Arc Plasma Generator Research Articles

High current positive ion source for Copernicus NBI based on a cold-cathode arc plasma generator

The NBI system based on positive ions to be applied for TAE’s next-generation field reversed configuration experiment, Copernicus, has been designed. The beamlines are longer in the new system, so the required beam divergence smaller relative to the NBI system on TAE’s current device. This requirement motivates a change from slot-shaped apertures to circular in the plasma grid. The influence of changing the aperture shape on the divergence and total beam current across the extraction area has been examined. When considering spatial uniformity in calculations, it is expected that a beam current value of 173 A and a beam divergence angle of 17 mrad will be achieved, exceeding the required values by 15%. An octagonal-shaped ion source has also been developed for a future upgrade targeting 2.5 s long pulse operation, and the estimation indicates 83% source plasma uniformity with concurrent suppression of thermal loads. The development of multiple plasma diagnostics for assessing uniformity and proton ratios has been completed to validate these estimations and optimize the ion source dimensions.

Stable DC vacuum arc plasma generation from a 100 mm TiB2 cathode

Titanium diboride exhibits outstanding properties for hard and wear resistant coatings. However, efficient physical vapor deposition (PVD) processing through DC vacuum arc, with a deposition rate unreachable for any other PVD technique, is comparatively unexplored for TiB2 thin films due to challenges associated with the film synthesis process. In this work, we used an industrial scale arc plasma source having a plane cathode of 100 mm in diameter and a permanent magnet on its back side. We present analysis of the cathode surface, plasma generation/composition, as well as analysis of collected macroparticles. The cathode weight loss and the amount of generated macroparticles were measured as a function of process parameters (arc current and pressure, in both Ar and N2 gas). Plasma analysis shows average ion energies around 120 and 25 eV for Ti and B, respectively, and plasma ion composition of approximately 50 % Ti and 50 % B. The cathode weight loss was around 0.3–0.5 g/min, of which at least 25 % is estimated to be macroparticles. Notably, the intensity of the macroparticle generation was reduced with an increase in N2 pressure. Altogether, the results show a stable and reproducible plasma generation process and a high potential for the use of the cathodic arc as an efficient and useful method for deposition of metal borides.

Heat treatment of ground surface using an electric arc plasma generator

The article presents a generalization of the results of experimental and theoretical studies on the intensive thermal effect on the surface of foundations from cohesive soils (as opposed to deep heat treatment) using an electric arc generator of low-temperature plasma (plasmatron). A plasmatron with massive consumable electrodes made of borosilicated graphite and a wide "blurred" plasma torch was used for heat treatment. Physical and mathematical modeling of the thermal effect on the surface of clay soil by a moving high-temperature source has been performed. For the first time, a special installation was manufactured and experimental studies were carried out on the heat treatment of ground surfaces on the site with an electric arc plasma torch. It is established that the effective heat flux density reaches 2.5-.3.5 kW/cm2. The main part of the thermal energy for the used plasmatron enters the material due to radiant heat transfer. An analytical mathematical model of the temperature field of a three-dimensional semi-bounded body in the technological process under consideration is given by an essentially nonlinear boundary value problem for a nonlinear heat equation with nonlinear boundary conditions of the second kind. When solving thermophysical problems, the ground semi-bounded space was considered as a quasi-homogeneous medium having a constant initial temperature and initial thermophysical parameters that change in the process of temperature increase. The effective values of the thermophysical characteristics were determined on the basis of experimental data. Calculations and experiments have shown that the temperature boundary leading to significant changes in the structural properties of soils drops to a depth of 4-6 cm from the surface, despite the boiling of the ground melt with a temperature of 2500 ...2800 K on the ground surface. Therefore, a new technological principle of heat treatment is proposed, which consists in building up the ground melt in layers of 4-5 cm up from the initial surface. The impossibility of obtaining a positive effect even with the use of a powerful high-temperature source of exposure in the case of traditional surface heat treatment technology has been confirmed. The new plasma technology of surface heat treatment of ground surfaces to the stage of silicate melt allows to obtain a common layer of the required thickness. At the same time, the efficiency of surface heat treatment is significantly increased. The new technology of layer-by-layer surface deposition reduces cracking in the layer when the melt cools, but does not eliminate this negative process.

