Modeling of a chain of three plasma accelerator stages with the WarpX electromagnetic PIC code on GPUs

Abstract

The fully electromagnetic particle-in-cell code WarpX is being developed by a team of the U.S. DOE Exascale Computing Project (with additional non-U.S. collaborators on part of the code) to enable the modeling of chains of tens to hundreds of plasma accelerator stages on exascale supercomputers, for future collider designs. The code is combining the latest algorithmic advances (e.g., Lorentz boosted frame and pseudo-spectral Maxwell solvers) with mesh refinement and runs on the latest computer processing unit and graphical processing unit (GPU) architectures. In this paper, we summarize the strategy that was adopted to port WarpX to GPUs, report on the weak parallel scaling of the pseudo-spectral electromagnetic solver, and then present solutions for decreasing the time spent in data exchanges from guard regions between subdomains. In Sec. IV, we demonstrate the simulations of a chain of three consecutive multi-GeV laser-driven plasma accelerator stages.

HiPACE++: a portable, 3D quasi-static Particle-in-Cell code

“…The multigrid solver is an expensive operation, but does not required multiple iterations of PIC operations (although an implicit solver happens inside the multigrid solver). Figure 2 shows a comparison between HiPACE++, the legacy code HiPACE, and the full GPU-capable 3D electromagnetic PIC code WarpX [15]. The accelerating field E z /E 0 , where E 0 = cm e ω p /e is the cold non-relativistic wave breaking limit, shows excellent agreement between these three codes.…”

“…Simulation of a multi-GeV plasma-based accelerator typically requires modeling sub-micron-scale structures propagating over meter-scale distances, hence full electromagnetic PIC simulations require millions of time steps due to the Courant-Friedrichs-Lewy (CFL) condition [7], which makes them unpractical. Several methods were developed to circumvent this limitation and enable larger time steps, including running PIC in a Lorentz-boosted frame [8] or using a quasi-static approximation [9][10][11], both of which have proved performant for modeling of high-energy plasma accelerator stages [12][13][14][15].…”

Absorption of charged particles in Perfectly-Matched-Layers by optimal damping of the deposited current

“…All simulations were run with the open-source PIC code WarpX [18], available at https://github.com/ECP-WarpX/WarpX. transform in x, y and t: 3 dω dk x dk y e ikxx+iky y−iωt F (k x , k y , z, ω)…”

Low divergence proton beams from a laser-plasma accelerator at kHz repetition rate

“…We have explored such interactions through 2D particle-in-cell (PIC) simulations using the code WarpX (v21.04-86) [43]. The initial plasma density is uniform n p0 = 250 n c for z < 0, and for z > 0 it falls as n p = n p0 exp(−z/L g ), where L g = 8 nm (see [41] for details).…”