Effect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion Plasma

This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ion flux from the cathode region of a vacuum arc

The properties of the ion flux generated in a vacuum arc are reviewed. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (~10% of the total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, although some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of the solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages but decrease with increasing arc current for a particular material. The main theories concerning ion acceleration in cathode spots are the potential hump theory and the gas dynamic theory. Experimental data indicate that these theories serve reasonably well when used to predict the mean values of the charge state, ion potential, and ion energies for the ion flux, but are quite insufficient when compared with the results for the potentials and energies of individual ions     

Ion Flux from the Cathode Region of a Vacuum Arc

This paper reviews the properties of the cathode ion flux generated in the vacuum arc. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (～10% of total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, though some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply-charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages, but decrease with increasing arc current for a particular material. The main theories concerning ion acceleration in cathode spots are the potential hump theory (PH), which assumes that all ions are created at the same potential, and the gas dynamic theory (GD), which assumes that all ions are created with the same flow velocity. Experimental data on the potentials and energies of individual ions indicates that these theories in their original forms are not quite correct, however extensions or modifications of the PH and GD theories seem very likely to be able to predict correct values for the charge states, potentials, and energies of individual ions.     

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采用PIC/MCC模型,通过数值模拟的方法研究了束线离子和靶台复合加速离子注入过程中靶台偏压大小对注入过程离子动力学行为的影响,重点考察了不同偏压作用下离子的注入能量、注入剂量、注入角度以及注入范围的变化.结果表明,靶台上施加脉冲偏压后,在束流离子的作用下空间电荷分布发生变化,束流正下方的电势线会发生凹曲,凹曲的电场同时又作用于空间中的带电粒子,影响粒子的运动;靶台偏压越高,零电势线距离靶台越远,靶台电场对离子的作用范围越大.离子的注入剂量、注入能量随着靶台偏压的增大而增大,而偏压对离子注入角度的影响并不大,大部分离子都以垂直入射的方式注入到靶台表面.另外,离子注入到靶台上的面积会因束流离子在靶台电场中飞行偏转而增大,并且偏压越大注入面积增大越明显.     

Ion emission from a hollow-cathode discharge with the plasma penetrating into the high-voltage acceleration gap

The general features of ion emission from a gas-discharge plasma are considered under conditions such that the plasma penetrates into the acceleration gap. It is found that the wall sheath limiting the open plasma surface substantially affects the stability of the penetrating plasma. It is shown that there are two plasma states with different positions of the plasma boundary. The stable state corresponds to the inequality r/R > 0.54, where r is the plasma radius in the accelerating electrode and R is the radius of the aperture of the accelerating electrode. It is shown that the plasma-sheath system within the aperture of the accelerating electrode can exist only if the voltage drop across the sheath does not exceed a certain limiting voltage, which depends on the plasma parameters.     

用于材料表面改性的多功能等离子体浸没离子注入装置

详细叙述了新近研制的多功能等离子体浸没离子注入（ＰⅢ）装置，在装置设计中，考虑了等离子体产生手段、高压脉冲电源和真空抽气系统多项功能要求，把离子注入、涂敷和溅射沉积结合起来，该已实现了多种气体等离子体注入、气－固离子混合与注入、金属等离子体沉积与注入、离子束混合与离子束增强沉积等，以满足不同材料制成的不同零件对多种表面处理工艺的需要，初步应用结果证明，该装置对于改进４５号钢、Ｔｉ－６Ａｌ０－４Ｖ和     

离子注入结合离子交换技术制备KTiOPO4光波导特性研究

用离子注入结合离子交换技术形成了 KTiOPO₄ 平面光波导,研究了离子注入对离子交换波导结构的影响.使用棱镜耦合法测量了波导特性,结果显示形成了表面折射率升高的多模波导,通过背散射技术研究了离子交换后的 Rb 离子分布.实验表明,注入离子导致样品晶格损伤,在 2.8 μm处对离子交换形成了阻挡层,阻止了交换向KTP晶体的更深处进行.     

