High-gain, free-electron laser amplifiers: Design considerations and simulation

The design and performance of variable-wiggler, free-electron laser (FEL) amplifiers was studied by using a one-dimensional computer model which incorporated separate sections for design and simulation. Resonant-particle equations were used in the design phase. The variation of the wiggler parameters was not predetermined (linear, exponential, etc.) but was carefully tailored to match the electron energy throughout the FEL amplifier. The simulation section of the model self-consistently tracked the phase-space trajectories of 500 particles for the length of the amplifier. In this way the designs were tested not only for overall gain and efficiency but also for resistance to irregularities in laser input power, electron-beam power, electron-beam-energy spread, and wiggler construction. High-current-density electron beams (electron-beam power g laser-beam power) were found to be essential for stable and efficient amplifiers. Some designs demonstrated better performance under conditions of nonresonant input particles.