Energy Spread Research Articles

Assessing grain boundary variability through phase field crystal simulations

Characterization of grain boundaries (GBs) typically focuses exclusively on ideal minimum-energy structures, thus offering a limited perspective on the potential structural diversity and related property variations of GBs. In this study, phase field crystal (PFC) simulations are employed to systematically explore alternative GB states through γ-surface sampling. A large number of tilt and twist GBs are examined in both fcc and bcc bicrystal structures. It is demonstrated that identifying variants in GB structure necessitates considering a set of microscopic degrees of freedom (DOF), comprising the components of relative crystal translation, in addition to the GB's five macroscopic DOF. Taking GB energy and excess volume as examples of key GB properties, a significant spread in GB energy is revealed, stemming from variations in the microscopic DOF, while maintaining constant macroscopic DOF. In addition, the significant variations found in GB excess volume and energy when GB variants are considered challenge the common assumption of a strong correlation between them. Taken together, the findings underscore the importance of recognizing a range of GB structures and properties for each macroscopic GB configuration, rather than relying on singular ideal minimum-energy GB structures, as is usually done. Published by the American Physical Society 2024

Research and application of chromatic effect in laser-driven proton therapy

Based on the rapid development of ultra high-power laser technology and due to the urgent need for miniaturized particle radiotherapy accelerator construction, compact laser accelerators have been studied as a research focus. The collection of the beam with large divergence angle and the selection of beam energy spread from initial generated beam are core issues in the design of laser accelerator. Chromatic effect is an effective method of energy selection while collecting beam. However, it is found that the nonlinear effect introduced by the actual edge field of a strong magnetic field and the special beam distribution produced by laser acceleration directly affect the energy selection. Based on the design of CLAPA-II, we analyze chromatic effect of energy selection by combining the 3-D strong magnetic field of particle collecting solenoid and the initial particle library of laser acceleration generated by PIC. We further propose a more compact laser-driven proton therapy design using the chromatic effect and energy reducer. And we research a broad-spectrum treatment planning system corresponding to it. It can effectively reduce proportion of low energy particles and complete energy selection after considering nonlinear effect of high 3-D magnetic field and special initial distribution. This can be applied in the design of gantry, which can be lighter than the traditional gantry. And for head, neck, and lung tumor models, dose delivery can be completed in 10 min and 20 min.

Synchronous decomposition match-reassigning transform and its application in planetary gearbox fault diagnosis

Abstract Under time-varying operating conditions, the instantaneous frequency (IF) of the vibration signal of the planetary gearbox exhibits non-stationary time-varying closely spaced characteristics as well as non-proportional and non-synchronous characteristics, making it difficult for traditional time-frequency analysis (TFA) methods to accurately identify its fault features and obtain accurate time-frequency representations (TFR). To address this challenge, this paper proposes a TFA method based on Synchronous Decomposition Match-Reassigning Transform (SDMRT). Firstly, the successive variational mode decomposition (SVMD) is used to adaptively separate non-synchronous frequency components in the original vibration signal. Then, the chirp rate (CR) describing the signal harmonic structure is used to synchronously match each frequency component, obtaining the TFR corresponding to each component. Next, all TFRs are merged to obtain a complete TFA result. Finally, Finally, the energy spread is re-aggregated to the ridge of the IF using the reassignment principle, resulting in a new frequency estimation operator called the Synchronous Decomposition Match-Reassigning Operator (SDMRO). SDMRT can adaptively separate non-proportional and non-synchronous IFs and achieve precise matching of time-varying closely spaced IFs, thereby completing the TFR of the vibration signal generated by the planetary gearbox. By analyzing simulated signals and measured vibration signals from planetary gearboxes, the method proposed in this paper is significantly superior to other TFA methods, thereby validating the effectiveness and superiority of SDMRT.

