Plasma Erosion Research Articles

Effect of contact materials on the transient characteristics of vacuum arc plasma and anode erosion

In this study, the mechanisms of the anode phenomena and anode erosion with various contact materials were investigated. Arc parameters were calculated, and the anode temperature was predicted with a transient self-consistent model. The simulation results predicted a constricted arc column and obvious anode phenomena in Cu–Cr alloy contacts than in W–Cu alloy contacts. This observation could be the reason for the concentrated anode erosion in Cu–Cr alloys. For the contacts made by pure tungsten (W) and W–Cu alloy, the anode temperature increased rapidly because of the low specific heat of W. However, the maximum energy flux from the arc column to the anode surface was lower than in other cases. The simulation results were compared with experimental results.

Microstructuring of fused silica by laser-induced microplasma using a pyrographite target for phase optical elements fabrication

In this paper, we purpose to use laser-induced microplasma occurred from a pyrographite target by laser ablation for microstruturing of fused silica plate to fabricate phase optical elements. Laser parameters for erosive plasma torch formation and subsequent etching of fused silica were determined based on preliminary experimental studies and estimated energy calculations. The influence of the overlap coefficients in the focal spot on the reproducibility of etching depths results and the deviation accuracy of etching depths with the found laser parameters was experimentally studied. The best results in terms of accuracy (no more than 0.1 μm) in deviations of etching depths are achieved with the overlap coefficient of 0.5. Moreover, the paper presents estimated calculations of the speed and efficiency of ablation, as well as the coefficient of energy conversion from laser radiation to the ablation energy of fused silica, which was ∼ 0.25. Based on achieved results an attempt was made to fabricate the 6-sector SPP for the wavelength of 355 nm.

Correlative characterization of plasma etching resistance of various aluminum garnets

AbstractPlasma etching is a crucial step in semiconductor manufacturing. High cleanliness and wafer‐to‐wafer reproducibility in the etching chamber are essential in order to successfully achieve nanometer‐sized integrated functions on the wafer. The trend toward the application of more aggressive plasma compositions leads to higher demands on the plasma resistance of the materials used in the etching chamber. Due to its excellent etch resistance, yttrium aluminum garnet Y3Al5O12 (YAG) is starting to replace established materials like SiO2 or Al2O3 in this kind of application. In this study, reactive spark plasma sintering (SPS) was used to manufacture highly dense YAG ceramics from the respective oxides. In addition, yttrium was replaced with heavier lanthanoids (Er, Lu), intending to investigate the role of the A‐site cation in the garnet type structure on the plasma erosion behavior. The produced materials were exposed to fluorine‐based etching plasmas mimicking the conditions in the semiconductor manufacturing apparatus and the erosion behavior was characterized by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), and profilometry. The induced chemical gradient in the samples is limited to a few nanometers below the surface, which makes its characterization challenging. For advanced analysis, we developed a correlative characterization method combining SIMS and scanning TEM (STEM)–energy‐dispersive spectroscopy (EDS) enabling us to examine the structural and chemical changes in the reaction layer locally resolved. In the case of lanthanoid aluminates, an altered reaction layer and reduced fluorine penetration compared to YAG were found. However, a correlation between the characteristics of the induced chemical gradient and the determined physical erosion rates was not evident.

Molybdenum erosion in iodine plasma at hollow cathode conditions

In this study, the authors investigate the erosive effects of iodine plasma on molybdenum. By exposing molybdenum samples to three different test cases of iodine vapor, iodine plasma, and argon plasma, the plasma enhancement of erosion was characterized. A roughly exponential behavior with respect to temperature was found in iodine plasma at hollow cathode conditions and erosion rates as high as 70.1 ± 7.7 μm/h. Despite an oxygen content of <1%, evidence of oxidation was found in all test cases. Behavior consistent with preferential oxidation based on grain orientation was found in the iodine test cases.

