Acceleration Electrode Research Articles

Influence of acceleration stage electrode voltage on the performance of double-stage Hall effect thruster with adjustable zero magnetic point

The configuration of electrode voltage and zero magnetic point position has a significant impact on the performance of the double-stage Hall effect thruster. A 2D-3V model is established based on the two-magnetic peak type double-stage Hall thruster configuration, and a particle-in-cell simulation is carried out to investigate the influences of both acceleration electrode voltage value and zero magnetic point position on the thruster discharge characteristics and performances. The results indicate that increasing the acceleration voltage leads to a larger potential drop in the acceleration stage, allowing ions to gain higher energy, while electrons are easily absorbed by the intermediate electrode, resulting in a decrease in the anode current and ionization rate. When the acceleration voltage reaches 500 V, the thrust and efficiency are maximized, resulting in a 15% increase in efficiency. After the acceleration voltage exceeds 500 V, a potential barrier forms within the channel, leading to a decrease in thruster efficiency. Further study shows that as the second zero magnetic point moves towards the outlet of the channel, more electrons easily traverse the zero magnetic field region, participating in the ionization. The increase in the ionization rate leads to a gradual enhancement in both thrust and efficiency.

Correlation of source parameters and beam properties in the early operation of the full size ITER negative ion beam source

One of the requirements of Heating and current drive Neutral Beam injectors for ITER is a beam homogeneity greater than 90%, to achieve an optimal beam transmission while keeping the heat load consistently low on the acceleration electrodes. The large size and complexity of ITER negative ion source play a key role in determining the homogeneity of the negative ion current of each of the 1280 beamlets and their divergence, and it is studied in the full-scale prototype source SPIDER. In this work the plasma properties are studied by spectroscopic and electrostatic measurements in the drivers, where the plasma is generated, and in the expansion region, where the plasma drifts and negative ions are produced, and they are correlated with the properties of the beam. The non-homogeneous plasma density profile is related to the non-homogeneous availability of negative ions along the beam vertical profile, with and without cesium evaporation. Visible tomography, a technique capable of characterizing isolated beamlet properties, is used to study the beam’s dependence on plasma uniformity along the entire beam profile. Using these tools, it has been demonstrated how an increase in plasma density is linked to an improvement in beam homogeneity. The latter has been directly correlated with plasma homogeneity. The magnetic filter field and biases of the plasma grid and bias plate are responsible for the variation in plasma density and its homogeneity. Non-uniformities in the plasma’s top/bottom and left/right distributions have been studied and partially addressed experimentally. The first issue was resolved by adjusting the radio-frequency power supplied to the plasma in different vertical regions, while the second issue was addressed by reversing the direction of the magnetic filter field and increasing the plasma density.

Experimental investigation of the characteristics of the plasma flow generated in quasi-stationary plasma accelerator using optical methods

The spatial and temporal dependencies of the characteristics of the hydrogen plasma flow generated in quasi-stationary plasma accelerator were investigated. The spatiotemporal structure of discharge radiation in the interelectrode gap was studied. The range of changes in the length of the plasma glowing region in the interelectrode gap during the discharge pulse was determined. The region with bright plasma radiation located in the output face of the accelerator electrode system was observed. The presence of impurities and increased electron concentration values were observed in this region. Fluctuations in the radiation intensity of the plasma flow were detected along the entire length of its propagation. The spatial and temporal characteristics of these fluctuations were determined. The electron concentration values near the output face of the electrode system were obtained by measuring the Stark broadening of the Hβ line. For the first time, the time dependence of the electron concentration of free plasma flow was obtained using two methods simultaneously. The measurements were conducted at a distance, which significantly exceeds the characteristic size of the electrode system and where the influence of interelectrode processes of plasma flow generation is reduced. The first is based on measuring the Stark broadening of Hβ. As a second method, heterodyne interferometry was used.

