Optimization and numerical simulation for the extraction system of the H- multicusp ion source

A new ion source has been designed and manufactured for the CYCLONE30 accelerator, which has a much advanced performance compared with the original. It is expected that the newly designed ion source extraction system will transport a very large percentage of the beam without deteriorating the beam optics, which is designed to deliver an H- beam at 30 keV. The accelerator assembly consists of three circular aperture electrodes made of copper. The simulation study was focused on finding parameter sets that raise the beam perveance as large as possible and which reduce the beam divergence as low as possible. Ion beams of the highest quality are extracted whenever the half-angular divergence is minimum, for which the perveance current intensity and the extraction gap have optimum values. The triode extraction system is designed and optimized by using CST software （for Particle Beam Simulations）. The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that it is possible to achieve this goal by decreasing the thickness of the plasma electrode, shortening the first gap, and adjusting the acceleration electrode voltage.     

多峰离子源的三维数值模拟优化与设计

本文理论计算了多峰离子源永磁体, 采用二体碰撞模型处理电子之间的库仑碰撞, 运用空碰撞方法处理电子与氢元素相关粒子碰撞, 开发了全三维粒子模拟-蒙特卡罗模拟算法, 并采用此软件对热门多峰离子源JET-60U的两种优化设计模型进行数值模拟研究, 探索了两种离子源空间分布特性和体积负氢离子产率相关问题, 提出了负氢离子源设计的基本思想: 适当调整离子源多峰磁场分布情况可以输出均匀离子束; 适当调整引出磁场大小和离子源结构, 可以达到离子束空间均匀性和高产率兼顾的效果.     

J-PARC多峰离子源体积产生效率三维数值模拟研究

深入阐述了拥有自主知识产权的粒子模拟-蒙特卡罗算法, 并采用该算法数值研究了J-PARC多峰离子源放电特性, 分析了J-PARC离子源的放电机理, 并在单、双校正磁体下讨论了该离子源体积产生效率. 结果显示: 在单校正磁体下, 校正磁体中心与离子源顶端相距50 mm时, 体积产生效率最大; 在双校正磁体且固定顶端磁体下, 两磁体相距越大体积产生效率越低.     

Optimization and numerical simulation for the extraction system of the H~- multicusp ion source

A new ion source has been designed and manufactured for the CYCLONE30 accelerator, which has a much advanced performance compared with the original. It is expected that the newly designed ion source extraction system will transport a very large percentage of the beam without deteriorating the beam optics, which is designed to deliver an H^- beam at 30 keV. The accelerator assembly consists of three circular aperture electrodes made of copper. The simulation study was focused on finding parameter sets that raise the beam perveance as large as possible and which reduce the beam divergence as low as possible. Ion beams of the highest quality are extracted whenever the half-angular divergence is minimum, for which the perveance current intensity and the extraction gap have optimum values. The triode extraction system is designed and optimized by using CST software (for Particle Beam Simulations). The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that it is possible to achieve this goal by decreasing the thickness of the plasma electrode, shortening the first gap, and adjusting the acceleration electrode voltage.     

Thermal analysis of the CSNS H- ion source

There are two cooling systems to maintain the thermal stability of the CSNS H ion source during its operation: Air-cooling in the source body of the discharging chamber and water-cooling in the flange on which the discharging chamber is installed.The optimal cooling parameters to ensure the operation of the H-ion source are determined through a thermal analysis. In addition, a transient analysis is also performed to know exactly the transient temperature variation during the whole 40 ms period of the pulsed mode operation of the ion source.     

A numerical model for lithium plasma process in a hybrid microwave ion source

Lithium ions are widely used in many scientific fields; in order to get these ions, it is necessary to study lithium plasma process thoroughly. Recently, a hybrid ⁷Li³⁺ ion source has been designed and tested at Peking University (PKU). To understand the lithium plasma behaviour inside the plasma chamber and to provide some guidelines for ion source optimization to generate ⁷Li³⁺, a numerical model based on the plasma equilibrium equations is developed in this work, which is helpful not only for our ion source, but also for understanding the physical process of lithium plasma from ECR ion sources with different frequencies. This model can describe the density and fraction of lithium ions in various system parameters. The dependences of the Li⁺, Li²⁺, and Li³⁺ ion density and fraction on electron temperature, gas pressure, microwave power, surface ionizer, and the magnetic field are investigated systematically.     

