TUSBC3
Tech-X, Boulder, Colorado, USA
CIPS, Boulder, Colorado, USA
UNL, Lincoln, USA
Simulations of laser-plasma acceleration (LPA) play a key role in understanding the effect of initial conditions on injected beam parameters. Here we present a method for improving the accuracy of simulated particle beams from the LPA self-injection process. We recently demonstrated the ability to compute the collection volume of an injection process – the range of initial locations of injected particles*. We find that the collection volume consists of an annular region around the propagation axis. By loading this region with higher particle statistics than in other locations, we can significantly increase the number of macroparticles in the injected beam. We show that this technique captures much finer detail of particle phase space than does uniform loading, and results in lower noise. We demonstrate convergence of key beam parameters in 2D, and present results of full 3D simulations. In addition, we present results of a novel technique in which particles can deform and split if they expand, effectively self-generating statistics. We also discuss a perfect dispersion algorithm and its impact on self-injection results.
*B. M. Cowan et al., "Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime," accepted for publication in J. Plasma Phys. (2012)
Tech-X, Boulder, Colorado, USA
LBNL, Berkeley, California, USA
Because of their ultra-high accelerating gradient, laser plasma based accelerators (LPA) are contemplated for the next generation of high-energy colliders and light sources. The upcoming BELLA project will explore acceleration of electron bunches to 10 GeV in a 1 meter long plasma, where a wakefield is driven by a PW-class laser. Particle-in-cell (PIC) simulations are used to design the upcoming experiments where boosted frame simulations are used to model the full scale stages. As criteria on energy spread and beam emittance become more stringent, PIC simulations become more challenging as high frequency noise artificially increases those quantities. We show that calculating the beam self-fields using a static Poisson solve in the beam frame dramatically reduces particle noise, allowing for more accurate simulation of the beam evolution. In particular, this method gets correct cancellation of the transverse self-electric and magnetic fields of the beam, eliminating artificial self-forces, which is usually not true when using the standard PIC algorithm based on the staggered (“Yee”) electromagnetic field solver.