DC Vacuum Research Articles

Prospects for IGBT application in electrical power converters for industrial high-current DC loads

The paper presents the research data of the electrical power converters used for a powering industrial vacuum DC arc furnace. The authors have analyzed energy performance of the power converter with a parametric current source (PCS) and the converter based on switched-mode power supply (SMPS) units with IGBT switches. The research shows that the converter with SMPS units has greater efficiency, thereby reducing specific energy consumption. To improve power quality in industrial power grids, which provide electricity to high-current DC loads, a converter design based on current-source-type active rectifiers is proposed. The simulations carried out by the authors have shown that desynchronization of AR switching processes in the proposed converter system allows one to reduce total harmonic distortion (THD) of the mains voltage.

Ultra high fluence implantation of aluminum ions into CP–Ti

This study describes the possibility of ultra-high fluence low ion energy aluminum implantation for surface modification of titanium. The DC vacuum arc source was used to produce dense metal plasma. Plasma immersion aluminum ions extraction and their ballistic focusing in equipotential space of negatively biased hemispherical electrode were used to obtain high-intensity aluminum ion beam with the maximum amplitude of 0.6 A at the ion current density up to 200 mA/cm2. The original filtration system was used to prevent the deposition of vacuum arc aluminum macroparticles onto the irradiated area of titanium sample. Aluminum low energy ions (mean ion energy 2.6 keV) were implanted into titanium with the fluences reaching 1021 ion/cm2. The effect of substrate temperature, ion current density on the phase composition, microstructure and elemental distribution was studied by X-ray diffraction, scanning electron microscopy, glow-discharge optical emission spectroscopy and transmission electron microscopy. The results show the appearance of Ti3Al intermetallic phase after Al implantation. The depth of aluminum penetration into titanium increases with the substrate temperature and multiply exceeds the projected ranges of ions of given energies and reaches several dozens of μm.

Magnetic and Magnetotransport Characteristics of Cr-Substituted Ni55Mn34Sn11 Thin Films Grown by Magnetron Sputtering

Highly oriented Cr-substituted Ni55Mn34Sn11 Heusler thin films having thickness ~ 400 nm were deposited by Ultrahigh vacuum dc magnetron sputtering on MgO (100) substrates. At room temperature, the films exhibit a mixture of dominant L21 cubic austenite phase, as revealed by the intense (002) and (004) peaks, along with small fraction of the orthorhombic–martensitic phase. Surface morphology of the thin films showed distribution of Cr-rich and Cr-deficit regions together with patterned and aligned magnetic domains, thus bringing out the inherent room temperature ferromagnetism of the film. At temperatures above the Curie temperature, TC ~ 321 K, the magnetic behaviour of the films is seen to follow the Curie law rather than the Curie–Weiss law. Ferromagnetic to antiferromagnetic transition appears at TN ~ 247 K, which gives rise to exchange bias at low temperatures due to the coexistence of the two magnetic orders. This phase coexistence also leads to the formation of a spin glass state deep into the martensitic region. The film exhibits metal-like nature at high temperature and semiconductor-like behaviour with the lowering of temperature. A reentrant metallic state is observed at T ≤ 38 K during cooling that persists up to ≤ 62 K in warming cycle. The hysteresis in the ρ–T curve spread over a very wide temperature range confirms the magnetic phase coexistence in the martensitic state in the present thin films. The magnetoresistance (MR) first increases (2.4% at 300 K and H = 50 kOe) with temperature and maximizes to around ~ 3.25% at T = 150 K and then starts decreasing. Its value in the glassy state is very small. This shows that a magnetic liquid like state is more conducive to larger MR.

Study of metallic thin films on epoxy matrix as protective barrier to ultraviolet radiation

Epoxy based composites are widely being used in aviation, automotive and construction industries due to their high strength and stiffness to weight ratios and good electrochemical corrosion resistance properties. During their exposure to harsh environmental conditions such as ultraviolet (UV) radiation and high temperature, the epoxy matrix suffers significant degradation leading to detrimental effects on the mechanical properties of the entire composite. In this study the benefits of application of thin metallic films that can act as protective barriers to UV radiation's damaging effects on the epoxy are evaluated. Aluminum, copper, titanium and zirconium coatings are deposited on the epoxy substrates using high vacuum DC magnetron sputtering technique. All metallic coatings provided protection to the epoxy substrate exposed to UV radiation where the aluminum offered the highest and zirconium the least amount of protection.

