Plasma Electrode Research Articles

Overall Concept Design of 2.45 GHz ECR Ion Source with Tunable Magnetic Field

The design of the ECR ion source was made for an operating frequency of 2.45 GHz. The ion source is considered to be used for producing protons and double charged helium ions. The source construction as well as the separate components design are presented in the study. The operating modes include both ECR and microwave operating regimes. The extraction system with the beamforming was developed. The beam adjustment is implemented by the longitudinal shifting of the electrodes against the plasma electrode position. The performance of the 2.45 GHz waveguide line to provide the stable power injection into the plasma chamber is considered. The numerical simulation of the waveguide line components was made and optimised.

Design, development and test of single beamlet microwave ion source with spot-dense plasma system

In this paper, an efficient ion source with unique characteristics is introduced and proposed. It outlines the generation of a spot-dense plasma just below the plasma electrode aperture of the extractor system through the utilization of a 2.45 GHz microwave plasma source with a power of 1000 W, in the absence of a magnetic field. This source utilizes a 2.45 GHz microwave plasma generator operating at 1000 W, resulting in the generation of a spot-dense plasma just below the plasma electrode aperture of the extractor system, all achieved without the need for a magnetic field.The spot-dense plasma results in the extraction of an ion beam with high current density. Furthermore, the suggested ion source can be utilized in a smaller size using a higher frequency. Therefore, our findings indicate that the proposed method not only substantially enhances the extracted positive ion beam current but also significantly reduces the size of the ion beam source system. Based on the design and simulation results, an experimental model of the ion beam source is constructed. The diagnostic tools provided the beam current density and system efficiency values of 99mA/cm2 and 7×10−6A/W, respectively.

Application of a Film Model to Mass Transfer and Chemical Reaction at a Plasma-Liquid Interface

Abstract Plasma electrodes provide novel ways of conducting electrochemical processes in liquids, in particular because of the ability to generate unique reactive radical species. However, the radicals injected into the liquid and their ensuing reactions are often confined to a narrow region near the interface of the plasma and the liquid. Thus, mass transfer has been found to play an important role in the observed kinetics and a modeling framework that includes both transport and kinetics is required to interpret experimental data. Here, we apply the idea of a film model for interphase mass transfer to plasma-liquid electrochemical processes, whereby transport is described by a stagnant film that is inherently linked to the concentration boundary layer and the mass transfer coefficient. Equations that govern the transport and reaction of radicals and substrates within the film are solved assuming a quasi-steady state approximation. The model is applied to specific case studies from the literature to estimate important parameters that cannot easily be measured in experiments, such as the mass transfer coefficient. Our study shows that a film model can elucidate the effect of mass transfer on observed conversion rates and allow the intrinsic kinetics to be unraveled.

Ion velocity separation mechanism during vacuum spark stage

Abstract Supersonic ion jets produced in vacuum arc discharges have a wide range of applications, where precise control of ion kinetic energy is crucial. However, a comprehensive understanding of the ion acceleration mechanism remains elusive, particularly regarding whether there is ion velocity separation in the vacuum spark stage. In this paper, a 1D spherical implicit particle-in-cell (PIC) with Monte Carlo collision (MCC) model is employed to investigate the ion velocity separation in multi-charged vacuum arc plasma with varying electrode bias voltages and plasma ion densities. The results show that ion kinetic energy can reach hundreds of electron volts due to continuous acceleration by the formed potential valley, which leads to ion velocity separation at low electrode bias voltage or low plasma density. An increasing electrode bias voltage flattens the potential valley, reducing the electric field acceleration. While increasing the plasma density deepens the valley and intensifies Coulomb collisions, resulting in nearly-equal velocities across ions in different charge states. These findings can theoretically explain the discrepancies observed in previous experiments regarding the dependence of the ion velocity on its charge state during the vacuum spark stage.