(Invited) Ionic Liquid Electrospray Ion Sources for Space Propulsion

The number of microspacecraft launched has significantly increased since 2013, and more than 300 nano/microsatellites (< 50 kg) were launched in 2017. Although some microspacecraft already have a propulsion system, a commonly used propulsion system is a cold-gas thruster, which has a low delta-v (a few 10s of m/s), and thus, high delta-v (> 1 km/s) thrusters are required for more advanced missions. One of the candidates for such thrusters is ion thrusters, which were already mounted on two 50 kg-class microsatellites and successfully operated in space. However, it is not easy to miniaturize ion thrusters so that they can be mounted on even 10 kg-class nanosatellites unless high-pressure gas-feeding systems are removed. Moreover, ion thrusters require electron sources to neutralize ion beams, which consume additional propellants and power. Since most recently launched microspacecraft are less than 10 kg, more compact thrusters are required. Ionic liquid electrospray ion sources are attractive devices for such electric propulsion, especially for microspacecraft. Electrospray thrusters typically consist of many emitters, an extractor electrode, and an accelerator electrode optionally. When a high voltage between the emitter and the extractor is applied, the ionic liquid is transported to the emitter tips, and a strong electric field deforms the ionic liquid into a conical shape known as a Taylor cone. When the force of the electric field is stronger than the surface tension pressure of the ionic liquid, ions evaporate directly from the liquid surface. The extracted ions are then accelerated by the potential difference between the emitter and extractor to produce the thrust. Since the ionic liquid is composed of only cations and anions without solvent, its vapor pressure is negligible; therefore, it can exist in the liquid phase in vacuum, simplifying the propellant feed system and reducing the size of the entire propulsion system. Moreover, the direct acceleration of ions without discharges can be possible, and no neutralizers are required, which also contributes to the power and size reduction together with high efficiency. The key component of electrospray thrusters is the emitter, where there are typically three types of structures: externally-wetted (or needle-shaped), internally-wetted (or capillary), and porous ones. Each has ion emission characteristics depending on the structure. Here, we have fabricated these three types of emitter structures with a wide range of scale: 1 to 100 micrometers. Using these emitters, we have conducted ion emission experiments and beam diagnostics. We obtained a high current density over a few 10 mA/cm2 with 1-micrometer scale emitters, a high current of approximately 1 mA with porous emitters, and a high efficiency with externally-wetted emitters. The emitter structures as mentioned earlier and experimental results will be presented at the conference site.

An advanced radio-frequency quadrupole ion cooler for accelerator mass spectrometry

An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS.The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure.

Electrospray propulsion: Modeling of the beams of droplets and ions of highly conducting propellants

This article presents a model for the beams of charged droplets and ions typical of electrospray thrusters. The model is applied to a typical highly conducting propellant operating in the mixed droplet-ion emission regime but can be extended to simulate other emission regimes. A key feature of the model is the separation of the beam in two zones: a small inner region including the droplet emission area, where the equations of motion of all droplets are integrated simultaneously while retaining direct droplet-on-droplet Coulomb interactions and a much larger outer region where the beam is treated as a continuum. In addition to the geometry of the electrodes, inputs to the model include the distribution of diameters and charge-to-mass ratios of the droplets and their initial positions and velocities. Most of this information is determined from experiments. The analysis of the numerical solution confirms that lateral oscillations of the slender jet producing the droplets is an important factor in the expansion of electrospray beams, and that droplets in flight are the main sources of ion emission in these propellants. In addition to improving the knowledge of the physics of electrospray beams, the model is a significant tool for designing the extractor and accelerator electrodes of electrospray thrusters and for minimizing the deposition of beam particles on the surfaces of spacecrafts.