Chemically robust superhydrophobic surfaces with a self‐replenishing nanoscale liquid coating

AbstractDue to poor chemical robustness, superhydrophobic surfaces become susceptible to failure, especially in a highly oxidative environment. To ensure the long‐term efficacy of these surfaces, a more stable and environmentally friendly coating is required to replace the conventional salinization layers. Here, soot‐templated surfaces with re‐entrant nanostructures are precoated with polydimethylsiloxane (PDMS) brushes. An additional nanometer‐thick lubricant layer of PDMS was then applied to increase chemical stability. The surface is superhydrophobic with a nanoscale liquid coating. Since the lubricant layer is thin, ridge formation is suppressed, which leads to low drop sliding friction and fast drop shedding. By introducing a bottom “reservoir” of a free lubricant as an oil source for self‐replenishing to the upper layer, the superhydrophobic surface becomes more stable and heals spontaneously in response to alkali erosion and O2 plasma exposure. This design also leads to a higher icing delay time and faster removal of impacting cooled water drops than for uncoated surfaces, preventing icing at low temperatures.

Robust and Autonomous Space Weather Charge Mitigation Coatings

National Space Weather Strategy and Action plan calls for the need to enhanceProtection of National Security, Homeland Security, and Commercial Assets and Operations against Effects of Space Weather. Extreme space weather event like solar flares, cosmic rays, and radiation belts cause ionizing radiation that can damage electronics, solar arrays, and optical systems on satellites reducing their functionality and lifetimes, by inducing an ionic charge on the spacecraft’s surface, when a spacecraft fly in and out of the ionosphere. This negative charge buildup can lead to ion sputtering/arcing, and producing irreparable damage in spacecraft components. Therefore, the local application of materials systems that can passively mitigate the negative charge build up by emitting the electron back into space, while improving resistance to erosion during ion sputtering is of interest. Accordingly, Faraday Technology is developing a low-cost, efficient and scalable manufacturing process for the local deposition of lightweight passive highly emissive and erosion resistant coating onto spacecraft viable substrates that can mitigate charging and erosion effects from ionizing radiation. The composite coating showed a ~1500% increase in maximum (Emax) total electron yield over bare aluminum, extending by 4 times the range of electron yields between crossover energies >1, and demonstrated the potential for erosion resilience in modeled International Space Station plasma erosion conditions. The composite coating could be applied to various spacecraft platforms include spacecraft skin, solar arrays, circuit boards, and emitters such that their lifetime, effectiveness and durability within LEO/GEO environments events can be enhanced. Acknowledgements:The financial support of NASA SBIR/STTR program through contract No.80NSSC22PB020 is acknowledged.

Grain size effect on the plasma etching behavior of spark plasma sintered yttria-stabilized zirconia ceramics

Yttria-stabilized zirconia (YSZ) ceramics with various grain sizes were fabricated via a spark plasma sintering (SPS), and their plasma etching properties were investigated, particularly focusing on the effect of grain size on plasma etching behavior. All the sintered YSZ ceramics were fully densified (∼99.8 % relative density) and the grain size was varied by controlling the sintering conditions. The plasma etching test was conducted by an inductively coupled plasma (ICP) chamber using CF4. The sintered YSZ ceramics exhibited a low etching rate compared to that of the conventional plasma-resistant materials such as Al2O3 and SiC. The superior plasma erosion resistance of YSZ ceramics can be attributed to the yttrium (Y) enrichment and YF3 formation in the plasma etched surface. Interestingly, the grain size of the YSZ ceramics barely affected the etching depth and mass loss. On the other hand, the surface roughness increased with the increasing grain size. The YSZ ceramics with the large grain size showed a much rough surface after the plasma exposure. The obtained results indicated that the grain size could affect the surface properties of the ceramics during plasma etching, which should be considered when fabricating the future plasma-resistant materials.