Effect of Substrate Temperature on Structural, Morphological, Magnetic, and Electrical Properties of Fe2CoSi Heusler Alloy Thin Films for Spin-Based Device Applications

Fe2CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L21 crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe2CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (Ms = 948 emu/cc) and low coercivity (Hc = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe2CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin ­based device applications.

Investigations on the safe stroke of mechanical HVDC vacuum circuit breaker

Here, a DC vacuum arc interruption test based on the hybrid high-speed actuator and the method of commutation is carried out in the synthetic loop system. The safe stroke is one of the basic breaking parameters. The minimum safe stroke directly determines the commutation time and breaking property of the mechanical DC vacuum circuit breaker. The main circuit breaker is a high-speed vacuum switch driven by electromagnetic repulsion actuator. In order to simplify its control system, the commutation switch also adopts high-speed vacuum switch. The main current source for verification test of this DC breaker system is provided by a LC oscillator circuit with lower frequency. Simulations with some experiments were completed on breaking process of this system by PSCAD. The breaking current is 4 kA by the DC breaker system proposed here, the opening speed is about 2.417 m/s in this experimental system; From the results, the simulation and experimental waveforms are compared and analysed, and some effects on safe stroke of the DC vacuum circuit breaker is studied. The shortest arcing time is about 0.89 ms and the minimum safe stroke is about 2.15 mm under the lower voltages.

Process development for stabilization of vacuum arc plasma generation from a TiB2 cathode

Herein, we present stable and reproducible arc plasma generation from a TiB2 cathode. The process development contains three complimentary features: Use of a Mo cylinder around the TiB2 cathode improves arc ignition and stabilizes the process by keeping the arc spot at the cathode surface. The evolution of the cathode surface during erosion and the process stability is further improved by addition of 1wt% carbon in the cathode, with no resulting change in plasma characteristics (ion energy, ion charge states, macroparticles). Finally, an increased plasma density through use of a separate anode provides the last key point, which together with the other two contributes to highly controlled plasma generation from TiB2 using DC vacuum arc, and complete utilization of the cathode material. The combined results provide a novel and efficient route for synthesis of metal borides.

Optimisation of commutation circuit parameters for DC vacuum circuit breakers

As the environmental problems caused by the consumption of the non-renewable fossil energy are getting increasingly serious, the new energy power generation has received wide attentions. Multi-terminal high voltage DC (HVDC) transmission is one of the key technologies for improving the reliability and stability of new energy power generations. Besides, HVDC circuit breakers (CBs) become the bottleneck of the development and application for multi-terminal HVDC transmission power systems. Here, the active DC vacuum circuit breaker (VCB) is taken as the research object. Meanwhile, the optimisation design of the commutation circuit for the DC VCB is realised. According to Kirchhoff's law, the genetic algorithm is used to calculate the commutation parameters under different optimisation objectives, to obtain the lowest cost and the shortest sheath development time. Based on the software package MATLAB, the simulations and analyses of different optimisation objectives and parameters are carried out. Through the comparative analyses of the two optimisation objectives, the relationships between the development time of the sheath gap and the cost have been obtained.

DC vacuum breakdown in an external magnetic field

The subject of the present theoretical and experimental investigations is the effect of the external magnetic field induction on dark current and a possibility of breakdown. The generalization of the Fowler–Nordheim equation makes it possible to take into account the influence of a magnetic field parallel to the cathode surface on the field emission current. The reduction in the breakdown voltage due to the increment in electron-impact ionization was theoretical predicted. Experimentally shown that the presence of a magnetic field about a tenth as a large as the cutoff magnetic field (Hull, 1921) reduces the breakdown voltage by 10% to 20% for practically all cathodes no matter what their surface treatment.

Study on the variation of the arc area in vacuum DC interruption

The variation of the arc area in DC interruption was investigated. By the use of the vacuum interrupter with glass shielded, DC interruptions were carried out to obverse the arc appearance in the situation of axial magnetic. Meanwhile, using the CMOS high speed camera, arc images were obtained under the conditions of different commutation frequency, arcing time and pre-charged capacitor voltage. Subsequently, the arc area was obtained through the image processing technology. According to the obtained arc area, the factors influencing on the arc area were investigated, including the commutation frequency, arcing time and pre-charged voltage. The results indicated that the duration time of the commutation stage became shorter and the arc area decreased with the increase of commutation frequency. The rise rate of arc area in initial stage and the drop rate of arc area in commutation stage present the same trend under different arcing time. Considering the experimental results in this paper, arcing time of 2 ms is better for DC interruption. High pre-charged capacitor voltage leads to the increase of the current going through load. The capacitor voltage can be charged a little higher than the rated value for the reliable interruption of DC current.

