A self-consistent numerical approach to track particles in FEL interaction with electromagnetic field modes

TL;DR

This paper introduces a new numerical method for simulating free-electron laser interactions by decomposing electromagnetic fields into modes, enabling accurate modeling of complex FEL dynamics including dispersion and space charge effects.

Contribution

It presents a self-consistent, mode-based simulation approach that extends existing tools, capable of handling long-wavelength waveguide FELs and low-charge systems without period averaging.

Findings

Successfully modeled a single pass FEL amplifier

Simulated high-efficiency TESSA266 scenario

Analyzed a THz waveguide FEL in zero-slippage regime

Abstract

In this paper we present a novel approach to FEL simulations based on the decomposition of the electromagnetic field in a finite number of radiation modes. The evolution of each mode amplitude is simply determined by energy conservation. The code is developed as an expansion of the General Particle Tracer framework and adds important capabilities to the suite of well-established numerical simulations already available to the FEL community. The approach is not based on the period average approximation and can handle long-wavelength waveguide FELs as it is possible to include the dispersion effects of the boundaries. Futhermore, it correctly simulates lower charge systems where both transverse and longitudinal space charge forces still play a significant role in the dynamics. For free-space FEL interactions, a source dependent expansion approximation can be used to limit the number of transverse modes required to model the field profile and speed up the calculation of the system evolution. Three examples are studied in detail including a single pass FEL amplifier, the high efficiency TESSA266 scenario and a THz waveguide FEL operating in the zero-slippage regime.