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.     

1.053μm激光辐照金箔靶发射X射线能谱的实验研究

在“星光-Ⅱ”单束高功率激光装置上利用束匀滑的钕玻璃基频激光辐照不同厚度的金箔靶,测量了金箔靶前向和背向的X射线能谱、X射线辐射能量角分布及X射线能谱时间变化过程,研究了金箔靶中激光烧蚀及辐射烧蚀过程;获得了不同厚度金箔、不同激光功率密度及不同角度等几种条件下其前后向X射线能谱的定量测量结果,同时从不同厚度的金箔背侧X射线能谱时间过程观察到明显的辐射热波时间延迟. 关键词： 金箔靶 X射线能谱 辐射烧蚀 辐射热波     

Tilted foil polarization of radioactive beam nuclei

Tilted foil polarization has up to now been mostly applied to nuclear reaction products recoiling out of a target traversed by a primary particle beam. Being a universal phenomenon it can be applied equally well to beams of particles, primary or secondary, radioactive or other. There are however some technical considerations arising from the nature of the beam particles. Radioactive beams are associated with ground state nuclei. They usually have low nuclear spin and as a consequence-as will be shown later-low polarization. Secondary beams are usually low in intensity and do not impose any constraints on the foils they traverse; unlike intense primary heavy ion beams which, if they traverse the foils, essentially limit the foil material to carbon. We review here briefly the tilted foil polarization process and then discuss an experiment with an isomer beam. Finally we review experiments with radioactive beams, past, present and planned for the future.     

电子束与烟气相互作用机制模拟分析

 电子束在烟气中穿透深度和剂量分布将直接影响废气中硫、氮氧化物的脱除效率。通过理论计算和蒙特卡罗模拟计算得到不同能量电子穿过各种厚度加速器箔窗后能量损失情况；对不同入射能量电子束在烟气中透射深度和轨迹分布进行了模拟计算。结果表明：电子束反应最佳能量为700 keV；利用产生1 m长线状束流的电子加速器进行双面照射，烟道反应室横截面最佳尺寸为1.0 m×3.5 m。     

The Electrostatic Trapping of an Intense Relativistic Electron Beam in a Magnetic Mirror

Observations of rapid axial oscillations of an intense relativistic electron beam in a magnetic mirror are reported. The mirror field primarily provides radial confinement of the relativistic electrons. The axial confinement was achieved by placing thin aluminized mylar foils at the conjugate mirror field maxima. The region between these foils was filled with a few Torr air to provide a beam induced plasma for charge and current neutralization. The regions outside these foils were maintained at ~10-4 Torr. One foil formed the anode of a space-charge limited relativistic electron diode which launched the beam into the mirror. When the beam passed through the second foil it was no longer charge neutralized. In a manner quite similar to the anode foil oscillations observed by others, a space-charge limited electrostatic well was established which stopped the electrons and re-accelerated them through the foil-thereby reflecting the beam. When the reflected electrons re-entered the diode, they were once again "electrostatically" reflected. This process continued until the oscillating beam was either lost through the "virtual cathodes" outside the foils, dissipated in the drift region or quenched in the diode plasma after gap closure.     

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.     

An electron microscope investigation of domain structures in thin terbium foils

Thin foils have been prepared from a high quality terbium single crystal for investigation in the transmission electron microscope. The preparation process involved spark machining, chemical polishing and ion beam thinning. The electron microscope was used to examine both the foil microstructure and its magnetic domain structure down to a temperature of 150 K. Below 230 K a narrow periodic magnetic structure running parallel to the in-plane b-axis was formed. This persisted over a temperature range of 10 K before giving way to a less regular pattern. As the temperature was lowered to 150 K the density of domain walls decreased and their deviation from the b-direction became more pronounced. A qualitative explanation of the observations is given.     

Interaction of H_2~+ molecular beam with thin layer graphene foils

The interaction of MeV H_2~+ molecular ions with thin layer graphene and graphite foils was studied by using a highresolution electrostatic analyzer.A large number of fragment protons were observed at zero degree(along the beam direction) when the H_2~+ beam was passing through the monolayer graphene foil, which indicates that the electron of the H_2~+ molecular ions can be stripped easily even by the monolayer graphene foil.More trailing than leading protons were found in the energy spectrum, which means significant wake effect was observed in the monolayer graphene foil.The ratio of the numbers of trailing protons over leading protons first increased with the thickness for the much thinner graphene foils, and then decreased with the thickness for the much thicker graphite foils, which indicates that the bending effect of the wake field on the trailing proton varied with the foil thickness.     