Generation of pulsed proton beams in a vacuum diode with a passive anode

The paper presents the results of a study of a pulsed proton beam generated of in a diode with a metal anode (stainless steel, titanium, and copper) operating in bipolar-pulse mode. The experiments were carried out on the TEMP-6 accelerator (250–300 kV, 120 ns) with a focusing diode geometry in a mode of self-magnetic insulation of electrons. For analysis of the ion beam parameters, we used the infrared imaging diagnostics of the beam energy density (spatial resolution of 2 mm) and the time-of-flight diagnostics of the beam compositions (time resolution 1 ns). It was found that with continuous supply of hydrogen into a hollow anode (with holes on the working surface) and a hydrogen pressure in the diode chamber of 30–80 mPa, the proton content in the beam exceeds 80%. An increase in the first pulse duration leads to an increase in the ion current density up to 100 A/cm2 and the energy density at the focus up to 3 J/cm2. We analyzed various mechanisms of proton beam generation: ions acceleration from the gas plasma in the plasma erosion mode; ions acceleration from the explosive emission plasma of a metal anode the near-surface layer of which is saturated with metal hydrides (anode material). It was found that hydrogen embrittlement of the near-surface layer of the anode occurs during the injection of hydrogen, and during the explosive emission of electrons, part of the material is sprayed in the form of finely dispersed clusters.

The Erosion of selected tungsten coatings by ion beam and plasma sources compared to calculated predictions

Tungsten is proposed as a tokamak divertor armour due to its good erosion resistance. Combining tungsten coatings with copper as a base material can overcome problems with machinability, lower the weight and reduce the component cost. The erosion rate must be known to estimate the lifetime of plasma facing components.This work aims to compare selected tungsten coatings to check if the erosion rate remains as good. It also compares the experimental data to a developed code based on previous work that aims to be quick and simple while giving reasonable results.In this study a set of erosion experiments were undertaken to measure the sputter yield in different conditions at partner organisations; Helium ion beam erosion at Huddersfield University, Helium plasma erosion at the University of Liverpool, Argon plasma erosion at Plasma Quest Ltd and Xenon Focussed Ion Beam (FIB) erosion at University of SurreyThis work compares sputter yields different tungsten samples: sheet material, Chemical Vapour Deposition tungsten coating, Additive Manufacture deposited tungsten and tungsten coatings laid down by Thermal Plasma Spray. These coatings are available commercially so are ready to deploy today.The experimental sputter yields were compared to theoretical predictions, based on previously published work. While the experimental results agreed well with the models in trend and angular dependence the quantitative agreement was only well predicted to within a factor of four.It was found that the coatings have similar, and sometimes slightly lower sputter yields, and therefore, on occasion, slightly better erosion performance than the stock tungsten sheet samples.

Microstructural characterization, mechanical properties and erosion behavior of Y2O3–MgO nanocomposite films by magnetron sputtering

The effect of Y2O3: MgO ratio on the microstructures, mechanical properties, and plasma erosion behaviors of Y2O3–MgO (YM) nanocomposite films were investigated. The columnar growth structure of the YM nanocomposite film is disrupted as the MgO content increases, resulting in the refinement of the Y2O3 grains. When the Y2O3: MgO ratio is 40 : 60, the columnar crystal structure of the YM nanocomposite film can be refinement effectively due to thermodynamic incompatibility of Y2O3 and MgO. As a result, YM nanocomposite film is strengthened significantly with the maximum hardness and elastic modulus of 16.78 ± 0.8 GPa and 149.24 ± 4.7 GPa, respectively. X-ray photoelectron spectroscopy revealed few changes in the elemental and chemical compositions of the surface layer after fluorination in the YM nanocomposite film, confirming the chemical stability of the YM nanocomposite samples. The etching depth is ∼48% lower on the YM nanocomposite film (with a MgO content of 60%) than on the commercial Y2O3 film. The findings show that the strengthened YM nanocomposite film is more erosion resistant than the commercial Y2O3 coating.

Vacuum plasma erosion resistant 2D nanocomposite coating Avinit for compressor blades of gas turbine engines of aircraft engines

