Velocity bunching in travelling wave accelerator with low acceleration gradient

We present the analytical and simulated results of our study of the influence of the acceleration gradient in the velocity bunching process, which is a bunch compression scheme that uses a travelling wave accelerating structure as a compressor. Our study shows that the bunch compression application with low acceleration gradient is more tolerant to phase jitter and more successful in obtaining a compressed electron beam with symmetrical longitudinal distribution and low energy spread. We also present a transverse emittance compensation scheme to compensate the emittance growth caused by the increase of the space charge force in the compressing process, which is easy to adjust for different compression factors.     

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns （FWHM） electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm （FWHM） in diameter and the corresponding beam divergence is about 10.5 mrad.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source （LUCX） is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm·mrad to 3.66 πmm·mrad.     

Pulsed sextupole injection for Beijing Advanced Photon Source with ultralow emittance

In this paper we present the physical design of the pulsed sextupole injection system for Beijing Advanced Photon Source （BAPS） with an ultralow emittance. The BAPS ring lattice is designed in such a way that two options of pulsed sextupole injection are allowed, i.e., with septum and pulsed sextupole in different drift spaces or in the same drift space. We give the magnetic parameters of the injection system and the optimal condition of the optical flmctions for both options. In addition, we find that the pulsed sextupole induces position-dependent dispersive effect and causes a non-ignorable effect on the injection efficiency in a storage ring with a relatively small acceptance, which should be well considered.     

低β四分之一波长腔中的束流偏转的分析性研究(英文)

目前加速速度范围在0.01 c—0.3 c 的粒子的超导腔主要使用四分之一波长腔型。用于不同加速器上的频率范围在50—240 MHz 的四分之一波长腔在建造或者预研中。这种腔型的一个不足是其横向电磁成分会造成束流偏转效应,从而导致发射度的增长和束流的溢漏, 在强流重离子加速器中这种效应尤为严重。对中国科学院近代物理研究所超导直线加速器中的频率为80.5和161 MHz的四分之一波长腔的偏转效应进行了分析,计算结果表明,在四分之一腔体的设计时需要考虑到束流偏转的修正, 这通常需要在漂移管端面上削适当大小的倾角来实现。Superconducting(SC) cavities currently used for acceleration of ions in the velocity range from 0.01 cto 0.3 c are based frequently on quarter wave resonators(QWR). Various types of QWR cavities across a frequency extent from 50 to 240 MHz have been constructed or are proposed for numerous applications. A drawback of this kind of cavities is the beam steering caused by transverse magnetic and electric field components, which can creat emittance growth. In this paper, the analytical studies on beam steering in quarter wave resonator of frequency=80.5 and 161 MHz of the SC linac has been done in Institute of Modern Physics, Chinese Academy of Sciences, the calculated results have told us that the correction for beam deflection should be a consideration during the design of the QWR cavity, which generally involves the shaping the inner drift tube.     

Beam transport design for a 1 MeV prototype dielectric wall accelerator

The beam transport design of a novel proton dielectric wall accelerator is introduced in this paper. The protons will be accelerated from 40 keV to nearly 1 MeV under an accelerating gradient that is as high as 20 MV/m. A consideration of the beam line as well as the transport simulation is presented. The influences of the injection timing jitter and the accelerating pulse timing jitter are also discussed.     

Recent progress on RF superconducting cavities

RF superconducting （SRF） cavities can work in continuous wave mode or long pulse mode. SRF technology has been developing rapidly since the end of the last century. RF superconducting technology is widely used in particle accelerators around the world. As the key elements, research on superconducting cavities is carried out worldwide. Besides Europe, the United States and Japan, many countries have already started SRF projects, such as Canada, India, Korea, etc. Great improvements on SRF technology have been made in China in recent years. Progress in SRF cavities is introduced in this paper.     

An untuned MA-loaded cavity for HIRFL-CSR

In order to realize high energy density physics and plasma physics research at HIRFL-CSR, a magnetic alloy （MA）-loaded cavity has been studied. According to the theoretical calculation and simulation for the MA-loaded cavity, we achieved a better result. The MA-loaded cavity had a higher μQf value, with a higher shunt impedance and a higher accelerating gradient. The accelerating gradient was about 95 kV/m at 1.8003 MHz, 130 kV/m at 0.9000 MHz. Compared with the ferrite-loaded cavities that are used at HIRFL-CSR, with about 10 kV/m accelerating gradient, the MA-loaded cavity obviously has an advantage. The results of the theoretical calculation and the simulation, which meet the design requirements are in good agreement.     

