arXiv subjects

Xiaochun Ma

Publications and source records attributed to Xiaochun Ma.

3 recordsLinked to original sources

arXiv2026

An Electromagnetic Particle-Particle Method for Relativistic Electron Bunch Dynamics from Early Expansion to Long-Range Transport

Particle-mesh methods, such as the particle-in-cell (PIC) method, cannot retain exact pairwise interaction at sub-cell scales. For dense nonneutral relativistic electron bunches, this makes it difficult to accurately capture the inter-particle electromagnetic interaction and the associated bunch divergence. In this work, the previously developed electromagnetic particle-particle (EM-PP) model for relativistic two-particle interaction is extended to many-particle electron bunch transport in the Earth's magnetosphere. The method combines the Liénard--Wiechert fields, an improved retarded-time evaluation procedure, and a relativistic particle pusher, and adopts a two-stage strategy to couple the dense early self-field-dominated evolution to the later long-range geomagnetic-field-controlled transport. The method provides a practical mesh-free approach for accurately simulating long-range transport of relativistic electron bunches when short-range electromagnetic interaction is important.

physics.plasm-ph↗

arXiv2025

An Electromagnetic Particle-Particle Model on Solving Relativistic Binary Collision

With the significant advancements in parallel computing techniques, the particle-particle (PP) model has been effectively utilized in various plasma-related applications. However, PP has been limited for solving only electrostatic problems under Coulomb's law, by analogy to the particle-in-cell (PIC) model solving Poisson's equation. While electromagnetic PIC is common with coupled solutions of Maxwell's equations, we propose an electromagnetic (EM) PP model taking advantage of Lienard-Wiechert potentials for point charge in this paper. In addition, this EM-PP model can contribute to simulate relativistic binary collisions with high accuracy, thus its results are used as a baseline to compare with the classical Frankel's relativistic scattering angle, and the accuracy and applicable scope of Frankel's formula are discussed.

physics.plasm-ph↗

arXiv2025

Comparison between electrostatic PP and PIC simulations on electron bunch expansion

With the great development of parallel computing techniques, the particle-particle (PP) model has been successfully applied in a number of plasma applications. Comparing to particle-mesh (PM) models, for example the widely used particle-in-cell (PIC) method, PP has the advantages of high accuracy in solving Coulomb interactions. In this paper, it is shown that PP is also advantageous to simulate non-neutral plasmas, such as electron bunch expansion in vacuum. The numerical effects of the macro-particle weight and the time step length are investigated for a PP model, accurate and convergent results can be obtained with less effort. On the contrary, PIC needs to simulate the same problem with extremely large effort. It is found that the simulation accuracy does not grow with reduced cell size monotonously, thus no convergence can be easily obtained. In the long run, PIC must apply large enough domain to cover all the expanding particles and avoid non-physical effects caused by imperfect infinite boundary condition, which may result in too heavy computation and make PIC infeasible.

physics.plasm-ph↗