Cathode Plasma Research Articles

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

Turbulence in hollow cathodes used for space propulsion is believed to play an important role in anomalous electron transport and ion heating. In this work, the implementation of coherent Thomson scattering to identify and characterize MHz-frequency ion acoustic turbulence and kHz-frequency oscillations in the plume of a hollow cathode is achieved. In the presence of a background magnetic field of a Hall thruster, a number of unstable modes are observed. A directive ion acoustic mode propagating predominantly within a restricted angle around the magnetic field is found, exhibiting an energy scaling with wavenumber k of the form k−5.2±0.58, which differs from the classic Kadomtsev k−3 scaling for unmagnetized conditions. Bi-directional ion acoustic mode fluctuations propagating over a range of angles with respect to the magnetic field have been measured, possibly signifying the existence of a large-amplitude plasma wave, similar to the Buneman instability. Finally, electron density fluctuations in the kHz-frequency range, a possible consequence of drift-driven instabilities in the plane perpendicular to the magnetic field, have also been identified. These results not only are an indication of the diversity of wave types that exist in hollow cathode plumes but also point to the key role played by the presence of, and the configuration of, the magnetic field in their appearance.

FABRICATION AND WEAR BEHAVIOR OF PEC/N HARDENED LAYER ON PURE IRON

In this paper, the antifriction carbonitriding (PEC/N) layers were prepared on pure iron by cathodic plasma electrolytic treatment (PET) in glycerin and carbamide aqueous solution under 360[Formula: see text]V for 1, 3 and 10[Formula: see text]min. Influence of discharge time on morphology, structure, surface roughness and microhardness of PEC/N layer was analyzed. The tribological performance of the PEC/N layer, growth mechanism and diffusion process during PEC/N treatment was investigated. The thickness of the PEC/N layer grew to 48[Formula: see text][Formula: see text]m for 10[Formula: see text]min treatment and the growth of the saturation layer met the parabolic law. The highest microhardness of the surface was up to 811 HV, which was 5 times of that of iron substrate. The PEC/N layer consisted of [Formula: see text]-Fe, Fe[Formula: see text]N, Fe4N, Fe3C, Fe5C2 phases and a little FeO phase. The wear rate of the PEC/N layer reduced by five-sixes comparing with the iron substrate and the surface of the wear track was much smoother. The temperature close to the surface during PEC/N fitted by the tested temperature values inside the sample was 801∘C (1074[Formula: see text]K), and the combination diffusion rate of C and N into pure iron during PET at 360[Formula: see text]V reached [Formula: see text][Formula: see text]m2/s. The electron temperature fluctuates between 3000[Formula: see text]K and 8000[Formula: see text]K. The antifriction PEC/N layer displayed a very good wear resistance and the higher diffusion rate makes plasma electrolytic carbonitriding a very effective technique for surface modification of pure iron.

Combined plasma treatment of AISI-1045 steel by hastelloy deposition and plasma nitriding

AISI-1045 steel is medium strength steel, and it needs surface modification to use in machine components. The surface properties of steel can be improved by plasma nitriding. The nitriding performance can be upgraded by introducing special alloying elements (nitride forming elements such as chromium, molybdenum), which have a strong affinity with nitrogen. Here, the combination of cathodic cage plasma nitriding (equipped with hastelloy cathodic cage, containing nitride forming elements) and conventional plasma nitriding is used to improve the surface properties. Thus, it is used to deposit such alloying elements, and subsequent plasma nitriding is performed to cause nitrogen diffusion to improve the coating adhesion and hardness gradient formation. The substrate hardness (346 HV) is increased up to 982 HV, 1426 HV, and 1692 HV by hastelloy deposition and post-nitriding at 400 and 450 °C, respectively. Additionally, the duplex treated samples show a favorable hardness gradient. The treated samples show the formation of iron nitrides Fe4N, Fe2−3N, chromium, and nickel phases. The voids and pores have appeared on the hastelloy deposited sample, removed by post-nitriding. The wear resistance is significantly improved by duplex treatment. The duplex treatment reported here can be used effectively to improve the surface hardness and wear resistance of AISI-1045 steel. Additionally, a single processing unit is required, needs low-processing temperature, surface uniformity, the whole processing time is relatively short, and the compatibility of this system with the industry proposed that this work would be helpful for the industrial requirement.