Plasma Energy Loss by Cathode Heat Conduction in a Vacuum Arc: Cathode Effective Voltage

The importance of understanding the energy loss specifics by the cathode for vacuum arc metallic plasma generation and its applications were emphasized. To this end, the heat conduction losses per unit current were characterized by the cathode effective voltage uef, which is weakly dependent on the current. In this paper, a physical model and a mathematical approach were developed to describe the energy dissipation due to heat conduction in the cathode body, which is heated by energy outflowed from the adjacent plasma. The arc plasma generation was considered by taking into account the kinetics of the heavy particle fluxes in the non-equilibrium layer near the vaporizing surface. The phenomena of electric sheath, heat and mass transfer at the cathode were taken into account. The self-consistent numerical analysis was performed with a system of equations for a copper cathode spot. The transient analysis starts from the spot initiation, modeled by the plasma arising at the initial time determined by the kind of arc triggering, up to spot development. The results of the calculations show that the cathode effective voltage uef is determined by the cathode temperature as a function of spot time. The calculated evolution of the voltage uef shows that the steady state of uef is approximately 7 V, and it is reached when the cathode temperature reaches a steady state at approximately one microsecond. This essential result provides an explanation for the good agreement with the experimental cathode effective voltage (6–8 V) measured for the arc duration from one millisecond up to a few seconds.

A comparison of plasma generation, plasma transport, and film formation for a DC vacuum arc source with Ti–X compound cathodes (X = W, C, Al, and Si)

This investigation reports the influence of Ti–C and Ti–W cathode composition on an industrial-scale dc vacuum arc plasma source. Further, we analyze the influence of plasma generation and plasma properties on the resulting cathode surface after the operation and on basic film properties. The results are compared with previous work focused on Ti–Al and Ti–Si compound cathodes. For all Ti–X compound cathodes (X = W, C, Al, and Si), a direct correlation between plasma ion energy/charge and the cohesive energy of the cathode was demonstrated, with a small number of exceptions to a limited set of specific cathode compositions. Hence, the “velocity rule” and effects from different electron temperatures were suggested to be important for gaining a more detailed understanding of plasma properties. A discrepancy was found between the cathode and plasma ion composition, though the difference was reduced in a corresponding comparison between the cathode and the deposited film composition. A significant contribution of a flux of neutrals and/or macroparticles to the final film composition was, therefore, suggested. The effect of the melting point of the cathode phase composition on the intensity of macroparticle generation and the smoothness of the cathode surface operation was also investigated. The presented results contribute to the fundamental understanding of vacuum arc plasma generation and transport and are of importance for further development and applicability of Ti-based coatings from arc deposition.

Magnetoplasmadynamic acceleration of solid body in a railgun

A physical model and a mathematical approach were developed to describe ponderomotive acceleration a body pushed by plasma column of high-current arc in a railgun. In contrast to the previously published studies, the arc plasma generation was considered by taking into account kinetics of heavy particle fluxes in a non-equilibrium layer near the vaporizating (ablating) rails and the phenomena of heat and mass transfer and electric sheath at rail surfaces. The self-consistent numerical analysis has been conducted for a wide range of arc currents (up to 2MA). It has been shown that the electron temperature was determined mainly by the Joule energy dissipation supporting high degree of ionization. It has been determined that the arc voltage is about 102 V. The rails temperatures are relatively low (~ 3000 K) and therefore, the electron flux emitted from the cathode manly due to thermionic emission enhanced by Schottky effect is lower than the flux of ions from the plasma, which supported the current continuity at the cathode region. The calculated velocity vs of the plasma-solid body increased with the arc current (I) showing tendency to saturation. In range of I = 0.5–2 MA the vs slightly increased from 5 × 105 to 10 × 105 cm/s when the rail length increased from 1 to 3 m respectively. The dependence of the velocity on the arc current and the calculated plasma parameters are in range of those values observed experimentally. The nature of the velocity with arc current saturation is explained by presence of the dynamic pressure resulting in predicted velocity dependence on the arc current as 4-th root.

