arXiv subjects

Yinjian Zhao

Publications and source records attributed to Yinjian Zhao.

At least 19 recordsLinked to original sources

arXiv2026

Particle-resolved pathways to energetic-ion formation in a fluctuating low-current hollow-cathode plume

Energetic-ion formation in a low-current hollow-cathode plume is investigated using experiments, self-consistent electrostatic particle-in-cell (PIC) simulation, and particle-resolved analysis. Retarding potential analyzer measurements show a substantial energetic-ion population over discharge currents of 0.8-3.5 A, while probe measurements reveal broadband plume fluctuations. Two-point phase-derived frequency-wavenumber measurements do not resolve a continuous ion-acoustic dispersion branch within the principal apparent-wavenumber interval. Because the inferred wavenumber is obtained from a cross-spectral phase defined modulo 2pi, the fluctuation diagnostics do not provide an unambiguous modal attribution for the energetic-ion population. A representative PIC plume, used as a qualitative kinetic reference, likewise develops broadband time-dependent electrostatic fluctuations together with a nonthermal energetic-ion population. Particle-resolved analysis shows that the energetic outflow is dominated by ions generated through ionization inside the plume, while source localization biases access to distinct trajectory and escape families. Matched field controls further show that time-averaged and frozen fields strongly suppress access to high-energy trajectories relative to the full time-dependent field over the analyzed interval. At the single-particle level, ion kinetic-energy gain is determined by electrostatic-field work accumulated along the actual trajectory, with different escape families exhibiting distinct radial and axial work contributions. These results establish a source-trajectory-field-work pathway for energetic-ion formation that can be identified without first assigning the fluctuating plume to a unique resolved plasma mode.

physics.plasm-ph↗

arXiv2026

Dual-decomposition multi-GPU particle-in-cell method for cylindrical plasmas: Batched Fourier-mode multigrid and balanced particle slabs

Three-dimensional electrostatic particle-in-cell (PIC) simulations combine irregular particle operations with a globally coupled Poisson solve, whose preferred parallel decompositions conflict. We introduce a dual-decomposition multi-GPU method: complete azimuthal Fourier modes are owned during the field solve, whereas spatial slabs own particles. Exact full-spectrum diagonalization and batched matrix-free geometric multigrid keep collectives outside the V-cycle, after which every GPU reconstructs the full field. Peer migration, cell reordering, warp-aggregated deposition, and capacity-constrained dynamic cuts restore particle locality and balance. CPU/GPU Poisson solutions agree to relative L2 errors below 6.9e-16; all 65 physical modes on eight V100 GPUs are solved in 9.350 ms with relative errors below 8.2e-15. For an identical 512*128*400 problem containing 707,788,800 particles per species, the complete PIC loop reaches 0.149108 s per step and strong-scales from five to eight GPUs with 91.81% efficiency. A separate cross-resolution production study shows approximately threefold aggregate particle-update and Poisson-cell throughput relative to a single RTX 5090 calculation; this measures refined-problem capability rather than a hardware speedup or formal convergence order.

physics.plasm-ph↗

arXiv2026

AlgoPlasma: Open Algorithms for Plasma Modeling

AlgoPlasma is an open-source library in which core numerical algorithms for plasma modeling are implemented as modular, well-documented, and independently testable components. Rather than offering a complete simulation code, it allows researchers to select, adapt, and assemble the required components into application-specific workflows. The current release is centered on particle-based simulation, while AlgoPlasma is designed to encompass a broader range of approaches to plasma modeling. It provides components for particle initialization and advancement, particle--grid coupling, field solution, collision modeling, parallel data exchange, input/output, and selected fluid updates. Documentation links mathematical formulations to source implementations, interfaces, and usage, while verification and validation cases evaluate numerical accuracy and physical behavior. AlgoPlasma thus establishes a shared algorithmic foundation for plasma modeling, transforming repeatedly reimplemented numerical methods into open, reusable, tested, and explainable components for research, verification, education, and collaborative development.

physics.plasm-ph↗

arXiv2026

Simulation Study of Coupling Effects Between a Hall Thruster and a Power Processing Unit

