Multi-layer phenomena in petawatt laser-driven acceleration of heavy ions

Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei) is employed to simulate the entire process of Station of Extreme Light(SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum,ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.

Poloidal magnetic field reconstruction by laser-driven ion-beam trace probe in spherical tokamak

The poloidal magnetic field( B_(p)) plays a critical role in plasma equilibrium, confinement and transport of magnetic confinement devices. Multiple diagnostic methods are needed to complement each other to obtain a more accurate B_(p) profile. Recently, the laser-driven ion-beam trace probe(LITP) has been proposed as a promising tool for diagnosing B_(p) and radial electric field( E_(r)) profiles in tokamaks [Yang X Y et al 2014 Rev. Sci. Instrum. 85 11E429]. The spherical tokamak(ST) is a promising compact device with high plasma beta and naturally large elongation. However, when applying LITP to diagnosing B_(p) in STs, the larger B_(p) invalidates the linear reconstruction relationship for conventional tokamaks, necessitating the development of a nonlinear reconstruction principle tailored to STs. This novel approach employs an iterative reconstruction method based on Newton's method to solve the nonlinear equation. Subsequently,a simulation model to reconstruct the B_(p) profile of STs is developed and the experimental setup of LITP is designed for EXL-50, a middle-sized ST. Simulation results of the reconstruction show that the relative errors of B_(p) reconstruction are mostly below 5%. Moreover, even with 5 mm measurement error on beam traces or 1 cm flux surface shape error, the average relative error of reconstruction remains below 15%, initially demonstrating the robustness of LITP in diagnosing B_(p) profiles in STs.

Spatial and spectral measurement of laser-driven protons through radioactivation

The simultaneous measurement of the spatial profile and spectrum of laser-accelerated protons is important for further optimization of the beam qualities and applications.We report a detailed study regarding the underlying physics and regular procedure of such a measurement through the radioactivation of a stack composed of aluminum,copper,and CR-39 plates as well as radiochromic films(RCFs).After being radioactivated,the copper plates are placed on imaging plates(IPs)to detect the positrons emitted by the reaction products through contact imaging.The spectrum and energy-dependent spatial profile of the protons are then obtained from the IPs and confirmed by the measured ones from the RCFs and CR-39 plates.We also discuss the detection range,influence of electrons,radiation safety,and spatial resolution of this measurement.Finally,insights regarding the extension of the current method to online measurements and dynamic proton imaging are also provided.

Calibration of CR-39 solid-state track detectors for study of laser-driven nuclear reactions

It is of particular interest to investigate nuclear fusion reactions generated by high-intensity lasers in plasma environments that are similar to real astrophysical conditions.We have experimentally investigated2H(d,p)3H,one of the most crucial reactions in big bang nucleosynthesis models,at the Shenguang-Ⅱlaser facility.In this work,we present a new calibration of CR-39 solidstate track detectors,which are widely employed as the main diagnostics in this type of fusion reaction experiment.We measure the dependence of the track diameter on the proton energy.It is found that the track diameters of protons with different energies are likely to be identical.We propose that in this case,the energy of the reaction products can be obtained by considering both the diameters and gray levels of these tracks.The present results would be very helpful for analyzing the2 H(d,p)3H reaction products recorded with the same batch of CR-39 solid-state track detectors.

Laser-driven flier impact experiments at the SG-III prototype laser facility

Laser-driven flier impact experiments have been designed and performed at the SG-III prototype laser facility. The continuum phase plate（CPP） technique is used for the 3 ns quadrate laser pulse to produce a relatively uniform irradiated spot of 2 mm. The peak laser intensity is 2.7×10^13W/cm^2 and it accelerates the aluminum flier with a density gradient configuration to a high average speed of 21.3 km/s, as determined by the flight-of-time method with line VISAR. The flier decelerates on impact with a transparent silica window, providing a measure of the flatness of the flier after one hundred microns of flight. The subsequent shock wave acceleration, pursuing, and decay in the silica window are interpreted by hydrodynamic simulation. This method provides a promising method to create unique conditions for the study of a material＇s properties.