Characteristics of high frequency interruption for vacuum DC breakers

Post arc current can reflect the residual plasma in the electrode gap and the zero zone characteristics, so it has a great influence on the interruption of the breakers. In this paper, a permanent magnet-repulsive force hybrid actuator is designed, and the post arc current measurement system is established. Based on the forced current zero method, a series of high frequency DC interruption experiments are carried out in the synthetic test circuit with vacuum interrupters. The influence of the commutation frequency and recovery voltage on the vacuum DC interruption is investigated. The results show that a short lag phase about 80 ns exists between the post arc current and recovery voltage. High commutation frequency leads to the rise of the post arc current, which is disadvantageous for the vacuum DC interruption. The post arc current also rises with the increase in the recovery voltage. The interruption is not just affected by the di/dt and du/dt. In this study, failing interruption at the first current zero happens when the transient recovery voltage is near 2800 V. The current chopping occurs easily at high commutation frequency. And the chopping current value is proportional to the commutation frequency, which is up to 120 A at 4.0 kHz.

High intensity, macroparticle-free, aluminum ion beam formation

We describe a vacuum arc based system for the generation of repetitively pulsed metal ion beams with very high current density, and the results of experimental investigations of the performance of this new system, as well as the results of numerical simulations. Our approach uses a DC vacuum arc as a metal plasma source, and the beam-forming technique is a hybrid method using features of conventional gridded ion extraction together with some plasma immersion attributes. A hemispherical grid is located some distance from the plasma source so as to intercept part of the metal plasma flow and repetitively pulse-biased to the requisite ion beam energy. Ions are accelerated in the high voltage sheath that forms in front of the biased grid and focused into a converging beam that can be of a very high current density. Space charge neutralization is provided by cold plasma that streams through the grid during the bias-off part of the cycle. At the same time, macroparticles in the vacuum arc plasma are blocked from viewing the target by a metal disk positioned centrally on the hemispherical grid. In the work outlined here, we formed 5 keV aluminum ion beams with a current density up to 470 mA/cm2 at a negative bias amplitude of 3 kV and a pulse repetition rate of 105 pulse per second. The experiments and numerical simulations demonstrate the formation of high-intensity macroparticle-free aluminum ion beams for material surface modification and other possible applications.

Mechanism of vacuum breakdown in radio-frequency accelerating structures

It has been investigated whether explosive electron emission may be the initiating mechanism of vacuum breakdown in the accelerating structures of TeV linear electron-positron colliders (Compact Linear Collider). The physical processes involved in a dc vacuum breakdown have been considered, and the relationship between the voltage applied to the diode and the time delay to breakdown has been found. Based on the results obtained, the development of a vacuum breakdown in an rf electric field has been analyzed and the main parameters responsible for the initiation of explosive electron emission have been estimated. The formation of craters on the cathode surface during explosive electron emission has been numerically simulated, and the simulation results are discussed.

Kinetics of Zr-Al intermetallic compound formation during ultra-high vacuum magnetron sputter-deposition of Zr/Al2O3(0001) thin films

Zr layers are grown on Al2O3(0001) substrates by ultra-high vacuum dc magnetron sputter-deposition in pure Ar discharges at temperatures Ts between 873 K and 1173 K. We investigate the Ts-dependent evolution of microstructure and composition across the Zr/Al2O3(0001) interfaces using X-ray diffraction, transmission electron microscopy, and X-ray energy dispersive spectroscopy. We obtain fully-dense, close-packed hexagonal structured Zr(0001) thin films with smooth surfaces at 873 K ≤ Ts ≤ 973 K and increasingly porous, 0002-textured layers with highly corrugated surfaces at Ts > 1023 K. At the Zr/Al2O3 interfaces, we observe thin crystalline films of Zr-Al intermetallic compounds, whose thicknesses increase from 10 ± 4 nm at Ts = 873 K to 116 ± 4 nm at Ts = 1173 K. The interfacial layers are composed of hexagonal Ni2In-structured Zr2Al phase at Ts = 973 K and both orthorhombic-structured Zr2Al3 and hexagonal Mn5Al3-structured Zr5Al3 phases at Ts > 973 K. The thicknesses of both the intermetallic phases increase with increasing Ts, however, the Zr2Al3 layer grows faster than the Zr-rich phase at higher Ts. We attribute the formation of Zr-rich Zr2Al, rather than the thermodynamically more stable Al-rich Zr2Al3 layers, to the presence of dissolved oxygen and epitaxial registry with Al2O3(0001). Our results indicate that reaction-diffusion kinetics rather than thermodynamics govern the interfacial layer composition and we suggest that the Zr/Al2O3(0001) interfacial stability is controlled by the supply of Al from the Al2O3(0001) substrate during sputter-deposition of Zr.

