Particle accelerators are used in many areas of fundamental research. A total of 30% of all Nobel prizes in physics since 1939 and four of the last 14 Nobel prizes in chemistry have been enabled by this technology. Among the candidate new technologies for compact accelerators, the advent of plasma-based particle accelerators stands apart as a prime game-changing technology. The development of these devices depends critically on high-performance, high-fidelity modeling to capture the full complexity of acceleration processes that develop over a large range of space and timescales. WarpX is developing an exascale application for plasma accelerators that enables the exploration of outstanding questions in the physics of the transport and the acceleration of particle beams in long chains of plasma channels. These new breeds of virtual experiments, which are not possible with present technologies, will bring huge savings in research costs, leading to the design of a plasma-based collider, and even bigger savings by enabling the characterization of the accelerator before it is built.
Simulations of plasma accelerators are extremely computationally intensive due to the need to resolve the evolution of a driver (laser or particle beam) and an accelerated beam into a structure that is orders of magnitude longer and wider than the accelerated beam. Studies of various effects—including injection, emittance transport, beam loading, tailoring of the plasma channel, and tolerance to non-ideal effects (e.g., jitter, asymmetries) that are needed for the design of high-energy colliders—will necessitate a series of tens to hundreds of runs. This will require an orders-of-magnitude speedup over the present state of the art, which will be obtained by combining the power of exascale computing with the most advanced computational techniques.
This project combines the Adaptive Mesh Refinement (AMR) framework AMReX with novel computational techniques that were pioneered in the Particle-in-Cell (PIC) code Warp to create a new software application (WarpX) and generalizes the algorithms to exascale platforms. WarpX’s team has been incorporating the most advanced algorithms in the code, including the optimal Lorentz boosted frame approach, scalable spectral electromagnetic solvers, and mitigation methods for the numerical Cherenkov instability. It is also improving these algorithms or inventing new ones along the way. To ensure speed and scalability, WarpX is taking advantage of performance-portable, parallel C++ primitives for mesh-refined, particle-mesh routines in AMReX, as well as dynamic load-balancing the computational work. It further integrates modern linear algebra routines from SLATE for advanced geometries, advanced I/O routines from ADIOS, and in situ visualization from Ascent to compute and analyze plasma accelerator modeling challenges at scale. For productivity on leadership-scale supercomputers, WarpX can be deployed to users through the Spack package manager into the Extreme-scale Scientific Software Stack (E4S).
The new software enables the exploration of outstanding questions in the physics of the transport and the acceleration of particle beams in long chains of plasma channels, such as beam-quality preservation, hosing, and beam breakup instabilities.
The exascale challenge problem involves modeling a chain of tens of plasma acceleration stages. Realizing such an ambitious target is essential for the longer-range goal of designing a single- or multi-TeV electron-positron high-energy collider based on plasma acceleration technology. The WarpX application uses AMReX for AMR and employs PIC methodology to solve the relativistic charged particle dynamics with Maxwell’s equations to model the accelerator system. The minimum completion criteria are designed to demonstrate that the project is on track toward the modeling of multi-TeV high-energy physics colliders based on tens to thousands of plasma-based accelerator stages. The main goals are to enable the modeling of an increasing number of consecutive stages to reach higher final energy and to increase simulation precision by performing simulations at higher resolutions in a reasonable clock time.