电流型电火花加工脉冲电源的研究

分析了传统独立电火花加工脉冲电源和逆变式电火花加工脉冲电源的不足,论述了电源型电火花加工脉冲电源的工作原理,大量的样机和独立式脉冲电源的对比工艺试验表明,电流型脉冲电源不仅满足了电火花加工多项性能指标的要求,而且达到了高效节能的效果。     

Influence of discharge gap on the discharge stability in a short vacuum arc ion source

The influence of the discharge gap between cathode and anode on the discharge stability in a short vacuum arc (SVA) ion source is presented in this paper. Planar cathode and cylindrical hollow anode made of titanium are investigated. There is a great need in present accelerator injection research for SVA source to produce the small deviation of the ion current beam. Current research shows that increasing the short discharge gap can reduce the level of ion current deviation and ion charge deviation from 29% and 31% to 15% and 17%, respectively. A microplasma plume generation mechanism in SVA and scanning electron microscopic results can be used to explain this interesting phenomenon.     

An ion thruster internal discharge chamber electrostatic probe diagnostic technique using a high-speed probe positioning system

Extensive resources have been allocated to diagnose and minimize lifetime-limiting factors in gridded ion thrusters. While most of this effort has focused on grid erosion, results from wear tests indicate that discharge cathode erosion may also play an important role in limiting the lifetime of ring-cusp ion thrusters proposed for future large flagship missions. The detailed characterization of the near-cathode discharge plasma is essential for mitigating discharge cathode erosion. However, severe difficulty is encountered when attempting to measure internal discharge plasma parameters during thruster operation with conventional probing techniques. These difficulties stem from the high-voltage, high-density discharge cathode plume, which is a hostile environment for probes. A method for interrogating the discharge chamber plasma of a working ion thruster over a two-dimensional grid is demonstrated. The high-speed axial reciprocating probe positioning system is used to minimize thruster perturbation during probe insertion and to reduce heating of the probe. Electrostatic probe measurements from a symmetric double Langmuir probe are presented over a two-dimensional spatial array in the near-discharge cathode assembly region of a 30-cm-diameter ring-cusp ion thruster. Electron temperatures, 2-5 eV, and number density contours, with a maximum of 8 x 10(12) cm(-3) on centerline, are measured. These data provide detailed electron temperature and number density contours which, when combined with plasma potential measurements, may shed light on discharge cathode erosion processes and the effect of thruster operating conditions on erosion rates.     

A source of gas, vapor, metal, and carbon ions based on a low-pressure hollow-cathode discharge

A compact source of gas, vapor, metal, and carbon ions based on a cold-hollow-cathode reflective discharge has been developed, in which a 6-mm-diameter flat target (Cu, Mo, W, C) is installed on the bottom of the cold cathode insulated from it. The density of the ion flow from cathode plasma reaches 100 mA/cm² at an accelerating voltage of up to 10 kV and a discharge current of 0.2-0.5 A. Vapors produced during ion sputtering of the target are ionized in the cathode and anode cavities. A beam containing ions of the plasma-producing gas and vapor is extracted throug h the channel in the reflector cathode. A fraction of the vapor of the sputtered target, the flow of which is sufficient for growing layers at a rate of ∼0.03 nm/s at a distance of 10 cm from the emission channel under the action of an ion beam, is extracted together with ions. The fraction of metal ions in the extracted beam is 0.05-0.10. The total current of the ion beam is 20-30 mA.     

High frequency operation of a hot filament cathode for a magnetized plasma ion source

A tungsten filament cathode has been operated with an ac heating current to excite a plasma in a linear magnetic field. Both the discharge current and the ion saturation current in plasma near the extraction hole of the ion source exhibited fluctuations. The discharge current fluctuated with the amplitude less than 2% of the average, and the frequency two times the frequency of the heating current. Fluctuation amplitude of the ion saturation current was about 10% of the average, while the frequency was the same as that of the heating current. The ac operation has prolonged the lifetime of a hot filament cathode by about 50%.     