Low energy, high intensity metal ion implantation method for deep dopant containing layer formation

This study describes the first results of high intensity macroparticle-free aluminum ion beam formation and its application to low ion energy implantation. A DC vacuum arc was used to produce aluminum plasma flow. A repetitively pulsed macroparticle-free high intensity aluminum ion beam was formed using a plasma immersion ion extraction combined with ion beam focusing. A very high current ion beam with the current up to 0.475 A at bias pulse duration of 4 μs and the pulse repetition rate of 105 pulses per second was obtained. Nickel substrates were irradiated by aluminum ions with very high current densities up to 100 mA/cm2 and accelerating voltages up to 2.1 kV. The maximum fluence of implantation reached 1.2 × 1021 ion/сm2. The results of the element composition of the modified layer were also investigated.

Ultrahigh vacuum dc magnetron sputter-deposition of epitaxial Pd(111)/Al2O3(0001) thin films.

Pd(111) thin films, ∼245 nm thick, are deposited on Al2O3(0001) substrates at ≈0.5Tm, where Tm is the Pd melting point, by ultrahigh vacuum dc magnetron sputtering of Pd target in pure Ar discharges. Auger electron spectra and low-energy electron diffraction patterns acquired in situ from the as-deposited samples reveal that the surfaces are compositionally pure 111-oriented Pd. Double-axis x-ray diffraction (XRD) ω-2θ scans show only the set of Pd 111 peaks from the film. In triple-axis high-resolution XRD, the full width at half maximum intensity Γω of the Pd 111 ω-rocking curve is 630 arc sec. XRD 111 pole figure obtained from the sample revealed six peaks 60°-apart at a tilt angles corresponding to Pd 111 reflections. XRD ϕ scans show six 60°-rotated 111 peaks of Pd at the same ϕ angles for 11[Formula: see text]3 of Al2O3 based on which the epitaxial crystallographic relationships between the film and the substrate are determined as [Formula: see text]ǁ[Formula: see text] with two in-plane orientations of [Formula: see text]ǁ[Formula: see text] and [Formula: see text]ǁ[Formula: see text]. Using triple axis symmetric and asymmetric reciprocal space maps, interplanar spacings of out-of-plane (111) and in-plane (11[Formula: see text]) are found to be 0.2242 ± 0.0003 and 0.1591 ± 0.0003 nm, respectively. These values are 0.18% lower than 0.2246 nm for (111) and the same, within the measurement uncertainties, as 0.1588 nm for (11[Formula: see text]) calculated from the bulk Pd lattice parameter, suggesting a small out-of-plane compressive strain and an in-plane tensile strain related to the thermal strain upon cooling the sample from the deposition temperature to room temperature. High-resolution cross-sectional transmission electron microscopy coupled with energy dispersive x-ray spectra obtained from the Pd(111)/Al2O3(0001) samples indicate that the Pd-Al2O3 interfaces are essentially atomically abrupt and dislocation-free. These results demonstrate the growth of epitaxial Pd thin films with (111) out-of-plane orientation with low mosaicity on Al2O3(0001).

Joint influence of steered vacuum arc and negative repetitively pulsed bias on titanium macroparticles suppression

This paper presents the results of an experimental study of titanium macroparticle accumulation on a negatively biased substrate immersed in DC vacuum arc plasma generated by an evaporator with an axial magnetic field and a steered arc evaporator. Using a steered arc with a tangential magnetic field strength of 200 Gs reduced the generation of macroparticles 5-fold compared to a plasma source with an axial magnetic field. The application of repetitively pulsed negative bias significantly decreased macroparticle assembly on the substrate surface for both evaporator designs. After 20 min of ion-plasma treatment with negatively pulsed bias (−2 kV, 7 μs, 105 p.p.s.) and steered arc, the observed macroparticle surface density appeared to be 2 orders of magnitude smaller than after vacuum arc plasma deposition at the anode potential using an evaporator with an axial magnetic field. The possibility of high–frequency short–pulse plasma immersion ion implantation by implementing DC vacuum arc plasma is discussed.

