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Paper   IPM / Physic / 6610
School of Physics
  Title:   Free Electron Laser in A Partially Filled Waveguide
1.  B. Maraghechi
2.  S. Mirzanejhad
  Status:   Published
  Journal: Phys. Plasmas
  No.:  55
  Vol.:  4
  Year:  1997
  Pages:   2727-2735
  Supported by:  IPM
A linear theory for a free electron laser with a one-dimensional helical wiggler an axial magnetic field in the collective regime is presented. The configuration consists of a cylindrical waveguide with arbitrary ratio of electron beam radius a to waveguide inner radius R. Parametric decay of the wiggler pump wave, in the beam frame, into a space-charge wave and an electric-magnetic (EH) waveguide mode is analyzed in three dimensions. A nonlinear wave equation for the three-wave interaction is derived and employed to obtain a formula for the spatial growth rate of the excited eigenmodes. It was found that the relativistic treatment of the electron oscillations in the wiggler field destroys the cyclotron resonance which appears in the nonrelativistic case. Nevertheless, appreciable amplification was found. Numerical analysis is conducted to study the growth rate, radiation wavelength, and required relativistic factor as functions of axial magnetic field B0 and radius ratio a/R. The suitable value for a/R was found to be around 0.65 for our choice of parameters.

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