MEVVA金属离子源的研制与调试

本文介绍的ＭＥＶＶＡ源采用电动推进式可更换单阴极弧放电机构和加减速三栅引出系统，耐压水平在于５０ｋＶ，平均束流大于５ｍＡ，束班约Ф１５０，束的不均匀度小于±２０％。束的分布测量表明，在中心区有约Ф４０的平顶区。我们已获得了Ａｌ，Ｔｉ，Ｃｒ，Ｆｅ，Ｎｉ，Ｃｕ，Ｙ，Ｚｒ，Ｍｏ，Ｔａ，Ｗ，Ｃ，ＬａＢ６等的离子束流及其最佳的运行条件。     

Penning型负氢离子源诊断

为了给小型医用回旋加速器提供负氢离子,研制了一台Penning型负氢离子源。采用发射光谱法对该负氢离子源进行了诊断,同时结合离子源功率变化对离子源工作状态进行了分析。实验测量了不同氢气流量、离子源弧流及磁场条件下,该离子源等离子体氢原子巴尔末系中前三条谱线的相对光强和离子源功率变化,分析了不同工作条件对离子源工作状态的影响。结果表明：在可调节范围内,该离子源的工作状态主要受氢气流量的影响,对离子源弧流及磁场的变化不敏感。     

Penning型负氢离子源诊断

 为了给小型医用回旋加速器提供负氢离子,研制了一台Penning型负氢离子源。采用发射光谱法对该负氢离子源进行了诊断,同时结合离子源功率变化对离子源工作状态进行了分析。实验测量了不同氢气流量、离子源弧流及磁场条件下,该离子源等离子体氢原子巴尔末系中前三条谱线的相对光强和离子源功率变化,分析了不同工作条件对离子源工作状态的影响。结果表明：在可调节范围内,该离子源的工作状态主要受氢气流量的影响,对离子源弧流及磁场的变化不敏感。     

强流RF 离子源研制及初步实验

介绍了RF离子源驱动源的结构设计及RF线圈的热流固耦合分析。RF离子源采用外置天线的感应耦合方式,采用双射频驱动源设计,每个射频驱动源功率约60kW,总体功率为120kW,可产生均匀高密度的等离子体,以满足稳定的长脉冲运行的要求。在完成上述工作的基础上完成了RF离子源样机组装和初步实验测试。     

高频离子源等离子体的光谱诊断

 采用发射光谱法研究了高频离子源的等离子体性质。该离子源应用于ZF-200keV中子发生器中，是一种电感耦合型无极环形放电高频离子源。实验采用绝对定标后的光学多道分析系统测定了离子源等离子体在不同阶段氢原子巴耳末谱线系中前三条谱线的强度，并采用部分局部热力学平衡状态的理论，计算出了相应阶段高频离子源等离子体的电子温度、氢原子浓度、氢离子浓度等参数，并进行了简要分析。     

Feasibility study on high current ion beam extraction from anode spot plasma for large area ion implantation

In this paper, we have investigated the feasibility of the high current beam extraction from anode spot plasma as an ion source for large area ion implantation. Experiments have been carried out with the ambient plasma produced by inductive coupling with radio-frequency (RF) power of 200 W at the frequency of 13.56 MHz. Anode spot plasmas are generated near the extraction hole of 2 mm in diameter at the center of a bias electrode whose area exposed to the ambient plasma can be changed. It is found that the maximum ion beam current is extracted at the optimum operating pressure at which the area of bias electrode exposed to ambient plasma is fully covered with the anode spot plasma whose size is dominantly determined by the operating pressure for given gas species. It is also observed that the extracted ion beam current increases nonlinearly with the bias power due to the changes in size and shape of the anode spot plasma. With the well-established anode spot plasma operating at the optimum gas pressure, we have successfully extracted high current ion beam of 6.4 mA (204 mA/cm²) at the bias power of 22 W (∼10% of RF power), which is 43 times larger than that extracted from the plasma without anode spot. Based on the experimental results, criteria for electrode design and operating pressure for ion beam extraction from larger extraction aperture are suggested. In addition, the stability of anode spot plasma in the presence of ion beam extraction through an extraction hole is discussed in terms of the particle balance model.     

Two-dimensional particle-in-cell plasma source ion implantation of a prolate spheroid target

A two-dimensional particle-in-cell simulation is used to study the time-dependent evolution of the sheath surrounding a prolate spheroid target during a high voltage pulse in plasma source ion implantation. Our study shows that the potential contour lines pack more closely in the plasma sheath near the vertex of the major axis, i.e. where a thinner sheath is formed, and a non-uniform total ion dose distribution is incident along the surface of the prolate spheroid target due to the focusing of ions by the potential structure. Ion focusing takes place not only at the vertex of the major axis, where dense potential contour lines exist, but also at the vertex of the minor axis, where sparse contour lines exist. This results in two peaks of the received ion dose, locating at the vertices of the major and minor axes of the prolate spheroid target, and an ion dose valley, staying always between the vertices, rather than at the vertex of the minor axis.     

