Objective.This study aims to investigate the impact of the beam temporal profile on the radical dynamics and inter-track interactions of FLASH radiotherapy, supporting parameter optimization for the equipment development, radio-biological experiments and clinical implementation.Approach.Monte-Carlo simulations based on the independent reaction time method were performed to analyze the dynamics after irradiation, including single-pulse or multi-pulses irradiation, pulse repetition rate, pulse width and dose. The physicochemical experiments were performed to measure the hydrated electron lifetimes for validation. The generation and recombination of hydroxyl radicals and hydrated electrons were recorded under 6 MeV electron irradiation with varying beam temporal profiles. The radial distributions of the radicals were statistically analyzed, and the inter-track interactions were assessed through a mathematical model.Main Results.The spatial distribution and temporal evolution of radicals were significantly affected by the beam temporal profiles. Compared with multi-pulses irradiation, single-pulse irradiation mode with a pulse width less than 1/10 of the radical lifetime, a repetition interval longer than the radical lifetime, and a dose exceeding 1 Gy/pulse can lead to rapid consumption of radicals within the first 30% of their lifetime, hence reduced the residual radical content. Instantaneous high dose rates induced overlapping of radical tracks. When the single-pulse dose exceeded 1 Gy, the overlap probability approached 100%, aligning with the dose threshold for the instantaneous radical combination.Significance.Under a low-duty cycle and high instantaneous dose-rate temporal profile, the radicals were rapidly consumed through track overlap, affecting FLASH effect. The optimized temporal profile can be used to guide the development of equipment and parameter settings in clinical practice to maximize the FLASH effect, such as the laser accelerators and superconducting photocathode guns.

Achieving diffraction-limited focusing of high-power laser pulses to generate ultrahigh intensities is crucial for developing compact laser-driven particle accelerators and exploring strong-field quantum electrodynamics. However, accurately diagnosing and optimizing the focal spots of petawatt (PW) laser pulses remains a significant challenge. In this work, we present an experimental methodology utilizing a twin-focus scheme to precisely characterize the intensity distribution and wavefront of focused PW femtosecond laser pulses, and employ it to elucidate their power-dependent evolution. Furthermore, we optimize the focal spots at full power via our in situ wavefront correction method called “HotLoop,” achieving a Strehl ratio of 0.80 for 1 PW laser pulses. Consequently, the cutoff proton energies in laser proton acceleration experiments are significantly enhanced. The success of this approach underscores the necessity of in situ high-energy wavefront correction for ultrahigh-intensity laser–matter interactions.

A novel pre-pulse system for a 200 TW laser platform has been developed, providing adjustable delay, dispersion control, selectable energy, and coaxial alignment between the main and ablation pulses. The system splits the laser before the final amplifier into two beams: one compressed and the other delayed. These beams are recombined in the final amplifier for simultaneous amplification and compression, generating a configurable pre-pulse. This design mitigates spatiotemporal-coupling challenges, enhancing stability and reproducibility in ablation-assisted laser acceleration experiments. The adjustable parameters simplify ablation-assisted laser-matter interaction studies while offering a versatile platform to investigate ablation’s parametric effects on laser-driven particle acceleration.

The centroid oscillation of an offset laser pulse propagating in a preformed plasma channel is investigated through theoretical analysis and three-dimensional particle-in-cell simulations. For non-relativistic laser pulses, the mode leakage of a finite channel and the temporal walk-off between the fundamental and high order modes of a finite-duration laser induce a decay in the laser centroid oscillation. An analytical model characterizing these decay mechanisms is derived and validated by simulations. For relativistic laser pulses, the slice-based centroid oscillation frequency develops an axial chirp due to relativistic channel modification and photon deceleration. This chirp leads to phase mixing across different axial slices of the pulse, resulting in a rapid damping of the overall centroid oscillation. Understanding this oscillation damping is crucial for mitigating electron beam pointing jitter and maintaining beam quality in high-energy, channel-guided laser wakefield accelerators.

In this paper, we report the detection of the very-high-energy (VHE, 100 GeV < E < 100 TeV) and ultra-high-energy (UHE, E > 100 TeV) γ-ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended γ-ray source was detected with a significance of ∼16 σ by KM2A and ∼17 σ by WCDA, respectively. The angular extension of this γ-ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the γ-ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.

Experimental validation of laser intensity is particularly important for the study of fundamental physics at extremely high intensities. However, reliable diagnosis of the focal spot and peak intensity faces huge challenges. In this work, we demonstrate for the first time that the coherent radiation farfield patterns from laser–foil interactions can serve as an in situ, real-time, and easy-to-implement diagnostic for an ultraintense laser focus. The laser-driven electron sheets, curved by the spatially varying laser field and leaving the targets at nearly the speed of light, produce doughnut-shaped patterns depending on the shapes of the focal spot and the absolute laser intensities. Assisted by particle-in-cell simulations, we can achieve measurements of the intensity and the focal spot, and provide immediate feedback to optimize the focal spots for extremely high intensity.

