arXiv subjects

Yuanjie Bi

Publications and source records attributed to Yuanjie Bi.

6 recordsLinked to original sources

arXiv2026

Fast prediction of electron-beam parameters using transfer maps and machine learning in a digital model of a MeV $γγ$ collider

Tuning the electron beam of a MeV-scale $γγ$ collider, first in the design and later in a digital twin of the machine, requires the beam parameters at the interaction point (IP) for many injector states. Start-to-end particle tracking is too slow for this and needs the full particle distribution, which an operating machine cannot measure. We address this problem for the 200-MeV transport line of the collider with two fast predictors. For design, second-order transfer maps from the transport entrance to the IP are applied to every particle. For a digital twin, an extremely-randomized-trees (ExtraTrees) model predicts the IP parameters from the means and rms widths of the beam at the transport entrance. On 89 held-out start-to-end simulations, the map predictor reproduces Elegant tracking for the mean energy, momentum spread, bunch length, transverse rms sizes and normalized emittances with coefficients of determination ($R^2$) of 0.97--1.00 and is ten times faster. The ExtraTrees model reaches an average $R^2$ of 0.88, compared with 0.58 when the injector settings are used as input, and performs similarly with eleven inputs that can be measured or reconstructed. Under a 2% input perturbation, the average $R^2$ of the six parameters other than the mean energy decreases only from 0.917 to 0.895, whereas the mean energy requires an accurate momentum calibration. The two predictors provide the IP-beam evaluation for the collider design and the prediction layer of a future digital twin.

physics.acc-ph↗

arXiv2026

OPALX: A performance-portable framework for particle accelerator simulations

Accurate charged-particle beam simulations require self-consistent collective fields and realistic accelerator models, while their computational cost motivates efficient use of heterogeneous computing systems. We present OPALX, a performance-portable accelerator simulation framework that builds on the beam-dynamics capabilities of OPAL. Its modular architecture uses the Independent Parallel Particle Layer (IPPL) and Kokkos to support distributed-memory execution on multicore CPUs and GPUs from a common codebase. The framework combines relativistic particle tracking with prescribed accelerator fields, particle-in-cell space charge calculations, and spin tracking. We describe the physical and numerical models and their integration into the simulation workflow. The implementation is assessed using disorder-induced heating and frozen-spin test cases, together with comparisons of spin evolution with G4Beamline and beam transport with TraceWin. A three-dimensional space charge benchmark evaluates throughput on CPU and GPU systems, reaching approximately $10^9$ macroparticles per second on a single NVIDIA A100 GPU for this benchmark. These results provide initial verification of the implemented models and demonstrate CPU and GPU execution of self-consistent space charge calculations. OPALX provides a common foundation for extending accelerator models and numerical methods across heterogeneous computing platforms.

physics.acc-ph↗

arXiv2025

Estimation of the Inverse Compton Scattering Background in MeV Gamma-Gamma Collider

The MeV Gamma-Gamma Collider would provide a direct experimental platform for elastic light-by-light scattering ($γγ\to γγ$) and the Breit-Wheeler process with two real photons ($γγ\to e^+e^-$). A Monte Carlo code, the Genie Background Evaluation Tool (GBET), has been developed to fully simulate two successive inverse Compton scatterings in the linear regime, including $e^- + \text{laser} \to e^-+ γ$ and $e^- + γ\rightarrow e^- + γ$. GBET overcomes the inherent information loss in traditional luminosity-spectrum-based chain simulations, preserving full particle-level information and achieving higher physical fidelity. The effectiveness of the code is verified by benchmarking against the simulation results of CAIN. GBET shows that the event rate of background photons generated by the first inverse Compton scattering is $6.24 \times 10^7$/s, with energies below 18 eV; the second inverse Compton scattering generates background electrons at 51.99/s and photons at 0.99/s, both with energies below 11 MeV. In addition, Møller scattering contributes background electrons at 0.56/s with energies around 200 MeV. The count rates of background electrons and positrons originating from the Breit-Wheeler process are 1312.2/s and 1314.3/s, respectively, with energy distributions ranging from 511 to 720 keV.

physics.ins-det↗

arXiv2008

Time-dependent energetic laser-ion acceleration by strong charge separation field

The laser-ion acceleration in the ultra-short and ultra-intense laser-matter interactions attracts more and more interest nowadays. Since electrons gain relativistic energy from laser pulse in a period of several femtoseconds and driven away by the ponderomotive force of laser pulse, a huge charge-separation field pulse is generated. In general cases, the ion acceleration is determined by this charge-separation field. A novel general time-dependent solution for laser-plasma isothermal expansions into a vacuum with different types of the scale length of the density gradient which correspond to different charge separation forms is obtained. The previous solutions are some special cases of our general solution. A series of new solutions have been proposed and may be used to predict new mechanisms of ion acceleration. However, many unaccounted idiographic solutions that may be used to reveal new acceleration mode of ions such as shock wave acceleration, may be deduced from our general solutions.

physics.plasm-ph↗

arXiv2008

Time-dependent energetic proton acceleration and scaling laws in ultra-intense laser pulses interactions with thin foils

A two-phase model, where the plasma expansion is an isothermal one when laser irradiates and a following adiabatic one after laser ends, has been proposed to predict the maximum energy of the proton beams induced in the ultra-intense laser-foil interactions. The hot-electron recirculation in the ultra-intense laser-solid interactions has been accounted in and described by the time-dependent hot-electron density continuously in this model. The dilution effect of electron density as electrons recirculate and spread laterally has been considered. With our model, the scaling laws of maximum ion energy have been achieved and the dependence of the scaling coefficients on laser intensity, pulse duration and target thickness have been obtained. Some interesting results have been predicted: the adiabatic expansion is an important process of the ion acceleration and cannot be neglected; the whole acceleration time is about 10-20 times of laser pulse duration; the larger the laser intensity, the more sensitive the maximum ion energy to the change of focus radius, and so on.

physics.plasm-ph↗

arXiv2008

Two-dimension plasma expansions with anisotropic pressure

A two-dimension self-similar solution is proposed for a plasma expansion with anisotropic pressure. With the solution, it depends on the relationship between the ratio of the longitudinal and the transverse temperature of the plasma, $κ^2$ and the electron-ion mass ratio, $μ$, that the plasma front is composed by a part of hyperbolic (or a plane) and a small pointed projection at the center or a part of an ellipse. Zhang and coworkers's experiments (PRL, 99, 167602 (2007))support our results for $κ^2\in(τ,1]$. For $κ^2\leqτ$, there is an anomalous high-energy plasma emission at the angle of near $90^{\text{o}}$ due to longitudinal Coulomb explosion.

physics.plasm-ph↗