*Advancing accelerator physics and computing with state-of-the-art simulation tools*

BELLA Center computer modeling covers a wide range of topics needed to understand and design laser-plasma accelerators (LPA). The center uses and supports a comprehensive set of simulation tools that range from from simplified models providing fast turnaround to detailed first-principles multiphysics codes for high fidelity.

The array of physical phenomena (e.g., electromagnetic relativistic plasmas, lasers, gas dynamics, radiation and scattering) and the wide range of space and time scales (e.g., laser light with submicron wavelength propagating in meter-long plasmas) demand advanced models and the use of massively parallel supercomputers. Separation of time scales allows us to use complementary sets of simulations, therefore addressing time scales that run the gamut from picoseconds for laser-plasma interaction and evolution of electron beam dynamics, to nanoseconds for plasma formation in capillary discharges, to milliseconds for neutral gas evolution that sets up the target for the LPA.

**Gas dynamics**: The spatial and temporal evolution of gas flow is essential to predicting the initial state of the target density before initiating the discharge that will create the plasma channel. Computational Fluid Dynamics (CFD) modeling with the open-source code OpenFOAM, allows for the consideration of fluid effects in the capillary such as compressibility and high Knudsen numbers.

**Plasma sources**: Three-dimensional description of the discharge dynamics is needed for accurate prediction of laser guiding and evolution in the plasma channel. Magnetohydrodynamic (MHD) modeling of the plasma capillary discharges is performed with the 3-D parallel code MARPLE.

**Laser-plasma acceleration**: Predicting accelerated particle beam performance demands integrated modeling of the laser propagation together with the generation, guiding and acceleration of the particle beams. The parallel codes INF&RNO and Warp are used for 1-, 2-, and 3-D integrated modeling. Both include fully electromagnetic relativistic Particle-In-Cell (PIC) models that provide detailed kinetic description of various phenomena, including the injection and acceleration of electron beams, the evolution of energy spread and emittance, and staging. To efficiently cover the wide range of time scales involved, laser envelope, fluid, and quasistatic models are used in INF&RNO. Warp focuses the computer’s processing power where it is most needed via the Lorentz boosted frame technique.

**Electromagnetic radiation**: Betatron, Thomson and Compton emissions produced by LPA electron beams cover frequency ranges that are typically not accessible to standard PIC codes, and are modeled using specialized methods. The Virtual Detector of Synchrotron Radiation (VDSR) code is used to track particle trajectories in given electromagnetic field configurations, such as focused laser fields, plasma waves, and magnetic undulators, and calculates the incoherent radiation. It can also perform Monte-Carlo calculations of the Compton effect. Free electron lasing is modeled using the eikonal approximation with Ginger or from first principles with Warp.

**Beam transport** : Standard accelerator lattices can come after, or be interleaved with, LPA stages. Tracking of charged-particle beams through these lattices is performed with 3-D parallel codes from BLAST, the Berkeley Lab Accelerator Simulation Toolkit. The code Impact models transport through lattice elements using maps; Warp provides first-principles modeling of transport through lattice elements.

**Laser driven ion acceleration** : Detailed simulations of laser-plasma interaction, ion beam formation, and acceleration are performed in 2-D with the parallel, relativistic electromagnetic PIC code REMP (Relativistic ElectroMagnetic Particle code). The code has been successfully used for more than 14 years for modeling of laser driven acceleration of electrons and ions, as well as generation of X-ray and gamma sources in laser plasma interactions.

**Advancing simulation tools**: In addition to using these tools to push the frontier of accelerator science and technology, BELLA’s team is also pushing the computing frontier in accelerator modeling itself. We have pioneered numerous novel numerical techniques, including