Some New Solitary Wave Solutions to a Compound KdV-Burgers Equation

Abstract In terms of the solutions of an auxiliary ordinary differential equation, a new algebraic method, which contains the terms of first-order derivative of functions f （ξ）, is constructed to explore the new solitary wave solutions for nonlinear evolution equations. The method is applied to a compound KdV-Burgers equation, and abundant new solitary wave solutions are obtained. The algorithm is also applicable to a large variety of nonlinear evolution equations.     

Electron Acceleration and Bunch Generation by Intense Femtosecond Laser Pulse in Preplasma of a Target

We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target by an intense femtosecond laser pulse. Electrons in the preplasma are trapped and accelerated by the ponderomotive force as well as the wake field. Two-dimensional particle-in-cell simulations show that when the laser pulse is stopped by the target, electrons trapped in the laser pules can be extracted and move forward inertially. The energetic electron bunch in the bubble is unaffected by the reflected pulse and passes through the target with small energy spread and emittance. There is an optimal preplasma density for the generation of the monoenergetic electron bunch if a laser pulse is given. The maximum electron energy is inverse proportion to the preplasma density.     

Numerical simulation for all-optical Thomson scattering X-ray source

Energy spectra, angular distributions, and temporal profiles of the photons produced by an all-optical Thomson scat- tering X-ray source are explored through numerical simulations based on the parameters of the SILEX-I laser system （800 nm, 30 fs, 300 TW） and the previous wakefield acceleration experimental results. The simulation results show that X-ray pulses with a duration of 30 fs and an emission angle of 50 mrad can be produced from such a source. Using the optimized electron parameters, X-ray pulses with better directivity and narrower energy spectra can be obtained. Besides the electron parameters, the laser parameters such as the wavelength, pulse duration, and spot size also affect the X-ray yield, the angular distribution, and the maximum photon energy, except the X-ray pulse duration which is slightly changed for the case of ultrafast laser-electron interaction.     

Representations and Classification of Traveling Wave Solutions to sinh-GSrdon Equation

Two concepts named atom solution and combinatory solution are defined. The classification of all single traveling wave atom solutions to sinh-Gordon equation is obtained, and qualitative properties of solutions are discussed. In particular, we point out that some qualitative properties derived intuitively from dynamic system method are not true. Finally, we prove that our solutions to sinh-Gordon equation include all solutions obtained in the paper [Z.T. Fu, et al., Commun. Theor. Phys. （Beijing, China） 45 （2006） 55]. Through an example, we show how to give some new identities on Jacobian elliptic functions.     

New Agegraphic Dark Energy in Brans-Dicke Theory

In this paper, we investigate the new agegraphic dark energy model in the framework of Brans-Dicke theory, which is a natural extension of the Einstein＇s general relativity. In this framework the form of the new agegraphic dark energy density takes as pq = 3n^2Ф（t）η^-2, where η is the conformal age of the universe and Ф（t） is the Brans-Dicke scalar field representing the inverse of the time-variable Newton＇s constant. We derive the equation of state of the new agegraphic dark energy and the deceleration parameter of the universe in the Brans-Dicke theory. It is very interesting to find that in the Brans-Dicke theory the agegraphic dark energy realizes quintom-like behavior, i.e., its equation of state crosses the phantom divide ω= -1 during the evolution. We also compare the situation of the agegraphic dark energy model in the Brans-Dicke theory with that in the Einstein＇s theory. In addition, we discuss the new agegraphic dark energy model with interaction in the framework of the Brans-Dicke theory.     

Study on Duality of Wave and Particle of Turbulence Using CML Models

A family of coupled map lattice （CML） models has been developed to simulate the evolutional mechanism of interactions of convection, diffusion, and dispersion in both weakly and strongly coupled cases. Not only coherent and turbulent properties as well as their relations, but also the transitional states between convection dominating, diffusion dominating and dispersion dominating are analyzed to demonstrate the essential characteristics of any state. Numerical results show that the models are capable of simulating both layered coupling and stochastic mechanism, and lead us to understand whether or not turbulence coherent structure is formed by modulation of wave packet. The duality of wave and particle characters of turbulence is illustrated in the numerical simulation; a sketch picture is given to explain the questions associated with the turbulent inverse cascade, which is the result of the mutual interactions among the physical factors of nonlinearity, dissipation and dispersion.     

Multi-mode Spiral Wave in a Coupled Oscillatory Medium

Multi-mode spiral wave and its breakup in 1-d and 2-d coupled oscillatory media is studied here by theoretic analysis and numerical simulations. The analysis in 1-d system shows that the dispersion relation curve could be nonmonotonic depending on the coupling strength. It may also lead to the coexistence of different wave numbers within one system. Direct numerical observations in 1-d and 2-d systems conform to the prediction of dispersion relation analysis. Our findings indicate that the wave grouping can also be observed in oscillatory media without tip meandering and waves with negative group velocity can occur without inhomogeneity.     