二次电子发射对质子束流测量精度的影响

二次电子发射直接影响法拉第探测器测量质子束流的精度,减小或消除二次电子发射的影响是提高束流测量精度的关键。根据二次电子补偿原理设计了二次电子补偿型同轴法拉第探测器,实验发现探测器测量质子束流强度时不能完全实现二次电子补偿。为改进和完善探测器的设计,从理论上分析了补偿片未能完全消除二次电子对束流测量影响的原因,是由于补偿片前向发射二次电子数目大于收集极后向发射二次电子数目所致。为此设计了质子束穿过金属箔发射二次电子测量装置,测量得到能量为5~10MeV质子穿过10μm厚铜箔时前向与后向发射二次电子产额,验证了理论分析的正确性。     

Coherent transition radiation from thin targets irradiated by high intensity laser pulses

A theoretical examination on coherent transition radiations (CTR) from the surface of thin solid density target irradiated by high intensity laser is presented. The theory is extended to consider the expansion dynamics of thin foils. The motion of target surfaces leads to the modulation on the temporal structure of micro bunches in the electron beam as well as the spectrum of CTR. The spectral shifts of radiation are owing to the enhancement of electron bunch separation and the relativistic Doppler effects. The radiation power distribution is strongly affected by the temporal coherence of electron beam structure, so thus the electron temperature and velocity dispersions. With these effects accounted for, the spectral properties of coherent transition radiation can provide insights into the expansion of thin foil targets irradiated by intense laser pulse as well as the fast electron transport through it.     

Backscattering of Relativistic Electrons Incident on a Planar Foil at a Small Angle to Its Surface

Photographs of cross sections of an electron beam backscattered from a thin tungsten target have been obtained on a dosimetric film. The procession of images makes it possible to obtain the spatial distribution of backscattered particles. The angles of back reflection θ_br of electron beams from foils have been measured. A 7.4-MeV microtron has been used as a source of electrons. The experiments have been performed with a tungsten foil 386 mg/cm² (200 μm) thick and a tantalum foil 1328 mg/cm² (800 μm) thick. Particles have been injected at an angle of α = 10° to the foil surface. The Monte Carlo simulation of the scattering of relativistic electrons incident on a planar target at small angles to its surface has been performed. The spatial and energy distributions of backscattered particle fluxes both transmitted through the target and reflected from it have been calculated. The dependences of fluxes on the direction of injection of particles and on the material and thickness of the target have been considered.     

高能质子束流强度绝对测量的二次电子补偿原理研究

高能质子入射到金属接收体表面诱发的二次电子直接影响束流强度的测量精度,如何消除二次电子影响是实现束流高精度测量的关键.根据高能带电粒子在金属表面诱发二次电子发射理论,对高能质子束流强度测量的二次电子补偿原理进行了研究,设计了二次电子补偿结构.采用三块金属极板构成的实验装置在高能质子源上开展实验研究,实验测得在中间极板上输出的电流与入射质子束流强度的比值小于0.7%,中间极板上二次电子得到补偿,验证了二次电子补偿原理的正确性.研究表明,采用设计的二次电子补偿结构对高能质子束流强度进行测量时二次电子贡献小于1%.     

一种带孔箔聚焦可重复运行的分离腔振荡器

 设计了一种有孔箔聚焦电子束的高功率分离腔振荡器，并对其进行了理论和数值研究。这种器件采用孔箔聚焦电子束，可以增加重复运行的次数，有效延长导电薄膜的寿命，而且不需要外加磁场聚焦电子束，波束相互作用区短，功率容量大，结构简单，输出信号稳定。还设计了电子束收集极来减小反射电子对器件的影响。对同一器件使用不同电压和电流的电子束，可以得到从50~900MW功率的微波输出。     

