. One of the key components of the PAL-XFEL is the undulator system which consists of 20 units of Hard X-ray undulators, and 7 units Soft X-ray FELs. The basic design concept is based on the EU-XFEL undulator, but it also requires modification reflecting PAL-XFEL requirements. In this report, PAL efforts to modify, re-design, manufacture, take measurements, tune, install, and commission the undulator system will be summarized.  
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, Sayo-cho, Sayo-gun, 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).