A high-linearity DC planar Ionic anemometer

A high-linearity DC planar ionic anemometer which can measure the airflow velocity of boundary-layers near a surface was constructed and tested. The differential anemometer described in this paper includes two symmetrical cathodes and one anode with a sharp tip. High voltage is applied to the anode to generate a symmetrical ionic discharge, and then the airflow deflects the symmetrical ion distribution and produces a differential current between the two cathodes. It can detect bidirectional airflow velocity and is more crash-resistant than traditional hot-wire anemometers. It has minimum impact on the airflow profile because of its thin-shape design and achieves high measurement accuracy. A series of tests have been done for the static characteristics and dynamic performance by changing structural parameters such as cavity depth, gap width, anode tip angle, cathode width and length. The results show that the cavity depth is the most important structural parameter since it has the greatest effect on the stability of the gas discharge, which is affected by ion mobility and friction between ions and the bottom of cavity. The gap width plays a decisive role in the current and sensitivity values. Besides, the uncertainties of the tests have been analyzed by introducing the error bars and the testing errors are in reasonable ranges. The anemometer is cost-effective and offers the possibility of building a MEMS version in the future.     

Electrical discharge when machining medium-density fibreboard and tool wear

Electrical potentials between the workpiece and cutting tool have been shown to be generated when cutting green and dry wood. The voltages have been reported as relatively constant. A series of turning tests on medium-density fibreboard (MDF) were undertaken to characterize the electrical potentials in wood machining. The results indicated numerous discharges generally from the MDF-workpiece (cathode) to the tool (anode). However, both voltage and current reversals or discharges occurred from the tool to the MDF-workpiece. The reversals occurred simultaneously with electrostatic discharges within the MDF-workpiece. The possibility of an electric discharge machining effect on tool wear is also discussed. These electrical discharge characteristics from wood machining could provide insight for the wear mechanisms for dry wood and wood products as well as for other dielectric materials.     

An arc generator of a broad plasma stream

The design and basic parameters of an arc plasma generator based on a combined cathode are described. The cathode consists of a hot tungsten filament located in the hollow cathode. A plasma stream with a cross section of 150×10 cm² and a density of ∼10¹⁰ cm⁻³ at a pressure of 0.1–1 Pa is generated at a discharge current of up to 60 A without a cathode spot. The plasma generator can be utilized for final cleaning and activation of surfaces of materials and articles before depositing functional coatings on them and in plasma-assisted deposition by using either vacuum arc or magnetron discharges.     

Improvement of four anode rods ion source

In this work, an improved form of a saddle field ion source has been designed and constructed. It consists of four anode rods made from copper and two copper cathode discs. The two cathode discs are placed symmetrically on both sides of the four anode rods. The electrical discharge and output ion beam characteristics were measured at different pressures using argon gas. The optimum distance between each two anode rods was determined. Also the optimum distance between the four anode rods and any cathode disc was obtained. It was found that the optimum distance between each two anode rods equal to 6 mm, while the optimum distance between the four anode rods and any cathode disc equal to 16 mm, where a stable discharge current and maximum output ion beam current can be obtained. The effect of negative extraction voltage applied to both the extractor electrode and Faraday cup on the output ion beam current was studied. The sputter yield of copper and aluminum targets using argon ions of different energies was determined.     

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m³ are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is n _e ∼ 10¹⁰–10¹¹ cm⁻³ and the electron temperature is T _e ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.     

A low-pressure gas-discharge ion source with a hollow cathode and an output-aperture diameter of 420 mm

A gas-discharge ion source with a hollow cathode 700 mm in diameter and 500 mm in length is described. Two small-area anodes are positioned at the ends of the hollow cathode opposite to each other. A 420-mm-diameter extracting electrode is placed along the lateral wall of the hollow cathode at a distance of 250 mm from its center symmetrically relative to the anodes. A hot cathode is placed opposite to the extracting electrode. A beam of oxygen ions with a current density of up to 0.2 mA/cm² and a nonuniformity <12% over a 420-mm-diameter area at a distance of 200 mm from the extracting electrode was obtained. The optimal operating parameters of the ion source working with oxygen are as follows: a discharge current of 0.8–1.2 A, an operating pressure of (0.6–0.8) × 10^?4 Torr, and an extracting voltage of up to 400 V.     

