Influence of a current jump on vacuum arc parameters

Based on time of flight method, influence of short time vacuum arc current jump on arc plasma parameters were investigated. Superposition of the current pulse of a vacuum arc with a high operating voltage results in the appearance of ions of higher charge state in the discharge plasma and in an increase in the mean ion charge state for most of the cathode materials used in the experiment. The method of a “short-time current jump” can be also used to investigate the parameters of a vacuum arc, in particular to estimate the ion direct velocities in vacuum arc plasmas. Our estimates show that in the presence of a current step the ion velocities are almost identical for all differently charged ions and depend only on the peak current and the ion mass     

Effect of the discharge parameters on the generation of deuterium ions in the plasma of a high-current pulsed vacuum arc with a composite zirconium deuteride cathode

We have studied the mass and charge composition of an ion beam extracted from the plasma of a vacuum arc with a zirconium deuteride cathode for various durations of the arc current pulse (half width at half amplitude) of 2, 4, 7, and 17 μs. It has been established that the fraction of deuterium ions in the vacuum arc plasma increases with the current and the dependence achieve saturation for current of about 1 kA. For the fraction of deuterium atoms in the cathode at a level of 40%, the fraction of deuterium ions in the vacuum arc plasma can exceed 80%. The experimental results have been interpreted theoretically. It has been shown that the main sources of deuterium ions in a microsecond arc discharge are cathode spots. We have developed a model of deuterium desorption during the operation of cathode spots for quantitatively estimating the concentration of deuterium ions in the arc plasma.     

Mechanism of ion flow generation in vacuum arcs

The ecton model of the cathode spot is used to analyze the main parameters of ion flow in vacuum arcs (ion erosion, mean charge, and velocity). It is shown that the arc plasma is formed as a result of microexplosions at the cathode surface, induced by the Joule heating by the high-density current of explosive electron emission. Ionization processes are localized in a narrow region of the order of a micrometer near the cathode and the ionization composition of the plasma subsequently remains unchanged. Under the action of the electron pressure gradient, ions acquire directional velocities of the order of 10⁶ cm/s even over small distances of the order of several micrometers.     

Study of directed ion velocities in a vacuum arc by an emission method

Directed ion velocities in a vacuum arc discharge plasma are measured on the basis of a study of the ion emission current response to a rapid change of arc current. It is shown that these velocities are about 10⁶ cm/s, are determined by the cathode material, and are almost independent of the ion charge number. Applying a magnetic field results in an increase in the directed ion velocity. As the gas pressure increases, the directed ion velocity decreases; this is the only case where the directed velocities are observed to depend on the ion charge number.     

Determination of the specific ion erosion of the vacuum arc cathode by measuring the total ion current from the discharge plasma

The specific ion erosion γ_i of cathodes made of C, Mg, Al, Ti, Co, Cu, Y, Mo, Cd, Sm, Ta, W, Pt, Pb, and Bi is determined by measuring the total ion current from the vacuum arc plasma. It is demonstrated that the ratio of the total ion current to the discharge current, α_i in a vacuum arc varies from 5 to 19%, depending on the cathode material. It is found experimentally that the ion current fraction α_i is inversely proportional to the atomic bond energy of the cathode material. It is shown that an increase in the total ion current extracted from the discharge plasma when applying an external magnetic field to the cathode region of the discharge is related solely to the appearance of ions with higher charge numbers in the plasma, while the magnitude of the specific ion erosion γ_i remains unchanged.     

纵磁作用下真空电弧单阴极斑点等离子体射流三维混合模拟

真空电弧的特性直接受到从阴极斑点喷射出的等离子体射流的影响,对等离子体射流进行数值仿真有助于我们深入了解真空电弧的内部物理机制.然而,磁流体动力学和粒子云网格仿真方法受限于计算精度和计算效率的原因,无法有效地应用于真空电弧等离子体射流仿真模拟.本文开发了一套三维等离子体混合模拟算法,并在此基础上建立了真空电弧单阴极斑点射流仿真模型,模型中将离子作宏粒子考虑,而电子作无质量流体处理,仿真计算了自生电磁场与外施纵向磁场作用下等离子体的分布运动状态.仿真结果表明,单个阴极斑点情况下真空等离子体射流在离开阴极斑点后扩散至极板间,其整体几何形状为圆锥形,离子密度从阴极到阳极快速下降.外施纵向磁场会压缩等离子体,使得等离子体射流径向的扩散减少并且轴线上的离子密度升高.随着外施纵向磁场的增大,其对等离子体射流的压缩效应增强,表现为等离子体射流的扩散角度逐渐减小.此外,外施纵向磁场对等离子体射流的影响也受到电弧电流大小的影响,压缩效应随电弧电流的增加而逐渐减弱.     