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介绍了一种广泛应用于离子刻蚀、预清洗和离子束辅助镀膜的阳极层离子源的工作原理,分析了磁场对其性能的影响。给出了线性阳极层离子源磁路的设计。采用ANSYS有限元分析软件对线性阳极层离子源的静态电磁场进行了模拟分析,并与实验结果进行了比较,结果令人满意。通过ANSYS编码对电磁场模拟,可为具体的阳极层离子源的改进设计提供指导。     

电子回旋共振离子源等离子体的密度测量

 诊断电子回旋共振离子源等离子体的传统方法是采用传统的单探针无发射时测量伏安曲线,并根据曲线的拐点由理论公式计算出的等离子体密度。本文设计并研制了等离子体密度的测量装置。采用单根朗缪尔探针（该探针可以用来发射电子）测量等离子体的伏安特性。在探针有发射和无发射两种状态下测量得到两条伏安曲线,根据这两条曲线的"分叉点"得到等离子体电位,然后根据该电位直接由计算机计算出电子温度、电子密度。采用该新方法,测量得到的等离子体参量空间电位约为17 V,悬浮电位约为-5 V,电子温度约为4.4 eV,离子密度为1.10×10¹¹cm^-3,与传统方法计算出的等离子体1.12×10¹¹cm^-3相比,两者相差仅1.8％,但新方法效率和精度更高。     

Optimisation of cold cathode ion source model

This paper represents the results of the optimisation of cold cathode ion source model with 5 cm extraction aperture diameter. In this model, the glow discharge is utilised for generation of electrons in the cathode of the ion source. The various models with different lengths of cathode and anode are tested. The shortest model with 4.5 cm in length of cathode and anode each shows satisfactory operation and can be used in cases when the high values of extracted ion current are not required. The best model from the point of view of ion beam current value and efficiency of the discharge is the model with cathode length of 7 cm and anode length of 7 cm. In this case, the obtained maximum ion beam current is 110 mA when the discharge current is 1000 mA. In case when moderate values of extracted ion beam current are necessary, it is possible to operate the ion source even without the anode magnetic system.     

RF离子源引出特性的研究

 为了使RF离子源具有良好的引出特性,测试了吸极几何参数、振荡器板压和引出电压对离子源聚焦度的影响,对实验结果进行了分析。在其它参数不变的情况下,吸极的外径D与内径d之比存在最佳值,增加D/d,有利于过聚焦的离子束恢复聚焦状态。吸极的长度为L,石英套管比吸极长l。当l/D增大时,聚焦度上升,引出束流下降。L/d之比减小时,聚焦度增大。当L/d小于4时,聚焦度增加趋势变缓。综合考虑聚焦度、引出束流和气压,D/d,l/D,L/d适宜的选择范围分别为1.6～2.1,0.7～1.1,4～7。增加振荡器功率会使离子束呈弱聚焦,而增加引出电压会使离子束呈过聚焦。振荡器功率和引出电压都存在最佳值。     

A technique for positron spectroscopy of monovacancies formed by low-temperature ion implantation of silicon

A system for positron beam-based Doppler broadening spectroscopy of the formation and evolution of monovacancy defects in silicon is described. The apparatus allows in situ ion implantation at low temperatures (∼50 K) followed by positron beam assay. First measurements for 6 keV He implantation, at post-implant temperatures between 60 and 300 K are presented. Benefits and drawbacks of this system are discussed.     

Technical issues related to the design of third generation ECR ion sources

The design of third generation electron cyclotron resonance ion sources (ECRIS) had to take into account some technical issues that are usually not relevant for conventional ECRIS, either in terms of microwave power management or in terms of stray magnetic field. In fact, strong magnets originate high stray fields that are detrimental for beam optics, for the pumping system lifetime and mainly for the gyrotron normally used for power generation. Additionally, the presence of intense X-ray fluxes generated by the ECRIS plasma, observed in many experiments, can generate an unexpected heat load upon the thermal balance of the superconducting ECRIS cryostat, which can trigger a warm-up in the case of closed-loop cryostat connected to a cryocooler setup. These and other issues are presented by the authors along with a study of possible solutions.     

等离子体离子源发射面的理论计算与数值模拟

 等离子体离子源发射面的位置和形状决定了离子束的传输特性,而发射面的位置与形状又取决于等离子体参数、引出电压、电极结构等,并自动地调节到某个平衡状态。介绍了一种2维情况下等离子体离子源发射面的位置与形状的理论计算方法,即非磁化等离子体不能扩散进入外加电场中大于一定临界值的区域,等离子体离子源发射面的位置及形状可以通过直接求解引出系统的Laplace方程而得到。利用基于PIC的OOPIC程序对不同引出结构的发射面位置及形状和引出束流进行了数值模拟,结果与理论计算的结果十分接近。