The work is devoted to the search for new vacuum-plasma coatings with high hardness to increase the durability of the compressor blades of the GTE of aircraft engines Ti-Al-N-based vacuum-plasma coatings obtained by Avinit technologies, which ensure the application of hard, high-quality coatings with dramatically reduced micro-arc damage, were selected as candidates. Avinit multilayer coatings have higher functional characteristics than TiN (microhardness, crack resistance, temperature resistance, erosion and corrosion resistance) and may be promising for applying erosion-resistant coatings for compressor blades. Avinit technologies are technologically closest to the vacuum-plasma technologies used in industrial production for applying TiN protective coatings. New multi-layered 2D nanocomposite wear-resistant ion-plasma hard coatings Avinit (TiN-AlN)n have been developed. The created software products made it possible to reach a qualitatively new level in terms of further modification and improvement of the designs of Avinit functional coatings, stability of technologies and improvement of their quality control when applying such coatings for use in the production of compressor blades of gas turbine engines of aircraft engines. Special attention is paid to methods of preliminary ion-plasma treatment of surfaces before coating. Metallographic studies of the chemical and phase composition and structure of Avinit (TiN-AlN)n coatings have been carried out. The thickness of the coatings is 7-9 μm, the microhardness is 34-35 GPa (compared to the serially used TiN coating: 27.4 GPa). The use of three-stage ion-plasma treatment in Avinit technologies using a double vacuum-arc discharge followed by the application of strengthening coatings in a single technological cycle eliminates the formation of cracks and ensures the production of tightly bonded, high-quality coatings of a given composition with the maximally reduced share of the droplet component. The developed coatings (TiN-AlN)n were applied to experimental batches of working compressor blades of GTE aircraft engines for bench tests.

Interaction dust–plasma in Titan's ionosphere: Feedbacks on the gas phase composition

Titan's organic aerosols are formed and spend some time in the ionosphere, an atmospheric layer ionized by solar VUV photons and energetic particles coming from the magnetosphere of Saturn, forming a natural N2-CH4-H2 plasma. Previous works showed some chemical evolution processes: VUV photons slightly alter the aerosols nitrile bands, hydrogen atoms tend to hydrogenate their surface and carbon-containing species participate to the growth of the aerosols. This work investigates the effect of the other plasma species, neglected until now, namely the N2-H2 derived ions, radicals and electronic or vibrational excited states. Industrial plasmas often use N2-H2 discharges to form ammonia-based fertilizers, for metal nitriding, and to erode organic surfaces. Consequently, these are likely to affect Titan's organic aerosols.We therefore developed the THETIS experiment (for Tholin Evolution in Titan's Ionosphere Simulation) to study the interactions between analogues of Titan's aerosols (tholins) and the erosive N2-H2 plasma species found in Titan's ionosphere. Following a first paper on the investigation of the evolution of the solid phase by Scanning Electron Microscopy and IR transmission spectroscopy (Chatain et al., 2020a), this second paper focuses on evolution of the gas phase composition, studied by neutral and ion mass spectrometry.In the presented experiments, newly formed HCN, NH3-CN and C2N2 are extracted in quantity from the tholins as well as some other carbon-containing species and their derived ions. On the other hand, the production of ammonia strongly decreases, probably because the H, NH and N radicals are rather used for the production of HCN at the surface of tholins. Heterogeneous processes are suggested based on the experimental observations: chemical processes induced by radicals at the surface would modify and weaken the tholin structure, while ion sputtering would desorb small molecules and highly unsaturated ions. The effect of plasma erosion on aerosols in Titan's ionosphere could therefore lead to the formation of CN bonds in the aerosol structure, as well as the production of HCN or R-CN species in the gas phase.

FEATURES OF THE DYNAMICS OF EROSION PLUMES AT THE ACTING OF INTENSIVE NANOSECOND LASER PULSES ON A GRAPHITE TARGET IN VACUUM

The temporal characteristics of the glow intensity of erosion laser plumes near the surface under the action of nanosecond laser pulses on a carbon target are experimentally studied. The interaction of laser radiation with the destruction products of plume is minimal due to the formation of erosion plasma with a delay relative to the acting laser pulse. Using a modernized spectrometer, the spectral characteristics of an erosion
 laser plume near the surface of a carbon target with a time resolution of 10–8 s are studied, and the characteristic plasmodynamic times in the plume are ~10–6 s. It is shown that the emission of spectral lines of carbon appears with a delay relative to the glow of the continuous background, when the erosion plume is cooled during expansion. The results of the study make it possible to optimize some characteristics of the laser-
 plasma source for the deposition of nanocoatings.

