A simple code for the growth rates of free-electron lasers

Abstract EN

A model for a free-electron laser (FEL) with helical and axial magnetic fields has been investigated theoretically.

The dispersion relations of transverse and longitudinal modes for the one-dimensional linear case &e derived exactly using the fluid model for the electron beam.

The modes with positive and negative heJicities are selected clearly.

An analytically solvable expression for the growth rates ofthe modes, exactly in resonance with the beam, is obtained.

We present a simple computer code G REEL, based on analytical formulae and obtained within the context ofthe theory of FEL, that requires negligible CPU time and runs on small computers.

Fixing three of the five parameters ofthe FELs (the wiggler field, the axial magnetic field, the wiggler wavevcctor, the electron relativistic factor and the plasma frequency), GRFEL sweeps the spectrum of the remaining parameters, giving three dimensional curves ofthe growth rate.

This enables us to select the best operating zones and exclude the forbidden regions for the FEL being investigated.

An output sample of ORFEL describing the dependence ofthe growth rate on the parameters ofthe system is given.