Enhancement of Lettuce Growth by PAW Spray Gliding Arc Plasma Generator

The effect of non-thermal air plasma on green oak lettuce farming has been proposed. A gliding arc plasma generator (GAPG) was designed for plasma-activated water (PAW) spray generation. A PAW spray was generated at 8, 10, and 12 kV by a custom-made ac high voltage power supply. Four hydroponic green oak lettuce trays were treated by PAW spray at different conditions for 10 min, three times a day for nine days. The experimental results showed that all the plasma-treated green oak lettuce sprouts had a greater growth rate than the control group. The best condition was found in the PAW spray generated at 8 kV source voltage, which led to the longest average height and width of sprouts of 10.88 ± 0.33 cm and 10.09 ± 0.08 cm, respectively. Moreover, its average dried weight was also significantly greater than that of the control group by 1.69 times. It was found that the concentration of total Kjeldahl nitrogen (TKN), mainly ammonium, was enhanced in every PAW spray condition. However, the highest TKN concentration was found in the 8 kV PAW spray, which was 3.67 times higher than that of the control group. The amount of nitrite (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> ) and nitrate (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> ) in PAW spray was also enhanced but in the opposite trend to TKN concentration. Moreover, the electrical conductivity (EC) and pH levels could be improved by air plasma. It could be confirmed that the plasma treatment could be effectively applied to green oak lettuce farming, and the PAW spray generated by the GAPG could enhance the amount of nitrogenous fertilizer in treated water, which is essential for plant growth stimulation.

Spheroidization of Tungsten Powder by a DC Arc Plasma Generator with Multiple Cathodes

Spheroidization of Tungsten Powder by a DC Arc Plasma Generator with Multiple Cathodes

Arc discharges operation in “elion” mode

This paper presents the results of a study of an electron-ion-plasma alitization system using two arc plasma generators: a gas plasma generator based on a non-self-sustained arc discharge with a thermionic cathode “PINK” and a gas-metal plasma generator based on an arc discharge with a cathode spot. The system for discharges supplying and biasing of the samples assumes two sub-modes of operation: the ion cleaning sub-mode (ion sub-mode) and the sub-mode of samples electron heating (electron sub-mode), thus realizing the “elion” mode of the system operation. During the experiments, both the dependences of the average values of currents and voltages of discharges burning and probe measurements of the instantaneous plasma parameters values in both system operating sub-modes were investigated. It is shown, that the electron sub-mode of system operation is characterized by an increased burning voltage, which is caused by the formation of a positive anode drop of more than 10 V in the plasmas. Such a potential distribution in the discharges ensures effective heating of the samples by the discharges plasmas electron component.

Hybrid a free arc into constraint-arc to improve arc pressure control behavior

Decoupling the arc pressure and heat output improves the controllability of the arc. In this study, an innovative torch was successfully developed for this purpose by adding an outer electrode under the orifice to a conventional plasma arc welding (PAW) torch. The arc rooting from the added electrode merges with the main/PAW arc forming a hybrid arc system with two cathodes and one anode. While the major arc is constrained, the added arc is allowing to change the anode heat while the pressure is still primarily controlled by the main arc. The coupling behavior was experimentally studied through analysis arc column image and arc pressure measurement. The results show that the added free arc formed by the outer electrode is fully absorbed and coupled into the constraint arc to form a single hybrid arc. The arc pressure peak value in the hybrid arc is little sensitive to outer free arc current compared with that by adjusting the center constraint arc current. Because the sided outer tungsten electrode is isolated to the center inner tungsten electrode and the cooper nozzle in the arcing torch system, the range of arc current applied by the outer tungsten electrode is large. The torch system provides a novel arc plasma generation method to improve the control precision in manufacturing process.

