James Cooley

QUICKPIC: a highly efficient particle-in-cell code for modeling wakefield acceleration in plasmas

A highly efficient, fully parallelized, fully relativistic, three-dimensional particle-in-cell model for simulating plasma and laser wakefield acceleration is described. The model is based on the quasi-static or frozen field approximation, which reduces a fully three-dimensional electromagnetic field solve and particle push to a two-dimensional field solve and particle push. This is done by calculating the plasma wake assuming that the drive beam and/or laser does not evolve during the time it takes for it to pass a plasma particle. The complete electromagnetic fields of the plasma wake and its associated index of refraction are then used to evolve the drive beam and/or laser using very large time steps. This algorithm reduces the computational time by 2-3 orders of magnitude. Comparison between the new algorithm and conventional fully explicit models (OSTRIS) is presented. The agreement is excellent for problems of interest. Direction for future work is also presented.

Trapping and acceleration of nonideal injected electron bunches in laser wakefield accelerators

Most conceptual designs for future laser wakefield accelerators (LWFA) require external injection of precisely-phased, monoenergetic, ultrashort bunches of MeV electrons. This paper reports simulation and Hamiltonian models of several nonideal injection schemes that demonstrate strong phase bunching and good accelerated beam quality in a channel-guided LWFA. For the case of monoenergetic, unphased (long bunch) injection, there is an optimum range of injection energies for which the LWFA can trap a significant fraction of the injected pulse while producing an ultrashort, high-quality accelerated pulse. These favorable results are due to a combination of pruning of particles at unfavorable phases, rapid acceleration, and strong phase bunching. Also, the plasma channel introduces a favorable shift in the region of accelerating phase where electrons are focused, which can significantly reduce the required injection energy. Simulation results agree well with the predictions of the Hamiltonian model. Simulations of phased injection with a broad injected energy spread also exhibit final accelerated bunches with small energy spread. These results suggest that relatively poor quality injection pulses may still be useful in LWFA demonstration experiments.

QuickPIC: a highly efficient fully parallelized PIC code for plasma-based acceleration

A highly efficient, fully parallelized, fully relativistic, three-dimensional particle-incell model for simulating plasma and laser wakefield acceleration is described. The model is based on the quasi-static approximation, which reduces a fully three-dimensional electromagnetic field solve and particle push to a two-dimensional field solve and particle push. This is done by calculating the plasma wake assuming that the drive beam and/or laser does not evolve during the time it takes for it to pass a plasma particle. The complete electromagnetic fields of the plasma wake and its associated index of refraction are then used to evolve the drive beam and/or laser using very large time steps. This algorithm reduces the computation time by 2 to 3 orders of magnitude without loss of accuracy for highly nonlinear problems of interest. The code is fully parallelizable with different domain decompositions for the 2D and 3D pieces of the code. The code also has dynamic load balancing. We present the basic algorithms and design of QuickPIC, as well as comparison between the new algorithm and conventional fully explicit models (OSIRIS). Direction for future work is also presented including a software pipeline technique to further scale QuickPIC to 10,000+ processors.

Further Developments For A Particle‐In‐Cell Code For Efficiently Modeling Wakefield Acceleration Schemes: QuickPIC

We describe the present status of the development of a three‐dimensional fully parallel Particle‐In‐Cell (PIC) code, called QuickPIC. QuickPIC embeds a two‐dimensional plasma simulation code in a three‐dimensional beam and/or laser simulation code utilizing the quasi‐static approximation [1,2]. In this paper, we will provide a brief review of the quasi‐static approximation and the current algorithm in QuickPIC, as well as the future plans to improve the code. Preliminary results will be presented, which include comparing QuickPIC Plasma wakefield simulations with OSIRIS [3] simulations, and which include laser propagation simulations.