Electrochemical Plasma-Activated CO2 Reduction at a Plasma-Water Interface

The development of technologies and processes to decarbonize chemical and fuel production is key to reducing global anthropogenic greenhouse gas emissions. Electrochemical carbon dioxide reduction enables a sustainable pathway to circularize carbon-based chemical products by upgrading recovered carbon dioxide using renewable energy sources. Electrochemical CO2 reduction has successfully been employed to produce chemicals such as methanol and ethylene, but it has been hindered by dependence on elevated temperature to achieve high yields and limited ability to generate higher order carbon products. Non-thermal carbon dioxide plasma can be generated at ambient temperature and pressure and contains energetically excited oxygen and carbon species. When introduced to an electrocatalyst, these reactive species could more readily participate in reaction pathways with higher activation barriers towards forming higher order carbon species compared to electrochemical reactions involving ground-state reactants. Further, plasma discharges over water in an electrochemical cell generate plasma-activated water, introducing solvated electrons and secondary reactive oxygen species.In this work, we investigate how the use of plasma-activated carbon dioxide and a plasma-water interface impacts electrochemical product generation. We design a novel non-thermal plasma electrode to discharge carbon dioxide plasma into water in an electrochemical cell with a Cu nanoparticle electrocatalyst. Results suggest the potential for a plasma-water electrochemical system to generate value-added products that are less commonly generated in electrochemical processes at ambient pressure and temperature.

Prospective life cycle assessment of titanium powder atomization

The environmental sustainability of titanium powders production mainly depends by atomization that is the most diffused technology in this field, ensuring the environmental advantages of high mass flow rate, energetical efficiency and reduced waste which have greatly encouraged its diffusion on an industrial scale. However, few quantitative assessment studies have been proposed on atomization sustainability and none of them consider the many technological evolutions of atomization that the industries are working on. This study proposes a prospective life cycle assessment (LCA), of the ex-ante type, of future new Electrode Induction Gas Atomization (EIGA) and Plasma Rotating Electrode Process (PREP) that will produce Ti6Al4V powders in 2035. This time point, referring to a medium-term view is considered to ensure the relevance and the reliability of technology forecasts based on quantitative estimates. Both the systems have been modelled through data retrieved from patents to assess their future impacts. The prospective LCA shows that in the future EIGA the average impact, in each indicator, will be 50% lower for electrical consumption and 98% lower for argon consumption compared to future PREP. The future EIGA and future PREP are more sustainable than the mature EIGA (of the crucible and crucible-free type) and mature PREP (of the traditional and supreme-speed plasma type) currently on the market. The average impact reductions, respectively passing from future to mature EIGA and PREP, are 65% and 23% for electricity consumption and 11% and 28% for argon consumption. The variabilities in technological solutions, scalability and future scenarios about electricity and argon production scale all the impacts without reverse the ranking. At a structural level, the most sustainable solutions are the optimization of the geometries of the titanium bar in the future EIGA and the optimization of the disposition of the plasma gun in the future PREP. This study shows which technological advancement increase the sustainability of EIGA and PREP atomization process in the future and to what extent in the two cases.

Optimizing electrode arrangement in plasma actuators: a study on induced velocity and efficiency

This study investigates the performance of two types of multi-encapsulated electrode (MEE) plasma actuators, compared to typical dielectric barrier discharge (DBD) plasma actuators, in quiescent air. The objective is to determine whether the multiple encapsulated structure can enhance the performance of the plasma actuator. In the present paper, flow characteristics are investigated by using particle image velocimetry (PIV) and Schlieren visualisation. In addition, the distribution of body force over the gas volume based on the Navier–Stokes equations is calculated from velocity measurements. The obtained results demonstrate that the starting vortex behavior is influenced by electrode arrangement. Specifically, it can be observed that when the first encapsulated electrode is positioned closer to the exposed electrode, then a significantly higher induced velocity can be obtained compared to the baseline condition. In fact, the induced velocity can be increased by up to 1.5 times under this optimize configuration. These results highlight the importance of electrode arrangement in the plasma actuator design. Based on body force estimation, MEE plasma actuators exhibit a significantly higher momentum transfer, particularly in the wall normal direction. The investigation on the mechanical efficiency also reveals that the optimized configuration proposed in the present study can significantly enhance the efficiency. In fact, a four-fold increase in maximum efficiency compared to the typical configuration is observed. These results suggest that the proposed configuration could be considered a promising solution for improving the mechanical efficiency of plasma actuators.

Dynamic Change of the Work Function of Plasma Electrode Materials due to Hydrogen Plasma exposure

It has been known that the work function of plasma electrode (PE) surfaces such as Cs-covered Mo and C12A7-electride can be decreased when the surfaces are immersed in hydrogen (or deuterium) plasma. We discovered that the work function of the C12A7-electride changed right after the termination of plasma exposure with the time constant of a few minutes. This phenomenon was not observed on the surface of clean metals (Mo or Ta). By extrapolating the dependence of work function against time to determine the value at the plasma termination, the work function during plasma exposure was estimated to be 2.4 – 2.5 eV, which can be compared with the value of the electride exhibiting metallic conductivity.