Investigation of ISIS and Brookhaven National Laboratory ion source electrodes after extended operation

Linac4 accelerator of Centre Europe?en de Recherches Nucle?aires is under construction and a RF-driven H(-) ion source is being developed. The beam current requirement for Linac4 is very challenging: 80 mA must be provided. Cesiated plasma discharge ion sources such as Penning or magnetron sources are also potential candidates. Accelerator ion sources must achieve typical reliability figures of 95% and above. Investigating and understanding the underlying mechanisms involved with source failure or ageing is critical when selecting the ion source technology. Plasma discharge driven surface ion sources rely on molybdenum cathodes. Deformation of the cathode surfaces is visible after extended operation periods. A metallurgical investigation of an ISIS ion source is presented. The origin of the deformation is twofold: Molybdenum sputtering by cesium ions digs few tenths of mm cavities while a growth of molybdenum is observed in the immediate vicinity. The molybdenum growth under hydrogen atmosphere is hard and loosely bound to the bulk. It is, therefore, likely to peel off and be transported within the plasma volume. The observation of the cathode, anode, and extraction electrodes of the magnetron source operated at BNL for two years are presented. A beam simulation of H(-), electrons, and Cs(-) ions was performed with the IBSimu code package to qualitatively explain the observations. This paper describes the operation conditions of the ion sources and discusses the metallurgical analysis and beam simulation results.     

交流脉冲式磁控溅射靶极电源的研制

本文介绍了一种中频交流脉冲式磁控溅射靶极电源。该电源采用全桥逆变拓扑电路、PWM控制方式、输出功率叠加的方案，具有快速的过流检测与保护功能。在等离子体负载下进行了抑制弧光放电和空心阴极效应的实验，同低频直流脉冲电源相比，交流脉冲放电对其抑制是非常有效的。这表明该电源作为磁控溅射靶极电源是完全可行的，也为进一步探索交流磁控溅射新工艺提供了可靠的研究设备。     

A source of a wide-aperture gas-discharge plasma flow

The described generator produces a wide-aperture flow of charged plasma particles (electrons, positive and negative ions) with a cross-sectional diameter of at least 120 cm, which propagates to a distance of 50 cm or more (depending on the operating mode and the geometric dimensions of the vacuum chamber). The uniform distribution of charged particles in the cross section of the plasma flow is at least 98%. The discharge current reaches 1 A or more at an accelerating voltage of 0.3–6 kV. The energy of particles in the plasma flow under such conditions was 10–6000 eV at current densities of up to 10 mA/cm². The generator structure contains coaxially positioned meshes of the anode grid and the cathode grid. The latter closes the cavity inside the cathode volume at a depth of 3–5 mean free paths of electrons in the gas-discharge plasma flow. The cathode is manufactured so that the cavity diameter exceeds the diameter of the through cavity in the cathode insulation, the latter being determined by the size of the plasma-flow cross section. The distance between the grid anode and the cathode grid is equal to the Aston dark space of a glow discharge, thus permitting the cathode lifetime to be increased to 3 years. It is shown that the duration of the cathode continuous operation is determined by the chosen values of its cavity depth and accelerating voltage.     

Decrease in the ignition pressure of anomalous glow discharge in a magnetron with an ion-beam-irradiated cathode

The influence of an ion beam injected along the axis of the anode electrode of a planar magnetron on the initiation of an anomalous low-pressure glow discharge in a magnetron has been considered. The characteristics of the discharge ignition at pressures <8 × 10^?2 Pa and the properties of a planar magnetron with an ion-beam-irradiated cathode are determined. It is established that the discharge ignition voltage decreases with an increase in the ion energy and exhibits a threshold behavior as a function of the ion-beam current. It is shown that there is a prospect for extending the functional capabilities of planar magnetrons through matching of the modes of sputtering of the magnetron anode and cathode by an ion beam and plasma ions of an anomalous glow discharge, respectively.     