离子注入层的X射线光电子能谱分析

采用金属蒸汽真空弧（MEVVA）离子源发出的强束流脉冲钨离子,对H13钢进行了离子注入表面改性研究,借助X射线光电子能谱（XPS）考察了注入表面层中钨,氧,铁的化学状态,研究发现,钨离子注入层中钨元素以替位钨和三氧化钨形式存在,铁元素以金属铁和三氧化二铁形式出现,而且各价态元素的原子比随深度而变化。     

Theoretical Study on Ion Escape in Martian Atmosphere

Based on the observation that Martian magnetic moment is gradually reducing from the ancient to the present, we investigate the O^＋ ion flux distribution along magnetic field lines and the ion escaping flux in Martian tail with different assumed Martian magnetic moments. The results show that the O^＋ ion flux along magnetic field lines decreases with distance from Mars; the ion flux along the field line decreases more quickly if the magnetic moment is larger; the larger the magnetic moment, the smaller the ion escaping flux in the Martian tail. The ion escaping flux depends on Z-coordinate in the Martian tail. With decrease of the magnetic moment, the ion escaping flux in the Martian tail increases. The results are significant for studying the water loss from Mars S uFface.     

Dynamics of femtosecond laser-produced plasma ions

We investigated the ion laser-produced plasma plume generated during ultrafast laser ablation of copper and silicon targets in high vacuum. The ablation plasma was induced by ≈50 fs, 800 nm Ti:Sa laser pulses irradiating the target surface at an angle of 45°. An ion probe was used to investigate the time-of-flight profiles of the emitted ions in a laser fluence range from the ablation threshold up to ≈10 J/cm². The angular distribution of the ion flux and average velocity of the produced ions were studied by moving the ion probe on a circle around the ablation spot. The angular distribution of the ion flux is well described by an adiabatic and isentropic model of expansion of a plume produced by laser ablation of solid targets. The angular distribution of the ion flux narrows as the laser pulse fluence increases. Moreover, the ion average velocity reaches values of several tens of km/s, evidencing the presence of ions with kinetic energy of several hundred eV. Finally, the ion flux energy is confined in a narrow angular region around the target normal.     

Characteristic features of the emission properties of pulsed broad-beam ion and plasma sources utilizing the evaporation of metal by a vacuum arc

An experimental confirmation was obtained of the anode potential fall effect in pulsed broad-beam ion and plasma sources utilizing the evaporation of metal by a vacuum arc. An increase in the overall voltage across the arc discharge was discovered. The investigations demonstrated that the magnitude of the positive anode fall depends on the structural features of the ion source and are determined by the ratio of the plasma flux directed onto the lateral surface of the anode to the total plasma flux from the cathode spot. It was established that the anode fall effect is controlled and makes it possible to influence the homogeneity of the ion current distribution over the beam cross section, the efficiency of extracting ions from the plasma, and the charge composition of the ion flux.Scientific-Research Institute of Nuclear Physics, Polytechnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 82–92, February, 1994.     

Localization of plasma in the extended hollow cathode of a ribbon-electron-beam plasma source at forevacuum pressures

The results of a study of the plasma density distribution in the slit aperture of a right-angled extended hollow cathode used in a ribbon-electron-beam plasma source operating at forevacuum pressures (1–10 Pa) are presented. It is shown that a local peak of plasma density appears in some region of the slit aperture as the slit width is decreased. This results in the appearance of a region of increased current density when the ribbon beam forms. The uniformity of the beam current density distribution is additionally disturbed by the reverse ion flow whose effect on the emission properties of the plasma is significant in the region of elevated pressure. A model which describes the development of plasma density nonuniformity in a hollow cathode is proposed which is based on the idea that the electron current flows predominantly through the slit aperture regions that are associated with local openings of the cathode layer ion sheaths. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–9, June, 2007.     

Effect of Discharge Voltage on an Ion Sheath Formed at a Grid in a Multi-Dipole Discharge Plasma

It is experimentally demonstrated that a relatively strong ion-rich sheath formed at a fixed negative bias of the grid can be changed to a rather weak ion sheath （sheath potential weakly retards electrons） only by increasing the discharge voltage in the system. At sufficiently high negative grid bias, an increase of discharge voltage enhances the ion collection current at the grid. An explanation is put forward in support of this experimental observation. A slight density enhancement with a fall in plasma electron temperature is also observed with the increasing negative grid bias.     

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.     

