Author: Vermeulen, M.A.
Paper Title Page
Scanning Problems of FLARE, a THz-FEL Waveguide  
  • R.T. Jongma, D. Arslanov, M.A. Vermeulen, A.F.G. van der Meer
    Radboud University, Nijmegen, The Netherlands
  • M. Fujimoto
    ISIR, Osaka, Japan
  • V.O. Yatsyna
    University of Gothenburg, Gothenburg, Sweden
  • V. Zhaunerchyk
    Uppsala University, Uppsala, Sweden
  Funding: FLARE is part of the NCAS project funded through the “Big Facilities” programme of the Netherlands Organisation for Scientific Research (NWO).
The (0.2 – 3) THz free-electron laser FLARE is equipped with a waveguide extending over the full cavity length. Therefore, the tuning gaps observed in the long-wavelength range of FELIX, FELBE and CLIO, which were attributed to mode-conversion at the waveguide free-space transitions, are avoided. Unfortunately, an even more severe scanning problem is observed and continuous tuning of the photon energy is up to this moment impossible. The origin of this problem is not yet understood and experiments to gain insight into the problem are ongoing. We have investigated the (coherent) spontaneous emission as a function of wavelength, the gain build-up in the vicinity of tuning gaps, and the operation at a micro-pulse repetition frequency at which only a single photon bunch circulates in the cavity. The latter is explored to investigate if the low-frequency mode (the slow wave) that can also build up in a wave-guided cavity and travels at lower group velocity than the electron bunches, interferes with the efficient power build-up of the desired high-frequency mode in the trailing bunches. Status and results of the experiments will be discussed.
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