Simulation of laser plasma wakefield acceleration with external injection based on Bayesian optimization

Abstract In laser wakefield acceleration (LWFA), injecting an external electron beam at certain energy is a promising approach to achieving high-quality electron beam with low energy spread and low emittance. In this paper, the process of laser wakefield acceleration with an external injection at 10 pC has been studied in simulations. A Bayesian optimization method is used to optimize the key laser and plasma parameters, so that the electron beam is accelerated to the expected energy with a small emittance and energy spread growth. The effect of rising edge of the plasma on the transverse properties of the electron beam is simulated and optimized in order to ensure that the external electron beam is injected into the plasma without significant emittance growth. Finally, a high-quality electron beam with an energy of 1.5 GeV, the normalized transverse emittance of 0.5 mm·mrad and the relative energy spread of 0.5% at 10 pC is obtained.

GEANT4 simulation for controlling and focusing of laser-accelerated proton beam for particle therapy using pulsed power solenoids

Laser-accelerated proton beams (LAP) have inspired innovative applications that can leverage proton bunch properties distinct from those of conventionally accelerated proton beams. A new multifunctional LAP beamline has been proposed, utilizing the GEANT4 toolkit, and the solenoids have been simulated using high-precision components.We present the design of the initial segment of the transport beamline and energy selection system for the effective transport of a radiation pressure acceleration source with a high energy spread. This study examines the effects of solenoids on proton beam quality, specifically focusing on profiles, FWHM, and transmission efficiency. The results obtained using our developed GEANT4 toolkit validate the analytical formulas and findings from the DYNAMION code regarding emittance and proton profiles. Additionally, the presented GEANT4 LAP beamline is capable of calculating the flux of secondary particles, such as neutrons and photons. It was observed that careful attention to the precise structure of the solenoids is critical.

Reduction of arrival time jitter or energy spread with arclike variable bunch compressors

Synchronizing free-electron laser pulses for time-resolved experiments is necessary as an unsynchronized system reduces the effective repetition rate of the experiment. Additionally, free-electron laser longitudinal coherence and spectral brightness are limited by electron beam energy spread. In this paper, a variable bunch compressor design and compression schemes were developed to: reduce klystron-induced arrival time jitter by 85% while preserving peak current and transverse emittance and to minimize electron beam correlated energy spread for potential self-seeding or HB-SASE modes. Published by the American Physical Society 2024

Generation of quasi-monoenergetic proton beams from near-critical density plasmas irradiated by picosecond laser pulses

Laser-driven high-quality ion beams hold immense potential for applications in diverse fields such as tumor therapy, fast ignition, and so on. However, current experimental ion beams are often constrained by either a large energy spread or relatively low energy. In this paper, we proposed a novel scheme for generating quasi-monoenergetic proton beams by irradiating near-critical-density plasmas, which have a density gradient with a picosecond laser pulse. This approach leverages two key aspects: first, the sustained interaction between the laser pulse and the plasma enhances the duration of magnetic vortex acceleration, thereby promoting extended ion acceleration. Second, the utilization of a multi-species target facilitates the formation of a dual-peaked electric field, which leads to the accumulation of protons in the negative gradient of the accelerating phase, resulting in a quasi-monoenergetic proton beam. The two-dimensional particle-in-cell simulation reveals that by employing a laser intensity of 1.37 × 1020 W/cm2 with a pulse duration of 0.5 ps, we can achieve a carbon ion beam with an energy of 50 MeV/u, and a quasi-monoenergetic proton beam exhibiting a cutoff energy of 160 MeV/u, a peak energy of 75 MeV/u, an energy spread of 3.1 %, and an angle divergence of ∼ 3.2°. Furthermore, the quasi-monoenergetic property is corroborated in three-dimensional simulation results, underscoring the robustness and effectiveness of our proposed scheme.

Beamline analysis for a laser-driven proton therapy accelerator using superconducting bends

Peking University is implementing new superconducting magnets in a laser-driven proton accelerator, resulting in a lighter and more compact proton therapy facility. To efficiently transport protons with a wide energy spread, we propose a double-bend achromat design that rotates particles by 90 degrees and suppresses dispersion. Two focusing options are considered: integrating quadrupole magnets within the dipole magnets to create a hybrid field, or separating the quadrupole for independent focusing and bending. We first delve into the related lattice design, followed by an in-depth analysis of coil selection for each option. The magnetic field of the coil is indeed calculated using a combination of the Biot–Savart law and the Multi-Level Fast Multipole Method (MLFMM). We assess field quality and feasibility using TraceWin and zgoubi simulations in fieldmap, accounting for dipole-induced dispersion and quadrupole-induced chromatic effect. Through the analysis of superconducting magnets and beam dynamics, and by considering the transmission requirements of laser-plasma-accelerated protons, we have indeed developed a beam transport scheme. This scheme is anticipated to integrate laser-accelerated protons into a compact proton therapy facility, and it will eventually be implemented.