Design of magnet and control of the beam emittance for Penning H- ion source

The design requirement and principle of the deflection magnet for Magnetron and Penning H- ion source are discussed.It is proved that there exists a maximum emittance for the beam that may be transformed by the magnet into a state with equal Twiss parameters of αr=αy and βr =βy,which is the requisite condition to get a minimum emittance at the entrance of RFQ after transporting by a LEBT with solenoids.For this maximum emittance,the corresponding magnetic field gradient index is 1.     

Observation of clusters in a sputtering ion source

This paper reports previously unpublished results which were obtained in 1966. We systematically investigated the dependence of cluster ion intensities on the bombarding gases He⁺, Ar⁺ and Xe⁺ (energies: 4 to 12 keV, current densities: 100 mA/cm²). Frequently, the observed structures in the relative cluster intensities were quite puzzling, e.g. for A1 and Si. Attempts to correlate these structures to crystal configurations failed, nor did any pattern develop from simple valency considerations alone. Initial ion energy distribution measurements from 0 to 1200 eV showed significant differences for atomic ions and cluster ions. This effect is used to reduce interference problems caused by cluster ion peaks in SIMS applied to trace analysis of solids. The results are discussed and compared with those of other investigators, also including cluster formation by vaporization and sparking. Extending known theoretical considerations may possibly afford a general understanding of the intensity structure. The formation and ejection mechanisms of clusters, however, remain unknown. Thermal effects to explain the latter are definitely discounted by the magnitude of the observed initial cluster energy (> 10 eV). Also discussed are two phenomena which demonstrate the presence of the bombarding gas in the surface.     

Shape of a liquid metal ion source

A model of the liquid-metal ion-source shape consisting of a jet-like protrusion on the end of a Taylor cone shape is shown to be consistent with a field evaporation mechanism of ion formation, fluid dynamic considerations, space charge effects and recent TEM observations. The diameter of the ion emitting area is found to be only a few tens of Å. Self-consistent numerical calculations of electric potential and particle trajectories predict emission characteristics which compare favorably with experimental results.On leave from Trinity Hall, Cambridge, UK     

Influence of ion-beam plasma on ion extraction efficiency in a single-grid ion source

The influence of ion-beam plasma on ion extraction efficiency in a single-grid ICP ion source is researched. The single-grid ion source is considered as a system with two plasmas, ion-beam plasma and the source plasma, separated by an extraction grid. Results of experimental measurements of the potentials of the two plasmas and the ion beam current dependence on these potentials are presented. It is shown that the ion extraction efficiency depends equally on both the acceleration potential and on the potential of the ion-beam plasma. The obtained results demonstrate the key role of the ion-beam plasma in the ion source operation, which is important in technological applications and space thrusters.     

Pulsed operation of a liquid metal ion source

Short ion pulses (100 ns FWHM) have been produced from an In liquid metal ion source (LMIS) of the needle type by superimposing short voltage pulses (500 ns) onto a subcritical extraction field. Extractor-pulsed LMIS are thought to be useful as primary ion sources in time-of-flight (TOF) mass spectrometers, particularly for space applications, where extended charge life time and reduced power consumption are of great importance.     

Investigation of a tin liquid metal ion source

In view of its importance in materials research, tin is a metal worth studying in a liquid metal ion source configuration, even if results complement or extend previous work. This is the more so if the new work corrects misconceptions of the past and adds to current thinking. We, therefore, prepared a Sn liquid metal ion source employing a Ni needle to anchor the liquid, cone-shaped, emitter. Source properties, such as the current–voltage curve, the mass spectra of the beam and the energy spread of the main ionic species, were studied in detail. The mass spectra show a considerable amount of Sn clusters, apart from the dominant species, Sn⁺ and Sn⁺⁺. The source was stable down to 1-A emission current, corresponding to an energy spread for the singly charged ions of 7 eV. Theoretical arguments, involving the peak energy deficit of the ion-energy distribution, strongly suggest that both Sn⁺ and Sn⁺⁺ are emitted by direct field evaporation from the liquid surface. The same conclusion is reached from a careful examination of the beam mass spectra of the source. PACS 07.77.Ka; 33.15.Ta; 61.25.Mv