(Invited) Atomic Layer Neutral Beam Processes for Nanofabrication and Interface Engineering

Introduction In the fabrication of semiconductor devices, reactive plasmas are widely used in key processes such as microfabrication, surface modification and film deposition, and there are now demands for processing precision at the atomic layer level, and for deposition accuracy that allows the control of structures at the molecular level. However, in ultra-miniature nanoscale devices that will become the mainstream in the future, the use of plasma processes can cause serious problems such as breakdown of insulation films by the accumulation of ions or electrons emitted from the plasma and the formation of surface defects (dangling bond) of over a few tens nm in depth by exposure to ultraviolet (UV) emissions from the plasma.1,2) In particular, since nano-scale devices have a larger surface area compared with the bulk material, plasma processes can have a large influence on the electrical and optical properties of devices due to process-induced defects caused by ultraviolet exposure, since future nano-devices will require size control of three-dimensional structures at the atomic layer level, it will be absolutely essential to control surface chemical reactions with high precision and selectivity at the atomic layer level.To achieve charge-free and UV photon irradiation damage-free processes, we have developed a new neutral beam generation system based on my discovery that neutral beams can be efficiently generated from the acceleration of negative ions produced in pulsed plasmas. This paper introduce the neutral beam generation technique and discusses its application to atomic layer etching (ALE), modification (ALM) and deposition (ALD) that have recently been pursued.3,4) Neutral Beam Source and Its Applications for Nano-devices Our proposed neutral beam source3) has evolved from the pulse modulated plasma with an on/off switching time of 50 microseconds (Fig.1). This source uses an inductively coupled plasma (ICP) source, and has carbon ion acceleration electrodes situated at the top and bottom of the quartz plasma chamber. Gas is introduced from the upper electrode in the form of a shower, and ions accelerated from the plasma pass through apertures formed in the lower graphite carbon electrode, where ions are neutralized and UV photons are perfectly absorbed by colliding with the aperture sidewalls. We found that a neutral beam formed by the neutralization of mainly negative ions using a pulse-modulated plasma is able to form a neutral beam with higher density and lower energy. Using the neutral beam processing, for the first time, we successfully demonstrated damage-free ALE, damage-free ultra-thin gate dielectric film/low dielectric film ALDs for sub-10 nm Fin-FETs (Fig.1), transition metal oxidation for ReRAM, damage-free ALE of magnetic materials for MRAM, damage-free InGaN ALE for micro-LED, damage-free ALM of 2D materials and ALE/ALM of superconducting materials for quantum computer.3,4) Conclusions This paper has reviewed our research into cutting-edge nanodevices using the neutral beams. In the advanced nano-devices of the future, it will be essential to use ideal surface chemical reactions that do not cause surface/interface defects and can be controlled at the atomic layer level. The neutral beam process is an intelligent nano-process that completely suppresses the UV rays and electrical charges emitted from a plasma, and is thus able to achieve ideal surface atomic layer reactions in agreement with the computational analysis. We are currently studying how to apply this technique forming ultra-thin films and reforming (etching and modification) the surface of semiconductor/metal/dielectric materials, and we hope that this technique will make a large contribution to the development and implementation of new nanodevices in the future. References 1).T. Nozawa and T. Kinoshita: Jpn. J. Appl. Phys. vol.34 (1995)pp. 2107.2).Mitsuru Okigawa, Yasushi Ishikawa, Yoshinori Ichihashi and Seiji Samukawa, J. Vac. Sci. and Technol. B, vol.22, No.6 (2004) pp.2818.3).Seiji Samukawa, IEEE Nanotechnology Magazine, vol.13, No.6(2019) pp.21.4).Kexiong Zhang, Tokio Takahashi, Daisuke Ohori, Guangwei Cong, Kazuhiko Endo, Naoto Kumagai, Seiji Samukawa, Mitsuaki Shimizu and Xuelun Wang, Semiconductor Science and Technology, vol.35(2020) pp.075001. Figure 1

음의 가속전계 형성에 따른 이온풍 추력 특성

This study is a basic research on the ionic wind propulsion technique, and the thrust characteristics of the ionic wind propulsion device of a two-stage series structure with an acceleration electrode applied with a negative voltage are studied based on various theoretical equations suggested in previous studies. Experimental results show that the current measured at the acceleration electrode increased as the amount of corona current decreased as the negative voltage applied to the accelerating electrode increased. The ionic wind velocity increased as the negative voltage applied to the acceleration electrode increased, and the thrust increased by up to 72.9%. In the condition of the applied voltage with the maximum thrust, the thrust efficiency decreased rapidly, but the kinetic energy efficiency decreased less.