Crowd Density Estimation via Global Crowd Collectiveness Metric

Drone-captured crowd videos have become increasingly prevalent in various applications in recent years, including crowd density estimation via measuring crowd collectiveness. Traditional methods often measure local differences in motion directions among individuals and scarcely handle the challenge brought by the changing illumination of scenarios. They are limited in their generalization. The crowd density estimation needs both macroscopic and microscopic descriptions of collective motion. In this study, we introduce a Global Measuring Crowd Collectiveness (GMCC) metric that incorporates intra-crowd and inter-crowd collectiveness to assess the collective crowd motion. An energy spread process is introduced to explore the related crucial factors. This process measures the intra-crowd collectiveness of individuals within a crowded cluster by incorporating the collectiveness of motion direction and the velocity magnitude derived from the optical flow field. The global metric is adopted to keep the illumination-invariance of optical flow for intra-crowd motion. Then, we measure the motion consistency among various clusters to generate inter-crowd collectiveness, which constitutes the GMCC metric together with intra-collectiveness. Finally, the proposed energy spread process of GMCC is used to merge the inter-crowd collectiveness to estimate the global distribution of dense crowds. Experimental results validate that GMCC significantly improves the performance and efficiency of measuring crowd collectiveness and crowd density estimation on various crowd datasets, demonstrating a wide range of applications for real-time monitoring in public crowd management.

Experimental Demonstration of an Emittance-Preserving Beam Energy Dechirper Using a Hollow Channel Plasma.

Plasma-based acceleration has emerged as a highly promising candidate for future colliders and compact x-ray free electron lasers owing to its capability to efficiently accelerate electron and positron beams with high brightness over short distances. However, a major obstacle to its application in free electron lasers and colliders is the imposition of a substantial energy chirp on the output beams, resulting from the longitudinally dependent acceleration field. This Letter presents the first experimental demonstration of a beam energy dechirper using a hollow plasma channel. This novel approach simultaneously enables the mitigation of energy chirp and preservation of beam emittance. Experimental results demonstrate a substantial reduction in energy spread by nearly 1 order of magnitude (from 0.93% to 0.11% FWHM), while maintaining a negligible increase in emittance. Simulation suggests that the corrected energy spread may have been reduced to ∼10 keV (0.025%), thereby meeting the stringent requirement of colliders or x-ray free electron lasers.

The comparative analysis of energy dissipation behaviour of woven and UD para-aramid fabrics

This research examines how impact energy spreads across para-aramid fabrics, comparing woven and unidirectional types, using 2-D Thin Plate Spline analysis. The experiment involved dropping a weighted hemisphere onto fabric samples and measuring their deformation across different layer counts. To assess how yarn orientation affects energy dispersion, panels with 0º/90º and 0º/90º/±45º configurations were tested. By analysing the fabric's shape changes under impact, the study revealed patterns of energy propagation. Calculations of bending energy and expansion factors provided insights into this behaviour. The findings indicate that unidirectional fabrics outperform woven structures in distributing impact energy across their surface. Moreover, incorporating ±45º fibre reinforcements in both fabric types enhances energy dispersion and mitigates impact effects.

Gravitational-wave and Gravitational-wave Memory Signatures of Core-collapse Supernovae

In this paper, we calculate the energy, signal-to-noise ratio (SNR), detection range, and angular anisotropy of the matter, matter memory, and neutrino memory gravitational-wave (GW) signatures of 21 three-dimensional initially nonrotating core-collapse supernova (CCSN) models carried to late times. We find that inferred energy, SNR, and detection range are angle-dependent quantities, and that the spread of possible energy, signal to noise, and detection ranges across all viewing angles generally increases with progenitor mass. When examining the low-frequency matter memory and neutrino memory components of the signal, we find that the neutrino memory is the most detectable component of a CCSN GW signal, and that DECIGO is best equipped to detect both matter memory and neutrino memory. Moreover, we find that the polarization angle between the h + and h × strains serves as a unique identifier of matter and neutrino memory. Finally, we develop a Galactic density- and stellar mass-weighted formalism to calculate the rate at which we can expect to detect CCSN GW signals with the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). When considering only the matter component of the signal, the aLIGO detection rate is around 65% of the total Galactic supernova rate, but increases to 90% when incorporating the neutrino memory component. We find that all future detectors (Einstein Telescope, Cosmic Explorer, DECIGO) will be able to detect CCSN GW signals from the entire Galaxy, and for the higher-mass progenitors even into the Local Group of galaxies.