γ-Fe Nano-particles from Fe(CO)_5 by CW CO_2 Laser-driven

γ-Fe nano-particles with size of 20-40 nm were produced by SF6-sensitized CW CO2 laser-induced gaseous pyrolysis of Fe(Co) 5, The γ-Fe stabte in reaction zone at above 910℃ was formed.The rapid quenching prevents from the γ-Fe transforming to α-Fe as rapidly cooling from high temperature to room temperature, The characteristics of the particles were examined at room temperature by TEM. electron diffraction and XRD. It was proved that about 70% of γ-Fe phase in the particles was present. In addition. the lattice constant of the γ-Fe was 0.364 nm in place of 0.360 nm

Analysis of the Intrinsic Uncertainties in the Laser-Driven Iron Hugoniot Experiment Based on the Measurement of Velocities

One of the most challenging tasks in the laser-driven Hugoniot experiment is how to increase the reproducibility and precision of the experimental data to meet the stringent requirement in validating equation of state models. In such cases, the contribution of intrinsic uncertainty becomes important and cannot be ignored. A detailed analysis of the intrinsic uncertainty of the aluminum-iron impedance-match experiment based on the measurement of velocities is presented. The influence of mirror-reflection approximation on the shocked pressure of Fe and intrinsic uncertainties from the equation of state uncertainty of standard material are quantified, Furthermore, the comparison of intrinsic uncertainties of four different experimental approaches is presented. It is shown that, compared with other approaches including the most widely used approach which relies on the measurements of the shock velocities of AI and Fe, the approach which relies on the measurement of the particle velocity of Al and the shock velocity of Fe has the smallest intrinsic uncertainty, which would promote such work to significantly improve the diagnostics precision in such an approach.

Topology optimization of on-chip integrated laser-driven particle accelerator

Particle accelerators are indispensable tools in both science and industry.However,the size and cost of conventional RF accelerators limits the utility and scope of this technology.Recent research has shown that a dielectric laser accelerator(DLA)made of dielectric structures and driven at optical frequencies can generate particle beams with energies ranging from MeV to GeV at the tabletop level.To design DLA structures with a high acceleration gradient,we demonstrate topology optimization,which is a method used to optimize the material distribution in a specific area based on given load conditions,constraints,and performance indicators.To demonstrate the effectiveness of this approach,we propose two schemes and design several acceleration structures based on them.The optimization results demonstrate that the proposed method can be applied to structure optimization for on-chip integrated laser accelerators,producing manufacturable structures with significantly improved performance compared with previous size or shape optimization methods.These results provide new physical approaches to explore ultrafast dynamics in matter,with important implications for future laser particle accelerators based on photonic chips.

Laser-Driven Light Sources for Nanometrology Applications

Laser-driven light sources(LDLS)have ultrahigh-brightness and broad wavelength range.They are ideal radiation sources for optical metrology tools for advanced process control in semiconductor manufacturing.LDLS sources,with their advantages of 170 nm to 2100 nm wavelength range,have been widely adopted and are being used in volume manufacturing for spectroscopic ellipsometry(SE),spectroscopic scatterometry(SS),and white light interferometry(WLI)applications.Such applications are used to measure critical dimensions(CD),overlay(OVL),and film thickness.

Detailed characterization of kHz-rate laser-driven fusion at a thin liquid sheet with a neutron detection suite

We present detailed characterization of laser-driven fusion and neutron production(-10^(5)/second) using 8 mJ, 40 fs laser pulses on a thin(<1 μm) D_2O liquid sheet employing a measurement suite. At relativistic intensity(~ 5 × 10^(18)W/cm^(2))and high repetition rate(1 kHz), the system produces deuterium±deuterium(D-D) fusion, allowing for consistent neutron generation. Evidence of D-D fusion neutron production is verified by a measurement suite with three independent detection systems: an EJ-309 organic scintillator with pulse-shape discrimination, a ~3He proportional counter and a set of 36 bubble detectors. Time-of-flight analysis of the scintillator data shows the energy of the produced neutrons to be consistent with 2.45 MeV. Particle-in-cell simulations using the WarpX code support significant neutron production from D-D fusion events in the laser±target interaction region. This high-repetition-rate laser-driven neutron source could provide a low-cost, on-demand test bed for radiation hardening and imaging applications.

miniSCIDOM: a scintillator-based tomograph for volumetric dose reconstruction of single laser-driven proton bunches