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7(16.3)×1020 protons on target in (anti)neutrino mode, the analysis finds a 1.9σ exclusion of CP conservation (defined as JCP=0) and a 1.2σ exclusion of the inverted mass ordering. Published by the American Physical Society 2025

Owing to their broad energy spectrum, short pulse width, and high particle numbers, laser-accelerated protons offer significant advantages for rapidly evaluating the durability of materials and understanding microscopic damage mechanisms. In this study, WO3 nanowires were synthesized to assess their resistance when exposed to irradiation from laser-accelerated proton beams. Unlike traditional bulk materials, the surface of WO3 nanowires showed no apparent damage after irradiation; however, advanced characterization techniques reveal a unique surface-to-core amorphization damage phenomenon in nanowires. Comparative experiments with a traditional accelerator (nine orders lower dose rate) confirm that ultrashort pulses are indispensable for triggering this amorphization. Our findings establish WO3 nanowires as promising radiation-resistant candidates and provide insight into how the microscopic damage process varies with the dosage of laser-driven protons.

We demonstrate, for the first time, that laser-accelerated protons can induce shock waves in materials. The ultra-short pulse width of laser-driven protons enables them to deposit energy instantaneously, leading to an intense thermodynamic effect that heats and pressurizes materials violently, thereby generating shock waves. In contrast, laser-accelerated electrons do not possess this capability. Our simulations and experiments reveal that the flow intensity of the proton beam, which includes information on both the proton number and pulse width, directly correlates with shock waves. This finding not only provides a new method for characterizing the high flow intensity of laser-driven protons but also expands their applications in studying extreme states of matter.

Intense terahertz (THz) radiation with multiple cycles is of great interest in many active research fields ranging from particle acceleration to space communication. However, its generation remains a challenge since multi-cycle pulses produced from crystal-based or plasma-based methods are usually characterized by non-relativistic intensity, while plasma-based techniques can deliver much more intense pulses but with few cycles. In this study, we propose a scheme to generate THz radiation with relativistic intensity and multi-cycle duration by shooting a ∼100 TW laser pulse into an underdense plasma with a structured density profile. In this process, laser photons are decelerated by the co-moving refractive index gradient formed by the laser–plasma interaction and slide back to be stored in the self-induced long plasma wake. Particle-in-cell simulations demonstrate the generation of THz radiation with a frequency of 21.4 THz, a pulse length of ∼100 μm (∼7 cycles), a pulse energy up to 18.5 mJ, and an energy conversion efficiency of ∼2%. These pulses may enable access to unexplored regimes of strong THz-material interaction, or open up possibilities for relativistic THz optics.

High-power laser pulses interacting with targets can generate intense electromagnetic pulses (EMPs), which can disrupt physical experimental diagnostics and even damage diagnostic equipment, posing a threat to the reliable operation of experiments. In this study, EMPs resulting from multi-petawatt laser irradiating nitrogen gas jets were systematically analyzed and investigated. The experimental results revealed that the EMP amplitude is positively correlated with the quantity and energy of the electrons captured and accelerated by the plasma channel. These factors are reflected by parameters such as laser energy and nitrogen gas jet pressure. Additionally, we propose several potential sources of EMPs produced by laser-irradiated gas jets and separately analyzed their spatiotemporal distributions. The findings provide insight into the mechanisms of EMP generation and introduce a new approach to achieve controllable EMPs by regulating the laser energy and gas jet pressure.

Plasma can support extremely high-gradient strong electromagnetic fields, making it suitable not only for laser acceleration but also for short-distance manipulation of the charged particle beams, thereby enabling the miniaturization of particle accelerators. Straight capillary discharge plasma lenses have previously garnered widespread attention from researchers for their excellent focusing capabilities. We introduced the theory of using a curved capillary discharge plasma channel to deflect charged particle beams [Phys. Rev. Accel. Beams 24, 031301 (2021)] and, in this paper, present the first experimental demonstration of plasma-based deflection and focusing of laser-accelerated proton beams. Combined with a dipole magnet, the emittance after transmission was measured, revealing that magnetic field nonlinearity and multiple Coulomb scattering tend to increase the proton beam's emittance. This work is of great significance for the development of compact beam transport systems.

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.

This paper provides an overview of the current status of ultrafast and ultra-intense lasers with peak powers exceeding 100 TW and examines the research activities in high-energy-density physics within China. Currently, 10 high-intensity lasers with powers over 100 TW are operational, and about 10 additional lasers are being constructed at various institutes and universities. These facilities operate either independently or are combined with one another, thereby offering substantial support for both Chinese and international research and development efforts in high-energy-density physics.

