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Li, R. K.

Paper Title Page
TUPMS088 Efficiency Enhancement Experiment with a Tapered Undulator in a Single-pass Seeded FEL at the NSLS SDL 1371
 
  • T. Watanabe, D. A. Harder, R. K. Li, J. B. Murphy, G. Rakowsky, Y. Shen, X. J. Wang
    BNL, Upton, Long Island, New York
  
  Funding: This work is supported by the Office of Naval Research under contract No. N0002405MP70325 and U. S. Department of Energy under contract No. DE-AC02-98CH1-886.

We report the experimental characterization of the FEL efficiency enhancement using a tapered undulator in a single-pass seeded FEL amplifier at the NSLS SDL. The last 3 m of the 10 m NISUS undulator was linearly tapered so that the magnetic field strength at the end of the undulator was reduced by 5 %. The FEL energy gain along the undulator was measured for both the tapered and un-tapered undulator. The FEL energy with the taper was measured to be about 3.2 times higher than that without the taper. We also experimentally characterized the spectrum and the transverse distribution of the FEL light for both the tapered and un-tapered undulator. The experimental results are compared with the numerical simulation code, GENESIS 1.3.

 
TUPMN054 Design of a Source to Supply Ultra-fast Electron and X-Ray Pulses 1046
 
  • W.-H. Huang, H. Chen, Y.-C. Du, Hua, J. F. Hua, R. K. Li, Y. Lin, J. Shi, C.-X. Tang, D. Xiang, L. X. Yan, P.-CH. Yu
    TUB, Beijing
  
  In this paper we report the preliminary design and considerations on a multi-discipline ultra-fast source, which is capable of providing the user community with femtosecond electron bunch and light pulses with the wavelength ranging from IR to X-ray. The facility is based on photocathode RF gun driven by a Ti:Sapphire laser system. The low emittance subpicosecond electron bunch at the gun exit can be used in femtosecond electron diffraction setup to visualize the ultrafast structural dynamics. After acceleration and compression, the electron beam with the energy of 50 MeV is further used to provide high peak brightness X-ray by inverse Compton scattering with TW laser. We also consider the possibility and reliability of storing the electron beam in a compact storage ring and the laser pulse in a super-cavity. Operating in this scheme may increase the average flux of the X-ray photons by orders of magnitude.  
TUPMN055 First Principle Measurements of Thermal Emittance for Copper and Magnesium 1049
 
  • D. Xiang, Y.-C. Du, W.-H. Huang, R. K. Li, Y. Lin, C.-X. Tang, L. X. Yan
    TUB, Beijing
  • J. H. Park, S. J. Park
    PAL, Pohang, Kyungbuk
  
  Funding: This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002.

There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation and laser shaping, we are approaching the limit-the uncorrelated thermal emittance. In this paper, we report the measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons are measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness* and laser incidence angle as well as its polarization state** affect the quantum efficiency and thermal emittance.

*X. Z. He, High energy physics and nuclear physics,28(2004)1007.**Dao Xiang,et al, NIM A,562(2006)48.