超短脉冲激光驱动束靶中子源产生及应用研究进展(特邀)

Research Progress of Beam-target Neutron Source and Applications Driven by Ultra-short Pulse Lasers(Invited)

短脉冲强激光驱动中子源具有微焦点、短脉宽、高注量率的特点,在创新研究和应用方面显示出独特潜力,得到了广泛关注。简要回顾了激光中子源的发展历史和现状,特别是超短脉冲激光驱动束靶中子源的最新研究进展。首先,介绍了激光中子源束流品质提升方面的研究工作。其中,产额提升是激光中子源研究以及实现相关应用的首要问题。当前的研究主要通过反应通道选择、离子加速优化等技术途径来实现激光中子源产额的提升。除了产额提升之外,人们还格外关注激光中子源的方向性提升,提出了削裂反应、逆反应动力学等新方案。其次,介绍了激光中子源参数的诊断方法与现状。通过对激光中子源能谱、角分布、脉宽和源尺寸等参数的精密表征,人们对激光中子源的特性有了更全面的了解,这有力支撑了其应用。最后,回顾了激光中子源目前已开展的应用演示实验。激光中子源适用于部分与传统中子源类似的应用场景,同时基于激光中子源超短脉冲、超高通量等新特性有望拓展出新的独特应用。

Significance With the rapid advancement of laser technology,the laser intensity reaches approximately 10^(22) W/cm^(2),and charged particles can be accelerated to hundreds of MeV or even several GeV.These energetic particles can trigger nuclear reactions and generate neutrons.Compared with traditional neutron sources,such as reactors,spallation neutrons,and radioactive neutron sources,laser-driven neutron sources(LDNS)have interesting features,such as short duration,which is approximately tens or hundreds of ps,and ultrahigh flux,which is 10^(18)‒10^(21)/(cm^(2)·s).Moreover,the neutron energy is easy to adjust by manipulating the laser accelerating process.Therefore,studies on LDNS have attracted considerable interest and have shown unique potential for innovative investigations and applications in the past two decades,particularly after the significant progress achieved by Roth et al.in 2013.LDNS is expected to be a powerful alternative to traditional neutron sources and may play an essential role in specific applications,such as the fast neutron resonance radiography and rapid neutron capture.This study briefly reviews the historical development and status of laser-driven neutron sources.Significant attention is given to the recent progress in beam-target neutron sources.Progress First,this study reviews the technical approaches to increase the yield of laser-driven neutron sources,which mainly include nuclear reaction channels and ion acceleration efficiency.Compared with deuterium-deuterium and proton-lithium reactions,deuterium-lithium nuclear reactions result in larger nuclear reaction cross-sections and,thus,have received special attention in this field.After determining the nuclear reaction channel,the improvement of the neutron yield mainly depends on the optimization of the deuterium acceleration efficiency.Various new schemes for eliminating the contamination layer within the target normal sheath acceleration(TNSA)acceleration process,such as target heating,laser cleaning,and heavy water spraying,have been established.The use of advanced acceleration mechanisms,such as break-out afterburner and collisionless shock acceleration,has also been proposed to increase the cut-off energy and charge of deuterium ions,and the neutron yield eventually reaches as high as 10^(10)/sr(Fig.2).In addition to yield,neutron directionality is also a critical parameter that influences neutron application.New schemes such as the stripping of D-Li reaction and reverse kinematic effects of heavy ions have also been proposed to generate directional neutron sources.By applying the inverse kinematic effect,the proof-of-principle experiments conducted thus far have achieved a neutron angular distribution with a significant forward impulse and full width at half maximum(FWHM)of 40°(Fig.6),which is nearly half lower than those of the D-D and D-Li reactions.In addition to optimizing the quality of the laser neutron source,the accurate characterization of laser neutron source parameters is also an integral process of the neutron application.This study introduces the experimental diagnostic methods of laser neutron source yield,angular distribution,energy spectrum,and source size.The analysis method of the pulse width is also explained.The wide range of energy spectrum and ultrashort pulse-width characteristics are suitable for fast-neutron resonance analysis applications based on the time-of-flight method.Finally,this study reviews the application status of laser neutron sources.Current applications mainly focus on traditional application scenarios,such as fast neutron photography,fast neutron moderation,and thermal neutron resonance absorption.However,the high flux and short pulse of laser-driven neutron sources also make them valuable in fast-neutron resonance imaging and rapid neutron capture.Conclusions and Prospects Research on laser neutron sources has aroused significant interest and demonstrates unique potential in terms of innovative research and application prospects.However,because of the limited yield,most of the current application experiments mainly focus on the application scenarios of the traditional neutron source,in which the LDNS does not have unique advantages in terms of neutron fluence.However,with the development of high repetition rate and high average-power laser technology,miniaturized laser neutron sources can gain advantages in terms of economy and flexibility to cope with more complex applications.In addition,because of the nonsubstitutable unique advantages of the short pulse width and high flux rate of LDNS,it also has potentials for new applications,such as fast neutron capture,diagnosis of the state of warm dense matter,and fusion material research.Finally,lasers have advantages in generating various particle sources,which can flexibly satisfy the needs of multiple application scenarios.For example,lasers can simultaneously generate multiple radiation sources,such as electrons,ions,γ-rays,and neutrons.The unique effects of combining radiation fields can lead to new applications,such as radiography implemented with thermal neutrons and X-rays.Overall,laser-driven neutron sources are expected to be widely used in scientific and industrial fields and can expand more distinctive application scenarios by adopting more stable and efficient neutron generation methods and more accurate neutron-source parameter characterization techniques.