Author: Ries, M.
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First Experimental Demonstration of the Mechanism of Steady-state Microbunching  
  • C.-X. Tang, X.J. Deng, W.-H. Huang, L.X. Yan
    TUB, Beijing, People’s Republic of China
  • A. Chao
    SLAC, Menlo Park, California, USA
  • J. Feikes, J. Li, A.N. Matveenko, Y. Petenev, M. Ries
    HZB, Berlin, Germany
  • A. Hoehl, R. Klein
    PTB, Berlin, Germany
  The concept of steady-state microbunching (SSMB) in electron storage rings implies a longitudinal bunch structure given by an optical or ultraviolet wavelength rather than a conventional radio frequency wavelength, typically six or more orders of magnitude smaller. The strong coherent radiation from the steady-state microbunches will support a facility with high-power, high-repetition-rate or continuous-wave, narrow-band, and short-wavelength radiation, which can provide unprecedented new possibilities for accelerator photon science and industry applications. It has been proved that the electron beam energy modulation induced by an externally applied 1064 nm laser in an undulator can yield microbunching and coherent radiation one turn later at exactly the same place where the modulation was applied. The results confirm that the phase of an electron beam relative to a laser in a storage ring can be locked turn-by-turn in a sub-laser-wavelength precision, therefore making SSMB possible. This validation represents the first key advance in the development of an SSMB high-power light source.
Phys. Rev. Lett. 105, 154801 (2010)
The SSMB collaboration: [FLS2018-THP2WB02]
X. Deng, et al. First Experimental Demonstration of the Mechanism of Steady-state Microbunching, under review.
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Alternating the Helicity of X-Ray Photons from an Undulator at Unprecedented Speed  
  • K. Holldack, F. Armborst, J. Bahrdt, W. Frentrup, P. Goslawski, N. Pontius, M. Ries, A. Schälicke, M. Scheer, Ch. Schüssler-Langeheine
    HZB, Berlin, Germany
  X-ray circular dichroism (XMCD), one of the main tools of modern X-ray physics for studying magnetism, benefits enormously from the capability of a fast alterable helicity of circularly polarized X-ray photons. Here we present a novel method, which allows boosting the alternating frequency between right- and left-handed photons to the MHz regime, more than three orders of magnitude faster than present state-of-the-art technologies. The method is based on a twin elliptical undulator installed in a low emittance electron storage ring being operated in a novel mode. Here, the electron optics is tuned close to a resonance where the electron bunches are spatially separated in so-called transverse resonance island buckets (TRIBs). Propagating through the magnetic structures of the twin undulator, electrons from different islands emit photons of the same wavelength but of opposite helicity. Radiation from these two helicity components can be alternated as fast as 2 ns, given by the radio frequency of the accelerator cavity. In the present proof-of-principle experiment at BESSY II we demonstrate a XMCD measurement at the L2,3 absorption edges of a Ni sample with an 800 ns helicity flip.  
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