Ion Acceleration in Laser-Plasma Interaction： Shock, Sheath, and Scaling

Some notes and comments on ion acceleration in laser-plasma interaction is given, in particular for the implication of shock, sheath and sealing. A simple model is proposed for ion acceleration by the combination of shock and sheath. The obtained scaling relations between the maximum ion energy and laser parameters （power, pulse duration） as well plasma parameter （plasma density）for example α PL 7/12 Eion,max α TL1/3 and Eion,max α ne2/3,are compared to the previous works. Some deficiencies and implications of model and results are discussed.     

Rational and Periodic Wave Solutions of Two-Dimensional Boussinesq Equation

Two new exact, rational and periodic wave solutions are derived for the two-dimensional Boussinesq equation. For the first solution it is obtained by performing an appropriate limiting procedure on the soliton solutions obtained by Hirota bilinear method. The second one in terms of Riemann theta function is explicitly presented by virtue of Hirota bilinear method and its asymptotic property is also analyzed in detail. Moreover, it is of interest to note that classical soliton solutions can be reduced from the periodic wave solutions.     

A New Algebraic Method and Its Application to Nonlinear Klein-Gordon Equation

In terms of the solutions of the generalized Riccati equation, a new algebraic method, which contains the terms of radical expression of functions f（ξ）, is constructed to explore the new exact solutions for nonlinear evolution equations. Being concise and straightforward, the method is applied to nonlinear Klein-Gordon equation, and some new exact solutions of the system are obtained. The method is of important significance in exploring exact solutions for other nonlinear evolution equations.     

Manipulation of plasmonic wavefront and light–matter interaction in metallic nanostructures: A brief review

The control and application of surface plasmons （SPs）, is introduced with particular emphasis on the manipulation of the plasmonic wavefront and light-matter interaction in metallic nanostructures. We introduce a direct design methodology called the surface wave holography method and show that it can be readily employed for wave-front shaping of near-infrared light through a subwavelength hole, it can also be used for designing holographic plasmonic lenses for SPs with complex wavefronts in the visible band. We also discuss several issues of light-matter interaction in plasmonic nanostructures. We show theoretically that amplification of SPs can be achieved in metal nanoparticles incorporated with gain media, leading to a giant reduction of surface plasmon resonance linewidth and enhancement of local electric field intensity. We present an all-analytical semiclassical theory to evaluate spaser performance in a plasmonic nanocavity incorporated with gain media described by the four-level atomic model. We experimentally demonstrate amplified spontaneous emission of SP polaritons and their amplification at the interface between a silver film and a polymer film doped with dye molecules. We discuss various aspects of microscopic and macroscopic manipulation of fluorescent radiation from gold nanorod hybrid structures in a system of either a single nanoparticle or an aligned group of nanoparticles. The findings reported and reviewed here could help others explore various approaches and schemes to manipulate plasmonic wavefront and light-matter interaction in metallic nanostructures for potential applications, such as optical displays, information integration, and energy harvesting technologies.     

The Analytic Solution of SchrSdinger Equation with Potential Function Superposed by Six Terms with Positive-power and Inverse-power Potentials

The analytic solution of the radial Schrodinger equation is studied by using the tight coupling condition of several positive-power and inverse-power potential functions in this article. Furthermore, the precisely analytic solutions and the conditions that decide the existence of analytic solution have been searched when the potential of the radial Schrodinger equation is V（r） =α1r^8 ＋α2r^3 ＋ α3r^2 ＋β3r^-1 ＋β2r^-3 ＋β1r6-4. Generally speaking, there is only an approximate solution, but not analytic solution for SchrSdinger equation with several potentials＇ superposition. However, the conditions that decide the existence of analytic solution have been found and the analytic solution and its energy level structure are obtained for the Schrodinger equation with the potential which is motioned above in this paper. According to the single-value, finite and continuous standard of wave function in a quantum system, the authors firstly solve the asymptotic solution through the radial coordinate r → ∞ and r →0; secondly, they make the asymptotic solutions combining with the series solutions nearby the neighborhood of irregular singularities; and then they compare the power series coefficients, deduce a series of analytic solutions of the stationary state wave function and corresponding energy level structure by tight coupling among the coefficients of potential functions for the radial SchrSdinger equation; and lastly, they discuss the solutions and make conclusions.