Study on CYCIAE-100 radiation field and residual radioactivity

The accelerators should be properly designed to make the radiation field produced by beam loss satisfy the dose limits. The radiation field for high intensity H^－ cyclotron includes prompt radiation and residual radiation field. The induced radioactivity in accelerator components is the dominant source of occupational radiation exposure if the accelerator is well shielded. The source of radiation is the beam loss when cyclotron is operating. In this paper, the radiation field for CYCIAE-100 is calculated using Monte Carlo method and the radioactive contamination near stripping foil is studied. A method to reduce the dose equivalent rate of maintenance staff is also given.     

Acceleration and radiation of externally injected electrons in laser plasma wakefield driven by a Laguerre-Gaussian pulse

By using three-dimensional particle-in-cell simulations, externally injected electron beam acceleration and radiation in donut-like wake fields driven by a Laguerre-Gaussian pulse are investigated. Studies show that in the acceleration process the total charge and azimuthal momenta of electrons can be stably maintained at a distance of a few hundreds of micrometers. Electrons experience low-frequency spiral rotation and high-frequency betatron oscillation, which leads to a synchrotron-like radiation. The radiation spectrum is mainly determined by the betatron motion of electrons. The far field distribution of radiation intensity shows axial symmetry due to the uniform transverse injection and spiral rotation of electrons. Our studies suggest a new way to simultaneously generate hollow electron beam and radiation source from a compact laser plasma accelerator.     

95 MeV射频电子直线加速器辐射防护分析

应相关建设安评、环评、稳评以及职业健康评估的要求,电子加速器设计过程中即应对其辐射情况进行分析。针对电子能量为40～95 MeV可调的光阴极微波电子枪直线加速器,对其辐射源项进行分析,并讨论了可能的辐射防护措施的效果。采用蒙特卡罗软件FLUKA对电子束流和加速器进行建模,通过模拟计算发现,加速器产生的等效剂量分布主要位于废束桶中,废束桶以外辐射剂量迅速下降,在电子加速器实验大厅四周设置混凝土墙体的情况下辐射等效剂量率将随墙体厚度迅速下降。若混凝土墙体厚度设置为1 m,则墙体外工作人员所在区域辐射等效剂量率不高于1 μSv/h量级,能够有效屏蔽加速器产生的电离辐射,给工作人员提供有效防护。研究方法及结果对同能区同类型加速器建设中的辐射分析及辐射防护评估具有一定的参考价值。     

蒙特卡罗模拟分析电子束发射度对照射量空间分布影响

加速器靶前正前方1 m处的照射量是衡量加速器光源辐射能力的重要物理参量。电子束轰击高原子序数靶产生的X射线空间分布具有很强的前冲性,照射量空间分布与电子束的发射度密切相关。采用高斯函数对不同电子束发射度条件下入射电子的空间分布和角度分布进行建模。应用蒙特卡罗方法对电子束打靶的轫致辐射过程进行模拟,分析电子束发射度对照射量的影响。同时还对整靶结构和叠靶结构下的轫致辐射光源照射量进行计算比较。结果表明,电子束的发散角是影响轫致辐射光源照射量的主要因素。与采用整靶结构相比,采用叠靶结构所获得的照射量空间分布基本一致,在正前方小角度范围内（0~4）的照射量有2%~3%的降低。     

同步辐射光源的反馈控制模型

同步辐射光源的不稳定性是客观存在的问题,产生不稳定性的原因很多。对系统中客观存在的物理现象进行了讨论,提出了一些解决问题的方法,特别是反馈控制。同步辐射加速器反馈控制是一个比较复杂的问题,它涉及到高能电子束团在相空间的稳定运动。在实际应用中,存在一些反馈系统在一定程度上改善了同步辐射光源的稳定性,对实际应用于同步辐射装置的反馈系统进行了分析,提出了适合于同步辐射光源的反馈控制模型。     

High-resolution gamma-ray radiography produced by a laser-plasma driven electron source

An electron beam from a laser-plasma accelerator is converted into a gamma-ray source using bremsstrahlung radiation in a dense material. The gamma-ray beam has a pointlike source size because it is generated by a high quality electron beam with a small source size and a low divergence. Using this gamma-ray source, the radiography of complex and dense objects with submillimeter resolution is performed. It is the first evidence of a gamma-ray source size of a few hundreds micrometers produced with laser-driven accelerators. This size is consistent with results from Monte Carlo simulations.     

