Summary report of working group 2: Computations for accelerator physics

Vay, Jean‐Luc; Arefiev, Alexey

doi:10.1063/1.4965596

Cited by 2 publications

(1 citation statement)

References 20 publications

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“…Pseudo-spectral solvers, however, act globally on the grid due to the needed Fourier transform, which limits efficient parallelization. An approach to overcome this limitation are arbitrary order pseudo-spectral solvers [13][14][15] , which only locally affect the fields when solving Maxwell's equations. On the downside, this -again -introduces spurious numerical dispersion and can make a simulation prone to NCR.…”

Section: Introductionmentioning

confidence: 99%

Accurate modeling of plasma acceleration with arbitrary order pseudo-spectral particle-in-cell methods

et al. 2017

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Particle in Cell (PIC) simulations are a widely used tool for the investigation of both laser-and beam-driven plasma acceleration. It is a known issue that the beam quality can be artificially degraded by numerical Cherenkov radiation (NCR) resulting primarily from an incorrectly modeled dispersion relation. Pseudospectral solvers featuring infinite order stencils can strongly reduce NCR -or even suppress it -and are therefore well suited to correctly model the beam properties. For efficient parallelization of the PIC algorithm, however, localized solvers are inevitable. Arbitrary order pseudo-spectral methods provide this needed locality. Yet, these methods can again be prone to NCR. Here, we show that acceptably low solver orders are sufficient to correctly model the physics of interest, while allowing for parallel computation by domain decomposition.

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Section: Introductionmentioning

confidence: 99%

Accurate modeling of plasma acceleration with arbitrary order pseudo-spectral particle-in-cell methods

et al. 2017

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Elimination of numerical Cherenkov instability in flowing-plasma particle-in-cell simulations by using Galilean coordinates

et al. 2016

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Particle-In-Cell (PIC) simulations of relativistic flowing plasmas are of key interest to several fields of physics (including e.g. laser-wakefield acceleration, when viewed in a Lorentz-boosted frame), but remain sometimes infeasible due to the well-known numerical Cherenkov instability (NCI). In this article, we show that, for a plasma drifting at a uniform relativistic velocity, the NCI can be eliminated by simply integrating the PIC equations in Galilean coordinates that follow the plasma (also sometimes known as comoving coordinates) within a spectral analytical framework. The elimination of the NCI is verified empirically and confirmed by a theoretical analysis of the instability. Moreover, it is shown that this method is applicable both to Cartesian geometry and to cylindrical geometry with azimuthal Fourier decomposition. INTRODUCTIONSimulating relativistic flowing plasmas is of importance in several fields of physics, including relativistic astrophysics (e.g. [1,2]) and laser-plasma acceleration [3]. More precisely, although in laser-plasma acceleration the plasma is typically at rest in the laboratory frame, it was shown [4] that simulating the interaction in a Lorentzboosted frame -where the plasma is flowing with relativistic speed -reduces computational demands by orders of magnitude.However, despite the interest surrounding simulations of relativistic flowing plasmas, performing these simulations with Particle-In-Cell (PIC) algorithms [5,6] remains a challenge. This is because a violent numerical instability, known as the numerical Cherenkov instability (NCI) [7][8][9][10][11][12][13][14], quickly develops for relativistic plasmas and disrupts the simulation.Several solutions have been proposed to mitigate the NCI [15][16][17][18][19][20][21][22]. Although these solutions efficiently reduce the numerical instability, they typically introduce either strong smoothing of the currents and fields, or arbitrary numerical corrections, which are tuned specifically against the NCI and go beyond the natural discretization of the underlying physical equation. Therefore, it is sometimes unclear to what extent these added corrections could impact the physics at stake.For instance, NCI-specific corrections include periodically smoothing the electromagnetic field components [7], using a special time step [8,9] or applying a wide-band smoothing of the current components [8][9][10]. Another set of mitigation methods involve scaling the deposited currents by a carefully-designed wavenumber-dependent * rlehe@lbl.gov factor [15,16] or slightly modifying the ratio of electric and magnetic fields (E/B) before gathering their value onto the macroparticles [17][18][19]. Yet another set of NCIspecific corrections [20][21][22] consists in combining a small timestep ∆t, a sharp low-pass spatial filter, and a spectral or high-order scheme that is tuned so as to create a small, artificial "bump" in the dispersion relation [20]. While most mitigation methods have only been applied to Cartesian geometry, this last set of method...

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Summary report of working group 2: Computations for accelerator physics

Cited by 2 publications

References 20 publications

Accurate modeling of plasma acceleration with arbitrary order pseudo-spectral particle-in-cell methods

Accurate modeling of plasma acceleration with arbitrary order pseudo-spectral particle-in-cell methods

Elimination of numerical Cherenkov instability in flowing-plasma particle-in-cell simulations by using Galilean coordinates

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