Extraction of ion beam from laser ion source for direct plasma injection scheme

Laser ion sources are expected to be used in various applications of heavy ion beam technology. The plasma direct injection scheme (DPIS) is a method in which ion beams extracted from a laser ion source are directly injected into a radio frequency quadrupole (RFQ) linear accelerator. In this study, a new shape of the plasma electrode with a concave surface for the DPIS was proposed to inject a converging beam to a cavity of RFQ accelerator. This approach allows the use of a large-diameter extraction electrode, which is not limited by the aperture of the RFQ electrode rods. The DPIS, using the concave surface electrode, was employed to accelerate C6+ ion beams. The results indicated that both the beam current and the number of ions increased nearly twice with the proposed electrode shape compared to values obtained with the conventional electrode. This enhancement corresponded to the increased extraction area of the beam.

The Child Langmuir Illusion

A Particle in Cell (PIC) model of ion beam extraction from a plasma provides strong evidence that the origin of the observed V(3/2) relationship between the applied extraction voltage and beam current is caused by meniscus shape and collimation on the extraction electrode, not by space charge limited extraction. Excellent correlation between the PIC model, a gun code and experiment is shown for 100 µA Ar+ beams. The s-shape in the emittance phase space is shown to be caused by the radial electric field created by the external edge of the plasma electrode.

Innovative Cesiation Deriving Incredible 145 mA Beam from J-PARC Cesiated RF-Driven H− Ion Source

In NIBS2022, the stable 8 hours operation of the J-PARC cesiated RF-driven H− ion source (IS) in a test-stand with a 69.9 keV 120 mA beam and a beam duty factor of 4 % (1 ms x 40 Hz) was reported. However, the Cesiation condition was produced after many times and rather large amount of Cs and H2Os injections. The fluctuation of the H− ion beam intensity (IH −) in a pulse and the transverse emittances were rather larger than those for the previous 65 keV 110 mA operation. The plasma electrode temperature (TPE) of 254 °C much higher than that not only for the usual J-PARC IS (about 70 °C) but also for the standard cesiated H− ion sources (180 ∼ 200 °C) suggested the existence of novel H2O mediated cesiation surviving against the high TPE. In this paper, the J-PARC IS improvements based upon a hypothesis of the best cesiation constituted of sub monolayer H2O (chemically bound with Mo) mediated cesiation and Cs half monolayer on remaining surface are presented. The innovative cesiation derived a 76.5 keV 145 mA beam stably with the small beam fluctuation and transverse emittances suitable for Radio Frequency Quadrupole LINACs of high energy LINACs. The measured results of the 145 mA / 83 mA beam, extraction electrode current and RF waveforms, parameter trends of an 8 hours 145 mA operation and the transverse emittances are presented. The optimum TPE was increased from 70 °C to 230 °C. Furthermore, the beam intensity for the J-PARC IS operation energy of 52.5 keV was increased from 72 mA to 83 mA, which was consistent with the 1.5 power perveance law on the beam energy compared with 145 mA for 76.5 keV.

Effect of a negative DC bias on a capacitively coupled Ar plasma operated at different radiofrequency voltages and gas pressures

The effect of a negative DC bias, |V dc|, on the electrical parameters and discharge mode is investigated experimentally in a radiofrequency (RF) capacitively coupled Ar plasma operated at different RF voltage amplitudes and gas pressures. The electron density is measured using a hairpin probe and the spatio-temporal distribution of the electron-impact excitation rate is determined by phase-resolved optical emission spectroscopy. The electrical parameters are obtained based on the waveforms of the electrode voltage and plasma current measured by a voltage probe and a current probe. It was found that at a low |V dc|, i.e. in α-mode, the electron density and RF current decline with increasing |V dc|; meanwhile, the plasma impedance becomes more capacitive due to a widened sheath. Therefore, RF power deposition is suppressed. When |V dc| exceeds a certain value, the plasma changes to α–γ hybrid mode (or the discharge becomes dominated by the γ-mode), manifesting a drastically growing electron density and a moderately increasing RF current. Meanwhile, the plasma impedance becomes more resistive, so RF power deposition is enhanced with |V dc|. We also found that the electrical parameters show similar dependence on |V dc| at different RF voltages, and α–γ mode transition occurs at a lower |V dc| at a higher RF voltage. By increasing the pressure, plasma impedance becomes more resistive, so RF power deposition and electron density are enhanced. In particular, the α–γ mode transition tends to occur at a lower |V dc| with increase in pressure.