Design and Optimization of a Hybrid Excitation System for Magnetically Driven Rotating DC Arc Plasma Generators

To eliminate the disadvantages of both the uncontrollability in the magnetic field of a permanent magnet excitation system and the high energy consumption of an electric excitation system in a traditional magnetically rotating arc plasma generator, a novel topology of a hybrid permanent magnet and electrically excited coil system is proposed. The proposed system will generate a large enough magnetic field to drive the arc rotation with a minimum consumption of materials and electric energy in the normal operation duty, and will guarantee a nearly zero magnetic field in the arc triggering stage. To optimize the hybrid excitation system, a comprehensive analysis and an optimization methodology; by combining finite element analysis, the moving the least squares approximation and an adaptive weighted particle swarm optimization, are proposed. Finally, a prototype hybrid excitation system is optimized with promising results in views of both saving a huge amount of electric power consumptions and ensuring a nearly zero magnetic field in the arc triggering.

Experimental Observation and Numerical Analysis of the Arc Plasma Axial Motion in a Magnetically Rotating Arc Plasma Generator

To better understand the arc plasma axial motion under an axial magnetic field, a high-speed charge-coupled device camera was used to observe the arc plasma images in a magnetically rotating arc plasma generator. Experimental results indicate that the arc plasma moves towards the cathode bottom as the magnetic field strength increases, while a higher arc current facilitates the cathode arc root to move to the cathode terminus. A two-dimensional coupled model was used to analyze the arc plasma axial motion under different magnetic field strengths. The numerical simulation shows that the arc plasma is axially compressed and curves towards the cathode bottom. It is proposed that the arc plasma structure is derived from the strong backflow from the anode outlet, which is induced by the low-pressure region near the cathode. Moreover, the coupled model predicts the movement of the cathode arc root in agreement with the experimental results. It is inferred that the movement of the cathode arc root is relevant to the energy flux, which is transported from the arc column plasma to the cathode surface.

Chosen Aspects of the Electromagnetic Compatibility of Plasma Reactors with Gliding Arc Discharges

This paper presents an analysis of electromagnetic disturbance interactions inside the three-phase gliding arc plasma generation installation. This is the main part of the electromagnetic compatibility analysis of the reactor installation. All elements of the nonthermal plasma installation are described from the point of view of disturbance generation and their influence on the power supply system. The analysis is based on the results of tests carried out in accordance with the guidelines of the electromagnetic compatibility (EMC) Directive and harmonised standards. The disturbances measured are large, over 20 dB above the limits. The disturbances measured allow valid conclusions to be reached in relation to this type of installation. The implication is the need for plasma reactors designed with elements that reduce radiated and conducted interference.

Characteristics of the arc plasma metal generator

Erosive electric arc plasma generator was developed and investigated. Studies were carried out at pressures from 1.3·10−3 to 105 Pa in the current range of 25-250 A. Plasma was obtained from the erosion products of titanium and copper electrodes.

Influence of rubber powder mass flow rate on process of plasma pyrolysis

The paper describes the experimental examination of thermal utilization of used rubber. The research was carried out to examine the influence of rubber powder mass flow rate on the process of plasma pyrolysis of rubber. An arc plasma generator has been applied. Ar and mixture of Ar and H2 were used as plasma gas. The analysis of composition of the gaseous products was done by the infrared absorption spectroscopy. All the rubber introduced to the plasma jet was decomposed. The outgoing gas did not contain any of toxic chemical compounds, like NOx or HCN.