X-ray laser experiments using double foil nickel targets

New target geometries for collisional excitation X-ray laser experiments (in nickel) were proposed, analyzed, and experimentally studied on the Glass Development Laser (GDL). Experiments using a short line focus lens with new target geometries showed general agreement with predictions. The new geometries are designed to yield a higher gain and reduced refraction due to: (1) a higher plasma density, (2) a wider lateral density profile, and (3) a concave lateral density profile. These new geometries were: (1) two parallel exploding (thin) foils, irradiated from one side only, (2) two ablating (thick) foils, one of which is irradiated on its inner face, and (3) an exploding foil in front of an ablating foil, irradiated by a single laser beam incident on the thin foil. New experiments with a long line focus are in progress. The intensity ratio of Ne-like and F-like Ni lines is used to deduce the temperature, and these results together with the absolute intensity, yield the density profile. The results show improvement achieved with the new target geometries: the density is higher (leading to a higher gain), and the concave density profile results in collimation rather than divergence of the X-ray laser beam. Theoretical developments included: (1) prediction of high gain on new type transitions in neon like ions involving the excitation of an inner (2s) electron, and (2) development of a ray tracing code for an amplifying medium of varying (e.g., collimating) lateral density profile. Results using this code are shown for concave lateral density profiles.     

注入激光腔的束电子能谱计算

介绍一种用于计算电子束穿透薄层物质后的能谱分布的简单蒙特卡罗模拟方法,并对具可靠性进行了论证。利用这种方法对相对论性电子束泵浦强激光时,具有一定能谱分布的电子束穿透阳极膜,撑条(HIBACHI)及主膜后的能谱变化进行了模拟计算。     

X-ray laser studies at LLE

New target geometries for collisional excitation X-ray laser experiments (in nickel) were proposed, analyzed, and experimentally studied on the glass development laser. The new geometries are designed to yield a higher gain and reduced refraction due to (1) a higher plasma density, (2) a wide lateral density profile, and (3) a concave lateral density profile. These new geometries were (a) two parallel exploding (thin) foils, irradiated from one side only, (b) two ablating (thick) foils, one of which was irradiated on its inner face, and (c) and exploding foil in front of an ablating foil, irradiated by a single laser beam incident on the thin foil. Long-line-focus experiments are described. Theoretical developments included development of a ray-tracing code for an amplifying medium of varying lateral density profile and prediction of high gain on new type transitions in neon-like ions, involving the excitation of an inner (2 s) electron     

箔-聚焦的强流电子束的平衡与稳定特性

 通过箔 聚焦的电子束的包络方程研究了电子束的平衡与稳定特性，从而得到了能够传输的电子束的参数与箔之间距离和波导半径之间的关系。     

Performance improvements with advanced design foils in high-currentelectron beam diodes

A design for the vacuum/pressure barrier of an electron-beam diode ready to be fielded on a large krypton-fluoride excimer laser is described. The barrier is a composite foil, fabricated from carbon fibers, Kapton-membrane, epoxy, and copper foil. This composite foil has advantages over more traditional metal foils, exhibiting particularly high tensile strength and a high modulus of elasticity. Other important properties of these composites for use in KrF excimer laser applications include: high electron transmission with low loss to scattering, chemical compatibility with fluorine, low porosity, and low reflectivity in the ultraviolet. The mechanical properties of the composite foil allow the design of support structures (hibachis) which incorporate larger openings than are possible with metal foils with similar electron transmission characteristics     

7MeV注入剥离膜系统设计

设计了一台注入能量为7 MeV的快循环同步加速器剥离膜装置，介绍了主体结构设计及高精度换膜运动结构，实现膜片精确定位及在线换膜功能。针对注入参数对膜片开展分析计算，分析了7 MeV的负氢离子束注入时相应的碳膜材料的反应截面及不同厚度的剥离效率，给出了膜片厚度的参数选择。对所设计膜片的温升和寿命进行分析，膜片的温升最高点达到755 K，远小于同类的加速器的剥离膜温度，具有更高的寿命和可靠性。     

Auger electron emission spectra from foil and gas excited carbon beams

Auger electron emission spectra from 2 MeV C⁺ ion excited by collisions with thin carbon foils and Ne gas are presented. The similarity of qualitative features for the C⁺ → C (foil) and C⁺ → Ne spectra indicates the similarity of ionization mechanisms for beam foil and beam gas excitation. The spectra were normalized to the lowest lying Li-like quartet state (1s 2s 2p)⁴P⁰ in carbon by comparison with time delayed foil excited electron decay-in-flight spectra. Comparison to Hartree-Fock calculated transition energies indicates that transitions in three and four electron carbon ions dominate the prompt spectra.