The complex and nonlinear load characteristics of Hall thrusters remain a key challenge in the design of propulsion power-supply output stages. In existing power-supply simu-lations for electric propulsion systems, the Hall thruster is often simplified as a fixed im-pedance or a prescribed current source, which makes it difficult to capture the real-time interaction between the power-supply output stage and the thruster discharge process. To address this issue, this study encapsulates a one-dimensional discharge model as an externally callable thruster slave and proposes a HallThruster.jl-Saber-Simulink co-simu-lation method. The proposed method enables synchronized closed-loop exchange be-tween the power-port voltage Vcmd and the thruster discharge current Iout . The results show that the discharge current under the co-simulation condition exhibits a sustained low-frequency response at approximately 11 kHz. Compared with a fixed-voltage standalone simulation, the co-simulation shows observable differences in port waveforms, spectral characteristics, and internal field distributions. This method provides a co-simu-lation basis for realistic load analysis of propulsion power supplies and subsequent stress evaluation of key components.

physics.plasm-ph↗

arXiv2026

Test Particle Study of EDI Driven Electron Transport in a Hall Thruster Using PIC Derived Electric Fields

Electron transport in a Hall thruster is investigated at the test particle level using prescribed electric fields derived from the electron drift instability (EDI) resolving three dimensional particle-in-cell (PIC) simulation. Four primary electric field configurations are considered: static averaged field, full PIC field, proper orthogonal decomposition (POD) reconstructed field, and a simplified analytical Ey field. Two additional control cases, the magnetic-field-only case and the denoised PIC field, are also included. Transport statistics show that the averaged field produces only weak axial cross field transport. In contrast, the full PIC field produces clear fluctuation driven transport, characterized by pronounced negative axial displacement, enhanced channel entry, finite channel residence, particle energization, and appreciable anode directed loss. POD analysis shows that the transport relevant EDI electric field structures are distributed over multiple coupled modes, and that a moderate truncation order of approximately 20 modes is required to recover the main transport signatures. The analytical Ey model separately examines the influence of azimuthal electric field fluctuations on axial electron transport and shows that fluctuation amplitude is a primary determinant.

physics.plasm-ph↗

arXiv2026

Semi-local Floquet theory for active azimuthal magnetic modulation of Hall-thruster high-frequency instabilities

A semi-local Floquet extension of a uniform-field kinetic electron drift instability (EDI) dispersion relation is developed to assess prescribed azimuthal magnetic-field modulation as a linear pre-screening tool for Hallthruster high-frequency instabilities. The uniform kinetic response is used as a local spectral kernel, while a sinusoidal magnetic modulation couples Floquet sidebands and replaces the scalar dispersion condition by a finite matrix dispersion problem. The numerical procedure combines scalar uniform-field predictors, determinant correction, singular-value diagnostics, sideband-weight analysis, and truncation checks. Because a single Floquet root contains multiple physical wave numbers, stability is assessed with the upper growth envelope over the Bloch zone rather than with an individual projected azimuthal wave-number branch. Parameter scans over modulation wavelength and amplitude show that sinusoidal azimuthal magnetic modulation broadens the coupled spectrum and redistributes unstable growth among low-wave-number modified-two-stream-like and cyclotron-resonant ranges. Some long-wavelength, moderate-to-large-amplitude cases reduce integrated positive growth measures, but these reductions are not accompanied by robust suppression of the peak growth envelope. No tested case produces a finite stable Bloch interval. Within the present cold-ion semi-local Floquet model, prescribed azimuthal magnetic modulation is therefore better interpreted as a spectral-redistribution mechanism than as a robust linear stabilization mechanism by itself.

physics.plasm-ph↗

arXiv2026

Free-Molecular Face-Flux Preprocessing for Reduced Neutral-Continuity Modeling in Hall Thrusters: Particle-Based Reference and Deterministic SN-DFEM Realization