AI-Based Electrode Optimisation for Small Satellite Ion Thrusters

Computing capacities for numerical modelling are available to an unprecedented extent today. The spread of various artificial intelligence (AI) -based solutions (which in many cases are also resource-intensive operations) is also facilitated by this increase in capacity, which offers several new opportunities in this area. On the one hand, optimization tasks can be done quickly, on the other hand, it is also possible to solve (estimate) problems where we cannot (for some reason) create a model for the initial problem. In our article, we investigate how to apply artificial intelligence-based solutions to electromagnetic field computing tasks as efficiently as possible. The required theoretical summary presents an implemented application: optimization of electrostatic ion engine accelerator electrodes for orbit correction operations. To solve each problem, we used methods from the supervised machine learning toolkit, usually along with LMS (least mean square method) update steps. All inputs required for AI were solved by numerical space calculation (primarily using the finite element method). The data input required to optimize the electrodes of an ion thruster can come from two sources: measurement data or simulation results. Given that the operating environment of a satellite can be modelled in a vacuum chamber, it is a particularly difficult issue to perform the measurement, but even more difficult in the case of optimisation. Therefore, an effective solution to the problem can only be achieved by simulation. The primary goal of this research is to optimise the fuel (in this case, the number of ions) during operation, with the stated aim of maximising the time of operation of the spacecraft.

Control of tokamak discharge parameters using a plasma jet

Results of the experimental study of the ability of plasma jet of coaxial accelerator to breakdown and ionization the working gas at the initial discharge phase in Globus-M2 spherical tokamak are presented. Studies of the development of the initial stage of discharge initiated with a plasma jet showed that the plasma current in the discharge began to grow earlier by 2 ms than using the standard inductive breakdown. The breakdown voltage decreased from 6.1 to 3.1 V (-49%) at 4.7 kV accelerator electrode voltage. The emission intensity of line Dα decreased during formation of the discharge with the help of plasma jet without additional gas puffing. Radiation level CIII in the discharge generated by the plasma jet was the same as the radiation in discharge produced by induction breakdown of the gas. At the stage of increase in the plasma current the most intense visible radiation of the plasma was found near duct through which the jet was injected. Discharge radiation decreased and spread out along the cross section of the plasma column during plasma current plateau.

Evaluation of a novel parabolic plasma electrode advantage in a triode extraction system of a helicon ion source: simulation and experiment

An industrial type of Amirkabir helicon ion source (AHIS-II) equipped with a novel triode extraction system has been designed and developed at the Helicon Plasma Laboratory of Amirkabir University of Technology for material-processing applications. An experimental study was conducted to investigate the effects of two new types of plasma electrodes on ion beam characteristics. In particular, the Khoshhal electrode as a new improved plasma electrode and the optimized Pierce plasma electrode were both compared in inductively coupled plasma in the m = +1, −1 helicon plasma modes of operation. In this work, the AHIS-II device, with its ability to work continuously, was able to extract a ∼1 mA argon ion beam using a triode extraction system equipped with a Khoshhal plasma electrode at a 20 kV extraction voltage in the m = +1 helicon mode of operation. As part of this work, the R parameter, the ratio of the voltageapplied to the plasma and acceleration electrodes in triode extraction systems was introduced, and its effects on ion beam characteristics including beam emittance, diameter, and current were studied. In this study, beam optical characteristics including beam emittance, diameter, current, and profile were calculated and measured by the IBSimu ion optical code. The analysis of the argon ion beam highlights that the ion beam characteristics can be affected not only by the plasma electrode geometry design, R parameter, and extraction voltage associated with the extraction process, but also by the plasma source’s operational parameters, such as the RF power delivered to the half-helix antenna and the gas flow rate.

