Statistical mechanics and Vlasov equation allow for a simplified hamiltonian description of single pass free electron laser saturated dynamics

TL;DR

This paper introduces a simplified Hamiltonian model for the saturated dynamics of a single pass free electron laser, using statistical mechanics and the Vlasov equation to accurately replicate complex particle behavior.

Contribution

It develops a reduced Hamiltonian framework that captures the saturated regime of the laser, incorporating a statistical mechanics approach to determine key parameters self-consistently.

Findings

The model reproduces the oscillating regime of the laser dynamics.

Particles form a dense cluster and a surrounding uniform sea.

Simulations match the original N-body dynamics.

Abstract

A reduced Hamiltonian formulation to reproduce the saturated regime of a single pass free electron laser, around perfect tuning, is here discussed. Asymptotically, $N\_m$ particles are found to organize in a dense cluster, that evolves as an individual massive unit. The remaining particles fill the surrounding uniform sea, spanning a finite portion of phase space, approximately delimited by the average momenta $\omega\_+$ and $\omega\_-$. These quantities enter the model as external parameters, which can be self-consistently determined within the proposed theoretical framework. To this aim, we make use of a statistical mechanics treatment of the Vlasov equation, that governs the initial amplification process. Simulations of the reduced dynamics are shown to successfully capture the oscillating regime observed within the original $N$-body picture.