Neutral gas transport directly affects the ionization source, propellant utilization, and low-frequency discharge oscillations in Hall thrusters. High-fidelity particle-based neutral models or DSMC methods can describe rarefied gas transport, but they are computationally expensive; in contrast, reduced neutral-continuity models are cheaper but require a closure for the neutral velocity or face-normal flux. Under a low-pressure collisionless approximation, this work adopts a free-molecular preprocessing strategy to provide a reference density field and the mean-velocity or face-normal-flux closure used by the reduced neutral-continuity equation in a manner consistent with the underlying transport model.On this basis, a particle-based free-molecular faceflux preprocessor is used as a stochastic reference, and an SN-DFEM deterministic free-molecular preprocessor is proposed to generate the corresponding reference density, velocity moments, and face-normal fluxes within a unified free-molecular transport framework. Results show that the SN-DFEM preprocessor preserves the main neutral-density and velocity structures and reduces the statistical error in face-flux closure by about three orders of magnitude in the baseline continuity-recovery test. A prescribed moderate ionization-loss case further demonstrates the extension of the framework to free-molecular preprocessing with volumetric neutral removal.

physics.plasm-ph↗

arXiv2026

Conservative Charge and Current Deposition on Nonuniform 3D Cylindrical PIC Meshes with Residual Self-Field Diagnostics

Particle-in-cell simulations on nonuniform cylindrical meshes require deposition schemes that respect cylindrical metrics while controlling numerical self-fields. This work develops cylindrical-volume-weighted charge and current deposition using nodal control volumes and swept-volume factors on logically structured stretched grids. Uniform-density and controlled-transport tests demonstrate accurate charge recovery, well-controlled current-density errors, and continuity residuals substantially lower than the corresponding current-density errors. Single-particle diagnostics show that charge-transport consistency alone does not ensure self-field cancellation; face-centered electric fields give the smallest residual, whereas cell-centered and shifted cell-centered layouts produce larger residuals.

physics.plasm-ph↗

arXiv2026

Likelihood topology and applicability limits of spatial anti-aliasing inversion for folded electron drift instability dispersion in Hall thrusters

The electron drift instability (EDI) is widely recognized as the leading mechanism for anomalous electron transport in Hall thrusters, but its millimeter and sub-millimeter wavelength makes conventional wave-probe analysis strongly limited by spatial aliasing. A multi-geometry spatial anti-aliasing algorithm provides a route for wave-probe diagnostics to break the spatial Nyquist limit, but its effectiveness for nonmonotonic, folded, multi-resonance EDI dispersion has not been quantified. Using the numerically solved linear kinetic EDI dispersion relation under typical Hall-thruster discharge parameters as a benchmark, this work evaluates two-dimensional maximum-likelihood spatial anti-aliasing inversion based on two-probe synthetic signals generated for 25 simulated angle-spacing configurations. For a sampling frequency fs = 100 MHz and signal-to-noise ratio SNR = 10, the method breaks the conventional Nyquist wavenumber limit of about 1 krad/m, extends the accessible range to about 22 krad/m, and recovers the dominant likelihood ridges associated with the first- to fifth-order EDI branches. Parameter scans further show that the statistical realization count L mainly determines the suppression of spurious alias peaks, whereas the frequency resolution delta f mainly determines local branch separation near folded extrema. These results provide benchmark sampling and segmentation constraints for multi-geometry wave-probe diagnosis of EDI dispersion under the present synthetic conditions and can guide future experiments.

physics.plasm-ph↗

arXiv2026

Full-gap kinetic limitation of thermionic-electron transport for electron transpiration cooling