A high-current plasma emitter of electrons based on a glow discharge with a multirod electrostatic trap

Pulsed electron guns that produce 170-mm-diameter beams with currents of up to 700 A, electron energies of 300 keV, and a pulse width of ～200 μs at a gas pressure of ～0.01 Pa are experimentally studied. Glow-discharge plasma with electron confinement in an electrostatic trap is used as the electron emitter. The trap is formed by a hexagonal prism that consists of 204 cathode rods, which are 5 mm in diameter, 200 mm in length and are spaced by 1.5 mm, as well as 780 cathode rods, which are 5 mm in diameter and 98 mm in length, the spacing between their axes amounting to 15 mm. The latter rods are inside the former system of rods. The plasma emitter fills the hexagonal prism, which is free of rods, at the trap center with a distance of 280 mm between opposite sides and a height of ～200 mm between the emissive grid connected to the anode and the trap bottom covered with 23-mm-diameter cathode disks. All the cathode rods and disks are insulated from one another and connected to the discharge power supply through TVO-2 430-Ω resistors. The current limitation in the circuit of each cathode element by a value of ～2 A at a pulse width of ～5 ms of the glow-discharge current of up to 1 kA fully excludes its glow-to-arc transitions and allows production of continuous pulsed electron beams with an energy capacity of up to 40 kJ and a uniform distribution of the current density over its cross-sectional area of ～0.025 m².     

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm²) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm².     

An Ion Source with an Open-End Small-Sized Anode

A small-sized gas-discharge ion source is described. The source contains a cylindrical hollow cathode made of a ferromagnetic material with longitudinal magnetization of up to 16 mT; a cone-shaped anode and a cathode-reflector in the form of a tube situated in axial symmetry inside the hollow cathode; and an external thermionic cathode. The overall dimensions of the ion source without the thermionic cathode are 45 × 44 mm. The source ensures an argon ion beam current of up to 80 mA at a discharge current and voltage of 1 A and 115 V, respectively, and a pressure of 1.5 × 10⁻² Pa in the chamber. The minimum operating pressure is 0.8 × 10⁻² Pa.__________Translated from Pribory i Tekhnika Eksperimenta, No. 3, 2005, pp. 147–149.Original Russian Text Copyright © 2005 by Stognij, Zavadskaya, Koryakin, Lobko, Yurchenko.     

A compact vapor source of conductive target material sputtered by 3-keV ions at 0.05-Pa pressure

A vapor source is developed its 80-mm-diameter and 15-mm-thick flat target being positioned on the bottom of a 120-mm-diameter and 70-mm-deep hollow cathode, isolated from the cathode and sputtered by 1–4-keV argon ions. A permanent magnet induces an axially symmetric heterogeneous magnetic field, the field induction on the target surface reaching 20 mT and the field lines of force being diverging from the target surface and crossing the cathode surface. The cathode bombardment by 1–3-keV secondary electrons emitted by the target results in an increase of the electron emission current in the cathode circuit and enables to reduce the argon pressure down to 0.05 Pa. It allows a collisionless transport of the sputtered metal atoms to a substrate thus keeping their initial energy amounting to tens of electronvolts. A higher energy of deposited atoms improves quality of coatings, for instance of Ti₃SiB₂ films, their deposition rate on a substrate distanced at 0.1–0.2 m from the target amounting to 10–20 μm/h at 1-A current in the target circuit and 3-keV energy of sputtering ions. This value is one order of magnitude higher in comparison with the target sputtering in a planar magnetron discharge by 300–500-eV argon ions at the same 1-A current in the target circuit.     

A Wide-Aperture,Low-Energy,and High-Current Electron Beam Source with a Plasma Anode Based on a Reflective Discharge

A source of low-energy (10–30 keV) high-current (up to 30-kA) electron beams efficiently and stably operating under conditions of oil-free vacuum has been developed. It is based on an electron gun with an explosive-emission cathode and a plasma anode, which is formed using a high-current reflective discharge. An external guide magnetic field ensures both discharge initiation and maintenance and beam transport. The source, the results of tests of it, and the experience of its operation are described. Methods for reducing the flow of erosion products ejected from the walls of the vacuum chamber to the processed target are proposed. The source is used in physical and technological studies of the modification of properties of surface material layers and for surface processing of articles.