Description
Laser-driven electrons sources are typically limited in charge for most of the envisaged applications when high energies and high beam quality (low divergence, small energy spread…) are also required. To overcome this limitation, at CEA, we propose a "hybrid injector", consisting of a gas-jet coupled with a plasma mirror. The key idea behind this concept is that the laser will eject a significant amount of charge from the high-density plasma mirror during the reflection, which can then be trapped in the accelerating structure formed in the gas jet.
The "hybrid injector" concept was validated with proof-of-principle experiments at the Laboratoire d'Optique Appliquée facility (LOA, France) in 2022. Following experiments from 2023 to 2025 in several facilities including a 40TW laser at LOA and the PW-class facility Apollon (France) further demonstrated the potential of this concept by obtaining electron beams with an excellent spectral charge density. In parallel, simulation campaigns have been conducted to support experimental results and study the hybrid injector further using the Particle-in-cell code WarpX. The work [1] describing these results as well as technical innovations realised in WarpX was awarded the Gordon Bell prize in 2022.
These numerical campaigns highlighted the significant cost of these simulations, with 3D Particle-in-Cell simulations requiring more than 10,000GPUh. While modeling laser-solid interaction requires a full Particle-In-Cell code like WarpX, the subsequent acceleration phase in the gas could in principle be modeled with a quasi-static Particle-In-Cell code, leading to substantial savings of computational time. In this contribution we will discuss the coupling of the WarpX code with the quasi-static code HiPACE++, successor of the DESY-LBNL code HiPACE, the Highly efficient Plasma Accelerator Emulator. Preliminary results using WarpX 2D simulations coupled with HIPACE++ show a run time more than 100 times faster for the acceleration phase, while preserving the physical properties of the accelerated electrons.
[1] L. Fedeli et al. SC22: international conference for high performance computing, networking, storage and analysis. IEEE, 2022.