• D. Li, K. Imasaki
  ILT, Suita, Osaka
• G.S. Park, Y. Yang
  SNU, Seoul

A renewed interest of Smith-Purcell system has been raised since J. Urata et.al observed a possible exponential gain in their experiment using electron microscope beam. Several theories were presented to calculate the exponential gain. We analyzed this problem in the way of particle in cell simulation, which provides many details in understanding the physics of the radiation from a grating.

• D. Li
  ILT, Suita, Osaka

The conventional cavity for a free-electron laser (FEL) oscillator forms Gaussian optical beam, transversely spreading along the interaction region. The transverse divergence will induce reduction of the FEL gain by three aspects: degenerating filling factor, causing diffraction loss and limiting the effective interaction distance. Bessel optical beam has been experimentally demonstrated diffraction-free characteristic, providing a possibility of improvement of FEL gain. In this paper, we present a conceptual design of a Bessel beam cavity for the free-electron laser. This cavity generates nondiffracting optical beam in the wiggler, which can improve the filling factor, decrease the diffraction loss and elongate the effective interaction distance.