A physical model of the low-current-density vacuum arc

A one-dimensional (1-D) physical model of the low-current-density steady-state vacuum arc is proposed. The model is based on the continuity equations for ions and electrons and the energy balance for the discharge system; the electric potential distribution in the discharge gap is assumed to be nonmonotonic. It is supposed that the ion current at the cathode is generated within the cathode potential fall region due to the ionization of the evaporated atoms by the plasma thermal electrons having Boltzmann's energy distribution. The model offers a satisfactory explanation for the principal regularities of a hot-cathode vacuum arc with diffuse attachment of the current. The applicability of the model proposed to the explanation of some processes occurring in a vacuum arc, such as the flow of fast ions toward the anode, the current cutoffs and voltage bursts, and the backward motion of a cathode spot in a transverse magnetic field is discussed     

含氢电极脉冲放电等离子体特性诊断

利用飞行时间质谱法诊断了含氢电极脉冲真空弧离子源放电等离子体成分、离子电荷状态及离子扩散速度等特性.实验结果表明,含氢电极脉冲真空弧离子源放电等离子体的离子成分主要由H+,Ti+,Ti2+和Ti3+组成,其中Ti2+占主要部分.当放电电流为40～80 A时,Ti离子的平均电荷数在1.95～2.13之间,随着放电电流的增...     

用于真空弧等离子体放电阴极温度场测量的多光谱高温计

阴极表面温度是真空弧等离子体放电过程中一个重要参数,对真空弧等离子体的形成、电极腐蚀预测、热传导以及离子源的寿命都有重要影响。真空弧离子源的阴极具有目标小,放电过程快等特点,其温度的测量,对于时间分辨率和空间分辨率要求都很高,阴极表面温度的测量技术的欠缺,使得仅靠理论解析获得的结果难以得到验证。并且等离子体放电过程中测量仪器极易受到弧光的影响,如何避免放电过程中等离子体的辐射也是采用辐射法测量阴极表面温度要考虑的问题。这无疑给其温度场的测试研究带来困难。针对脉冲真空弧等离子体开展阴极表面温度测试实验有着重要意义,在分析了真空弧等离子体放电特性以及背景辐射特性和等离子体放电阴极测温的实际需求,本文基于高速CCD相机研制了一种新型的多光谱高温计。该高温计采用单色高速CCD相机,主要避免RGB彩色相机不能完全滤除背景辐射的弧光。为使用单色CCD相机实现多光谱辐射测温,设计了高温计的光学系统,该系统采用4孔径分光系统。将4种不同波长的滤光片嵌入到1个滤光片中。该研究设计的高温计可用于2 000~6 000 K的等离子体温度测量。并在中国工程物理研究院电子工程研究所进行现场测试,测试过程中将研制的高温计,通过外部触发形式对等离子体放电过程进行跟踪拍摄,高温计完全拍摄到等离子体放电过程。利用真空弧等离子体金属电极阴极放电的实测数据对高温计进行了验证。实验结果表明,设计的新型多光谱高温计能够用于测量真空弧等离子体放电时阴极温度场信息,测量的温度值低于放电电极的沸点温度,与等离子体放电过程中出现气化现象相符,说明高温计测的是等离子体放电阴极的温度。     

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.     

Charge-state distribution of ions in a vacuum arc discharge plasma in a high magnetic field

It is shown that the fraction of multiply charged metal ions generated in a vacuum arc discharge plasma grows substantially in a high magnetic field. This effect was observed for more than 30 different cathode materials. A relation is established between growth of the mean charge of the ions and increases in the burning voltage of the arc. It is demonstrated that the burning voltage of the vacuum arc can be ultimately increased to 160 V. Zh. Tekh. Fiz. 68, 39–43 (May 1998)     

The Ecton Mechanism for the Generation of Ion Flows in a Vacuum Arc

The principal characteristics of the process of generation of the cathode plasma in a vacuum arc (ion erosion, mean charge of ions) are considered in terms of the ecton model of the cathode spot of a vacuum arc. The estimates of the parameters of ions obtained for a unit cell of a cathode spot – an ecton – are in good qualitative and quantitative agreement with experimental data. The following mechanism for the generation of the cathode plasma of a vacuum arc is proposed. When a region of the cathode is destroyed in an explosive manner due to Joule heating, the material of the cathode sequentially goes over a series of states: the condensed state and the states of imperfect and ideal plasma. During this transition the charge state of the plasma is formed and the ions are accelerated under the action of the pressure gradient in the plasma whose density decreases by several orders of magnitude over distances of 10 m from the cathode surface. The increase in current results in an increase in number of cells, and the principal parameters of the ions are formed as a result of the operation of a unit cell of the spot.     