Non-equilibrium Green's function analysis of charge plasma-based source-drain electrode P-type MoTe2 MOSFET for high sensitivity hydrogen sensing

—The paper presents a novel P-type molybdenum ditelluride (MoTe2) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) designed for high sensitivity hydrogen sensing applications. Through the utilization of palladium at the source-drain charge plasma electrode, P+ regions at both ends are generated, obviating the necessity for low-dimensional MoTe2 doping. Simultaneously, the inclusion of palladium on both regions act as the sensing area, resulting in notably heightened sensitivity. The study employs Non-Equilibrium Green's Function (NEGF) formalism to investigate the carrier transport properties of the device. The results provide valuable insights into less explored area of p-type MOSFET performance as Hydrogen(H2) gas sensor and its potential.

Coupling numerical simulation of plasma arc channel evolution and particle dispersion process

Arc discharge plasma (ADP) technology can be applied to disperse easily aggregated materials, such as the carbon nanotubes and Fe3O4. To investigate the evolution of the plasma arc channel and particle dispersion effect during the ADP process, a coupled electrode–plasma channel–workpiece (Fe3O4 clusters) and particle dispersion heat transfer model was established. The simulation results exhibited that the plasma arc formed at 0.05 s acted on the workpiece surface, forming a conical bottle-shaped structure with a wide arc column near the workpiece region and a narrow arc column near the electrode region due to the plasma column–workpiece interaction. With the continuous discharge, a discharge crater was formed on the workpiece surface due to the thermal-pressing effect of the plasma arc, and the dynamic pressure exerted by the arc column on the workpiece center increased continuously, driving the dispersion of the particles. In addition, ADP dispersion experiments were carried out on Fe3O4 to verify the simulation results. The experimental results showed that the morphologies of plasma arc channel evolution and discharge crater agreed with the simulation results. Moreover, the Fe3O4 particles dispersed by the ADP showed good dispersion morphology, which will further promote the spread of ADP technology in the dispersion and application of materials.

Development of a planar ICP ion source for fusion based neutron generator

In this paper preliminary results of a new planar ICP ion source for neutron generator is investigated. This ion source has a cylindrical planar Aluminum plasma chamber. Set of Niobium permanent magnets have been arranged as multicusp geometry around the chamber to improve the plasma density and reduce the operational pressure. A copper made helical antenna has been used which is connected to the 2 kW 13.56 MHz radiofrequency power source including matching network. Preliminary results of ion beam measurements using 1 and 3 mm diameter apertures on plasma electrodes, represents improvement of ion current from μA range to mA with Helium operational gas. A primary result with Deuterium gas indicates that the ion current improves up to 7 mA by applying multicusp magnetic field around the plasma chamber at similar operational parameters with 1 kW of RF power. Theoretical and experiments are performed to regulate the optimum distance between plasma and the accelerating electrodes to have parallel deuteron ion beam at around 65 kV electrical potential between them. Accelerating electrode configuration which suppresses the secondary electron generated on the target surface is designed and fabricated based on the simulation results.

Uniformity optimization of ion beam sputtering coating equipment based on strong current ion source

The widespread application of ion beam sputtering coating, especially in optical devices, requires the improvement of beam current intensity and uniformity of large-area uniform coatings. The advent of high current Penning sources offers a potential solution. This study introduces an automated optimization simulation method based on a three-electrode extraction system to investigate its influence on ion beam quality and uniformity. Focusing on high current intensity and uniformity, our simulation explores the effects of plasma electrode, inhibition electrode, and extraction electrode angles and distances on ion beam performance. Evaluation metrics include average beam intensity density, average energy of a single particle, and reciprocal variance of each macro particle position, which are achieved through normalization functions, allowing comprehensive comparison of simulation results. To assess coating efficiency, we estimate sputtering yield and depth. The study identifies patterns among electrodes and emphasizes the influence of different ion ratios on beam extraction. The results indicate that optimizing the angle of the plasma electrode and the distance of the suppressed electrode yields a highly uniform ion beam for low charge ions. However, for highly charged ions, similar optimization will reduce the current strength, so compensation needs to be achieved through electrode shape optimization. This research provides a model for systematically optimizing the three-electrode extraction system, guiding researchers in achieving optimal solutions based on ion source characteristics and application requirements. Additionally, we introduce a method of estimating the sputtering depth of mixed ion beams. This study provides valuable insights for advancing ion beam sputtering coating technology and reference for making the decision on design and application of ion source.