MAGNETIC FIELD DYNAMICS IN PLASMA OPENING SWITCH

Computer simulations for magnetic field penetration into plasma of plasma opening switch (POS), and current loop formation in it are presented for various initial plasma densities, currents, and POS geometries. It is shown that the current loop dynamics in the POS is determined by the fast magnetic field penetration in plasma due to the Hall effect. The strong dependence of the current loop longitudinal velocity on the transverse coordinate, together with the influence of the boundary conditions at the POS cathode and anode, lead to the formation of the narrow S-shaped current loop even in a homogeneous plasma. It is shown that the control parameters influencing the dynam-ics of the magnetic field and the motion of the current loop in the POS are the initial plasma density, driving current and cathode radius. The POS resistance is calculated for wide range of initial plasma densities, currents, and cath-ode radiuses. It is shown, that POS resistance is proportional to the total current, inversely proportional to plasma density, and is in the range 10-3…1 Ω for plasma densities 1012…1015 cm-3.

Surface topography generation and simulation in electrical discharge texturing: A review

Recent advancements in electrical discharge texturing (EDT) make it a suitable candidate for many novel and innovative applications. This paper presents a comprehensive review of experimental and modeling works on topography characterization of random and isotropic surface textures generated using the EDT process. Initially, the review examines the different modes of EDT for texture generation and different applications of EDT surfaces. Then, the review undertakes a comprehensive analysis of experimental characterizations of EDT surface topographies in terms of profile roughness (2D) and areal texture (3D) parameters. A better understanding of the correlation between surface topography and surface functionality is evolved from this study. This review also covers the evolution of simulations in EDT through its gradual progress from single-crater simulations to multi-crater simulations and finally to surface topography simulations. A suitable selection of individual discharge features of heat flux distribution, thermo-physical properties, cathode energy fraction, spark radius, and plasma flushing efficiency and extending it considering multi-crater aspects of spark distribution in location, energy level, and chronological order and crater overlap, advances to the simulation of EDT surface topography. Finally, the future research avenues in EDT are identified as developing new modes, topography quantification, functionality improvement, minimum quantity dielectric usage, improvement in surface topography simulations, and artificial intelligence for topography prediction.

Cathodic boriding and anodic polishing of medium-carbon steel by plasma electrolysis

The possibility of cathodic plasma electrolytic boriding of medium-carbon steel in an aqueous solution of ammonium chloride and boric acid followed by anodic plasma electrolytic polishing in an ammonium sulfate solution on the same equipment with a change in the operating voltage is shown. The morphology and roughness of the surface, microhardness of the modified layer have been investigated. Wear resistance was studied under dry friction conditions. It has been established that cathodic boriding at 850 °C for 5–30 min leads to the hardening of the surface layer up to 1050 HV with an increase in roughness by 1.5–2.5 times and wear resistance by 3.5 times. Subsequent anodic plasma electrolytic polishing of the boriding surface leads to a decrease in roughness with an increase in wear resistance by 2.3 times.

Suppression of instabilities in the transport of a high-power electron beam in the forevacuum pressure range using low-energy thermionic electrons

We report the results of our study on the effect of injection of low-energy thermionic electrons on the suppression of instabilities of the beam-plasma discharge (BPD) type in a beam plasma during the transport of a powerful continuous electron beam generated by a plasma–cathode electron source in the forevacuum range of pressure. As result of thermionic electron injection, the plasma electron temperature decreased to 0.3 eV and the plasma density decreased by an order of magnitude to 1015 m−3. The minimal thermoelectron current required for suppressing the BPD increases with increasing emission current and decreases with increase of the beam accelerating voltage.

Comparative study of PVD titanium nitride coating with cathodic cage plasma nitriding of austenitic 201 stainless steel for enhanced tribological properties

Comparative study of PVD titanium nitride coating with cathodic cage plasma nitriding of austenitic 201 stainless steel for enhanced tribological properties

Numerical simulation and experimental research on an inductively coupled RF plasma cathode

In this study, numerical simulation and discharge current tests were conducted on an inductively coupled radio frequency (RF) plasma cathode. Numerical simulations and experimental measurements were performed to study the factors influencing the electron extraction characteristics, including the gas type, gas flow, input power and extracting voltage. The simulation results were approximately consistent with the experimental results. We experimentally found that the RF input power mainly determines the extracted electron current. An electron current greater than 1 A was acquired at 270 W (RF input power), 2.766 sccm (xenon gas). Our results prove that an inductively coupled RF plasma cathode can be reasonable and feasible, particularly for low power electric propulsion devices.

Axial Distribution of Plasma Properties in a Hollow Cathode Plasma Discharge

Hollow cathode plasma discharge technology has several engineering and industrial applications. To further enhance these applications, information on plasma characteristics (such as its axial distribution inside the hollow cathode cavity) is essential. This work determines the axial distributions of electron temperature and density inside said cavity by inserting a triple probe. The temperature and density inside the hollow cathode cavity were approximately 4 eV and −1017 m−3, respectively. It was also confirmed that the plasma existed over almost the inside the cathode cavity and the electron temperature increased and the electron density decreased rapidly in the region near the anode.