含氘电极真空弧等离子体空间分布特性诊断研究

真空弧放电等离子体含有多种离子成分,并且各离子在空间上具有不同的分布规律.本文针对金属氘化物电极真空弧离子源,搭建了一台紧凑型磁分析装置,用来研究放电等离子体中氘离子与金属离子的空间分布.当离子源弧流为100 A左右时,该装置能有效地传输引出束流,并且具有较好的二次电子抑制效果,可准确获得各离子流强.利用该装置测量并获得了氘化钛含氘电极真空弧放电等离子体内氘离子和钛离子空间分布规律,结果表明:径向上,氘离子和钛离子都呈高斯分布,但氘离子分布均匀,而钛离子相对集中在轴线附近,导致轴线附近氘离子比例最低;轴向上,所有离子数量都以自然指数函数减少,而且相对幅度接近,所以氘离子比例几乎不变.本文研究结果不仅有助于理解真空弧放电等离子体膨胀过程,还可以指导金属氘化物电极真空弧离子源及其引出设计.     

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.     

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     

Experimental observations of steady anodic vacuum arcs withthermionic cathodes

Stationary plasma discharges have been investigated in a high vacuum ambient (background gas pressure <10^-2 Pa), with an externally heated cathode and a consumable hot evaporating anode. With various anode materials like chromium or copper, and electrode separations between 0.5 and 3 mm, the nonself-sustained discharge operates with DC arc currents in the range of 220 A. The waveform of the arc voltage is strongly influenced by the magnetic field of the cathode heating current, and arc voltages between a minimum of 3 V and a maximum exceeding 100 V have been observed. The voltage-current characteristics (V_CC) and the influence of the electrode separation have been measured separately for the minimum and the maximum of the arc voltages and show a different behavior. The metal plasma expands into the ambient vacuum toward the walls of the vacuum vessel and offers a macroparticle free deposition source of thin films. The arc voltage can be varied by external manipulations of the arc discharge, and the mean ion energy of the expanding metal plasma shows a linear dependence of the mean arc voltage     

含氢电极真空弧放电等离子体时空分布特性研究

真空弧离子源在真空镀膜、材料表面改性、真空大电流开关、加速器离子注入等领域有广泛应用,目前国内外对真空弧放电等离子体的研究主要针对纯金属或合金电极,对含氢电极的研究和公开报道较少.本文利用高时空分辨的四分幅图像诊断系统,结合氢和钛原子特征线单色器件,研究了含氢钛电极的真空弧微秒级脉冲放电等离子体的轴向和径向时空分布特性.研究表明:在真空击穿阶段,阳极区域发光更为明显,阳极电极解吸附释放的氢原子是引发击穿的主要放电介质;在真空弧阶段,阴极-绝缘-真空三结合点处产生圆锥状阴极斑,喷射出大量的等离子体以维持弧放电,同时电极内壁非阴极斑区域也有少量等离子体产生,等离子体中H原子的轴向和径向空间分布均比Ti原子均匀.     

Acceleration of a multicomponent plasma in the cathode region of a vacuum arc

A general solution to the problem of the steady-state spherical expansion of a current-carrying multicomponent plasma into a vacuum is derived. It is shown that, in vacuum arc discharges, the main force accelerating the cathode material, which becomes a plasma at distances of 1 to 300 μm from the cathode surface, is the electron pressure gradient force maintained by Joule heating. It is established that ions of different charges move with the same hydrodynamic velocity, which is uniquely determined by the mass and mean charge of the ions and the maximum electron temperature in the cathode region.     

Ion emission from arc discharge plasmas

Results are presented from studies of the ion-emission properties of the anode plasmas of low-pressure contracted arc discharges and vacuum arcs. It is shown that creating a longitudinal magnetic field in the anode region of a discharge changes the plasma parameters significantly and facilitates a large increase in the ion current. Space charge limited ion current in a vacuum arc leads to a reduction in the noise level of the total ion current and of its components with charges of up to +3, while creating Penning discharge conditions ensures that ions of different gases can be generated in this discharge system at fractions as high as 90%, depending on the type of plasma forming gas.Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vuzov, Fizika, No. 3, pp. 24–33, March, 1994.     

Residence time and charge state of silver and zinc ions generatedfrom microsecond vacuum arcs

One mm vacuum gaps with silver or zinc needle-cathode were fired by a 13 μs duration sinusoidal arc or a 9 μs duration exponentially decaying arc. Time-of-flight (TOF) ion measurements were made at variable ion extraction times after the arc ignition to measure the charge state and residence time of the ions. Ag⁺, Ag⁺⁺ and Ag⁺⁺⁺ ions were generated from silver cathode and Zn⁺ and Zn⁺⁺ were generated from zinc cathode. Residual gas atom ions were generated together with the metal ions. Residence times of silver and zinc ions at the acceleration space, which was 15-25 mm apart from the needle cathode, were 5 μs and 17 μs, respectively, regardless the waveform of the arc current. Charge state fractions of silver and zinc ions were determined from the TOF ion currents and were compared with the results by other researchers