X波段短脉冲相对论返波管设计与初步实验

 对基于短电子束脉冲超辐射机理的X波段相对论返波管进行了优化设计和粒子模拟，结果表明：在超辐射机理作用下，该器件能实现高峰值功率和高功率转换效率的微波辐射。在小型Tesla脉冲源基础上设计了阻抗变换段、二极管、磁场系统等装置，建立了一套小型窄脉冲电子加速器，以此为实验平台在低磁场条件下进行了器件的初步实验研究。在磁场0.73 T、束压约380 kV、束流约4.5 kA、脉宽3.1 ns条件下，实验获得的微波脉冲峰值功率约360 MW，脉宽1.10 ns，上升沿800 ps，频率9.15 GHz，功率转换效率为21%。     

Spatial coherence in the transition radiation spectrum

The formal expression of the spectral distribution of the transition radiation intensity will be here derived in the case of a relativistic three-dimensional charged beam. Charged beams with a particle density such as is typically encountered in a particle accelerator will be considered. In particular, a sufficiently high particle density will be supposed so that a continuous spatial distribution function can be reliably attributed to the charged bunch. The formula of the spectral distribution of the transition radiation intensity originated by a relativistic three-dimensional charged beam - already presented in a previous work - will be here submitted to a formal check and interpreted in the physical consequences. The present work contains an additional mathematical derivation of the radiation energy spectrum consisting in a different method to implement the continuous limit in the distribution function of the particle coordinates. In the former derivation of the formula, the average operation with respect to the continuous distribution function of the particle coordinates was applied to the radiation intensity of a N electron bunch. In the present one, it is applied to the radiation electric field of a N electron bunch. The comparison of the two alternative but in any case equivalent formal routes to the spectral distribution of the transition radiation intensity will offer the possibility to directly cross-check the mathematical self-consistency of the presented results within the limits of applicability of the continuous limit approximation. According to such results, both the flux and the angular distribution of the photons emitted at a given wavelength - even shorter than the longitudinal length of the bunch - are expected to undergo a modification as the beam transverse size is varied with respect to the observed wavelength. As a function of the beam transverse size the spatial coherence degree of the transition radiation source is thus expected to change. The physical consistency of such an effect occurring in the transition radiation emission by a charged beam can be argued on the basis of a compatibility criterion with other similar relativistic electromagnetic radiative phenomena and interpreted in the framework of the temporal causality and the Huygens-Fresnel principles. Finally, the aspect of the applicability of the continuous limit approximation to the case of a charged beam in a particle accelerator is treated in terms of a practical quantitative criterion.     

Low emittance lattice for the storage ring of the Turkish Light Source Facility TURKAY

The TAC(Turkish Accelerator Center) project aims to build an accelerator center in Turkey. The first stage of the project is to construct an Infra-Red Free Electron Laser(IR-FEL) facility. The second stage is to build a synchrotron radiation facility named TURKAY, which is a third generation synchrotron radiation light source that aims to achieve a high brilliance photon beam from a low emittance electron beam at 3 Ge V. The electron beam parameters are highly dependent on the magnetic lattice of the storage ring. In this paper a low emittance storage ring for TURKAY is proposed and the beam dynamic properties of the magnetic lattice are investigated.     

Physical design of a 10 MeV LINAC for polymer radiation processing

In China, polymer radiation processing has become one of the most important processing industries. The radiation processing source may be an electron beam accelerator or a radioactive source. Physical design of an electron beam facility applied for radiation crosslinking is introduced in this paper because of it’s much higher dose rate and efficiency. Main part of this facility is a 10 MeV travelling wave electron linac with constant impedance accelerating structure. A start to end simulation concerning the linac is reported in this paper. The codes Opera-3d, Poisson-superfish and Parmela are used to describe electromagnetic elements of the accelerator and track particle distribution from the cathode to the end of the linac. After beam dynamic optimization, wave phase velocities in the structure have been chosen to be 0.56, 0.9 and 0.999 respectively. Physical parameters about the main elements such as DC electron gun, iris-loaded periodic structure, solenoids, etc, are presented. Simulation results proves that it can satisfy the industrial requirement. The linac is under construction. Some components have been finished. Measurements proved that they are in a good agreement with the design values.     