Phenomenological plasma model for open-end emitter with orificed keeper hollow cathodes

Hollow cathodes are used as thermionic emitters in a variety of electric propulsion devices such as the Hall thruster. This work studies the derivation and discusses the results of a phenomenological (zero-dimensional) plasma model for a hollow cathode with open-end emitter and orificed keeper. This represents the first attempt to model the plasma in the three regions of hollow cathodes with open-end emitter geometry, i.e. the keeper orifice, the cathode–keeper gap, and the insert. The current continuity, ion balance, and plasma power balance equations are solved to compute the main plasma parameters in each of the aforementioned regions. One novelty of this work is the definition of mathematical fit functions for the dynamic viscosity and ionization and excitation rates for krypton. Moreover, the resistive losses in the cathode–anode region are estimated to model the cathode standalone diode testing with an external anode. The model delivers cathode operational parameters such as the discharge power and potential which are compared to experimental data for both xenon- and krypton-fed cathodes. Furthermore, the influence of the three regions’ geometries and the propellant flow rate as well as the discharge current on plasma parameters and cathode power budget of sample cathodes is discussed at length.

Novel corrosive behavior of titanium oxynitride film deposited on nickel–titanium alloy using cathodic cage plasma processing technique

AbstractIn this study, we used a cathodic cage plasma system to deposit an oxynitride coating on a nickel–titanium metallic substrate for three different processing gas compositions (60%H2 + 40%N2; NT1, 50%H2 + 50%N2; NT2%, and 40%H2 + 60%N2; NT3). The influence of various gas mixtures on surface morphology, chemical composition, and crystal structure of treated samples (NT1, NT2, and NT3) was investigated. A spectrophotometer is used to determine the amount of nickel ion leaching in a chloride‐containing saline electrolyte using atomic absorption spectroscopy. Potentiodynamic polarization curves and electrochemical impedance spectroscopy depict the enhanced corrosion resistance of treated samples as compared to the base Ni–Ti sample. Titanium oxynitride coating in NT3 samples shows an excellent barrier against corrosion behavior and nickel ion leakage in a corrosive environment.

The Electrodynamic Mechanism of Collisionless Multicomponent Plasma Expansion in Vacuum Discharges: From Estimates to Kinetic Theory

This paper is devoted to the study of collisionless multicomponent plasma expansion in vacuum discharges. Based on the fundamental principles of physical kinetics formulated for vacuum discharge plasma, an answer is given to the following question: What is the main mechanism of cathode plasma transport from cathode to anode, which ensures non-thermal metallic positive ion movement? Theoretical modeling is provided based on the Vlasov–Poisson system of equations for a current flow in a planar vacuum discharge gap. It was shown that the non-thermal plasma expansion is of a purely electrodynamic nature, caused by the formation of a “potential hump” in the interelectrode space and its subsequent movement under certain conditions consistent with plasma electrodynamic transportation. The presented results reveal two cases of the described phenomenon: (1) the dynamics of single-component cathode plasma and (2) multicomponent plasma (consisting of multiple charged ions) expansion.

Device for connecting elements of main oil and gas pipelines using electron beam welding

The article deals with the problem of connecting pipelines in the oil and gas industry. To improve the quality of welds on the oil pipeline, the article proposes an alternative method of welding and venting the beam into the atmosphere. This method includes a mobile installation for electron beam welding, in which, in manual mode, it is possible to adjust the seam speed, penetration depth, change the trajectory of the weld and the position of the installation relative to the pipe axis. Guns with a plasma cathode, which allow welding products in the atmosphere, are considered. The power of the generators is also calculated, and the generators are selected corresponding to the put forward requirements. In the course of the work, the authors are designing an electron beam welding unit, which in the future is planned to be developed as a mobile one. The mobile installation includes: a generator directing the belt to the pipe, a horizontal displacement motor, a welding positioner, an electron gun with a plasma cathode.

The problem of “anomalous” ion transport in high-current vacuum discharges

This paper gives an exhaustive theoretical description of the so-called “anomalous” ion transport phenomenon that exists in vacuum diodes with cathode plasma emission. The phenomenon is represented by the cathode plasma directed movement towards anode. In general terms, the “anomality” means that metal ions are accelerated towards an electrode with a higher electrostatic potential (anode). The theoretical description is given within the framework of a one-dimensional kinetic model, which is based on the Vlasov-Poisson system of equations for plasma and electrostatic field components. Time-dependent accurate numerical solution of this system describes the process evolution leading to “anomalous” ion transport. It was shown that the “anomalous” transport has fast electrodynamic nature.