Process intensification of microplasma nanoparticle synthesis enabled by gas flow design

The wide range of practical uses for nanometer-size metal particles has motivated many lab-scale aerosol synthesis processes. It is well known that the aggregation dynamics of aerosol particles impose a trade-off between particle size and concentration: methods that achieve sub-10 nm particles without aggregation are generally limited by low concentration and low flow rates of order 100 cm3/min. Thus, the intensification of aerosol nanoparticle synthesis and its development for industrial use remains a unique and important manufacturing challenge. We present a microplasma reactor system that has been developed to improve process intensification and reliability. The system utilizes an atmospheric pressure DC microplasma to synthesize iron-carbon particles from a ferrocene vapor precursor. The microplasma incorporates a novel focusing technique using a spatial gradient in gas composition to stabilize short-term fluctuations in performance, achieving an iron yield of up to 0.93. We identify the build-up of deposits between the plasma electrodes as the primary cause of reduced performance over time, and eliminate this build-up by indirectly supplying ferrocene to avoid dissociation in this region of the reactor. Further, we show that the design and conditions downstream of the microplasma have a similar influence on the final particle size distribution as those of the microplasma itself. By tuning the coupled process variables of both the microplasma and this downstream region, we synthesize aerosols with mean diameter from 2 to 7 nm and number concentration of 2 to 8×109 #/cm3 at the system outlet.

Plasma Electrode Dielectric Barrier Discharge: Development, Characterization and Preliminary Assessment for Large Surface Decontamination

Plasma Electrode Dielectric Barrier Discharge: Development, Characterization and Preliminary Assessment for Large Surface Decontamination

Evaluation of the Use of Monopolar Low-Temperature Plasma Electrode in Lumbar Spinal Canal Expansion, Decompression, Bone Grafting, and Fusion Internal Fixation Surgery

Objective: This study aims to explore the therapeutic effects of using a monopolar low-temperature plasma electrode and a high-frequency electrotome during lumbar spinal canal expansion, decompression, bone grafting, and fusion internal fixation surgery. The study also investigates the impact of these techniques on inflammatory indicators and quality of life in patients. Methods: A total of 100 patients with lumbar spondylolisthesis treated between June (January) 2022 and July (March) 2023 were selected for this study. They were randomly divided into a control group and an observation group, with 50 cases in each group. Both groups underwent lumbar spinal canal expansion, decompression, bone grafting, and fusion internal fixation surgery. The control group used a high-frequency electrotome during surgery, while the observation group used a monopolar low-temperature plasma electrode. Surgical indicators (operation time, intraoperative blood loss), inflammatory indicators, pain levels, and quality of life were compared between the two groups. Results: The operation time in the observation group was shorter than that in the control group (P<0.05). Postoperative levels of TNF-α and CRP were lower in the observation group than in the control group (P<0.05). The observation group had lower VAS scores and higher SF-36 scores compared to the control group (P<0.05). Conclusion: The use of a monopolar low-temperature plasma electrode in lumbar spinal canal expansion, decompression, bone grafting, and fusion internal fixation surgery yields positive therapeutic outcomes. It effectively reduces operation time, alleviates patient's inflammatory responses and pain levels, aids in postoperative recovery, and enhances quality of life. These results suggest the potential for wider adoption.

Improvement of miniaturized 2.45 GHz ECR plasma flood gun at PKU

In an ion implanter, plasma flood gun (PFG) is used to provide electrons to neutralize the accumulated charge on the wafer surface to avoid breakdown damage. With the development of ion implantation technology, four key requirements have been put forward for PFG. They are simple structure, plasma with high density and low electron temperature, no metal contamination and long life. The existing PFG, such as the filament type PFG, can hardly meet the above requirements at the same time. 2.45 GHz ECR ion source with the advantages of high beam density, high stability, long life time and no filament metal contamination, has shown great potential to work as PFG. Recently, a miniaturized 2.45 GHz permanent magnet electron cyclotron resonance PFG (PMECR-PFG) has been developed at Peking University (PKU). In our previous test, 8.8 mA electron extraction current was obtained with argon gas. In this work, by optimizing the magnetic field configuration to a resonant configuration, the performance of this ECR-PFG was greatly improved. With 100 W microwave power, an 80 mA electron current load was obtained under the extraction voltage of 0.1 kV. To minimize the metal contamination, a three-slit graphite plasma electrode was fabricated and a 50 mA load was generated at only 30 W RF power. During all tests, the gas consumption rate is lower than 0.6 sccm, which is beneficial to maintain the vacuum of implanter beamline.