Laser wakefield simulation using a speed-of-light frame envelope model

Abstract

Abstract. Simulation of laser wakefield accelerator (LWFA) experiments is computationally intensive due to the disparate length scales involved. Current experiments extend hundreds of laser wavelengths transversely and many thousands in the propagation direction, making explicit PIC simulations enormously expensive and requiring massively parallel execution in 3D. We can substantially improve the performance of laser wakefield simulations by modeling the envelope modulation of the laser field rather than the field itself. This allows for much coarser grids, since we need only resolve the plasma wavelength and not the laser wavelength, and therefore larger timesteps. Thus an envelope model can result in savings of several orders of magnitude in computational resources. By propagating the laser envelope in a frame moving at the speed of light, dispersive errors can be avoided and simulations over long distances become possible. Here we describe the model and its implementation, and show simulations and benchmarking of laser wakefield phenomena such as channel propagation, self-focusing, wakefield generation, and downramp injection using the model.

Modeling of 10 GeV-1 TeV laser-plasma accelerators using Lorentz boosted simulations

“…The accuracy of this assumption has been demonstrated by comparison between explicit codes which include both forward and backward waves and envelope or quasistatic codes which neglect backward waves. 7,21,27 After the idea and basic scaling for performing simulations of LPAs in a Lorentz boosted frame were published, 23 there have been several reports of the application of the technique to various regimes of LPA. 9,11,14,28-34 Speedups varying between several and a few thousands were reported with various levels of accuracy in agreement between simulations performed in a Lorentz boosted frames and in a laboratory frame.…”

Scaled simulations of a 10 GeV accelerator

“…Using a fully self-consistent Particle-In-Cell (PIC) algorithm to simulate such a stage is still impractical with state of the art computing facilities. The use of reduced models [7,8,9] is therefore required to model acceleration of particle beams to these high energies as it can greatly reduce the required number of simulation hours. Here we use the fully self-consistent PIC algorithm, implemented in the code VORPAL [10], to simulate the evolution of an externally injected electron bunch over the accelerating stage by scaling the physical quantities with the plasma density.…”

New Developments in the Simulation of Advanced Accelerator Concepts

“…The quasistatic algorithm step size can be as large as a fraction of a Rayleigh range, resulting in even greater speedup, but it requires special measures to correctly model the trapping and acceleration of electrons. The PGC algorithm in VORPAL includes particle trapping, making it well suited for simulations of downramp injection [46].…”

“…One such example is the ponderomotive guiding center (PGC) or "envelope" treatment of the laser pulse [44], which has been implemented in VORPAL [45,46] and other codes. A stronger approximation is the quasistatic algorithm, which has been implemented in WAKE (2D cylindrical) and also in the 3D QuickPIC code [47].…”