One-to-One Full-Scale Simulations of Laser-Wakefield Acceleration Using QuickPIC

We use the quasi-static particle-in-cell (PIC) code QuickPIC to perform full-scale one-to-one laser-wakefield- acceleration (LWFA) numerical experiments, with parameters that closely follow current experimental conditions. The propagation of state-of-the-art laser pulses in both preformed and uniform plasma channels is examined. We show that the presence of the channel is important whenever the laser self-modulations do not dominate the propagation. We examine the acceleration of an externally injected electron beam in the wake generated by ~10-J laser pulses, showing that, by using 10-cm-scale plasma channels, it is possible to accelerate electrons to more than 4 GeV. A comparison between QuickPIC and 2-D OSIRIS is provided. Good qualitative agreement between the two codes is found, but the 2-D full PIC simulations fail to predict the correct laser and wakefield amplitudes.

Effective Electron Beam Injection With Broad Energy Initial Beam

Laser Wakefield Accelerators (LWFA), in the resonant regime, require use of an injected electron beam. Several optical methods for generating electron bunches exist e.g., Laser Ionization and Ponderomotive Acceleration (LIPA) and Self‐Modulated LWFA among others. Each of these schemes produces an electron bunch with a characteristic energy distribution. We examine the trapping characteristics in a resonant LWFA for an injection electron beam with a broad energy spread that can be characterized using a Boltzmann distribution with an “effective temperature”. We present results of both analytic calculations and simulations which provide a methodology for optimizing the resulting accelerated electron bunch characteristics i.e., energy and energy spread, for a given LWFA configuration.

Three-Dimensional Structure of the Laser Wakefield Accelerator in the Blowout Regime

Three-dimensional particle-in-cell (PIC) simulations with the code QuickPIC are used to illustrate the typical accelerating structures associated with the interaction of an intense laser beam with an underdense plasma in the blowout regime. Our simulations are performed with an externally injected electron beam, which is positioned in the region of maximum accelerating gradients. As the laser propagates in the plasma, an almost complete electron cavitation occurs, leading to the generation of accelerating fields in excess of 1 GeV/cm.

Modeling Laser Wake Field Acceleration with the Quasi‐Static PIC Code QuickPIC

We use the Quasi‐static Particle‐In‐Cell code QuickPIC to model laser wake field acceleration, in both uniform and parabolic plasma channels within current state of the art experimental laser and plasma parameters. QuickPIC uses the quasi‐static approximation, which allows the separation of the plasma and laser evolution, as they respond in different time scales. The laser is evolved with a larger time step, that correctly resolves distances of the order of the Rayleigh length, according to the ponderomotive guiding center approximation, while the plasma response is calculated through a quasi‐static field solver for each transverse 2d slice. We have performed simulations that show very good agreement between QuickPIC and three dimensional simulations using the full PIC code OSIRIS. We have scanned laser intensities from those for which linear plasma waves are excited to those for which the plasma response is highly nonlinear. For these simulations, QuickPIC was 2–3 orders of magnitude faster than OSIRIS.

Effective coupling of ultraintense laser pulse to funnel-mouthed plasma waveguides

We present the results of experiments and simulations showing greatly improved coupling of an 80 mJ, 100 fs pulse to pre-formed plasma waveguides with end-funnels produced in backfill He gas.

High-fidelity plasma codes for burn physics

Accurate predictions of equation of state (EOS), ionic and electronic transport properties are of critical importance for high-energy-density plasma science. Transport coefficients inform radiationhydrodynamic codes and impact diagnostic interpretation, which in turn impacts our understanding of the development of instabilities, the overall energy balance of burning plasmas, and the efficacy of selfheating from charged-particle stopping. Important processes include thermal and electrical conduction, electron-ion coupling, inter-diffusion, ion viscosity, and charged particle stopping. However, uncertainties in these coefficients are not well established. Fundamental plasma science codes, also called high-fidelity plasma codes are a relatively recent computational tool that augments both experimental data and theoretical foundations of transport coefficients. This paper addresses the current status of HFPC codes and their future development, and the potential impact they play in improving the predictive capability of the multi-physics hydrodynamic codes used in HED design.