等离子体源离子注入过程中半圆形碗状样品的两维温度分布

等离子体源离子注入过程(PSII)中样品温度是一个非常重要的参量。由于注入到样品上的能量很大，导致样品温度很高，所以在实验中获知样品的温度分布有着很重要的意义。本文利用热传导方程建立了半圆形碗状样品内部温度升高模型，研究样品内温度演化过程。以注入离子束流作为能量输入项，热辐射为能量损失项，并考虑了热辐射过程中样品的形状因子的影响。考察了离子注入过程中样品上所施加负偏压的脉冲宽度和频率对样品温度分布的影响。研究结果显示，脉冲频率达到一定值后，样品温度不再随频率增加而升高。     

Expansion of an Ion Sheath into a Collision-Dominated Plasma

If a large negative voltage is applied to an insulated disc inserted in a collision-dominated plasma, the electrons are expelled from the region near the disc leaving a bare cloud of ions. This "transient sheath" is well documented in ion acoustic wave experiments. This paper examines the evolution of the ions in this sheath into a collision-dominated plasma. A new sheath whose dimension is of the order of twice the transient sheath dimension if found.     

空心圆管端点附近等离子体源离子注入过程中鞘层的时空演化

等离子体源离子注入过程中，鞘层的演化规律直接影响到离子注入到材料中的深度进而影响材料表面的性质和结构，对材料的不同部位这种影响是不同的.利用无碰撞两维流体动力学模型，研究了有限上升时间的电压脉冲作用下，共轴放置附加零电极的半无限空心圆管端点附近等离子体源离子注入过程中，鞘层的时空演化规律.通过计算得到了鞘层内随时间变化的电势分布和离子密度分布，计算了端点附近材料表面处的离子流密度分布和注入剂量分布随时间的变化规律.计算机模拟结果显示了空心圆管内部、外部及端点表面处的离子流密度分布和注入剂量分布存在很大差异.     

Influence of the Basic Process Parameters on the Ion/Atom Arrival Rate Ratio during Magnetron Sputter Deposition of Thin Carbon Films

The behaviour of the ratio of the argon ion flux and the sputtered atom flux to the substrate with the variation of the basic process parameters was studied in a planar magnetron sputtering system. Finding ways to control this ratio is important with respect to carrying out ion-assisted thin film growth by magnetron sputtering under well-defined conditions. Combined deposition rate measurements and plasma probe measurements were carried out in order to determine the ion/atom arrival rate ratio. In addition calculations of the neutral atom flux were performed on the basis of a simple model and the results compared with the measured values. A considerable change in the values of the ion/atom arrival rate ratio with the variation of the argon pressure and the discharge power was found under operating conditions, at which the back diffusion of the sputtered material is pronounced. The distribution of the ion flux over the substrate surface was found to become more homogeneous with the increase of the working pressure or the target-to-substrate distance.     

Dynamics of ablation plasma induced by a femtosecond laser pulse in electric fields

Direct observations of ablation plasma dynamics in electric field is presented. A time-resolved spatial profile of the ablation plasma induced by femtosecond laser ablation (fsLA) with high fluence is visualized using a planar-laser-induced fluorescence (P-LIF) method. The external electric field is produced by installing a mesh electrode at 6 mm from a Samarium solid target. The Sm ion plasma created by the fsLA showed collective motion regardless of the external electric field, until they reached close to the electrode. When the accelerating and decelerating field was applied, the ions almost disappeared behind the electrode from the field of view. The observations are understood utilizing a SIMION simulation with a conceivable potential gradient caused by Debye shield effect, which is that the ablation plasma keeps the same potential as the target voltage and follows electric potential gradient near the mesh electrode. It is also revealed that this effect degrades time-of-flight resolution at high fluence irradiation. This work gives a new direction for further developments of a fsLA time-of-flight spectrometer.     

PIC Simulation of the Motion of Plasma around Ion Sensitive Probes

The current‐voltage characteristics, the structure of electric potential around an ion sensitive probe and the particle flux on the ion collector have been simulated by the two dimensional particle‐in‐cell code (Berkeley Code). Concerning the separate mechanism of ions and electrons on the probe, the importance of electric potential profile around the electrode was pointed out. It was found that the E × B drift motion of electrons moving along the equipotential surface plays an essential role in the ISP measurement.