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Warp-X: a new exascale computing platform for beam-plasma simulations
J. -L. Vay, A. Almgren, J. Bell, L. Ge, D. P. Grote, M. Hogan, O. Kononenko, R. Lehe, A. Myers, C. Ng, J. Park, R. Ryne, O. Shapoval, M. Thevenet, W. Zhang
TL;DR
Plasma accelerators require high-performance, high-fidelity modeling across wide space and time scales. This paper presents WarpX, an exascale-oriented simulation tool combining Warp, AMReX, and PICSAR, and reports agreement with Warp plus mesh-refined accelerator simulations. Its application scope assumes localized witness-beam self-fields require higher resolution than the surrounding wake.
Problem
Plasma accelerators need high-performance, high-fidelity modeling of complex processes spanning wide space and time scales.
Method
WarpX combines Warp, AMReX, PICSAR, and WarpX-Source into a simulation tool tuned for efficient exascale execution.
Results
WarpX and Warp showed excellent agreement in 3-D accelerator simulations, while mesh refinement reproduced higher-resolution results around witness beams.
Takeaways & Limitations
WarpX provides an exascale-oriented framework for modeling particle beam-driven and laser-driven plasma accelerators with localized mesh refinement.
Takeaways & Limitations
The presented mesh-refinement applications assume witness-beam self-fields are comparable to driver-wake fields and require higher resolution because the beam is much smaller.
Abstract
from arXiv · showhide
Turning the current experimental plasma accelerator state-of-the-art from a promising technology into mainstream scientific tools depends critically on high-performance, high-fidelity modeling of complex processes that develop over a wide range of space and time scales. As part of the U.S. Department of Energy's Exascale Computing Project, a team from Lawrence Berkeley National Laboratory, in collaboration with teams from SLAC National Accelerator Laboratory and Lawrence Livermore National Laboratory, is developing a new plasma accelerator simulation tool that will harness the power of future exascale supercomputers for high-performance modeling of plasma accelerators. We present the various components of the codes such as the new Particle-In-Cell Scalable Application Resource (PICSAR) and the redesigned adaptive mesh refinement library AMReX, which are combined with redesigned elements of the Warp code, in the new WarpX software. The code structure, status, early examples of applications and plans are discussed.
1. Introduction
WarpX addresses the need for high-performance, high-fidelity modeling of multiscale plasma-accelerator processes by combining major simulation components for exascale computing. The paper introduces the tool and outlines its structure, status, early applications, and plans.
- High-performance, high-fidelity modeling is needed to develop plasma-based accelerators into mainstream scientific tools.
- WarpX is being developed through the DOE Exascale Computing Project to model particle-beam acceleration and transport on future exascale supercomputers.
- WarpX combines Warp, AMReX, and PICSAR and is tuned for efficient execution at scale on exascale supercomputers.
- The paper discusses WarpX’s code structure, development status, early application examples, and future plans.
2. Code structure description
WarpX orchestrates Warp, AMReX, PICSAR, and its own source code into a layered Particle-In-Cell application. The components divide physics operations, adaptive-mesh and parallel infrastructure, user interfaces, and workflow control.
- WarpX’s application combines Warp, AMReX, PICSAR, and WarpX-Source as coordinated software packages.
- Warp provides a Python interface and FORTRAN routines for fast computation, with optional control, steering, additional physics, and diagnostics.
- AMReX handles adaptive mesh refinement, communication, load balancing, and parallel I/O across grid and particle data.
- PICSAR implements elemental Particle-In-Cell operations, including charge and current deposition, Maxwell solving, field gathering, and particle pushing.
- WarpX-Source interfaces the components and orchestrates workflow at the main-loop level rather than merely stitching packages together.
3. Status
WarpX combined and benchmarked its component codes against Warp on basic plasma tests and particle- and laser-driven accelerator simulations. Its status work also implemented adaptive mesh refinement while addressing interface-related numerical effects.
- WarpX and Warp showed excellent agreement in 3-D simulations of wakefields driven by laser or electron beams.
- The combined code was benchmarked first on simple tests and then on particle beam-driven and laser-driven plasma accelerator models.
- WarpX implemented mesh refinement based on principles of minimizing spurious effects, user control, and implementation simplicity.
- The mesh-refinement implementation was tested on single-particle, synchrotron-radiation, and beam-oscillation cases before accelerator applications.
4. Application to the modeling of plasma-based accelerators with mesh refinement.
WarpX simulations of beam- and laser-driven plasma accelerators use local mesh refinement to resolve witness-beam self-fields while maintaining the wake at moderate base resolution. In 3-D, refinement reproduces higher-resolution emittance results for both accelerator types.
- Refinement is effective because witness-beam self-fields are comparable to driver-wake fields but vary over a much smaller spatial scale.This scale separation makes higher resolution necessary mainly near the witness beam.
- The simulations cover 2-D and 3-D BPA and LPA cases with progressively doubled base-grid resolution, both with and without mesh refinement.The main physical and numerical parameters are summarized in Table 1.
- Figure 2 compares longitudinal electric-field slices from WarpX and Warp for laser-driven and particle-driven accelerator simulations.
- Witness-beam emittance increases with resolution without refinement because localized self-fields become progressively better resolved.Emittance measures beam quality, with lower values preferred for a particle collider.
- Mesh refinement around the witness beam reproduces simulations without refinement at twice the resolution, while leaving the surrounding wake practically unchanged.The refinement patch doubles resolution along each dimension relative to the parent grid.
5. Plans
WarpX development plans add field solvers and physics capabilities needed for broader plasma-accelerator applications, followed by a planned public open-source release.
- Planned WarpX extensions include PSATD Maxwell solvers, multiple mesh-refinement levels, tunnel ionization, and impact ionization.
- The code was planned to become open source and publicly available toward the end of 2018.