Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime

Abstract

Electron self-injection and acceleration until dephasing in the blowout regime is studied for a set of initial conditions typical of recent experiments with 100 terawatt-class lasers. Two different approaches to computationally efficient, fully explicit, three-dimensional particle-in-cell modelling are examined. First, the Cartesian code vorpal (Nieter & Cary 2004) using a perfect-dispersion electromagnetic solver precisely describes the laser pulse and bubble dynamics, taking advantage of coarser resolution in the propagation direction, with a proportionally larger time step. Using third-order splines for macroparticles helps suppress the sampling noise while keeping the usage of computational resources modest. The second way to reduce the simulation load is using reduced-geometry codes. In our case, the quasi-cylindrical code calder-circ (Lifschitz et al. 2009) uses decomposition of fields and currents into a set of poloidal modes, while the macroparticles move in the Cartesian 3D space. Cylindrically symmetry of the interaction allow using just two modes, reducing the computational load to roughly that of a planar Cartesian simulation while preserving the 3D nature of the interaction. This significant economy of resources allows using fine resolution in the direction of propagation and a small time step, making numerical dispersion vanishingly small, together with a large number of particles per cell, enabling good particle statistics. Quantitative agreement of the two simulations indicates that they are free of numerical artefacts. Both approaches thus retrieve physically correct evolution of the plasma bubble, recovering the intrinsic connection of electron self-injection to the nonlinear optical evolution of the driver.

Generalized algorithm for control of numerical dispersion in explicit time-domain electromagnetic simulations

“…In any event, certain cases, such as bubble regime simulations or the modeling of a trapped bunch, require higher transverse resolution than that needed simply to resolve the plasma wavelength. Since increasing the longitudinal resolution is computationally impractical, this mandates a lower aspect ratio than p = , and the advantage of controlled dispersion is manifest [39].…”

Optically Controlled Laser-Plasma Electron Acceleration for Compact γ-Ray Sources

“…Yet this process, apart from limiting the energy gain, destroys e-beam most assuredly if acceleration extends through the pulse depletion. (A plethora of evidence exists to this effect, both in laboratory experiments and numerical simulations [16,19,[22][23][24][25][38][39][40][41][42].) To enable a new generation of compact particle and radiation sources [43,44], one has to bypass the limitations this of scaling by designing an optical driver resilient to self-phase-modulation and self-compression.…”

Optical control of electron phase space in plasma accelerators with incoherently stacked laser pulsesa)

“…The feedback of the collective plasma motion onto the laser pulse leads to evolution of both the carrier frequency and the pulse envelope, [11][12][13][14][15][16][17][18] in turn, leaving its imprint on electron phase space. [19][20][21][22][23][24][25][26][27][28] The tight coupling of driver dynamics to the structure of the beam phase space offers great flexibility in tuning beam characteristics. Specific examples of this tunability, associated with the pulse transient dynamics in a finite-length plasma, have been recently observed in experiments.…”