Laser wakefield simulations towards development of compact particle accelerators

Presenter: Cameron Geddes, LBNL
Authors: C.G.R. Geddes, E. Esarey, A.J. Gonsalves, B. Nagler, K. Nakamura, C.B. Schroeder, D. Panasenko, G. Plateau, C. Toth, J. van Tilborg, W. Isaacs, N. Stinus, W.P. Leemans, LBNL;
E. Michel, T. Cowan, UNR;
S. M. Hooker, Oxford University, UK;
D. Bruhwiler, A. Hakim, Tech-X;
J. Cary, Tech-X / U. Colorado

Laser driven wakefield accelerators produce accelerating fields thousands of times those achievable in conventional radio-frequency accelerators, potentially extending the frontiers of high energy physics and enabling laboratory scale ultrafast radiation sources. Because the plasma response is highly nonlinear, large-scale, self consistent particle simulations in 3D are important to understand and optimize this new acceleration process. Such simulations provide information on accelerator internal dynamics not accessible from experiments, and have shown that high quality electron bunches in recent LBNL and other experiments were formed by self trapping of electrons in the wake followed by loading of the wake by the trapped bunch, creating a bunch of electrons isolated in phase space. A narrow energy spread beam was then obtained by extracting the bunch as it outran the accelerating phase of the wake. These simulations have now been extended to three dimensions and high resolution under INCITE, and these MHour scale runs are providing more quantitative understanding of the experiments and methods for optimization. Challenges now include control and reproducibility of the electron beam, further improvements in energy spread, and scaling to higher energies. Experiments and simulations are hence in progress on controlled injection of particles into the wake and staging to further improve beam quality and stability.

   

Figure Captions
Large scale particle in cell simulations under INCITE7 are advancing understanding of laser driven wakefield accelerators, whose high accelerating fields may offer more compact machines for high energy physics, and whose ultrashort electron bunches may revolutionize applications of accelerators to radiation sources and applications including chemistry and biology. Recent experiments have demonstrated high quality beams from such accelerators, with accelerating fields thousands of times greater than conventional machines. Large scale three dimensional particle simulations done under INCITE clarify mechanisms of beam formation and evolution, and have begun to identify potential optimizations in this emerging field.

Above (top of page): A three dimensional visualization showing the density of the plasma wave driven by the laser (volume shading), and positions of particles accelerated by that wave (blue spheres) [Simulation, John Cary & Cameron Geddes; Visualization, Cristina Siegerist].
Below (left): a two dimensional cut through the simulation shows the plasma wave density (surface height), and reveals the particle momentum distribution versus position (spheres, height&color=momentum) [Simulation, Cameron Geddes; Visualization. Cameron Geddes & Peter Messmer].