Time-dependent simulation of free-electron laser amplifiers and oscillators

Henry P Freund

doi:10.1103/physrevstab.8.110701

Abstract

Time-dependent free-electron laser simulations use a variety of techniques. Particle-in-cell codes have been used to simulate free-electron masers; however, this is not feasible at short wavelengths. Most simulations use a slowly varying envelope approximation in both in $z$ and $t$, where the particles and fields are advanced in $z$ using the same process as in steady-state simulations and then the time derivative describing slippage is applied. We describe the inclusion of this technique in the non--wiggler-averaged code MEDUSA, which is then applied to study temporal behavior in amplifiers and oscillators.

Highlights

Time-dependent free-electron laser (FEL) simulations use a variety of techniques
A second technique uses an slowly varying envelope approximation (SVEA) in both in z and t [4], and the particles and fields are advanced in z using the same process as in steady-state simulations and the time derivative describing slippage is applied
We describe the inclusion of this technique in the non–wiggler-averaged code MEDUSA [8], which is applied to amplifiers and oscillators

Summary

INTRODUCTION

Time-dependent free-electron laser (FEL) simulations use a variety of techniques. Particle-in-cell codes have been used to simulate free-electron masers [1,2]; this is not feasible at short wavelengths. A second technique uses an SVEA in both in z and t [4], and the particles and fields are advanced in z using the same process as in steady-state simulations and the time derivative describing slippage is applied. This is used in wiggleraveraged codes such as PERSEO [5] in 1D and GINGER [6]. The time dependence (i.e., slippage) is imposed as an additional operation using the forward time derivative as an additional source term that couples the ith radiation slice to the i 1th slice It may be imposed on every spatial step, only after some spatial interval. This ensures that the wave-particle interaction is treated self-consistently in view of the fact that MEDUSA does not employ a wiggleraveraged orbit approximation

AMPLIFIER MODELING

OSCILLATOR MODELING

Findings

SUMMARY