Ignition of an ionic liquid dual-mode monopropellant using a microwave plasma torch

The blend of hydroxylammonium nitrate (HAN) and imidazole-based ionic liquid has shown good feasibility in chemical and electric dual-mode green space propulsion. As conventional catalyst-driven ignition faces challenges arising from long preheat delay and catalyst failure, this work designs a novel ignition actuator using a microwave plasma torch. The precise tuning of the ¼-λ resonant cavity and improvement in the quality factor (QF) of the microwave igniter make the device efficient and thus allow the propellant to be ignited at a power of approximately 100 W. In the present reduced test rig, the maximum fuel flow rate corresponds to 0.1 N chemical thrusters, and the plasma-assisted ignition is mainly attributed to thermal and kinetic effects. The temperature of the actuator and the plasma torch is investigated by infrared thermometry and spectral fitting of excited molecule nitrogen, respectively. First, the hot electrode tube helps evaporate water molecules and accelerate the liquid jet through rapid gas expansion. Then, the ionic liquid quickly decomposes to small species when the flow reaches the torch with a nitrogen vibrational temperature above 4000 K and rotational temperature above 2000 K. Meanwhile, the nonequilibrium plasma-excited species enhance the combustion of gaseous intermediates by direct impact dissociation, where the OH radical profile is visualized using the planar laser-induced fluorescence technique. In addition, the copper atoms released by plasma erosion are expected to exhibit a significant catalytic effect on ionic liquid decomposition, which is a critical step in controlling the overall reaction rate. It is also noted that such mild erosion does not affect the multi-start operations during the firing test that lasts for at least 30 min.

Features of Cathodic Plasma Electrolytic Nitrocarburizing of Low-Carbon Steel in an Aqueous Electrolyte of Ammonium Nitrate and Glycerin

The possibility of using an aqueous non-toxic electrolyte of ammonium nitrate and glycerin for the cathodic plasma electrolytic nitrocarburizing of low-carbon steel is considered in this paper. Surface morphology and roughness, element and phase compositions, and microhardness of the modified layer were investigated. Kinetic calculations of the processes of nitrogen and carbon diffusion into the steel surface are proposed, taking into account their mutual influence. Wear resistance was studied under dry friction conditions with tool alloy steel as a counter-body. Corrosion studies are performed using potentiodynamic polarization curves in 3.5% sodium chloride solution. The plasma electrolytic nitrocarburizing in an aqueous electrolyte with ammonium nitrate and glycerin is established to increase surface hardness up to 980 HV due to the formation of a nitrocarburized layer with 1.35 ± 0.12% carbon and 0.32 ± 0.08% nitrogen concentration. The influence of erosion in electrolyte plasma and high-temperature oxidation on the morphology and surface roughness is shown. The presence of a dense oxide layer, low surface roughness, and high hardness of the diffusion layer favor a decrease in the friction coefficient by 1.3 times, weight wear by 1.8 times and corrosion current density by 1.4 times.

Demonstration of One Hundred Kilogram Xenon Throughput by a Low-Power Hall Thruster

The Hall thruster component of the Ascendant Sub-Kilowatt Transcelestial Electric Propulsion System (known ASTRAEUS) successfully demonstrated a propellant throughput of over 100 kg of xenon and demonstrated a total of of impulse in a long-duration wear test. The thruster was operated for a total of 7205 h, with the test broken into five segments each with a different discharge power between 200 and 1350 W: 3291 h at 300 V/1000 W, 1739 h at 500 V/1000 W, 416 h at 400 V/600 W, 388 h at 200 V/200 W, and 1371 h at 300 V/1350 W. Telemetry and temperature measurements periodically recorded throughout the test revealed constant performance across each test segment and over the full test duration. Each segment was sufficiently long to obtain erosion rate data on the thruster by an optical profilometer. Subnominal magnetic field strengths were inadvertently applied to the thruster during the first 5 khr of the test due to an electrical ground-support equipment issue, which caused a downstream shift of the discharge plasma and higher erosion of the thruster’s pole covers than originally expected. This issue was corrected for the latter three test segments; however, the thruster performance and operational behavior at all reference operating conditions remained unaffected. The long-duration wear test was voluntarily terminated after the thruster processed 100.3 kg of xenon (Xe). This marks the world’s first long-duration wear test of a low-power magnetically shielded Hall thruster with a center-mounted hollow cathode wherein over 100 kg Xe throughput was demonstrated.

