A 6 MeV heavy ion beam probe for the Large Helical Device

A 6 MeV heavy ion beam probe (HIBP) is being designed for potential measurements on the Large Helical Device (LHD). This article describes a method to control the 3-D probing beam trajectories in the helical magnetic field, an estimate of beam attenuation and energy reduction arising from the long paths in the plasma, and a cylindrical analyzer as a candidate for the energy analyzer     

Initial Measurements of Plasma Potential in the Core of the MST Reversed Field Pinch with a Heavy Ion Beam Probe

Measurement of the plasma potential in the core of MST marks both the first interior potential measurements in an RFP, as well as the first measurements by a Heavy Ion Beam Probe (HIBP) in an RFP. The HIBP has operated with (20-110) keV sodium beams in plasmas with toroidal currents of (200-480) kA over a wide range of densities and magnetic equilibrium conditions. A positive plasma potential is measured in the core, consistent with the expectation of rapid electron transport by magnetic fluctuations and the formation of an outwardly directed ambipolar radial electric field. Comparison between the radial electric field and plasma flow is underway to determine the extent to which equilibrium flow is governed by E×B. Measurements of potential and density fluctuations are also in progress.Unlike HIBP applications in tokamak plasmas, the beam trajectories in MST (RFP) are both three-dimensional and temporally dynamic with magnetic equilibrium changes associated with sawteeth. This complication offers new opportunity for magnetic measurements via the Heavy Ion Beam Probe (HIBP). The ion orbit trajectories are included in a Grad-Shafranov toroidal equilibrium reconstruction, helping to measure the internal magnetic field and current profiles. Such reconstructions are essential to identifying the beam sample volume locations, and they are vital in MST's mission to suppress MHD tearing modes using current profile control techniques. Measurement of the electric field may be accomplished by combining single point measurements from multiple discharges, or by varying the injection angle of the beam during single discharges.The application of an HIBP on MST has posed challenges resulting in additional diagnostic advances. The requirement to keep ports small to avoid introducing magnetic field perturbations has led to the design and successful implementation of cross-over sweep systems. High levels of ultraviolet radiation are driving alternative methods of sweep plate operation. While, substantial levels of plasma flux into the HIBP diagnostic chambers has led to the use of magnetic plasma suppression.     

Microscopic analysis of merging processes of relativistic electron beams propagating in a high-density plasma

The dynamical processes of an energetic electron beam propagating through a high-density plasma have been analyzed using an electromagnetic two-dimensional hybrid simulation code. After an initially solid cylindrical electron beam breaks up into a number of small beamlets, they start to merge with each other by means of their mutual current attractive force. The results show that detailed processes which take place when a pair of beamlets merge into a single one are different for different sizes of beamlets. When the size of the beamlet is small, the merging process is accompanied by magnetic field generation and the energy of the beam electrons then decreases in time. On the other hand, when the beamlet becomes sufficiently large, the merging no longer generates an excess magnetic field, and the energy of beam electrons is kept constant. The difference comes from the magnitude of the return current induced in the surrounding background plasma.     

子束排列方式对固体激光器光束合成特性的影响

 建立了固体激光器矩形光斑光束合成的理论模型,对诺·格公司给出的2束、4束、8束合成实验结果进行分析,并通过数值模拟,得到了不同子束排列方式下合成光斑的远场图形。通过仿真模拟可以得出:排列结构影响远场光斑的形状;子束间距决定了合成光束远场光斑的衍射旁瓣的大小和多少。采用环围能量进行分析,研究了远场光斑中主瓣能量随激光阵列占空比的变化。结果显示,远场光束环围功率随子束间距的增大而逐渐下降,而且参与相干合成子束越多,下降越大。     