Laser plasma accelerators(LPAs)enable the generation of intense and short proton bunches on a micrometre scale,thus offering new experimental capabilities to research fields such as ultra-high dose rate radiobiology or material analysis.Being spectrally broadband,laser-accelerated proton bunches allow for tailored volumetric dose deposition in a sample via single bunches to excite or probe specific sample properties.The rising number of such experiments indicates a need for diagnostics providing spatially resolved characterization of dose distributions with volumes of approximately 1 cm^(3) for single proton bunches to allow for fast online feedback.Here we present the scintillator-based miniSCIDOM detector for online single-bunch tomographic reconstruction of dose distributions in volumes of up to approximately 1 cm^(3).The detector achieves a spatial resolution below 500μm and a sensitivity of 100 mGy.The detector performance is tested at a proton therapy cyclotron and an LPA proton source.The experiments’primary focus is the characterization of the scintillator’s ionization quenching behaviour.

Feasibility study of laser-driven neutron sources for pharmaceutical applications

We predict the production yield of a medical radioisotope^(67)Cu using^(67)Zn(n,p)^(67)Cu and ^(68)Zn(n,pn)^(67)Cu reactions with fast neutrons provided from laser-driven neutron sources.The neutrons were generated by the p+9Be and d+9Be reactions with high-energy ions accelerated by laser–plasma interaction.We evaluated the yield to be(3.3±0.5)×10^(5) atoms for^(67)Cu,corresponding to a radioactivity of 1.0±0.2 Bq,for a Zn foil sample with a single laser shot.Using a simulation with this result,we estimated^(67)Cu production with a high-frequency laser.The result suggests that it is possible to generate^(67)Cu with a radioactivity of 270 MBq using a future laser system with a frequency of 10 Hz and 10,000-s radiation in a hospital.

Synchronous post-acceleration of laser-driven protons in helical coil targets by controlling the current dispersion

Post-acceleration of protons in helical coil targets driven by intense,ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’self-discharge.The acceleration length of protons can exceed a few millimeters,and the acceleration gradient is of the order of GeV/m.How to ensure the synchronization between the accelerating electric field and the protons is a crucial problem for efficient post-acceleration.In this paper,we study how the electric field mismatch induced by current dispersion affects the synchronous acceleration of protons.We propose a scheme using a two-stage helical coil to control the current dispersion.With optimized parameters,the energy gain of protons is increased by four times.Proton energy is expected to reach 45 MeV using a hundreds-of-terawatts laser,or more than 100 MeV using a petawatt laser,by controlling the current dispersion.

Carbon nanotubes as outstanding targets for laser-driven particle acceleration

Under the irradiation of ultraintense laser pulses,targets made of gas,solid,or artificial materials can generate high-energy electrons,ions,and X-rays comparable to conventional accelerators or national light source facilities.Designing and creating high-performance targets are the core problems for laser acceleration.Nanotechnology and nanomaterials can help to build ideal targets that do not exist in nature.This paper reviews the advances in exploiting carbon nanotubes as outstanding targets for laser-driven particle acceleration in memory of Prof.Sishen Xie,the inventor of the fabrication method.We hope that the successful implementation of such targets in enhanced ion acceleration,high-efficiency electron acceleration,and brilliant X-ray generation could attract more interdiscipline interests and promote the development of this field.

Automated control and optimization of laser-driven ion acceleration

The interaction of relativistically intense lasers with opaque targets represents a highly non-linear,multi-dimensional parameter space.This limits the utility of sequential 1D scanning of experimental parameters for the optimization of secondary radiation,although to-date this has been the accepted methodology due to low data acquisition rates.High repetition-rate(HRR)lasers augmented by machine learning present a valuable opportunity for efficient source optimization.Here,an automated,HRR-compatible system produced high-fidelity parameter scans,revealing the influence of laser intensity on target pre-heating and proton generation.A closed-loop Bayesian optimization of maximum proton energy,through control of the laser wavefront and target position,produced proton beams with equivalent maximum energy to manually optimized laser pulses but using only 60%of the laser energy.This demonstration of automated optimization of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.