Pulsed power accelerator surface Joule heating models

Understanding the effects of contaminant plasmas generated within the Z machine at Sandia is critical to understanding current loss mechanisms. The plasmas are generated at the accelerator electrode surfaces and include desorbed species found in the surface and substrate of the walls. These desorbed species can become ionized. The timing and location of contaminant species desorbed from the wall surface depend non-linearly on the local surface temperature. For accurate modeling, it is necessary to utilize wall heating models to estimate the amount and timing of material desorption. One of these heating mechanisms is Joule heating. We propose several extended semi-analytic magnetic diffusion heating models for computing surface Joule heating and demonstrate their effects for several representative current histories. We quantitatively assess under what circumstances these extensions to classical formulas may provide a validatable improvement to the understanding of contaminant desorption timing.

RF Helicon-based Inductive Plasma Thruster (IPT) Design for an Atmosphere-Breathing Electric Propulsion system (ABEP)

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend such missions lifetime, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to be used as propellant for an electric thruster. The system would minimize the requirement of limited propellant availability and can also be applied to any planet with atmosphere, enabling new mission at low altitude ranges for longer times. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such species cause erosion of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems. IRS is developing within the DISCOVERER project, an intake and a thruster for an ABEP system. The paper describes the design and implementation of the RF helicon-based inductive plasma thruster (IPT). This paper deals in particular with the design and implementation of a novel antenna called the birdcage antenna, a device well known in magnetic resonance imaging (MRI), and also lately employed for helicon-wave based plasma sources in fusion research. This is aided by the numerical tool XFdtd®. The IPT is based on RF electrodeless operation aided by an externally applied static magnetic field. The IPT is composed by an antenna, a discharge channel, a movable injector, and a solenoid. By changing the operational parameters along with the novel antenna design, the aim is to minimize losses in the RF circuit, and accelerate a quasi-neutral plasma plume. This is also to be aided by the formation of helicon waves within the plasma that are to improve the overall efficiency and achieve higher exhaust velocities. Finally, the designed IPT with a particular focus on the birdcage antenna design procedure is presented.

Design and simulation of the parameters affecting the ion beam characteristics from a penning ion source

Today, many different kinds of ion sources have been developed. One of the most important ones is the penning or PIG ion source. Due to its simplicity of structure and longer lifetime, these ion sources are more widely considered than other ones. In this paper, design and simulation of the parameters affecting the ion beam characteristics from a penning ion source are performed using the CST software. Among the various structures of the permanent magnet around the source, the circular arrangement is found to be better for the confinement of particles inside the source. The electric potential of the anode, the cathode and the extraction electrode are found to be 15+, -500 and -3000 Volt, respectively. The decelerator and accelerator electrodes are used as ion source extraction systems. In addition, in the beam transport systems, high efficiency focusing in Einzel lens is more than that of immersion lens.

Electron beam injection from a hollow cathode plasma into a downstream reactive environment: Characterization of secondary plasma production and Si3N4 and Si etching

