Computation of the third-order matrizant for a sectorial electrostatic field

It is suggested to study the ion-optical properties of sectorial electrostatic charged-particle analyzers with the matrizant technique. The matrizants can effectively be used in investigating beam dynamics in sectorial electrostatic fields with consideration for edge effects within rectangular and smooth field models.     

Numerical simulation of particle dynamics in a storage ring by using BETACOOL program

The BETACOOL program, developed by electron cooling group of the Joint Institute for Nuclear Research (JINR), is a set of algorithms based on common format of input and output files. The program is oriented toward simulation of the ion beam dynamics in a storage ring in the presence of cooling and heating effects. The version presented in this report includes three basic algorithms: simulation of root-mean-square (rms) parameters of the particle distribution function evolving in time, simulation of the distribution function evolution using the Monte Carlo method, and a tracking algorithm based on a molecular dynamics technique. The general processes investigated with the program are intrabeam scattering in the ion beam, electron cooling, and interaction with residual gas and an internal target.     

Longitudinal momentum mining of beam particles in a storage ring

I describe a scheme for selectively isolating high density low longitudinal emittance beam particles in a storage ring from the rest of the beam without emittance dilution. I discuss the general principle of the method, called longitudinal momentum mining, beam dynamics simulations and results of beam experiments. Multi-particle beam dynamics simulations applied to the Fermilab 8 GeV Recycler (a storage ring) convincingly validate the concepts and feasibility of the method, which I have demonstrated with beam experiments in the Recycler. The method presented here is the first of its kind.     

Beam life time studies and design optimization of the Ultra-low energy Storage Ring

The Ultra-low energy electrostatic Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) will provide cooled beams of antiprotons in the energy range between 300 keV down to 20 keV. Based on the original design concept developed in 2005, the USR has been completely redesigned over the past few years by the QUASAR Group. The ring structure is now based on a ’split achromat’ lattice. This ensures compact ring dimensions of 10 m × 10 m, whilst allowing both, in-ring experiments with gas jet targets and studies with extracted beams. In the USR, a wide range of beam parameters shall be provided, ranging from very short pulses in the nanosecond regime to a coasting beam. In addition, a combined fast and slow extraction scheme will be featured that allows for providing external experiments with cooled beams of different time structure. Detailed investigations into the dynamics of low energy beams, including studies into the long term beam dynamics and ion kinetics, beam life time, equilibrium momentum spread and equilibrium lateral spread during collisions with an internal target were carried out. This required the development of new simulation tools to further the understanding of beam storage with electrostatic fields. In addition, studies into beam diagnostics methods for the monitoring of ultra-low energy ions at beam intensities less than 10 ⁶ were carried out. This includes instrumentation for the early commissioning of the machine, as well as for later operation with antiprotons. In this paper, on overview of the technical design of the USR is given with emphasis on two of the most important operating modes, long term beam dynamics and the design of the beam diagnostics system.     

Beam dynamics of the superconducting wiggler on the SSRF storage ring

In the SSRF Phase-II beamline project, a superconducting wiggler(SW) will be installed in the electron storage ring. It may greatly impact on the beam dynamics due to the very high magnetic field. The emittance growth becomes a major problem, even after correction of the beam optics. A local achromatic lattice is studied, in order to combat the emittance growth and keep the performance of the SSRF storage ring as high as possible. Other effects of the SW are also simulated and optimized, including the beta beating, the tune shift, the dynamic aperture, and the field error effects.     

无衍射特殊光束的产生与三维表征

无衍射光束(如贝塞尔光束、艾里光束)因具有无衍射、自愈合的特性, 在很多领域都有广泛的应用. 本文提出使用纯相位型空间光调制器对光场的复振幅进行调控, 从而可以产生多种复杂模式的无衍射光束, 如强度可独立调控的多个零阶贝塞尔光束, 两个高阶贝塞尔光束干涉生成的花瓣状无衍射光束, 具有多个主瓣的加速光束等特殊的无衍射光束. 通过在待测焦场附近放置一个平面反射镜, 使其沿光轴快速扫描光场, 并由数字相机同步拍摄反射回来的一系列二维光场强度分布信息, 可实现对无衍射光束三维光场强度分布的快速测量和表征. 本实验方法和技术可以快速产生各种复杂的特殊光场并获得其精确的三维可视化重建效果, 在光学显微、光学俘获、光学微加工等领域有潜在的应用价值.     