The ultra-high-energy (UHE) gamma-ray source 1LHAASO J0007+7303u is positionally associated with the composite SNR CTA1 that is located at high Galactic Latitude b ≈ 10.5°. This provides a rare opportunity to spatially resolve the component of the pulsar wind nebula (PWN) and supernova remnant (SNR) at UHE. This paper conducted a dedicated data analysis of 1LHAASO J0007+7303u using the data collected from December 2019 to July 2023. This source is well detected with significances of 21σ and 17σ at 8–100 TeV and >100 TeV, respectively. The corresponding extensions are determined to be 0.23°±0.03° and 0.17°±0.03°. The emission is proposed to originate from the relativistic electrons accelerated within the PWN of PSR J0007+7303. The energy spectrum is well described by a power-law with an exponential cutoff function dN/dE=(42.4± 4.1)(E 20 TeV)^-2.31± 0.11 exp(-E 110± 25 TeV) TeV−1 cm−2 s−1 in the energy range from 8 to 300 TeV, implying a steady-state parent electron spectrum dN_e/dE_e∝ (E_e 100 TeV)^-3.13± 0.16 exp[(-E_e373± 70 TeV)^2] at energies above ≈ 50 TeV. The cutoff energy of the electron spectrum is roughly equal to the expected current maximum energy of particles accelerated at the PWN terminal shock. Combining the X-ray and gamma-ray emission, the current space-averaged magnetic field can be limited to ≈ 4.5 µG. To satisfy the multi-wavelength spectrum and the γ-ray extensions, the transport of relativistic particles within the PWN is likely dominated by the advection process under the free-expansion phase assumption.

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.

BACKGROUND:With the advancement of ultra-short pulse technology and the rapid progress of FLASH radiotherapy, it is clinically desirable and technically possible to utilize the radiation acoustic effect of radiotherapy pulses for noninvasive real-time in vivo dose monitoring. PURPOSE:As a crucial foundation of in vivo dose monitoring using laser-accelerated proton acoustics, this study focuses on measuring, analyzing, and processing the acoustic signals to precisely position the Bragg peak of laser-accelerated monoenergetic proton pulses. MATERIALS AND METHODS:Nanosecond-scale high-energy broadband proton bunches were produced from the interaction of ultra-intense femtosecond laser pulses with thin film targets. After energy selection and focusing through an electromagnetic beamline, approximately 107 quasi-monoenergetic protons per shot were delivered into a water gel or tank. Ultrasonic transducers with different center frequencies detected acoustic signals across various frequency bands. Time and frequency domain analyses were conducted to achieve precise positioning of Bragg peaks. RESULTS:This study successfully achieved measurement of acoustic signals of laser-driven ultra-short monoenergetic protons for the first time. Subsequent analysis and processing of signals enabled the precise positioning of the Bragg peak with a deviation of 45 µm, demonstrating the potential of this method for dose monitoring. CONCLUSIONS:Our findings indicate that this method can be applied to single-shot in vivo dose monitoring in radiotherapy equipment based on laser proton accelerators. It can potentially promote the precise and effective dose delivery of radiotherapy.

The magnetized near detector (ND280) of the T2K long-baseline neutrino oscillation experiment has been recently upgraded aiming to satisfy the requirement of reducing the systematic uncertainty from measuring the neutrino-nucleus interaction cross section, which is the largest systematic uncertainty in the search for leptonic charge-parity symmetry violation. A key component of the upgrade is SuperFGD, a 3D segmented plastic scintillator detector made of approximately 2,000,000 optically-isolated 1cm3 cubes. The SuperFGD cube unit shows promising optical performance, including a high light yield of about 40 photoelectrons (p.e.) per channel, a low cube-to-cube crosstalk rate below 3%, and a sub-nanosecond time resolution of 0.96 ns. By combining tracking and stopping power measurements of final state particles, this novel detector enables precise 3D-imaging of GeV neutrino interactions with reduced systematic uncertainties. A detailed Geant4 based optical simulation of the SuperFGD building block, i.e. a plastic scintillating cube read out by three wavelength shifting fibers, has been developed and validated with the different datasets collected in various beam tests. In this manuscript the description of the optical model as well as the comparison with data are reported.

A search for hidden-charm pentaquark states decaying to a range of ΣcD¯ and Λc+D¯ final states, as well as doubly charmed pentaquark states to ΣcD and Λc+D, is made using samples of proton-proton collision data corresponding to an integrated luminosity of 5.7 fb−1 recorded by the LHCb detector at s=13 TeV. Since no significant signals are found, upper limits are set on the pentaquark yields relative to that of the Λc+ baryon in the Λc+→pK−π+ decay mode. The known pentaquark states are also investigated, and their signal yields are found to be consistent with zero in all cases. © 2024 CERN, for the LHCb Collaboration 2024 CERN

A comprehensive study of the angular distributions in the bottom-baryon decays Λ^0_b→Λ_c^+ h^-(h=π, K), followed by Λ_c^+→Λ h^+ with Λ→pπ^- or Λ_c^+→pK^0_S decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb^-1 collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 Te -0.1em V. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ^0_b →Λ_c^+ h^- decay parameters are measured. The most precise measurements of the decay parameters α, β and γ are obtained for Λ_c^+ decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays.