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.     

弯晶的引出效率与同步加速器的束流动力学稳定性

近年来,弯晶的束流控制技术得到了迅速发展．在加速器物理中,粒子能量和束流强度一直是人们追求的目标,而引出技术和引出效率则是保证柬流强度的关键．在经典力学框架内和偶极近似下,导出了粒子在弯晶中的一般运动方程．在准静态近似下,利用哈密顿原理分析了系统的稳定性;在相空间密度均匀分布假设下,利用相面积概念讨论了弯晶的引出效率．用Melnikov方法描述了系统的混沌行为及临界性质,给出了常曲率和变曲率弯晶的退道长度．     

Research progress in high intensity cyclotron technology

This paper briefly introduces several major application fields of high intensity proton accelerators and compares the developing status of various types of proton accelerators currently available at home and abroad. Technical parameters of typical accelerators are specified. The technical features of high intensity cyclotrons are summarized and a general introduction is given to the 3 major phases of research and development on high intensity cyclotrons at CIAE. In the end, emphasis is laid on the recent research of critical technology of high intensity cyclotrons as well as its developing progress.     

欧洲核子中心汇聚全球的努力筹划未来的巨大环型对撞机

 结合2014 年2 月参加“对未来环型对撞机研究的启动会议”的见闻,介绍了全球高能物理界正在讨论如何通过广泛国际合作、在欧洲核子中心（CERN）建造未来环形高能加速器和粒子对撞机的新动态,简要回顾了历史上高能加速器和对撞机建设的经验和教训,摘编了与会者提出的相关见解和建议,希望中国高能物理的长远发展可从中借鉴和参考。     

Design of a compact C-band high brightness photoinjector for an ultra-fast electron diffraction

A compact C-band high brightness photoinjector for ultra-fast electron diffraction （UED） is under development at Tsinghua Uni- versity. The C-band photoinjector, operating at 5.172 GHz, uses a 1.45-cell C-band RF gun as the electron source. The design of the RF gun has addressed the physics, beam dynamics and mechanical aspects, and based on these design studies, a prototype has been fabricated. In order to obtain optimized performance for the UED, beam dynamics simulation has been carried out using the particle tracking code Astra for the photoinjector consisting of an alternative multi-cell RF gun design and a C-band compressor downstream. The beam dynamics parameters that are optimized include the bunch length, peak current, horizontal emittance, and position of the minimum bunch length.     

强场原子分子物理实验研究中的符合测量技术及其应用

飞秒激光具有超短的脉冲宽度和超强的峰值功率，已经成为测量和操控原子分子超快动力学行为的重要工具．但是强激光场下，原子分子行为非常复杂，多个反应通道纠缠在一起．全微分符合测量技术能够提供特定反应通道精确的动力学数据，推动了强场原子分子物理研究的快速发展．本文结合北京大学新建的冷靶反冲离子动量谱仪，介绍全微分符合测量技术在强场原子分子物理实验研究中的重要应用以及在强场原子分子物理实验研究方面取得的一些重要进展．     

大亚湾与江门中微子实验

中微子物理是粒子物理中最活跃的分支之一,存在众多未解之谜,可能成为超出标准模型的新物理的突破口.本文总结了中微子物理的现状和主要的科学问题,着重介绍了我国正在进行的大亚湾中微子实验和建造中的江门中微子实验.通过研究反应堆中微子,2012年大亚湾实验发现新的中微子振荡,测得了中微子混合角13.本文介绍了大亚湾实验的物理背景和项目背景,简述了实验方法和设计思想,并描述了探测器设计和建造.许多新的想法和技术创新在探测器设计与建造中采用,使探测器相关的相对误差仅为0.2%.在未来几十年内,大亚湾将保持对这一基本参数的最高测量精度.江门中微子实验2008年提出建议,2013年正式启动.通过在53 km处探测反应堆中微子振荡,它将能确定中微子质量顺序,并精确测量3个中微子混合参数.采用一个设计能量精度为3%的2×104 t液体闪烁体探测器,江门实验在研究超新星中微子、太阳中微子、地球中微子、大气中微子、以及奇异现象寻找方面也极具吸引力.它将对多个物理目标进行国际领先水平的研究.文中我们介绍了实验设计和研发的进展.除了大亚湾和江门实验,我们也参与了无中微子双贝塔衰变实验EXO,设计了一个新式的加速器中微子束流线,进一步扩展了中微子研究.     

Lie map for the nonlinear transport of continuous intense beams in the axial-symmetric electrostatic fields

Nonlinear transport of intense continuous beam in the axial-symmetric electrostatic fields is analyzed with the Lie algebraic method. The K-V particle distribution is adopted in the analysis. The results obtained can be used in the calculations of the intense continuous beam dynamics in the beam optical systems consisting of drift spaces, electrostatic lenses, and DC electrostatic accelerating tubes. A computer code has been designed for practical simulations. To meet the needs of accurate calculation, all the elements are divided into many small segments, the electric fields in each segment are regarded as uniform fields, and the dividing points are treated as thin lenses. Iteration procedures are adopted in the code to obtain self-consistent solutions. The code can be used to design low energy dc beam transport systems, electrostatic accelerators, and ion implantation machines.     

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.     

反西格马负超子（Σ-）的发现前后

 因高能加速器建设滞后，中国粒子物理学科在发展早期只能开展理论研究、宇宙线观测或通过国际合作开展高能实验研究。多国合作的杜布纳联合原子核研究所的成立为中国高能物理发展创造了良机，反西格马负超子的发现更是中国物理学史上浓墨重彩的一笔。中国学者在杜布纳的系列科学成就，为此后中国亚原子物理发展奠定了重要的知识基础与人才基础。     

反西格马负超子（Σ-）的发现前后

 因高能加速器建设滞后，中国粒子物理学科在发展早期只能开展理论研究、宇宙线观测或通过国际合作开展高能实验研究。多国合作的杜布纳联合原子核研究所的成立为中国高能物理发展创造了良机，反西格马负超子的发现更是中国物理学史上浓墨重彩的一笔。中国学者在杜布纳的系列科学成就，为此后中国亚原子物理发展奠定了重要的知识基础与人才基础。     

从粗线条长距离的物理学发展到21世纪中国的科技前途

本文首先对物理学,特别是近代物理学的起源、发展过程及其影响进行了阐述。文中述及近代物理学起源于17世纪,经过一百多年(1666～1800)的发展,在欧洲近代的科学观念开始萌芽,并逐渐开花、结果。到19世纪近代物理学有了长足进步,并大大刺激了工业的发展。19世纪末20世纪初,由于相对论、广义相对论和量子力学的创立,使整个物理学出现了革命性的进展。此后,从1930年开始物理学进入了一个新的纪元,以固体物理学和液体物理学、原子和分子物理学、核物理学、基本粒子物理学为标志的近代物理学蓬勃兴起。本文认为,物理学的发展与技术的发展,是一连锁循环,而技术的发展与经济的发展又是一连锁循环。因而世界各国竞相重视,大量投资于物理学尖端的研究。本文后部分对中国科技的发展进行了回顾和展望,指出中国古代科学技术在世界上处于领先地位,但1600年后中国科技发展长期停滞,落后于西方科技300年。最后,本文对新中国成立后科学技术的突飞猛进作了高度评价,并预言21世纪中国将成为世界科技强国。     

串列加速器分束并行束线概念设计

为了使分束并行管道得到足够束流流强,首先对光阑分柬孔径处柬流流强进行理论计算,得出光阑孔径参数与束流流强之间函数关系式;在此基础上对理论计算进行了模拟验证,并考察了不同分柬孔径下柬流发射度的变化;最后对整条柬流线结构布局进行分析计算,得出各光学元件参数。计算结果准确可信,能够满足核物理实验终端用户对柬流品质要求．     

中日两国对撞机建设与运行对比：基于历史和科学计量视角

 从历史发展和运行表现2个角度，对比了中日两国的对撞机工程建设与运行情况。分析表明，建设相对更早的中国对撞机的参数受限于资金、技术等条件，其研究方向为能区较低的粲物理领域；有工程技术基础的日本在确立对撞机建设方向时更具针对性，瞄准了物理前景更为丰富的B物理领域。中日两国对撞机皆取得了重要的科学成果，日本在科研成果产出方面更为突出，国际合作程度更高；中国近年来的成果产出量提升明显，且在粲物理领域的研究方面保持了领先水平。     

模拟超高能区强子—强子相互作用的两分量模型

分析现有加速器数据,构造了描写强子相互作用的两分量模型。计算结果与从ISR能区到SPS能区的实验结果符合较好。由此提供了一种可以外推到超高能区并用于高山乳胶室实验Monte-Carlo模拟计算的强子相互作用模型。     

超级Z-工厂上的物理

本文在调查研究和理论分析的基础上,对超级Z-工厂上可开展的特色高能物理实验做了归纳和小结.文章指出超级Z-工厂中可以开展许多科学意义重要、别处不可替代的高能物理实验,归纳下来在下列四个方面具有突出优势：i）Z-玻色子性质的精确测量,寻找与Z-玻色子有关的稀有过程的实验研究;ii）韬（τ）轻子性质,寻找与韬轻子有关的稀有过程和发现关系到韬轻子和/或Z-玻色子的CP破坏（肯定与CKM矩阵相因子无直接联系）的实验研究;iii）重味和双重味强子的性质,其激发态质谱,奇异重味强子等的实验研究;iv）通过测量喷注形状直接测量QCD耦合常数αs（m2Z）,测定重味夸克和胶子到重味强子和双重味强子的碎裂函数,检验非微扰碎裂模型理论等的实验研究.另外,由于建造超级Z-工厂可以作为我国加速器高能实验物理未来基地规划中的一个选项,国内同行已经完成了相关的学术研究论文14篇,并已汇集成题为＂超级Z-玻色子工厂物理＂的专辑,发表在SciChina-Phys Mech Astron上,2010年11月份的53卷11期中.本文对这14篇论文做扼要概述,同时也做了一些补充.     

北京正负电子对撞机方案的初步提出与确立

从1957年到1977年,中国高能物理加速器的设计方案历经了“六上六下”的波折.1977年11月第7次上马的高能质子加速器工程——“八七工程”在1980年底遭遇下马.在以张文裕为首的高能物理学家们的努力争取之下,经邓小平批准,保留和利用“八七工程”预制研究的余款,经过一番分外曲折的探寻,借助中美高能物理合作的有利条件,正确采纳李政道、潘诺夫斯基等人关于建造正负电子对撞机的建议方案,几经论证最终选定了中国高能加速器的建设方案——正负电子对撞机,奠定了中国高能物理在世界高能物理研究领域占据一席之地的基础.     

强流加速器中束晕—混沌的小波函数控制研究

研究了用小波函数构造非线性反馈控制器进行控制强离子加速器中的束晕-混沌的方法。数值模拟结果表明,这种由特殊函数构造的控制器具有很好的控制束晕-混能力,只要调节知当的控制参数就能够对4种初始分布不同的离子束进行较理相的控制。研究结果可望为强离子加速器中束晕-混沌控制的实现提供有效参考。     

强流质子加速器束流匹配研究

为了使感生放射性降低到可以接受的水平,强流质子加速器必须减少柬流损失。不同加速段间的束流匹配是减少束流损失和发射度增长的关键之一。研究了一台常温加速结构不同段间的束流传输线的匹配设计问题。采用TRACE3-D软件以及其他多粒子模拟软件,研究了在不同匹配状态下的束流特性。结果表明,设计所采用的横向和纵向匹配手段,能够有效地控制束晕产生和束流发射度的增长。     

Design and Tool Flow of a Reconfigurable Asynchronous Neural Network Accelerator

Convolutional Neural Networks(CNNs) are widely used in computer vision, natural language processing,and so on, which generally require low power and high efficiency in real applications. Thus, energy efficiency has become a critical indicator of CNN accelerators. Considering that asynchronous circuits have the advantages of low power consumption, high speed, and no clock distribution problems, we design and implement an energy-efficient asynchronous CNN accelerator with a 65 nm Complementary Metal Oxide Semiconductor(CMOS) process. Given the absence of a commercial design tool flow for asynchronous circuits, we develop a novel design flow to implement Click-based asynchronous bundled data circuits efficiently to mask layout with conventional Electronic Design Automation(EDA) tools. We also introduce an adaptive delay matching method and perform accurate static timing analysis for the circuits to ensure correct timing. The accelerator for handwriting recognition network(LeNet-5 model)is implemented. Silicon test results show that the asynchronous accelerator has 30% less power in computing array than the synchronous one and that the energy efficiency of the asynchronous accelerator achieves 1.538 TOPS/W,which is 12% higher than that of the synchronous chip.