Electron transpiration cooling (ETC) can reduce aerothermal loads on sharp hypersonic leading edges, but its performance is governed by whether thermionically emitted electrons escape the hot surface or return as cathode-directed backflow. Here, a one-dimensional-in-space, three-dimensional-in-velocity electrostatic particle-in-cell/Monte Carlo collision model is developed for a full cathode--anode plasma diode, resolving thermionic emission, collisional plasma transport, emitted-electron backflow, and downstream collection. A helium benchmark is used to examine emitted-electron transport and backflow-limited current flow. With increasing imposed emission, the diode first remains in a weak-backflow regime, where net emitted-electron transport and downstream collection both increase with emission. Further increasing the emission produces a sharp transition to backflow-limited transport between $7.0\times10^{19}$ and $7.5\times10^{19},\mathrm{m^{-2},s^{-1}}$. At $7.25\times10^{19},\mathrm{m^{-2},s^{-1}}$, the backflow ratio reaches $54.03%$, while the net transport and downstream collection efficiencies fall to about $46%$. Above this transition, added backflow overcompensates the imposed emission increase, reducing useful emitted-electron transport rather than causing saturation. Boundary energy diagnostics show that stronger emission may still increase the nominal cathode-side cooling metric, but after transition this metric no longer indicates improved emitted-electron escape or full-gap transport. These results show that the present PIC-MCC framework captures the key kinetic processes governing ETC-relevant emitted-electron escape and backflow limitation.

physics.plasm-ph↗

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↗

arXiv2026

A Fully Electromagnetic Hybrid PIC-Fluid Model for Predictive Fusion Neutron Yield in Dense Plasma Focus

While magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) remain the primary routes toward controlled fusion, progress is still constrained by energy loss, plasma instabilities, and the cost and complexity of large-scale facilities. The Dense Plasma Focus (DPF) device presents a compact, pulsed-power-driven alternative for producing fusion-relevant conditions and neutron emissions. However, the quantitative prediction of neutron yield in DPF devices poses a significant numerical challenge, primarily due to the imperative of self-consistently resolving kinetic ion behavior, electromagnetic energy coupling, and vacuum field evolution. This complexity often impedes a definitive understanding of the underlying neutron production mechanisms. To address this, we develop a fully electromagnetic hybrid simulation framework: ions are advanced kinetically with particle-in-cell, electrons are a quasi-neutral fluid, and Maxwell's equations are solved in both plasma and vacuum. The generalized Ohm law includes resistive, electron pressure-gradient, and Hall terms, with a predictor-corrector update for current density. We apply the model to a non-hollow 180 kA DPF geometry similar to the LLNL configuration. The simulated ion density, ion temperature, and axial electric field reproduce sheath formation, axial rundown, radial compression, and post-pinch expansion. The outer sheath front position agrees with fully kinetic benchmarks within 10\% over the available comparison interval. With a compact fit to the D-D fusion cross section, the predicted total neutron yield is 0.296e7, comparable in order of magnitude to reported fully kinetic results at similar currents and nearly two orders of magnitude higher than earlier hybrid results.

physics.plasm-ph↗

arXiv2026

Near-Wall Pathways of Anomalous Electron Transport in Hall Thrusters Revealed by 3D PIC Simulations

Cross-field electron transport in Hall thrusters is widely attributed to high-frequency $E\times B$ instabilities, yet its net spatial pathway remains poorly resolved. Here we perform instability-resolving three-dimensional particle-in-cell simulations of a Hall thruster using a boundary-faithful and highly integrated framework. The model incorporates a realistic magnetic-field configuration, self-consistent dielectric wall charging, secondary electron emission, Monte Carlo ionization collisions, a self-consistent continuum neutral-gas evolution model, and an open near-plume outflow treatment. From the strongly oscillatory three-dimensional fields, we extract the net instability-driven transport by time and azimuthal averaging of the correlation term $\langle n_e E_y\rangle$ and the corresponding effective perpendicular mobility. The simulations reveal that anomalous electron transport is not distributed uniformly across the channel cross section. Instead, it self-organizes into persistent near-wall pathways connected to the near-exit region. By comparing conducting-wall, ceramic-wall-with-secondary-emission, and open-outflow closures, we show that the near-wall transport topology is robust, while the boundary treatment mainly redistributes the detailed strength of the pathway and its coupling to the exit and near-plume region. These results demonstrate a previously unresolved spatial organization of instability-driven anomalous transport in Hall thrusters and highlight the unique role of 3D PIC simulations in revealing it.

physics.plasm-ph↗

arXiv2026

Unperturbed-orbit integration and the 3D kinetic dispersion relation of the electron cyclotron drift instability

