Imperfect Energy Conservation of the Free-Electron Laser over the Timestep of Simulations

TL;DR

This paper investigates the limitations of current free-electron laser simulations, revealing that they do not accurately conserve energy over short timesteps due to fundamental physics constraints, impacting the fidelity of modeling X-ray laser behavior.

Contribution

The study highlights the discrepancy between simulation assumptions and Wheeler-Feynman theory, emphasizing the need to reconsider energy conservation in free-electron laser modeling at small timesteps.

Findings

Simulations preserve net energy conservation over the timestep.

Short timesteps violate Wheeler-Feynman time-symmetric theory.

Predicted electron-radiation evolution contradicts correct physics.

Abstract

Along the development of free-electron laser operating at the wavelength of X-ray, the importance of investigation on the radiation has increased. A theoretical simulation is an essential tool for studying existing and proposed experiments. The available simulations preserve net energy conservation over the timestep, upholding causality between the electrons' power and the radiated energy flux. However, according to Wheeler-Feynman time-symmetric theory, the timestep is too short to ensure this. Therefore, the time evolution of electrons and radiation field predicted by the simulations should contradict the correct physics, regardless of whether the stimulated emission dominates over the spontaneous emission or not.