Analytical treatment of the nonlinear electron cloud effect and the combined effects with beam-beam and space charge nonlinear forces in storage rings

In this paper we treat first some nonlinear beam dynamics problems in storage rings, such as beam dynamic apertures due to magnetic multipoles, wiggles, beam-beam effects, nonlinear space charge effect, and then nonlinear electron cloud effect combined with beam-beam and space charge effects, analytically. This analytical treatment is applied to BEPC Ⅱ. The corresponding analytical expressions developed in this paper are useful both in understanding the physics behind these problems and also in making practical quick hand estimations.     

Anomalous hollow electron beams in a storage ring

This Letter reports the first observations of an anomalous hollow electron beam in the Duke storage ring. Created by exciting the single-bunch beam in a lattice with a negative chromaticity, the hollow beam consists of a solid core inside and a large ring outside. We report the detailed measurements of the hollow beam phenomenon, including its distinct image pattern, spectrum signature, and its evolution with time. By capturing the postinstability bursting beam, the hollow beam is a unique model system for studying the transverse instabilities, in particular, the interplay of the wakefield and the lattice nonlinearity. In addition, the hollow beam can be used as a powerful tool to study the linear and nonlinear particle dynamics in the storage ring.     

Field enhanced dielectronic recombination of Si11+ ions

The enhancement of dielectronic recombination by applied electric fields has been observed and measured for the first time in a wide range of controlled and measurable fields using multiply charged ions. The heavy ion storage ring, CRYRING, at Stockholm University was used to store a beam of Si¹¹⁺ and collide it with a cold electron target. The observation of a substantial monotonic increase of the rate coefficient for the group of higher Rydberg states is in puzzling disagreement with theoretical calculations of electric field enhanced dielectronic recombination. This revised version was published online in July 2006 with corrections to the Cover Date.     

A tapered beam finite element for rotor dynamics analysis

The stiffness, mass and gyroscopic matrices of a rotating beam element are developed, a cubic function being used for the transverse displacement. Shear deflection is included by use of end nodal variables of shear strain, along with transverse displacement and cross-section rotation; rotatory inertia effects are included in the energy functional to provide a Timoshenko beam formulation. The gyroscopic effects for small perturbations are linearized as a skew symmetric damping matrix. The formulation is implemented by numerical integration for a linearly tapered circular beam. A technique of reduction of the shear nodal variable prior to global assembly is shown to provide little loss in accuracy with reduced system bandwidth. Numerical comparisons for three previously published beam models are included, with results presented for the case of forward and reverse precession to verify the gyroscopic effects. The utility of the element in a general program for rotor dynamics analysis is identified.     

A linear Paul trap for radiative lifetime measurements on ions

A linear ion trap has been designed for collimation and storage of ions from an effusive particle beam generated in a hollow cathode discharge. The motivation is to measure radiative lifetimes on multiply ionized atoms by using the time-resolved laser-induced fluorescence technique. The trap has been tested on iron and tungsten ions both as an ion guide and also as a storing device. Radiative lifetimes have been measured in the trap with a remarkably higher signal-to-noise ratio than in the original effusive atom beam.     

Femtosecond pulse laser scanning using Acousto-Optic Deflector

Acousto-optic modulation of the femtosecond laser beam has wide potential in various fields such as microscopic imaging, micromachining and optical storage because of its rapidity, high accuracy and good repeatability. This paper reviews the latest research on acousto-optic modulation of femtosecond laser, describes the effects of spatial and temporal dispersion of such lasers after acousto-optic modulation, introduces the theoretical outcomes on pulse width evolution of the Gaussian laser pulses after acousto-optic modulation, discusses the characteristics of contemporary dispersion-compensating techniques for the acousto-optic modulation of femtosecond laser, and finally refers to the challenges of this technique. Supported by the National Natural Science Foundation of China (Grant Nos. 60278017, 30328014, and 30370463) and the National Basic Research Program of China (Grant No. 2004CB520804)     

A general analysis of the electromagnetic wake-fields due to a relativistic electron beam moving through a cold plasma

Summary Detailed electromagnetic analysis of the wake-field accelerator is presented. Particular attention is given to the two-dimensional dynamics model to understand how the wake-field affects the self-consistent radial dynamics of the beam. The corrent fields, in zeroth and first order, are obtained by using Fourier transform in the radial field. The self-focusing of the driving beam in a plasma is a result of the transverse wake. The ratio of the transverse wake-field to the longitudinal wake-field within the beam is calculated for small and large radii beams.     