二氧化锆薄膜表面粗糙度的研究

采用电子束蒸发工艺,利用泰勒霍普森相关相干表面轮廓粗糙度仪,研究了不同基底粗糙度、不同二氧化锆薄膜厚度以及不同的离子束辅助能量下所沉积的二氧化锆薄膜的表面粗糙度。结果表明：随着基底表面粗糙度的增加,二氧化锆薄膜表面粗糙度呈现出先缓慢增加,当基底的粗糙度大于10nm后呈现快速增加的趋势;随着二氧化锆薄膜厚度的增加,其表面均方根粗糙度（RMS）先减小后增大;随着辅助沉积离子能量的增加,其表面粗糙度呈现出先减小后增加的趋势。     

On the formation of the central plasma sheet by echo clusters of ion beams

Multiple energy dispersion structures of H⁺ ions that were observed at the passage of the INTERBALL-Auroral satellite through the plasma sheet at a geocentric distance of about 3R _E, where R _E is the radius of the Earth, on November 3, 1996, have been analyzed. The structure in the plasma sheet boundary layer, which has direct dispersion in energy and invariant latitude, in the range of 0.5–10.0 keV (velocity-dispersed ion structure) is an “autograph” of accelerated ion beams (primary beamlets) generated in the current sheet along the geomagnetic tail. The central plasma sheet contains five dispersion structures c1–c5 with the average energy ranging from 2.80 to 7.36 keV. The average energy of the structures increases with a decrease in the latitude. The event under consideration is a case of the regime of formation of the central plasma sheet by echo beamlets of the accelerated ion beam in the absence of a diffusion thermalized population of ions. This phenomenon is possibly explained by the fact that a magnetically quite period was observed three days before the passage of the satellite, when the regime of long-term diffusion of particles from the central plasma sheet occurred.     

射频离子源束流特性分析

介绍了为HL-2A 装置设计的引出束功率为1MW 的射频离子源研制情况。目前,在测试平台上,该离子源已经成功引出了束能量和束电流分别为35keV 和12.4A、束质子比为79%、脉宽为100ms 的氢离子束,达到了其设计束功率的44%。用红外热成像的方法测量了离子束能量密度分布。结果表明,在距离引出系统地电极 1.3m 处,束密度分布遵循高斯分布。引出束的最佳导流系数为1.689×10^–6A•V^-3/2 左右,随射频功率改变有较小的变化。根据这些实验结果,采取了相关改进措施来改善离子源的引出束性能。     

利用消衍射透镜列阵及光谱色散平滑实现焦斑均匀辐照

提出将空间域的透镜列阵法和时间域的光谱色散平滑法结合起来实现靶面的均匀辐照. 消衍射型透镜列阵能获得边缘陡峭且顶部较平坦的准近场焦斑，光谱色散平滑则能有效地抹平焦斑内部由多光束干涉引起的细密条纹. 数值结果显示，通过该方案能获得均匀性较好的焦斑. 进一步分析了光谱色散平滑单元中位相调制和光栅的参数对辐照均匀性的影响，发现参数的选取要在焦斑均匀性和能量利用率之间取得合理平衡，以在整体上获得最佳的均匀辐照效果. 关键词： 光谱色散平滑 透镜列阵 衍射 多光束干涉     

基于束间动态干涉的快速匀滑新方法

针对高功率激光装置中靶面辐照均匀性的高要求,提出了一种利用束间动态干涉改善辐照均匀性的快速匀滑方法.基本原理是利用共轭相位板阵列对存在一定波长差的多束激光附加相位调制,从而使各子束在远场两两相干叠加以产生动态的干涉图样,进而引起焦斑内部散斑的动态扫动,在ps时间内抹平不均匀性.以典型惯性约束聚变装置中的激光集束为例,通过建立基于束间动态干涉的快速匀滑物理模型,定量分析了相位板类型、相位调制幅度和束间波长差等因素对焦斑动态干涉图样的影响及规律,进而对其束匀滑特性进行了讨论.结果表明,基于束间动态干涉的快速匀滑方法可以有效地实现多方向、多维度的焦斑内部散斑快速扫动,且通过与传统束匀滑技术的联用,可以在更短的时间内达到更好的焦斑均匀性.     

