Laser-plasma acceleration of quasi-monoenergetic protons from microstructured targets

Particle acceleration based on high intensity laser systems (a process known as laser-plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser-plasma acceleration--the very broad, exponential energy spectrum of the emitted particles--has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser-plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.     

Research progress on high intensity hadron accelerator in China

High intensity hadron beam has wide-range important applications.In recent years,several projects with intense-beam hadron accelerator are under design,development or construction in China.We are facing a lot of challenges in beam physics and key technology of the accelerators.Beam loss and beam emittance must be minimized for such a high intensity accelerator.Space charge effect and nonlinear dynamics should be taken into account in beam physics and accelerator design.In this paper we will present the recent research progress in China on beam dynamics,new technology development and beam experiments for intense beam hadron accelerators,including linear accelerator,synchrotron and cyclotron.     

超短超强激光与等离子体相互作用中质子发射一些研究进展

超短超强激光与等离子体相互作用中得到的高能质子在质子成像、粒子加速、诊断超短超强激光与等离子体相互作用的物理过程、“快点火”和治疗癌症等方面有一定的应用。使得对超短超强激光与等离子体相互作用得到的高能质子的研究成为目前的研究热点。文章综述了产生质子的两种主要加速机制以及在不同实验条件下超短超强激光与等离子体相互作用过程中得到质子的能量、角分布、产额以及相关的原理。     

The multi-disciplinary role of 'pion factories'

The multi-disciplinary role of intermediate energy proton accelerators in pure and applied nuclear physics is discussed with particular reference to the experimental programmes at LAMPF (Los Alamos Meson Physics Facility) and SIN (Swiss Institute for Nuclear Research, Zurich).     

核技术应用现状及发展趋势

 聚焦于核技术应用领域中射线产生装置、放射性同位素技术、核探测技术,概述了电子加速器、质子/重离子加速器、中子发生器等重要射线产生装置与放射性同位素制备、放射性药物、放射源以及核探测技术等的国内外研究现状,分析了国内射线装置与放射性同位素技术的发展趋势及前景。     

A laser-plasma accelerator producing monoenergetic electron beams

Particle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeV m(-1), owing to material breakdown at the walls of the structure. Thus, the production of energetic particle beams currently requires large-scale accelerators and expensive infrastructures. Laser-plasma accelerators have been proposed as a next generation of compact accelerators because of the huge electric fields they can sustain (>100 GeV m(-1)). However, it has been difficult to use them efficiently for applications because they have produced poor-quality particle beams with large energy spreads, owing to a randomization of electrons in phase space. Here we demonstrate that this randomization can be suppressed and that the quality of the electron beams can be dramatically enhanced. Within a length of 3 mm, the laser drives a plasma bubble that traps and accelerates plasma electrons. The resulting electron beam is extremely collimated and quasi-monoenergetic, with a high charge of 0.5 nC at 170 MeV.     

Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses

In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread <10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.     

基于SiC材料的激光加速质子束辐照特性研究

通过辐照核能材料SiC, 表征激光加速质子束连续宽能谱、短脉冲和高瞬态流强的特点。将SiC样品放置在距离靶体4 cm处, 连续进行300发满足指数能谱分布的能量为1~4.5 MeV的激光加速宽能谱连续质子束辐照。表面和截面拉曼光谱显示辐照后的SiC散射峰强度减小, 且拉曼光谱截面测量的整体趋势可以与SRIM模拟的能谱加权后的深度能损分布对应, 从而通过实验对能量连续分布的激光加速质子束进行表征。此外, 实验结果显示, 激光加速质子束的短脉冲特性可在SiC表面产生相当高的瞬时束流密度。这种快速的宽能谱辐照为模拟反应堆中子辐照提供了可能性。     

反质子的探索

作者用高能加速器实验和宇宙线实验总结出来的规律计算了宇宙空间中次级反质子的流强与质子流强之比。把计算结果与实验数据比较,发现1.在E>1.3GeV能区,原初反物质不可能存在;2.在1.1GeV<E<1.3GeV能区,宇宙空间中很可能存在反物质。     

Energy doubling of 42 GeV electrons in a metre-scale plasma wakefield accelerator

The energy frontier of particle physics is several trillion electron volts, but colliders capable of reaching this regime (such as the Large Hadron Collider and the International Linear Collider) are costly and time-consuming to build; it is therefore important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators, a drive beam (either laser or particle) produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultrahigh accelerating fields over a substantial length to achieve a significant energy gain. Here we show that an energy gain of more than 42 GeV is achieved in a plasma wakefield accelerator of 85 cm length, driven by a 42 GeV electron beam at the Stanford Linear Accelerator Center (SLAC). The results are in excellent agreement with the predictions of three-dimensional particle-in-cell simulations. Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of approximately 52 GV m(-1). This effectively doubles their energy, producing the energy gain of the 3-km-long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch. This is an important step towards demonstrating the viability of plasma accelerators for high-energy physics applications.     