Coherent high-harmonic generation with laser-plasma beams

Active energy compression scheme is presently being investigated for future laser-plasma accelerators. This method enables generating laser-plasma accelerator electron beams with a small, ∼10−5, relative slice energy spread. When modulated by a laser pulse, such beams can produce coherent radiation at very high, ∼100th harmonics of the modulation laser wavelength, which are hard to access by conventional techniques. The scheme has a potential of providing additional capabilities for future plasma-based facilities by generating stable, tunable, narrow-band radiation. Published by the American Physical Society 2024

Subdiffusion of heavy quarks in hot QCD matter by the fractional Langevin equation

The subdiffusion phenomena are studied for heavy quarks dynamics in the hot QCD matter. Our approach aims to provide a more realistic description of heavy quark dynamics through detailed theoretical analyses and numerical simulations, utilizing the fractional Langevin equation framework with the Caputo fractional derivative. I present numerical schemes for the fractional Langevin equation for subdiffusion and calculate the time evolution mean squared displacement and mean squared momentum of the heavy quarks. My results indicate that the mean squared displacements of the heavy quarks for the subdiffusion process deviate from a linear relationship with time. Further, I calculate the normalized momentum correlation function, kinetic energy, and momentum spread. Finally, I show the effect of subdiffusion on experimental observables, the nuclear modification factor. Published by the American Physical Society 2024

High-resolution anionic velocity map imaging apparatus for dissociative electron attachment dynamics study.

Dissociative electron attachment (DEA) of a molecular target XY, e- + XY → XY- → X + Y-, is an important process in plasma, atmosphere, interstellar space, and ionizing radiation. DEA dynamics, i.e., the formation and fragmentation of an electron-molecule resonant complex, can be unveiled by measuring the product Y- with the velocity map imaging (VMI) technique. However, it is still challenging to achieve a high-resolution VMI measurement. Recently, we developed a high-resolution DEA apparatus that combined the VMI technique with a trochoidal electron monochromator. The energy spread (around 500meV) of thermally emitted incident electrons can be reduced remarkably, but the monochromatized electrons become diffuse again in energy when being pulsed with an electric pulse applied on the grid electrode because the electron beam must be pulsed in the VMI measurement. Now this long-standing technical contradiction is settled by introducing a parallel resistance-capacitor circuit to the electrode of an electron gun. A delay-line detector is used for the VMI measurement, which allows the three-dimensional velocity or momentum images of multiple anionic yields to be recorded efficiently. Our high-resolution VMI apparatus works at a pulse frequency of 5kHz and an energy spread of about 120-150meV, and its credible performances are exhibited by the measurements of the DEA processes of CO(a3Π) and NO2.

Highly polarized energetic electrons via intense laser-irradiated tailored targets

A method for the generation of ultrarelativistic electron beams with high spin polarization is put forward, where a tightly focused linearly polarized ultraintense laser pulse interacts with a nonprepolarized transverse-size-tailored solid target. The radiative spin polarization and angular separation is facilitated by the standing wave formed via the incident and reflected laser pulses at the overdense plasma surface. Strong electron heating caused by transverse instability enhances photon emission in the density spikes injected into the standing wave near the surface. Two groups of electrons with opposite transverse polarization emerge, antialigned to the magnetic field, which are angularly separated in the standing wave due to the phase-matched oscillation of the magnetic field and the vector potential. The polarized electrons propelled into the plasma slab are focused at the exit by the self-generated quasistatic fields. Our particle-in-cell simulations demonstrate the feasibility of highly polarized electrons with a single 10 PW laser beam, e.g., with polarization of 60% and charge of 8 pC selected at energy of 200 MeV within 15 mrad angle and 10% energy spread. Published by the American Physical Society 2024

An influence of electronic structure theory method, thermodynamic and implicit solvation corrections on the organic carbonates conformational and binding energies.