High-intensity low energy titanium ion implantation into zirconium alloy

This research describes the possibility of ultra-high dose deep titanium ion implantation for surface modification of zirconium alloy Zr-1Nb. The developed method based on repetitively pulsed high intensity low energy titanium ion implantation was used to modify the surface layer. The DC vacuum arc source was used to produce metal plasma. Plasma immersion titanium ions extraction and their ballistic focusing in equipotential space of biased electrode were used to produce high intensity titanium ion beam with the amplitude of 0.5 A at the ion current density 120 and 170 mA/cm2. The solar eclipse effect was used to prevent vacuum arc titanium macroparticles from appearing in the implantation area of Zr sample. Titanium low energy (mean ion energy E = 3 keV) ions were implanted into zirconium alloy with the dose in the range of (5.4–9.56) × 1020 ion/cm2. The effect of ion current density, implantation dose on the phase composition, microstructure and distribution of elements was studied by X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectroscopy, respectively. The results show the appearance of Zr-Ti intermetallic phases of different stoichiometry after Ti implantation. The intermetallic phases are transformed from both Zr0.7Ti0.3 and Zr0.5Ti0.5 to single Zr0.6Ti0.4 phase with the increase in the implantation dose. The changes in phase composition are attributed to Ti dissolution in zirconium lattice accompanied by the lattice distortions and appearance of macrostrains in intermetallic phases. The depth of Ti penetration into the bulk of Zr increases from 6 to 13 μm with the implantation dose. The hardness and wear resistance of the Ti-implanted zirconium alloy were increased by 1.5 and 1.4 times, respectively. The higher current density (170 mA/cm2) leads to the increase in the grain size and surface roughness negatively affecting the tribological properties of the alloy.

Direct-Current Vacuum Circuit Breaker With Superconducting Fault-Current Limiter

The objective of this paper is to propose a dc current interruption technology for railway dc traction systems, consisting of a dc vacuum circuit breaker with a superconducting fault-current limiter (SFCL). To this end, a 1.5-kV dc circuit breaker prototype is designed, involving a dc vacuum circuit breaker and a resistive-type SFCL serially connected. The dc vacuum circuit breaker is developed with a commutation circuit to generate a reverse injection current, and the resistive-type SFCL is composed of yttrium barium copper oxide superconducting tape. An LC current source tested the 1.5-kV prototype, showing that, when the precharged capacitor voltage is 1.5 kV, the prospective current is 47 kA increasing at a rate of 9.4 A/μs. The SFCL limits this current to ~3 kA (peak value), and then, decreases the current to 2 kA after 6 ms, followed by successful clearance via the dc vacuum circuit breaker. The proposed 1.5-kV circuit breaker will successfully clear short-circuit faults up to 47 kA by first limiting the prospective current and then interrupting it.

Пропускная способность ограничителей перенапряжений в составе вакуумных выключателей постоянного тока

The article presents the results from numerical simulation and experimental investigation of the throughput capacity of Type 0PN-TP-3.0/4-UKhL 3 metal-oxide surge arresters (MOSA) used as part of a high-speed automatic DC vacuum circuit breaker for the maximal voltage equal to 4.1 kV. The vacuum circuit breaker operation principle isbased on forced lymaking the disconnected current to pass through zero by means of arranging opposite discharge of a pre-charged capacitor. A numerical model is proposed, whichhas been implemented in the Matlab 6.5 software package using the Sim Power Systems library. The applicability of the model has been experimentally confirmed in disconnecting a current by a vacuum circuit breaker through simulating a short-circuit fault current with different current growth rates. The investig a tions were carrie doutata heavy-current high-voltage test bench realizing an oscillatory circuit involving a capacitor bank for the maximal voltage of up to 6 kV and the total energy storage capacity of up to 1.8 MJ. The numerical model satisfactorily describes the processes in disconnecting acurrentina DC vacuum circuit breaker with forcedly making the current to cross zero. The model also make sit possible to estimate the amount of energy dissipated in the MOSA unit in disconnecting a short-circuit fault current. Byusing the proposed model itis also possible to estimate the number of parallel-connected MOSAs in disconnecting emergency currents in traction DC power supply networks with an inductance ranging from 5 to 15 mH.