Three-dimensional modeling of sputtered materials transport in diagnostic ducts of fusion devices

Migration of plasma erosion products in plasma facilities is studied experimentally and numerically within the framework of modeling transport of plasma-facing materials in the diagnostic ducts of fusion devices. Material transport simulation is discussed for two cases of low and high background neutral gas pressures. Monte Carlo software KITe was used to simulate transport at a neutral gas background pressure 0.1–0.5 Pa—typical during steady-state tokamak operation and during pressure pulses caused by edge localized modes (ELMs). The simulation approach was implemented to describe experiments at the MAGNUM-PSI facility. Fluid dynamic code FLUENT is used to simulate transport during pressure surges as high as 1000 Pa, which can occur in the case of severe disruptions in tokamak plasma discharges, such as vertical displacement events (VDE) or accidental events. The hydrodynamic approach was verified in simulation of target sputtering in the QSPA plasma gun facility.

Nonlinear impact of the porous nanostructure on the net tungsten erosion in the linear plasma device PISCES-A

The tungsten fuzz growth under non-erosive and erosive helium plasmas in the linear plasma device PISCES-A has been investigated by experiments and simulations. The simulation results benchmarked against the experimental measurements indicate a decayed net physical sputtering yield during fuzz growth under the erosive helium plasma. Further, a nonlinear dependence of the net tungsten erosion on the ‘effective’ porous nanostructure that can be sputtered by incident helium particles has been found.

Processing map to control the erosion of Y2O3 in fluorine based etching plasmas

AbstractDue to the increasing number of applications for ceramic components in reactive etching processes, the interest in the specific erosion behavior of highly etch‐resistant materials like yttrium oxide (Y2O3) has increased in the past years. Despite the large number of investigations already existing in this field, a more general understanding of the erosion mechanisms still lacks due to the limited comparability of these investigations. The huge difference in the kind of etching setups, processing parameters (bias voltage and plasma gas composition), and sample microstructures prevented consistent conclusions so far. To achieve a more general understanding, this study investigates the erosion behavior Y2O3 under a broad spectrum of plasma etching parameters. Therefore, the bias voltage is increased from 50 to 300 V and the plasma gas composition is gradually changed from Ar‐rich to CF4‐rich compositions. This systematic approach allows to directly correlate the morphology changes caused by plasma erosion with the related plasma etching parameters and enables to better understand their influence on the depth of physical and chemical interactions, surface damage, and etching rate. We discovered three distinct erosion regimes, which exhibit specific erosion characteristics. Using these observations, a schematic processing map for Y2O3 was developed, which could help to estimate the severity of the erosion attack dependent on the processing parameters.

Computational Investigation of Beryllium and Lithium Performance in Future Fusion Tokamaks

Low-z materials are exemplary candidates in tiling critical plasma-facing components in future fusion reactors due to their low ablation rates under intense high heat fluxes especially during abnormal and hard disruption events. Beryllium and Lithium as low-z materials show good performance as plasma-facing materials in current tokamak. Future tokamaks will exhibit long duration hard disruptions, which in turn requires further investigation of plasma-facing materials, as Li and Be, to judge their performance and evaluate their erosion rates. Electrothermal plasma capillary discharges are used to simulate the high-heat flux deposition on materials to assess their erosion rates. The electrothermal plasma code ETFLOW, which is written for capillary discharges to predict the plasma parameters and erosion rates is used to simulate the high-heat flux conditions similar to expected disruption events for simulated heat fluxes from as low as ~50 to as high as ~290 GW/m2 with a reconnoitering of generating the Be and Li plasmas up to the third ionization (Br+++, Li+++). Performance of Be and Li under the lowest capillary discharge currents (50 kA and 100 kA) is almost identical, however, Li shows sharper increase in the plasma pressure, heat flux, total ablated mass and the exit velocities than Be for higher discharge currents (150, 200 and 250 kA). This huge difference between the performance of Li and Be under low and high heat fluxes can be an important issue for the future magnetic fusion reactors.