Laser probing of ions in a storage ring: A method for selective determination of lifetimes of metastable states

A collinear laser probing technique is introduced for use in ion storage rings. This method can be used for high resolution studies of the decay properties of metastable states in ions. An experiment on singly charged xenon utilizing this technique is presented. By selective excitation of individual hyperfine states a drastic hyperfine induced quenching was observed. Systematic effects from ion beam neutralization in the rest gas and mixing effects occurring in the bending magnets are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of high intensity focused ultrasound transducers using acoustic streaming

A new approach for characterizing high intensity focused ultrasound (HIFU) transducers is presented. The technique is based upon the acoustic streaming field generated by absorption of the HIFU beam in a liquid medium. The streaming field is quantified using digital particle image velocimetry, and a numerical algorithm is employed to compute the acoustic intensity field giving rise to the observed streaming field. The method as presented here is applicable to moderate intensity regimes, above the intensities which may be damaging to conventional hydrophones, but below the levels where nonlinear propagation effects are appreciable. Intensity fields and acoustic powers predicted using the streaming method were found to agree within 10% with measurements obtained using hydrophones and radiation force balances. Besides acoustic intensity fields, the streaming technique may be used to determine other important HIFU parameters, such as beam tilt angle or absorption of the propagation medium.     

Storage ring with longitudinal magnetic field LEPTA (Stellatron)

The project of the Low Energy Particle Toroidal Accumulator (LEPTA) is dedicated to the construction of a positron storage ring with electron cooling of positrons circulating in the ring. Such a specific feature of LEPTA automatically enables it to be a generator of positronium (Ps) atoms, which appear in the recombination of positrons with cooling electrons inside the cooling section of the ring. The project has the following goals: particle dynamics in the modified betatron, electron cooling with a circulating beam, positronium generation in flight, positronium physics, and feasibility of antihydrogen generation in flight. All key elements of the ring—the kicker, electron beam injection system, helical quadrupole, septum magnet—have been tested, and the expected design parameters have been achieved for these elements. The construction of LEPTA has been completed, and the circulating electron beam has been achieved. This paper discusses the issues of particle dynamics in such an accelerator, the results of numerical simulation and experimental findings of the research into beam dynamics, measurement of betatron number and beam lifetime.     

Broadband impedance calculations and single bunch instabilities estimations of of the HLS-Ⅱ storage ring

The upgrade project of the Hefei Light Source storage ring is under way.In this paper,the broadband impedances of resistive wall and coated ceramic vacuum chamber are calculated using the analytic formula,and the wake fields and impedances of other designed vacuum chambers are simulated by CST code,and then a broadband impedance model is obtained.Using the theoretical formula,longitudinal and transverse single bunch instabilities axe discussed.With the carefully-designed vacuum chamber,we find that the thresholds of the beam instabilities are higher than the beam current goal.     

基于表面等离子体激元共振的飞秒抽运探测技术研究

对基于表面等离子体激元共振（SPR）的飞秒抽运探测技术进行了系统地数字分析.计算结果表明,利用SPR技术可将飞秒抽运探测信号强度ΔR/R提高2—3个数量级,其提高的比例依赖于金属膜的厚度和探测光的入射角,其中R和ΔR分别为探测光反射率的总量和变化量.特别地,对于金属-吸收介质体系,金属膜的介电常数变化对ΔR的影响仅为吸收介质影响的2%,所以ΔR/R主要反应吸收介质中的动力学过程,因此该技术对研究表面和界面的超 关键词： 超快光学 表面等离子体共振 飞秒抽运探测技术 信号强度     

Toward a storage ring with no shear

One barrier to the attainment of a crystalline ordered state for a well-cooled beam in a storage ring will be the viscous heating by the shear induced in the bending fields of the ring. Shear will transfer some of the energy of coherent motion to thermal energy and may prevent reaching the very low temperatures required for formation of the ordered state. A concept for a ring is proposed in which shear within a monoenergetic beam of finite size is substantially reduced by means of combined electrostatic and magnetic fields within the bending elements.