合肥光源储存环束流软慢加速控制

 合肥光源储存环为非满能量注入,束流以200MeV的能量注入到储存环后慢加速到800MeV。介绍了慢加速的理论依据及储存环主电源控制系统的硬件结构,详细描述了束流软慢加速方法中的慢加速表计算及慢加速过程控制。机器运行结果表明:软慢加速方法控制灵活,慢加速过程运行平稳,束流损失很少,能很好地满足合肥光源机器运行和研究的需要。     

强流短脉冲电子束束剖面测量技术

 束流剖面信息的获得对于加速器的研究有着重要的意义。对强流短脉冲电子加速器束剖面测量技术作了评述。目前，发展时间分辨的快响应的光学测量技术及实时在线测量为主要发展趋势。     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

A 1-MW, 1-mm continuous-wave FELtron for toroidal plasma heating

A powerful, continuous-wave millimeter radiation source is presented. An electrostatic Cockcroft-Walton accelerator (2.5 MV) drives an FEL (free-electron laser) of 1 MW power. The accelerator has a new design in order to obtain a very powerful (50 MW) electron beam and very small ripple. A recovery system is used to increase RF power and efficiency. The FEL oscillator is 1.5-m long, with a permanent magnet helical wiggler. The cavity is equipped with Bragg mirrors. The FEL is set at the high voltage terminal     

Monitoring radiation levels in the FEL accelerator hall

The radiation control system for the Free Electron Laser (FEL) monitors the radiation in its workplaces and accelerator hall. Gas-filled detectors installed in the accelerator hall are used for radiation monitoring and controlling beam losses in the vacuum chamber and for beam orbit correction.     

基于激光等离子体加速的自由电子激光研究新进展

激光等离子体加速器能够在cm尺度内产生GeV量级的高品质电子束,为研制台式化自由电子激光提供驱动源。但是受限于激光等离子体加速中的难点和现有技术发展,电子束的品质难以达到自由电子激光的需求,尤其在稳定性、发散角和能散等方面,阻碍了台式化自由电子激光的研制。介绍了基于激光等离子体加速器的自由电子激光的最新进展,整理了目前高增益自由电子激光实验过程中存在的主要挑战和对应的解决方案与实验进展,并展望未来的发展方向。最近的研究结果证明,通过控制和优化激光等离子体加速器的注入和加速过程产生的高品质电子束可以在指数增益区域实现自发辐射放大,产生高增益的辐射,这也推动基于激光等离子体加速器的自由电子激光研究进入了一个新的阶段。     

Design of Smith-Purcell emitter in femtosecond accelerator

Based on the femtosecond accelerator device, we are planning to build a broad band and tunable THz source using the Smith-Purcell radiation mechanism. Coherent Smith-Purcell radiation could be achieved owing to the super-short bunch produced in the device. To shorten the distance between the beam and grating, we use Transport to match the beta function producing a sheet beam on the grating surface. The optimization of grating length, groove depth and groove width are given in the paper. Then the radiation power for the shallow and deep grating using these parameters are presented. The detection devices and methods are also briefly discussed.     

Effects of initial electron beam parameters of a linear accelerator on the properties of bremsstrahlung radiation in a radiotherapy setting

The dependence of the initial electron-beam parameters on absorbed dose distributions have been investigated using a CyberKnife radiotherapy accelerator (Accuray, United States). To describe the initial electron-beam characteristics, simulations of the linear electron accelerator are performed and the electron distributions in the beam of a linac output are analyzed. The radial distributions of electrons are assumed exponential, whereas the energy electron distributions are approximated by monoenergetic and rectangular spectra. There is no significant dependence of depth-dose curves in a phantom on the shape of the electron beam. Importantly, a clear dependence of the radiation field profile on the size of the electron beam is observed not just in the penumbra region, but also in the open part.     

New developments in design and applications for pelletron accelerators

Most of the developments over the last several years related to Pelletron accelerator are in the field of accelerator mass spectrometry (AMS) and other low beam current applications with the exception of a very high DC electron recirculation Pelletron. High precision AMS systems based on tandem Pelletrons from 500 kV to 5 MV terminal potential are now in use for routine high precision AMS measurements. Their performance will be reported. In addition, there has been significant advancement in the design of the multi-cathode SNICS source for the use of both gas and solid samples within a single source. The latest performance of these sources will be discussed. New diagnostics is being developed for very low beam currents. The latest design of the low current beam profile monitor (LCBPM) will also be presented.     

环境温度对合肥光源束流轨道稳定性的影响

 环境温度是影响电子束流轨道稳定性的重要因素之一，国内外大多数加速器实验室为此都建立了较为完备的环境温度监测系统和恒温空调系统。合肥光源(HLS)是第二代光源，全环闭合轨道垂直方向上要求稳定在100 mm以内。为定量研究和分析环境温度对合肥光源的电子束流轨道的影响，建立了环境温度监测系统。着重介绍了环境温度监测系统的组成、辐射干扰问题以及数据分析方法。数据分析结果表明：环境温度与束流位置之间具有较强的相关性，垂直方向环境温度每变化1 ℃,束流位置变化10～20 mm。