Study of energy deposition and stripper temperature for CYCIAE-100

Nowadays high intensity proton accelerators are extensively applied, and this paper gives particular emphasis on CYCIAE-100, a 100~MeV high intensity compact cyclotron being constructed at CIAE. For accelerators of this type, the study is focused on how to improve the beam intensity. As for CYCIAE-100, the charge-exchange extraction is used to get protons. So it is crucial to enhance the lifetime of the stripping foil, which is largely determined by the energy deposition on it. For this cyclotron, due to the influence of the magnetic field, the electrons will spin near the foil and lose energy each time when they cross the foil. The energy deposition refers to all the energy deposition of protons and electrons. This paper stresses the stripper study of CYCIAE-100, in which the particle distribution on the foil is simulated and the energy deposition of the protons and electrons stripped from the H^－ ions are calculated. The temperature distributions are then calculated as a main reference for the foil design.     

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.     

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.     

Stripping extraction calculation and simulation for CYCIAE-100

A 100 MeV H- compact cyclotron is under construction at China Institute of Atomic Energy (CYCIAE-100). The proton beams of 75 MeV-100 MeV at an intensity of 200 μA will be extracted in dual opposite directions by charge exchange stripping devices. The crossing point at the switching magnet center is fixed inside the magnet yoke and the stripping points for various extraction energies are calculated by the code CYCTRS. With the code GOBLIN, we can calculate the transfer matrix including the dispersion effects from the stripping point to the switch magnet. The beam distribution just after stripping foil can be obtained from the multi-particle tracking code COMA and the extracted beam parameters after the switch magnet such as emittance, envelope, dispersion, energy spread, bunch length, etc. are given by the extraction orbit simulations.     

紧凑型回旋加速器物理问题及调束技术

介绍了紧凑型回旋加速器CYCIAE-100的特点及设计过程中重点考虑的一些物理问题,如紧凑型直边扇磁铁结构的轴向聚焦、异性高频谐振腔的设计、空间电荷效应等。研究了该加速器的调束技术,包括调束方案、诊断设备布局及径向靶测量的束流信息、物理图像。CYCIAE-100的主磁铁设计中,为降低磁铁和高频腔的加工难度而采用直边扇形磁极,为解决直边扇形磁极在大半径处的轴向聚焦力下降的问题,采用变气隙技术,从而有效提高轴向聚焦力。采用自行开发的基于PIC技术的宏离子模拟程序OPAL-CYCL进行了空间电荷效应的研究,结果表明,CYCIAE-100的极限流强为10 mA。     

100 MeV强流质子回旋加速器束流调试靶系统

中国原子能科学研究院正在建造一台100 MeV,200 A的强流质子回旋加速器,需要使用束流调试靶来调试加速器,为此设计了一套束流功率为20 kW的质子束调试系统。对该系统的束流输运线、靶材料的选取、靶结构、水冷计算、屏蔽结构等作了介绍。给出了整条束流输运线的匹配计算结果;通过对质子打靶后的中子产额、角通量、靶的活化等方面的比较,最终选用铝作为靶材料;根据加速器引出束流能量和功率,设计了分层式靶结构,同时对靶进行了水冷计算;打靶产生的出射粒子平均能量较高,导致产生的辐射剂量很大,考虑到对环境与工作人员的影响及费用,需要对其进行局部屏蔽,给出了屏蔽计算结果及屏蔽结构的设计。     

Design and construction progress of BRIF

A new RIB project, the Beijing Radioactive Ion-beam Facility (BRIF), has been running at CIAE since 2004. In this project, a 100 MeV H-cyclotron, CYCIAE-100, is selected as the driving accelerator providing a 75-100 MeV, 200-500 μA proton beam. An ISOL system employs two stage separators to reach the mass resolution of 20000. Its RIB beam will be injected into the existing Tandem and a superconducting booster installed down stream of the Tandem will increase the energy by 2 MeV/q. The progress of BRIF, giving special emphasis to CYCIAE-100, will be introduced in this paper.     

