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Paper   IPM / P / 7124
School of Physics
  Title:   Free Electron Laser in A Partially Field Waveguide with A Longitudinal Electrostatic Wiggler
  Author(s):  B. Maraghechi
  Status:   In Proceedings
  Proceeding: Proc. 1996 Int. Conf. On Plasma Physics, Nagoya, 1996, 1806-1809
  No.:  0
  Year:  1996
  Supported by:  IPM
An analysis of the parametric instability which forms the basis for operation of a free electron laser with a longitudinal electrostatic wiggler is presented. A theory is developed that allows for an arbitrary axial magnetic field and arbitrary ratio of the electron beam radius a to the waveguide inner radius R without imposing the electrostatic approximation on the space-charge wave. Dispersion characteristic of the eigenmodes of a magnetized electron beam inside a waveguide specially EH01 electromagneric and SC01 space-charge mode have been studied. A formula for the spatial growth rate of parametrically excited eigenmodes is derived. variations of the growth rate, efficiency, radiation wavelength, and required pump wavelength as functions of the ratio a/R are studied numerically. It is shown that excitation of the upper branch or lower branch of an EH01 waveguide mode can be achieved with suitable chosen values for the system parameters, and a fully electromagnetic analysis can produce modest changes on the operative quantities, as compared to the imposition of electrostatic approximation on the space-charge wave.

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