Experimental Observations of Constricted and Diffuse Anode Attachment in a Magnetically Rotating Arc at Atmospheric Pressure

At atmospheric pressure, the anode attachment can appear in two different modes: constricted and diffuse. In this paper, a magnetically rotating arc plasma generator is built to investigate dynamics of anode attachment. A constricted and diffuse anode attachment, as well as the transformation between the two modes, are obtained. Results show the constricted anode attachment to be preferable for low arc currents and a low magnetic field, whereas the diffuse anode attachment is favored by the opposite conditions. With an increase in arc currents/magnetic field, the constricted anode attachment can transfer from a “restrike mode” with high voltage fluctuation to a “sliding mode” with low voltage fluctuation and then to a diffuse anode attachment with a long arc-shaped structure. An expanding arc column and high-temperature anode are suggested as essential conditions for the diffuse anode attachment because a thinner and hotter anode boundary layer may be promoted. In addition, the time-resolved transformation of different modes exhibits a strong mutual influence between the arc column and anode attachment, which indicates complex coupling mechanisms exist in the near-anode region.

Spot and diffuse mode of cathode attachments in a magnetically rotating arc plasma generator at atmospheric pressure

Adjusting the strength of an axial magnetic field is an effective method to control the cathode attachment. In this paper, a magnetically rotating arc plasma generator is constructed to study the cathode attachment modes under different magnetic fields. Two cathode attachment modes are observed: a spot mode and a diffuse mode. Images of cathode attachments, temperature distribution of the cathode surface, and arc voltage characteristics correlating to different cathode attachment modes are investigated. Results show that the spot mode is favored by the low magnetic field. With an increase in the magnetic field, the cathode attachment region expands gradually, until the spot mode evolutes to the diffuse mode. The diffuse mode is associated with a significantly increased arc voltage, indicating that the transition is an abrupt process rather than a gradual process. For the diffuse mode, the cathode end has a higher average and lower peak temperature, but there exists varying temperature distribution on the cathode end, such as the ring-shaped high temperature region. Additionally, a two-dimensional coupled model is applied to qualitatively discuss the effect of magnetic field on the cathode attachment modes. Simulation results reveal that energy flux to the cathode surface increases with the increase of the magnetic field, and the major increment is thermal conduction heating from the arc column to the cathode surface, which possibly arises from the axial compression of arc plasma. Thus, the diffuse mode tends to always operate in the large magnetic field.

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.

Aerodynamic Dispersion of Anode Arc Attachment Through a Converging–Diverging Nozzle

Electrode ablation is a key factor that affects the life and performance of the direct current arc plasma generator, which is closely related to the near-electrode behavior of the arc. Compared with the constricted-type arc root, diffused-type arc root is more conducive to reduced thermal load, thereby improving the electrode life and the discharge stability. The attachment behavior of the arc root is related to the transport properties of the arc near the electrode wall and the aerodynamic and electromagnetic forces on the root of the arc. From this point of view, aerodynamical dispersion of the arc root using a converging-diverging nozzle was proposed, and the key factors that affect the dispersion were analyzed and verified.

An Experimental Investigation of Cathode Spot Motion in a Magnetically Rotating Arc Plasma Generator at Atmospheric Pressure

Cathode spots present complex forms in magnetically rotating arc plasma generators due to the coupling effect of the plasma flow and electromagnetic fields. In this paper, a magnetically rotating arc plasma generator is built to study cathode spot motion at atmospheric pressure. Cathode spot configuration is observed and discussed for different magnetic fields, arc currents, gas flow rates and cathode lengths. Results show that cathode spots with a slow rotation speed (less than 1 Hz) and different rotation directions occur on the cathode end. For a low magnetic field, low arc current, high gas flow, short cathode rod, the rotation direction of the cathode spot is consistent with the arc column rotation. With an increase in the magnetic field, increase in the arc current, decrease in gas flow, or increase in the cathode rod length, the rotation speed declines, and the cathode spot can move in a reversed direction (i.e., against the arc column rotation). The cathode spot area also appears to expand gradually when the spot motion shifts from the normal direction to the reversed direction, resulting in less cathode erosion at the reversed motion. Further analysis indicates that the cathode spot motion is similar to the retrograde movement that occurs in a vacuum arc with an external magnetic field. The rotation of cathode spot may thus be induced by the radial component of the magnetic field. The cathode spot area that affects the self-magnetic field in the cathode spot is potentially a direct determinant of spot motion.