中高温质子导体的结构及性能研究进展

中高温钙钛矿型质子导体具有较好的性能与应用前景.介绍了钙钛矿型质子导体的结构、性质和导电机理,概述了目前研究较多的几类质子导体,比较了各类质子导体的化学稳定性、强度及导电性能,叙述了质子导体的各种制备方法及表征手段,分析了不同组成对钙钛矿型氧化物质子导电性及稳定性的影响,说明提高材料性能的方法.阐述了国内外关于质子导体的最新研究成果,指出目前研究的重点为改进传统质子导体,开发新型质子导体,改进质子导体的制备工艺,以拓宽材料的工作温度,提高材料化学稳定性及电导率.     

加速器输出粒子的能量和轨道异常现象的实验分析——兼答陈绍光教授

作者完全运用狭义相对论分析,合肥、台湾、汉堡加速器输出的电子能量,其实没有狭义相对论专家计算的这么高,在恒定磁场中弯转的轨道半径也不是他们计算的值。     

狭叶四照花扦插繁殖试验

采用不同的枝条年龄和穗条类型、扦插基质、扦插时期、生根促进剂处理的不同水平,进行狭叶四照花夏季扦插试验,结果表明:一年生枝条扦插生根率显著高于多年生枝条扦插生根率,穗条带顶芽可以显著提高扦插生根率;在恩施地区最适于7月上旬和7月中旬采条扦插;不同的生根促进剂处理对狭叶四照花扦插生根率差异显著,用ABT-1合适的处理时间配合不同浓度,生根率差异不显著;河砂、生黄砂和耕作土做扦插基质,狭叶四照花夏季扦插生根率差异不显著.     

聚丙烯微孔发泡材料发泡助剂实验

讨论了发泡助剂纳米ZnO、普通ZnO、复合助剂对发泡剂分解及在聚丙烯基体中形成微孔的影响.通过TG技术讨论发泡剂、发泡剂加不同助剂在塑料中热分解的影响,扫描电镜观察助剂在塑料中的分散情况,复合助荆较好.并对不同助剂的PP发泡材料进行性能的比较和探索,冲击强度得到极大提高;筛选出了制备优质PP微孔发泡材料的理想发泡助剂.     

通过p+206Pb弹性散射提取核半径常数

高能质子与原子核的散射与光的夫琅禾费衍射在机制上有相似之处,利用核反应弹性散射和光的夫琅禾费圆孔衍射的对应关系能够计算得到核半径,并由此提取出核半径常数.本文以p+206Pb反应为例说明了上述对应关系,建立了利用角分布计算微分截面的模型,在微分截面取极值的条件下利用此模型计算得到核半径,并提取出核半径常数.结果表明,本模型预期的核半径常数与实验经验值符合得很好     

Physical mechanism of beam halo-chaos formation for high-current proton beam in a periodic-focusing channels and a nonlinear control strategy

The physical mechanism of the halo-chaos formation for a high intensity proton beam in a periodic-fo cusing channel is analyzed using the transfer mahix theory and a qualiative analysis method.Particles-in-cell simula tims are further used to explore the mechanism of the beam halo-chaos fomation, which concerns not only with thc non linear effect of the beam space charge but also with the lransverse energy exchange belween the particles and the particle core. as well as the chaos generated by the nonlinear resonance ovcrlap. A nonlinear control method is proposed for con trolling tie haho-chaos. Simulation results show lhal the melhod is efhclivc. Somc potemlial applications of the halo chaos conlrol in experimenls are discussed.     

Safety and coping strategy for high dam under complex natural conditions

In respect to current situation and new challenges for high dam construction in China,safety problems are analyzed for high dam construction under complex natural conditions such as high elevation,cold area,high seismic intensity,large-scale landslide and high dam and huge reservoirs with dam types such as concrete surface rock-fill,asphalt concrete core,roller compacted concrete(RCC) arch dam and so on.From several aspects,including risk response measures for high dam,strengthening safety awareness for high dam design and construction,improving high dam construction technique,intelligent dam safety management system based on IT,developing dam rehabilitation and maintenance technologies,useful dam safety and coping strategy is proposed.     

Q相-C2S-C4AF-C12A7系列水泥水化性能的研究

对在实验室内烧成的Q相-C2S—C4AF—C12A7水泥熟料水化性能进行研究，试验结果表明：Q相-C2S—C4AF—C12A7水泥具备早强性，各龄期的抗压强度高于52．5普通硅酸盐水泥。经XRD和DTA分析，它的水化物主要是CAH10和C2AH8晶体、AH3凝胶和C—S—H凝胶以及一定量的AFt相。     

提高静电加速器击穿电压方法分析

从高压电极与钢筒尺寸的选择，绝缘气体的成份和压力，高压电极的光洁度，绝缘支柱的层压式结构等4个方面，分析了提高静电加速器击穿电压的方法，给出了相关数据和关系曲线。     

质子辐照过程的统计分布研究

为了研究一定能量的质子在材料内穿行深度的变化,进而探讨对材料性能的影响,基于质子穿行过程中碰撞的随机性,建立了质子穿行过程的非平衡统计理 论模型。分别计算出了高能和低能质子穿行长大速率函数和穿行深度概率密度函数。并以Kapton薄膜为例,发现高能质子的最概然穿行深度与之对应的最大概率密度的乘积为一个定值;随着低能质子能量的增加,其乘积呈阶梯状递减到一定值;高能和低能的分界线大约在105 eV数量级处。