Comparison of a modal-decomposition and a grid based field solver for free-electron laser simulations

TL;DR

This paper compares a modal-decomposition field solver with a grid-based solver for free-electron laser simulations, demonstrating comparable accuracy in energy output and radiation profile.

Contribution

It introduces a new modal decomposition approach using fixed-width Gaussian modes and provides estimates for the number of modes needed for accurate representation.

Findings

Good agreement in total energy output

Matching transverse radiation profiles

Effective modal decomposition framework

Abstract

We present a comparison of the modal-decomposition based field solver MINERVA to the grid-based solver GENESIS. The modal decomposition used employs a set of fixed-width, zero-curvature Gaussian modes, as opposed to the more-commonly used basis of vacuum-diffraction eigenmodes. Besides providing the dynamical equations for the field modal amplitudes, we give first-principle estimates of the number of modes required to achieve completeness in terms of field and source modal representation as a function of the electron-current and mode size. As a practical application of this new framework, we present steady-state numerical results for several configurations. The numerical results show a good agreement between the modal expansion and the grid-based solver, not only in terms of the total energy produced, but also in terms of the transverse radiation profile.