基于PIC方法的二维束流动力学模拟程序及其初步应用

为了深入研究强流负氢束在强流质子回旋加速器CYCIAE-100轴向注入线中的传输, 利用split-operator方法分解外场和束流自身的空间电荷场的作用. 对外 场利用单粒子跟踪技术, 采用一阶线性近似; 对空间电荷场采用PIC方法, 利用 快速傅里叶变换求解Poisson方程. 用FORTRAN95语言开发了一个基于面向对象技术的二维宏粒子传输计算程序CYCPIC2D, 本程序可以计算任意分布的强流束在输运线上的传输.最后给出了对CYCIAE-100注入线的模拟计算结果, 并和程序ORBIT, TRACE 3-D的结果进行比对验证, 结果表明: 空间电荷效应在此注入线上有较大的影响, 而且3个程序计算的不同中性化的结果基本上一致; 束流强度达到几十毫安时, 基于PIC方法的两个程序CYCPIC2D和ORBIT的计算结果完全吻合, 而线性近似程序TRACE 3-D有明显差异.     

Influence of radial magnetic field on emittance in the median plane at CYCIAE-100

A 75—100 MeV H- compact cyclotron CYCIAE-100 is being constructed at China Institute of Atomic Energy (CIAE). About 200 μA proton beam will be provided by CYCIAE-100. The imperfection of magnetic fields will remarkably affect the acceleration orbit and beam envelope in CYCIAE-100. The effects to the accelerating beam by the imperfection fields, especially the field components Br on the mid-plane will be analyzed in detail with tracking code COMA. Poles misalignment that causes magnetic imperfection will be described in the paper. According to the simulation results, the tolerance of the poles machining and assembly will be illustrated in this paper.     

30MeV医用回旋加速器气体靶束流线的研制

中国原子能科学研究院于1994年研究建成我国第一台医用强流回旋加速器CYCIAE-30及配套放射性同位素生产线, 目前为了增加气体靶以生产新品种医用同位素, 在原有束流输运线的基础上开展了束流输运系统的升级改造方案设计, 包括束流线的总体布局考虑和光学设计, 并根据束流光学设计的结果, 进行了新增束流线上电磁元件的设计. 在物理设计的基础上, 还进行了施工设计以及各分系统的加工、调试、安装, 并以物理设计得到的参数为依据进行了束流调试, 靶上得到的束斑与理论值有较好的符合, 满足设计要求.     

Physics design of CYCAIE-100

The design and construction of Beijing Radioactive Ion-beam Facility (BRIF) was started at China Institute of Atomic Energy -CIAE) in 2004. In this project, a 100 MeV high intensity cyclotron, CYCIAE100, is selected as a driving accelerator for radioactive ion beam production. It will provide a proton beam of 75—100 MeV with an intensity of 200—500 μA. The scheme adopted in this design, i.e., stripping the accelerated H-, makes the structure more compact and construction cost much lower. At present, the design for each system has been accomplished. This paper depicts the basic physics design of the machine, including its major structure and parameters, beam dynamics and each relevant system, e.g. basic structure of the main magnet, numerical simulation of the RF resonant cavity, axial injection system, central region, and study on crucial physics problems concerning the extraction and beam lines. The major problems encountered during the design of CYCIAE-100 are also summarized in this paper.     

通道靶对超强激光加速质子束的聚焦效应

发散角过大是制约超强激光与固体靶相互作用加速产生高能质子束应用的一个重大物理难题.本文提出了一种结构化的通道靶型,与超强激光相互作用可提高质子束的发散特性,通道壁上产生的横向电荷分离静电场可对质子有效聚焦.采用二维particle-in-cell粒子模拟程序对激光通道靶相互作用过程进行了研究,分析了加速质子束的性能特点.模拟结果表明,与传统平面靶相比,通道靶可以在不过多损失能量的情况下产生具有更好准直性的质子束,尤其当通道靶的直径与激光焦斑尺寸和质子源尺寸相当时,横向静电场能够有效聚焦质子束,并且可保证相对较高的激光能量利用率.     