中国原子能科学研究院核物理基础研究最新进展与展望

核物理是物质科学研究的基础研究前沿和重大应用领域之一,对人类探索物质结构的微观层次、国家的地位与安全发挥了重大作用。中国原子能科学研究院(简称原子能院)核物理基础研究团队依托北京放射性核束装置、HI-13串列加速器、锦屏深地核天体物理加速器等实验设施,开展了核物理基础相关实验与理论研究,在质子晕核破裂机制、不稳定核衰变新模式、核天体反应深地高精度测量、激光驱动核反应等方面取得了多项创新研究成果。本文评述了“十四五”期间原子能院在核物理基础研究方面取得的一些最新进展,并展望了原子能院未来在核物理大科学装置、特色中小型装置、核理论、新型实验技术、学科交叉融合等方面的发展思路。

Generation of medical isotopes ^(47)Sc,^(67)Cu through laser-induced(γ,p)reaction

Short-lived medical isotopes and their generators are typically produced in nuclear reactors and cyclotrons that require extensive facilities.However,considering the environmental concerns and economic costs of these traditional approaches,modern laser technology,which provides extremely strong electric fields within tabletop-sized areas,can serve as a potential supplementary method.Focusing specifically on the(γ,p)generation of the vital medical isotopes^(47)Sc and^(67)Cu,we used both experimental results and PIC-GEANT4 simulations to demonstrate that laser-induced photonuclear reaction is a promising method for isotope production.We developed a model capable of calculating isotope yields under various laser conditions and acceleration mechanisms.The findings revealed that a 200 TW laser can sufficiently produce diagnostic amounts of^(47)Sc and^(67)Cu,while simultaneously providing high specific activity,which is significant in medical applications for improving treatment efficacy,enhancing image resolution,and reducing side effects.

Unique sandwich design of high-efficiency heat-conducting phosphor-in-glass film for high-quality laser-driven white lighting

Multi-color phosphor-in-glass(PiG)film has been considered as a promising color converter in high-quality laser lighting owing to its outstanding merits of phosphor versatility,tunable luminescence,and simple preparation.However,the opto-thermal properties of PiG film are severely affected by the photon reabsorption and backward scattering of phosphor structure and the heat conduction of substrate.Herein,a unique sandwich design of phosphor structure was introduced in the multi-color PiG film for high-quality laser lighting.By elaborately synthesizing the borosilicate glass with low glass transition temperature(T_(g)),similar expansion coefficient,and high refractive index(RI),the sandwiched PiGs were prepared by sintering(~600℃)broadband green and red phosphor glass films on the double sides of sapphire.The green and red PiG films were tightly coated on the sapphire with no delamination and maintained higher luminescence intensity than raw phosphors at high temperatures.By simultaneously coupling photon reabsorption and backward scattering,the sandwiched green PiG film-sapphire-red PiG film(G-S-R PiG)yields a high-quality white light with a high luminous efficacy of 163 lm/W and an excellent color rendering index(CRI)of 85.4 under a laser power of 2.4 W,which are the best comprehensive results yet reported.Benefiting from the ingenious sandwich design with heat-conducting sapphire and thin PiG films,the G-S-R PiG displays low working temperatures(<200℃)under high-power laser excitation.This work reveals the role of sandwiched phosphor structure in photon loss and heat dissipation,which provides a new strategy to design PiG films for high-quality laser lighting.

Laser-induced damage thresholds of ultrathin targets and their constraint on laser contrast in laser-driven ion acceleration experiments

Single-shot laser-induced damage threshold(LIDT)measurements of multi-type free-standing ultrathin foils were performed in a vacuum environment for 800 nm laser pulses with durationsτranging from 50 fs to 200 ps.The results show that the laser damage threshold fluences(DTFs)of the ultrathin foils are significantly lower than those of corresponding bulk materials.Wide band gap dielectric targets such as SiN and formvar have larger DTFs than semiconductive and conductive targets by 1–3 orders of magnitude depending on the pulse duration.The damage mechanisms for different types of targets are studied.Based on the measurement,the constrain of the LIDTs on the laser contrast is discussed.

基于数据驱动的激光切割工艺参数优化方法研究综述

近年来,数据驱动的激光切割工艺参数优化方法受到广泛关注和研究。因此,对该领域的主要研究进展进行梳理。对比基于数据驱动和基于机理模型的激光切割工艺参数优化方法,并明确数据驱动方法的研究对象。从工艺参数和工艺质量两个方面归纳当前数据驱动激光切割工艺参数优化的研究思想及进展,并总结已有研究中采用的数据驱动方法。概述数据驱动激光切割工艺参数优化的具体实现手段。总结比较各种数据驱动参数优化方法的优劣,并展望该领域未来值得进一步研究的方向,包括完善数据获取和数据增强方法,加强模型和算法的评估,并探索更高效智能的实现手段。