Study of intermixing and Zr-silicide formation using swift heavy ion irradiation

Swift heavy ion (SHI) beam induced irradiation is an established technique for investigating structural modifications in thin films depending on the S _e sensitivity of material. Intermixing due to 120 MeV Au ion irradiation at different fluences from 10¹² to 10¹⁴ ions/cm² has been reported as a function of ion fluence in a-Si/Zr/a-Si thin films on Si substrate. The samples are characterized before (pristine) and after irradiation using Grazing Incident X-ray Diffraction (GIXRD) and Rutherford Backscattering Spectroscopy (RBS), which confirm the formation of ZrSi at thin film interface. It is suggested that mixing is mainly due to electronic energy loss since the energy transferred from high energy ions seems to create a transient molten zone along the ion track. It is found that the interface mixing increases linearly with the increase in ion fluence. The mixing effect explained in the framework of Thermal spike model. The irradiation effect on the surface roughness of the system is measured using Atomic Force Microscopy (AFM) technique. The current conduction mechanism and Schottky barrier height are also calculated by taking I–V curves across the Metal/Si junction.     

Commissioning of electron cooling in CSRm

A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108 particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10-4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy, electron beam current, electron beam profile, expansion factor and injection interval have been performed. The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.     

S波段多注相对论速调管的小信号理论

多注相对论速调管利用多注电子注并行工作,各电子注在传输过程中彼此独立,利于提高注波互作用效率,抑制杂模振荡。分析多注相对论速调管的小信号理论,从谐振腔内电场的场形函数出发确定了不同腔体结构的耦合系数的计算方法,得到了不同电子注形状、注数时的基波电流分量轴向变化过程,并进行模拟验证。结果表明:同轴谐振腔的间隙耦合系数要大于圆柱腔的间隙耦合系数,采用同轴谐振腔更有利于注波互作用;电子群聚过程与每注电子注的势能密切相关,提高电子注数目有助于得到更大的基波电流分量。在电子注电压600 kV、电流5 kA、间隙电压30 kV的条件下,输入腔后的基波电流分量达800 A。     

Optical properties of silver clusters formed by ion irradiation

Precipitation of silver clusters in silica is achieved by different methods: ion implantation, ion beam mixing of superimposed layers and ion irradiation of films deposited by means of co-sputtering or sol-gel technique. Main features of the nanoparticles depending on the preparation method are investigated by TEM. The optical extinction resonance of these clusters is analysed in terms of sizes and interaction between the clusters on the basis of calculations. We found that resonances in sputtered and gel films with low metal concentrations are well described by plasmon polaritons in isolated clusters and calculations based on Mie theory allow the study of their growth under irradiation. This theory is not appropriate to describe the optical response of silver clusters in silica implanted with Ag concentrations higher than 5 at.% or in ion beam mixed films, because of the interaction between clusters. Using an effective medium model, it is demonstrated that the random dispersion of clusters in implantation films causes fluctuations and, on average, an increase of the clusters polarization. On the contrary, the particular arrangement of the clusters with a bimodal size distribution in ion beam mixed films induces a screening effect between the clusters of largest size. Received 10 January 2002 / Received in final form 26 April 2002 Published online 19 July 2002     

电子束参量对轫致辐射照射量角分布的影响

本文研究了电子束半径,发射度及能量等参量对闪光X射线照射量在1m处角分布的影响。求得了使中心照射量最大,束半径与发射度之间应满足的拟合关系,表明了电子束能量越高,发射度越小,那么中心照射量就越大,照射量的空间分布就越理想。对电子细束入射位置和入射方向使用了解析法和随机抽样法求出,两种方法的数值计算所得的照射量分布符合得比较好。     

Formation,Dynamics, and Characterization of Nanostructures by Ion Beam Irradiation