High-frequency instabilities in crossed-field ($\bm E\times\bm B$) plasmas are widely implicated in anomalous cross-field electron transport in Hall thrusters and related devices. Building on the fully kinetic 3D electrostatic dispersion relations reported by Ducrocq \emph{et al.} and later by Lafleur \emph{et al.}, we provide a concise, self-contained derivation of the key missing step: the magnetized-electron density perturbation $n_{e1}$ obtained from the linearized Vlasov equation via a retarded integration along unperturbed orbits, including finite-Larmor-radius effects and cyclotron harmonics. We collect the required mathematical identities in appendices and clarify the mapping between the Ducrocq Poisson-form and the Lafleur dielectric-form representations, including ion closures (cold-fluid versus kinetic Landau response). We conclude with a brief discussion of the assumptions and possible extensions toward more realistic configurations.

physics.plasm-ph↗

arXiv2025

3D PIC Simulations on Hall Thruster Electron Drift Instability: Influence of Magnetic Field on Electron Transport

Three-dimensional particle-in-cell simulations are employed to investigate electron transport characteristics in Hall thrusters, with particular focus on how magnetic field configuration affects the electron transport due to electron drift instabilities. Comparing analytic and realistic magnetic field models reveals significant differences in electron transport patterns, where radial variations in field strength lead to asymmetric transport enhanced in low-field regions. The derived effective electron mobility shows agreement with direct simulation diagnoses, and the obtained two-dimensional transport profiles provide a foundation for developing more accurate reduced-dimensional models.

physics.plasm-ph↗

arXiv2025

Electrospray Thruster Plume Dynamics: Insights from Precise PP Coulomb Field Simulation

Electrospray thrusters are one important type of micropropulsion systems being developed for next-generation space missions, yet the primary challenge to their operational lifespan is propellant overspray resulting from wide plume angles driven by Coulomb interactions among charged droplets. While existing models often employ truncated Coulomb field approximations, such simplifications compromise accuracy in predicting divergence dynamics. In this study, a particle-particle (PP) simulation method is used to directly calculate the interactions between droplets in an electrospray plume coupled with background electric field effects for simulation. The model integrates Boris pusher for numerical integration, validated through binary collision tests verification. Parametric analysis systematically evaluates six key variables, droplet charge, droplet mass, emission interval, droplet initial velocity, and electric field components, to quantify their impacts on plume divergence. The shape of the simulated electrospray plume and the velocity of the droplets in it are analyzed. Parametric analysis demonstrate that reducing droplet charge, increasing droplet mass, extending emission time intervals, and elevating initial drift velocity collectively reduce plume half-angle. These results quantitatively establish parameter plume relationships, providing direct guidance for thruster optimization.

physics.plasm-ph↗

arXiv2025

The effect of ion rotational flow on Hall thruster azimuthal instability via two dimensional PIC simulations

Previous experimental studies have found that the neutral gas rotational flow in the opposite direction of electron Hall drift can lead to better experimental results comparing to the same direction. In Hall thrusters, the core factor influencing operational states is the electron cross field transport, where the azimuthal instability serves as a key mechanism. The rotational flow of neutral gas may affect instability by altering initial azimuthal velocity of ions, which has not been investigated before. Therefore, to study the effects of ion rotational flow of varying magnitudes and directions on azimuthal instability, simulations are conducted in this work based on two benchmark particle-in-cell (PIC) cases: the azimuthal-axial and the azimuthal-radial. The results indicate that the ion rotational flow velocity can potentially complicate the coupling characteristics of the electron cyclotron drifting instability and the modified two stream instability, particularly when a reverse rotational flow velocity is added. In general, both co-directional and reverse ion rotational flow have been observed to inhibit azimuthal instability, which results in a decrease in axial electron mobility. A 1% addition of the ion rotational flow (compared to the electron drift) would result in a 10% change of the electron mobility due to varied azimuthal instability, and the decrease in electron mobility of the reverse ion rotational flow is greater than that of co-directional. In addition, detailed spectral analyses are carried out to study the relation between ECDI, MTSI, and resonant wave-wave interactions.

physics.plasm-ph↗

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↗