MITHRA 1.0: A full-wave simulation tool for free electron lasers

Abstract

Free Electron Lasers (FELs) are a solution for providing intense, coherent and bright radiation in the hard X-ray regime. Due to the low wall-plug efficiency of FEL facilities, it is crucial and additionally very useful to develop complete and accurate simulation tools for better optimizing a FEL interaction. The highly sophisticated dynamics involved in a FEL process was the main obstacle hindering the development of general simulation tools for this problem. We present a numerical algorithm based on finite difference time domain/Particle in cell (FDTD/PIC) in a Lorentz boosted coordinate system which is able to fulfill a full-wave simulation of a FEL process. The developed software offers a suitable tool for the analysis of FEL interactions without considering any of the usual approximations. A coordinate transformation to bunch rest frame makes the very different length scales of bunch size, optical wavelengths and the undulator period transform to values with the same order. Consequently, FDTD/PIC simulations in conjunction with efficient parallelization techniques make the full-wave simulation feasible using the available computational resources. Several examples of free electron lasers are analyzed using the developed software, the results are benchmarked based on standard FEL codes and discussed in detail. Program summaryProgram Title: MITHRAProgram Files doi:http://dx.doi.org/10.17632/9f5k4zbtkg.1Licensing provisions: GNU General Public License 3Programming language: C++Nature of problem: Full-wave simulation of the free electron laser radiation is accomplished by the code. MITHRA transforms the particle positions and momenta to the bunch rest frame using the Lorentz transformation. Electrons entering the undulator start radiating due to the induced wiggling motion. The back-effect of the radiation on the bunch results in the modulation of the electron position, which in turn generates a coherent radiation. This process as the main principle behind the operation of free electron lasers is simulated using Maxwell equations, electron motion equations and relativity principles.Solution method: Non-standard Finite Difference Time Domain (NSFDTD) combined with Particle-in-Cell (PIC) is implemented in the Lorentz-boosted framework to calculate the FEL radiation. Parallelization is done using both multi-threading (open-MP) and message passing interface (MPI) to maximize the computation efficiency.