Boosting OER activity of stainless steel by cathodic plasma surface modification

Developing an effective method to promote the electrocatalytic activity of stainless steel for oxygen evolution reaction (OER) remains challenging. In this paper, cathodic plasma bombardment (CPB) has been employed to modify the surface of 304 stainless steel by creating a nanoscale three dimensional structure with a large specific surface area, which could significantly improve the electrocatalytic OER performance of 304 stainless steel. The influence of CPB conditions on the electrocatalytic performance of 304 stainless steel was systematically investigated. The results indicate that the electrode prepared under the optimal CPB conditions only requires an overpotential of 323 mV to reach a current density of 10 mA cm−2 at a Tafel slope of 51 mV dec−1 in the 1 M KOH alkaline electrolyte. The work provides a new methodology for the development of highly active and low-cost stainless steel-based electrocatalytic electrodes.

Methods of increasing the dielectric strength of the accelerating gap in an electron source with a plasma cathode

This work represents the investigations for decreasing acceleration gap breakdown probability of plasma source of electrons SOLO, with grid stabilization of the boundaries of the arc cathode plasma. We increased the distance to the treated target, bent the transportation channel of the electron beam, created additional plasma in the anode space, and increased the beam front. The effect of the above measures on the breakdown probability when the target is exposed of a low-energy electron beam with a power density of up to 0.5 MW/cm2 with a diameter of 2.5 cm was investigated separately. Beam deflection is most effective at relatively long pulse durations of 150 μs and accelerating voltage of 20 kV, rather than a lower one. It was possible to double the maximum power for the same beam transport length applied to a low-melting target. Preionization in the anode proved to be effective for relatively short beams of 15 μs duration.

Discharge and plasma plume characterization of a 100 A-class LaB6 hollow cathode

This article reports on the characterization of a laboratory model 100 A-class hollow cathode with a sintered lanthanum hexaboride (LaB6) emitter for high-power Hall thrusters. The cathode has been fired up to 70 A with xenon as working gas. The cathode architecture, test setup, ignition procedure, and power consumption are described first. The second part of this contribution comments on the current–voltage characteristics and the discharge modes obtained for discharge currents in the 30–70 A range and flow rates in the 15–30 SCCM range. The cathode operates in a spot mode at high discharge currents and in a plume mode with large oscillations at low currents and low gas flow rate. Spectral analysis shows that most frequencies reside in the 10–200 kHz range with flat and sharp distributions in plume and spot modes, respectively. Finally, we present electron temperatures and densities measured in the cathode plasma plume by means of incoherent Thomson scattering. The two quantities decrease along the axis. The density is large (up to ∼1019m−3) and increases with both the ion current and the gas flow rate. The electron temperature increases with the current and decreases with the gas flow rate. The temperature remains relatively low (<1.5 eV) in spite of large currents and applied powers.

Experimental installation for studying cathode plasma processes in vacuum gap of pulsed electron accelerator with gas or liquid injection

One of the directions of using plasma sources is the formation of plasma emitters for electron beams as part of direct-action charged particle accelerators. The parameters of the accelerator generators require mutual matching with the characteristics of the plasma emitters. The paper describes the design, composition and diagnostic equipment of an experimental stand based on a vacuum chamber of a pulsed electron accelerator for testing plasma sources of pulsed electron beams. The stand includes a vacuum volume with a high-voltage bushing, pumping out pipes, diagnostic windows along the perimeter and a mounting flange of a complex device for diagnosing the characteristics of pulsed electron beams. The stand provides the possibility of controlled supply of gas and liquid to the formation region of the plasma emitter of electrons under the influence of an accelerating voltage pulse. The location of the diagnostic windows and flanges of the stand allows direct optical observations of the plasma formation region in the frontal and profile directions. The use of the stand will make it possible to determine the characteristics of the tested plasma emitters for their operation as part of a vacuum diode of pulsed electron accelerator.

Surface modification of hypereutectic silumin subjected to a millisecond modulated electron beam treatment

In this work, using a unique feature of the “SOLO” electron source with a grid plasma cathode based on a low-pressure arc discharge, which consists in the possibility of controlled operation of the beam power during a pulse of submillisecond duration, and, accordingly, the rate of energy input into the sample surface, we investigated the modes irradiation of samples of hypereutectic silumin. The irradiation modes had the same energy density during the first 200 μs of the pulse, equal to 20 J/cm2 and differed in different durations of further maintaining the surface temperature at 600°C for a time of up to 1 ms. The results of tribological tests and methods of diffraction microscopy of the investigated defect structure, the elemental and phase composition, the morphology of the strengthening phases of the modified layer of the hypereutectic silumin samples are presented.