Macro-particle FEL model with self-consistent spontaneous radiation

TL;DR

This paper introduces a self-consistent macro-particle model for simulating free-electron lasers (FELs) that accurately captures spontaneous radiation effects without requiring a seed, enabling detailed analysis of FEL optical fields.

Contribution

The paper presents a novel macro-particle model that accurately simulates spontaneous and induced radiation in 3-D FELs, overcoming limitations of previous codes.

Findings

Accurate simulation of multi-mode, multi-harmonic FELs.

Effective treatment of spontaneous radiation without a seed.

Complete temporal and spatial FEL field structure obtained.

Abstract

Spontaneous radiation plays an important role in SASE FELs and storage ring FELs operating in giant pulse mode. It defines the correlation function of the FEL radiation as well as its many spectral features. Simulations of these systems using randomly distributed macro-particles with charge much higher that of a single electron create the problem of anomalously strong spontaneous radiation, limiting the capabilities of many FEL codes. In this paper we present a self-consistent macro-particle model which provided statistically exact simulation of multi-mode, multi-harmonic and multi-frequency short-wavelength 3-D FELs including the high power and saturation effects. The use of macro-particle clones allows both spontaneous and induced radiation to be treated in the same fashion. Simulations using this model do not require a seed and provide complete temporal and spatial structure of the FEL optical field.