Ion beam irradiation is a potential tool for phase formation and material modification as a non-equilibrium technique. Localized rise in temperature and ultra fast (～10^?12 s) dissipations of impinging energy make it an attractive tool for metastable phase formation. As a matter of fact, a major component of materials science is dominated by ion beam methods, either for synthesis of materials or for its characterization. The synthesis of nanostructures, and their modification by ion beam technique will be discussed in this review article. Formation of nanostructures using ion beam technique will be discussed first. Depending on species (e.g., mass and charge state) and energy range, there are various modes for an energetic ion to dissipate its energy. The role of the electron will also be covered in this article as a basic principle of its interaction with matter, which is same as for an ion. By using a simple reactive ion beam or electron induced deposition, a secondary phase can be nucleated by ion beam mixing techniques, either by using inert gas irradiation or reactive gas implantation on any desired substrate. Nucleation of secondary phase can also be executed by electron irradiation and direct implantation of either negative or positive ions. Post implantation annealing processes are required for the complete growth of clusters formed in most of these ion irradiation techniques. Implantation processes being inherently a non-equilibrium technique, defects always have a role to play in phase formation, amorphization, and beyond (blister formation). When implanted with large energy, even electrons, one of the lightest charged particles, also manifest these properties. Electronic and nuclear energy losses of the impinging charged particle play a crucial role in material modification. Doping a nanocluster, however, is still a controversial topic. Some light will be shed on this topic with a discussion of focused ion beam.     

二次电子对离子束流品质影响的动态研究

基于粒子云网格的计算方法,建立了具有外电路的加速系统模型,模拟了氘离子束轰击靶面产生二次电子的过程,动态地分析了二次电子的产生对离子加速电压的影响以及对氘离子束束流品质和氘离子束轰击靶面能量的影响。结果表明,当有0.06 A的二次电子电流产生时,离子加速电压将会下降45%,从而导致氘离子束束流品质下降,参与氘氚反应的氘离子数减少,相应的氘离子束轰击靶面的能量下降43.8%。     

Laser array beam propagation through liver tissue

Laser array beam propagating through mouse liver tissue is investigated. The turbulence power spectrum of the liver tissue is employed in the extended Huygens–Fresnel method to obtain an optical intensity profile and beam broadening at the observation point in biological liver tissue. Variations of the beam profile and the beam broadening are simulated based on the number of beamlets, source size, wavelength and the ring radius of the array. A biological tissue, illuminated by the laser array beam, exhibits different beam profiles and beam spot radius variations when the number of beamlets, source size, wavelength and the ring radius of the laser array beam are varied. Examining these variations observed in the propagated optical beam and comparing them with the test cases, abnormalities such as cancer and tumor in a biological liver tissue can be diagnosed.     

Reduction of turbulence-induced scintillation by nonuniformly polarized beam arrays

We have explored a method to reduce turbulence-induced scintillation by using an incoherent beam array composed of beamlets with nonuniform polarization. It is shown that significant scintillation reduction of such an incoherent beam array can be obtained by using nonuniformly polarized beamlets whose scintillation properties are optimized.     

Output polarization states of a corner cube reflector irradiated at non-normal incidence

A method has been developed for determining the polarization state of the retro-reflected beam from a corner cube irradiated with an input beam of arbitrary polarization state and of arbitrary tilt angle to the cube. Experimentally, the output beam consists of six distinct beamlets of different polarization states that are focused into six non-overlapping regions in the active area of the detector. The overall polarization state of the beam as measured by the photodetector can thus be represented by the incoherent superposition of the polarization states of the six beamlets. Experiments have been performed that verify the theory for a linearly polarized input beam irradiating the corner cube.     

电子束亮度及多孔板法测量发射度的原理

本文探讨了利用多孔板法测量四维横向相空间中均匀分布以及高斯分布的电子束发射度的测量原理。结果表明,对于四维均匀分布的电子束,该法测量的是电子束的边发射度,并且光斑尺寸随着小孔位置不同而变化;对于高斯分布的电子束,该法测量的是电子束的均方根发射度,其光斑尺寸与小孔位置无关。