Accurately simulating nine-dimensional phase space of relativistic particles in strong fields

JOURNAL OF COMPUTATIONAL PHYSICS

卷:438

Article

Li, Fei¹  Decyk, K. Viktor²  Miller, G. Kyle²  Tableman, Adam²  Tsung, S. Frank²  Vranic, Marija³  Fonseca, A. Ricardo^3,4  Mori, B. Warren^1,2 

[1] Univ Calif Los Angeles, Dept Elect Engn, Los Angeles, CA 90095 USA

[2] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA

[3] Univ Lisbon, Inst Super Tecn, GOLP Inst Plasma & Fusao Nucl, Lisbon, Portugal

[4] ISCTE Inst Univ Lisboa, P-1649026 Lisbon, Portugal

关键词: Particle pusher;    Laser-plasma interaction;    Radiation reaction;    Spin precession;    Particle-in-cell algorithm;   

DOI  :  10.1016/j.jcp.2021.110367

来源: Elsevier

【 摘 要 】

Next-generation high-power laser systems that can be focused to ultra-high intensities exceeding 10(23)W/cm(2)are enabling new physics regimes and applications. The physics of how these lasers interact with matter is highly nonlinear, relativistic, and can involve lowest-order quantum effects. The current tool of choice for modeling these interactions is the particle-in-cell (PIC) method. In the presence of strong electromagnetic fields, the motion of charged particles and their spin is affected by radiation reaction (either the semi-classical or the quantum limit). Standard (PIC) codes usually use Boris or similar operator-splitting methods to advance the particles in standard phase space. These methods have been shown to require very small time steps in the strong-field regime in order to obtain accurate results. In addition, some problems require tracking the spin of particles, which creates a nine-dimensional (9D) particle phase space, i.e., (x, u, s). Therefore, numerical algorithms that enable high-fidelity modeling of the 9D phase space in the strong-field regime (where both the spin and momentum evolution are affected by radiation reaction) are desired. We present a new particle pusher that works in 9D and 6D phase space (i.e., with and without spin) based on analytical rather than leapfrog solutions to the momentum and spin advance from the Lorentz force, together with the semi-classical form of radiation reaction in the Landau-Lifshitz equation and spin evolution given by the Bargmann-Michel-Telegdi equation. Analytical solutions for the position advance are also obtained, but these are not amenable to the staggering of space and time in standard PIC codes. These analytical solutions are obtained by assuming a locally uniform and constant electromagnetic field during a time step. The solutions provide the 9D phase space advance in terms of a particle's proper time, and a mapping is used to determine the proper time step duration for each particle as a function of the lab frame time step. Due to the analytical integration of particle trajectory and spin orbit, the constraint on the time step needed to resolve trajectories in ultra-high fields can be greatly reduced. The time step required in a PIC code for accurately advancing the fields may provide additional constraints. We present single-particle simulations to show that the proposed particle pusher can greatly improve the accuracy of particle trajectories in 6D or 9D phase space for given laser fields. We have implemented the new pusher into the PIC codeOsiris. Example simulations show that the proposed pusher provides improvement for a given time step. A discussion on the numerical efficiency of the proposed pusher is also provided. (C) 2021 Elsevier Inc. All rights reserved.

【 授权许可】

Free