超短强激光脉冲驱动等离子体波加速电子方案

随着超短脉冲激光技术的发展, 人们可以在台面尺度获得光强超过10¹⁸W/cm²、脉宽小于100fs的超短脉冲激光.超短脉冲激光很容易把静止的电子加速到兆电子伏的能量. 而更重要的是超短激光脉冲可以通过其有质动力激发大振幅的等离子体波(称为激光尾波场), 后者可以在毫米空间尺度把电子加速到上百兆电子伏的能量.文章将介绍激光尾波场加速电子的物理机制和方案、这个领域的最新进展、以及目前存在的问题.     

Broad energy spectrum of laser-accelerated protons for spallation-related physics

A beam of MeV protons, accelerated by ultraintense laser-pulse interactions with a thin target foil, is used to investigate nuclear reactions of interest for spallation physics. The laser-generated proton beam is shown (protons were measured) to have a broad energy distribution, which closely resembles the expected energy spectrum of evaporative protons (below 50 MeV) produced in GeV-proton-induced spallation reactions. The protons are used to quantify the distribution of residual radioisotopes produced in a representative spallation target (Pb), and the results are compared with calculated predictions based on spectra modeled with nuclear Monte Carlo codes. Laser-plasma particle accelerators are shown to provide data relevant to the design and development of accelerator driven systems.     

Proton angular distribution research by a new angle-resolved proton energy spectrometer

The proton spectral and angular distributions simultaneously within the target normal direction and laser propagation direction by using an angle-resolved proton energy spectrometer are studied.For the protons generated in the interactions of 100 fs,800nm laser pulses with aluminum foil targets,the deviations of proton beam centers of different energies from the target normal direction towards the laser propagation direction are different.This is probably because of the toroidal magnetic fields generated at the rear target surface,which deflect protons transversely.As a result,protons in low energy range have large deviation angles,protons in middle energy range have the smallest deviation angles,while protons in high energy tail have large deviation angles.     

质子束团传输过程中的二次电子多级倍增

电子云不稳定性是强流质子加速器稳定运行的一个重大障碍。在电子云积累的过程中,二次电子多级倍增是电子云的主要来源。二次电子多级倍增机制可以用电子的运动和能量增益来分析。为了得到电子云的密度及分布,编写了一个模拟程序用来跟踪电子云的发展演化过程。分析了在质子束团作用下电子的运动,分析二次电子多级倍增的原因,并用模拟程序进行了计算,结果发现电子云与束团的纵向分布密切相关。     

Overlapping of resonances and stochasticity of electron trajectories in cyclotron masers

When an electromagnetic (EM) wave has a large amplitude and electrons have a large energy, the electron cyclotron frequency in the process of interaction with an EM wave can vary significantly. This can lead to overlapping of cyclotron resonances at different harmonics. It is shown that such an overlapping causes the stochasticity of electron orbits. Estimates show that this effect can be present in relativistic gyrodevices currently under development for driving future accelerators.     

Conceptual design of an intense positron source based on an LIA

Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.     

Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak

During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak, the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics. During electron cyclotron resonance heating, it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level, which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating. From the set of discharges studied in the present experiments, it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors: electron cyclotron resonance heating power and duration. These results have been analysed by using a test particle model. The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons. During electron cyclotron resonance heating with different powers and durations, the runaway electrons will experience different slowing down processes. These different decay processes are the major cause for influencing the efficiency of runaway suppression. This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.     

Resonant diffusive radiation in random multilayered systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. The resonant condition can be satisfied for the wavelength region representing visible light as well as soft X rays. The intensity of diffusive soft X rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at a photon energy of 99.4 eV, the intensity of resonant diffusive radiation (RDR) generated by 5-MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453 eV and 13 MeV, electrons passing a Be/Ti multilayer generate RDR exceeding the Cherenkov radiation generated by electrons passing Ti foils by a factor ≈130.