An impact of an electronic structure or force field method, gas-phase thermodynamic correction, and continuum solvation model on organic carbonate clusters (S)n conformational and binding energies is explored. None of the tested force field (GFN-FF, GAFF, MMFF94) and standard semiempirical methods (PM3, AM1, RM1, PM6, PM6-D3, PM6-D3H4, PM7) can reproduce reference RI-SCS-MP2 conformational energies. Tight-binding GFNn-xTB methods provide more realistic conformational energies which are accurate enough to discard the least stable conformers. The effect of thermodynamic correction is moderate and can be ignored if the gas phase conformational stability ranking is a goal. The influence of continuum solvation is stronger, especially if reinforced with the Gibbs free energy thermodynamic correction, and results in the reduced spread of conformational energies. The cluster formation binding energies strongly depend on a particular approach to vibrational thermochemistry with the difference between traditional harmonic and modified scaled rigid - harmonic oscillator approximations reaching 10 kcal mol-1.

Theory of particle beams transport over curved plasma-discharge capillaries

We present a new approach that demonstrates the deflection and guiding of relativistic electron beams over curved paths by means of the magnetic field generated in a plasma-discharge capillary. The active bending plasma (ABP) represents a promising solution that has been recently demonstrated with a proof of principle experiment. An ABP device consists of a curved capillary where large discharges (of the order of kA) are propagated in a plasma channel. Unlike conventional bending magnets, in which the field is constant over the bending plane, in the ABP, the azimuthal magnetic field generated by the discharge grows with the distance from the capillary axis. This features makes the device less affected by the beam chromatic dispersion so that it can be used to efficiently guide particle beams with non-negligible energy spreads. The study we present in the following aims to provide a theoretical basis of the main ABP features by presenting an analytical description of a single-particle motion and rms beam dynamics. The retrieved relationships are verified by means of numerical simulations and provide the theoretical matrix formalism needed to completely characterize such a new transport device. Published by the American Physical Society 2024

Simulation Study on Attosecond Inverse Compton Scattering Source from Laser Wakefield Acceleration with Near-Threshold Ionization Injection

We present the generation of attosecond gamma rays via inverse Compton scattering within the framework of laser wakefield acceleration through 2D Particle-In-Cell simulations. Utilizing the near-threshold ionization injection mechanism, an attosecond micro-bunched electron beam characterized by a comb-like current density profile can be achieved with a linearly polarized laser at an intensity of a0 = 1.5. The micro-bunched beam provides a beam energy of approximately 300 MeV and achieves a minimum relative energy spread of about 1.64% after undergoing 2 mm of acceleration. In the inverse Compton scattering scheme, these attosecond electron micro-bunches interact with the reflected driving laser pulse, resulting in the attosecond gamma-ray radiation exhibiting similar structures. Individual spatial-separated gamma-ray pulses exhibit a length of approximately 260–300 as, with a critical energy of 2.0 ± 0.2 MeV. The separated attosecond gamma-ray source owns a peak brilliance of ~1022 photons s−1 mm−2 mrad−2 0.1% BW. This brilliance is competitive in a laboratory for multi-MeV γ-ray sources with a laser intensity of I = 5 × 1018 W/cm2. Such attosecond gamma-ray radiation offers promising applications requiring ultrashort X-ray/gamma ray sources.

Beam energy spectra in the presence of cell-to-cell phase advance errors

The parameters of the accelerating structures of linear accelerators have a strong influence on the beam parameters such as the mean energy and the energy spread. One of the most common types the accelerating structures is based on disk loaded waveguides. Imperfections in such structure parameters may be critical for subsequent beam dynamics. We analytically study the influence of the errors of the cell-to-cell phase advance on the beam energy spread and the mean energy on the example of the constant gradient structure. Derived expressions were applied to the case of a large number of accelerating structures, which is relevant for GeV linacs, to obtain accelerated beam parameters in terms of the probabilistic analysis for several values of the injected beam duration.