arXiv subjects

Yinjian Zhao

Publications and source records attributed to Yinjian Zhao.

25 records · Page 2Linked to original sources

arXiv2025

3D PIC Study of Magnetic Field Effects on Hall Thruster Electron Drift Instability

To fully characterize electron drift instability, a critical phenomenon governing electron transport in Hall thrusters, large-scale three-dimensional (3D) particle-in-cell (PIC) simulations are essential, as the instability inherently exhibits 3D features. While prior 3D PIC studies of this instability exist, their setups remain oversimplified to mitigate computational costs, often employing analytical approximations for ionization and magnetic fields. Notably, these models typically assume a purely radial magnetic field, significantly deviating from real thruster configurations. This work presents the first 3D PIC study incorporating realistic magnetic fields with both radial and axial components, coupled with a Monte Carlo collision model for ionization and a self-consistent fluid solver for neutral gas density. These advancements enable a systematic investigation of magnetic field effects on electron drift instability. Results demonstrate that both the spatial configuration and strength of the magnetic field profoundly influence instability dynamics.

physics.plasm-ph↗

arXiv2025

Impact of Azimuthal Magnetic Field Inhomogeneity on Hall Thruster high-frequency azimuthal instability via 2D radial-azimuthal PIC simulations

For the SPT-type Hall thrusters, the magnetic structure with magnetic conductive columns leads inherent to azimuthally inhomogeneous magnetic configurations. This azimuthal magnetic inhomogeneity may impact electron azimuthal closed-drift motion and cross-field transport characteristics. This study systematically investigates the effects of azimuthal magnetic field gradient on high frequency azimuthal instability and associated anomalous electron transport through 2D radial-azimuthal Particle-in-Cell (PIC) simulations. The results reveal dual mechanisms of magnetic inhomogeneity on electron cyclotron drift instability (ECDI) characteristics: (1) The azimuthal drift velocity distribution becomes modulated by the magnetic field inhomogeneity, with increased average drift velocity enhancing ECDI intensity under stronger inhomogeneity; (2) Simultaneously, the ECDI wavenumber spectrum broadens with elevated magnetic inhomogeneity, reducing discrete ECDI spectral peaks. Under the dual influence of magnetic field inhomogeneity, when the inhomogeneity level is below 5%, the ECDI saturation amplitude and electron cross field mobility remains largely unchanged. However, a notable reduction of 13.4% in ECDI saturation intensity and a 15.7% decrease in electron mobility are observed when magnetic field inhomogeneity reaches 10%.

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↗

arXiv2025

Numerical study on wave attenuation via 2D fully kinetic electromagnetic particle-in-cell simulations

The propagation and absorption of electromagnetic waves in plasma is one of the fundamental issues in plasma physics. The electromagnetic particle-in-cell method with the finite-difference time-domain solver plus Monte Carlo collision model would be the most accurate method to simulate the wave-plasma interaction. However, the numerical effects of this method have not been carefully investigated especially in two dimensions. In this paper, the 2D PIC method is used to study the electromagnetic wave attenuation by fluorescent lamp plasma tubes. The study finds that the number of macro-particles and the incident electromagnetic wave amplitude have minor effects on the wave attenuation within a certain appropriate parameter range. Furthermore, the effects of electromagnetic wave frequency, the plasma distribution structures, and collision types on wave attenuation are investigated. Particularly, it is found that the staggered way of arranging the plasma distribution structures can achieve better wave attenuation than the parallel way, which agrees with our recent experimental observation.

physics.plasm-ph↗

arXiv2025

Formation of Anomalously Energetic Ions in Hollow Cathode Plume by Charge Separation Instability

Hollow cathodes are becoming the bottleneck of many electric propulsion systems, because of the sputtering and erosion on both cathodes and thrusters from the generation of anomalously energetic ions. So far, it is believed that energetic ions are formed by waves and instabilities always accompanied in cathode discharge, but there is no evidence yet that those proposed instabilities can lead to such high ion energies measured in experiments. In this work, a new mechanism of charge separation instability in hollow cathode plume is found via fully kinetic PIC simulations, which can easily produce energetic ions to the same level as measured in experiments.

physics.plasm-ph↗

arXiv2021

Overcoming timestep limitations in boosted-frame Particle-In-Cell simulations of plasma-based acceleration

Explicit electromagnetic Particle-In-Cell (PIC) codes are typically limited by the Courant- Friedrichs-Lewy (CFL) condition, which implies that the timestep multiplied by the speed of light must be smaller than the smallest cell size. In the case of boosted-frame PIC simulations of plasma-based acceleration, this limitation can be a major hinderance as the cells are often very elongated along the longitudinal direction and the timestep is thus limited by the small, transverse cell size. This entails many small-timestep PIC iterations, and can limit the potential speed-up of the boosted-frame technique. Here, by using a CFL-free analytical spectral solver, and by mitigating additional numerical instabilities that arise at large timestep, we show that it is possible to overcome traditional limitations on the timestep and thereby realize the full potential of the boosted-frame technique over a much wider range of parameters.

physics.acc-ph↗