A material etching system was developed by combining beam electron injection from a direct current hollow cathode (HC) electron source with the downstream reactive environment of a remote CF4/O2 low temperature plasma. The energy of the injected beam electrons is controlled using an acceleration electrode biased positively relative to the HC argon discharge. For an acceleration voltage greater than the ionization potential of Ar, the extracted primary electrons can produce a secondary plasma in the process chamber. The authors characterized the properties of the secondary plasma by performing Langmuir probe measurements of the electron energy probability function (EEPF) 2.5 cm below the extraction ring. The data indicate the existence of two major groups of electrons, including electrons with a primary beam electron energy that varies as the acceleration voltage is varied along with low energy electrons produced by ionization of the Ar gas atoms in the process chamber by the injected beam electrons. When combining the HC Ar beam electron with a remote CF4/O2 electron cyclotron wave resonance plasma, the EEPF of both the low energy plasma electron and beam electron components decreases. Additionally, the authors studied surface etching of Si3N4 and polycrystalline Si (poly-Si) thin films as a function of process parameters, including the acceleration voltage (0–70 V), discharge current of the HC discharge (1–2 A), pressure (2–100 mTorr), source to substrate distance (2.5–5 cm), and feed gas composition (with or without CF4/O2). The direction of the incident beam electrons was perpendicular to the surface. Si3N4 and polycrystalline silicon etching are seen and indicate an electron-neutral synergy effect. Little to no remote plasma spontaneous etching was observed for the conditions used in this study, and the etching is confined to the substrate area irradiated by the injected beam electrons. The electron etched Si3N4 surface etching rate profile distribution is confined within a ∼30 mm diameter circle, which is slightly broader than the area for which poly-Si etching is seen, and coincides closely with the spatial profile of beam electrons as determined by the Langmuir probe measurements. The magnitude of the poly-Si etching rate is by a factor of two times smaller than the Si3N4 etching rate. The authors discuss possible explanations of the data and the role of surface charging.

침대 링형 구조에서 다단 가속전극 적용에 따른 이온풍 발생 특성

침대 링형 구조에서 다단 가속전극 적용에 따른 이온풍 발생 특성

스마트대전력 및 고전압기술] 가속전극의 적용에 따른 이온풍 발생 특성

Currently, the devices to generate ion winds in air are mainly composed of corona electrodes and induction(ground) electrodes, of which the corona electrodes mainly use needles or wires as electrodes and the induction electrodes use plate electrodes of ring or mesh type. Ion winds can be effectively generated through a diverse combination of corona electrodes and induction electrodes mentioned above. However, only changing the form and structure of corona electrodes and induction electrodes has a limit in raising the speed of ion winds. This paper conducted a study on the characteristics of ion wind generation by additionally installing acceleration electrodes in addition to corona electrodes and induction electrodes to increase the speed of ion winds.

Optimizing lateral homogeneity of ion-induced surface modifications of non-planar dielectric polyethylene components employing ion fluence simulations and optical measurements of the sp2-dependent reflectivity

Abstract An approach to enhance the durability of artificial joint replacements is to modify the surface of their polymeric bearing material to diamond-like carbon (DLC) by ion-induced polymer-to-DLC-transformation in a plasma-immersion ion implantation process. Due to the dielectric character of the polymer and thus the impossibility of direct application of high voltage pulses to the component, this process requires an additional accelerator electrode above the surface. We here present two useful tools to optimize the geometry of such electrodes. First, we simulate the ions’ trajectories for various electrode geometries and receive the resulting fluence distribution across the surface of the treated part. Second, we introduce a novel optical method to determine non-destructively the local ratio of sp2 hybridized carbon atoms and thus the locally implanted fluence utilizing changes in reflectivity. Combining both tools, we here optimize, by way of example, the geometry of a grid electrode to obtain a homogeneous DLC-modification of a typical hip replacement inlay.

Conceptual Design of Beam Tube of 300 KeV Electron Electrostatic Accelerator

The column of electron electrostatic accelerator is one of the critical components in electrostatic accelerator. The geometrical design of such accelerator must be as such that in the case of applying voltage to its electrodes, not only should its equipotential surfaces and its gradient accelerate the beam particles up to desired energy, but also it should focus the beam and hinder broadening of energy distribution of accelerated particles. The immersed electrodes in the field are, geometrically, perpendicular to optical axis around the medial plane. Numerous models that can be used in the distribution of axial potential, have been presented and linear model, analytical model, double-column electrode model and polynomial electrode model are among them. In this paper, series expansions based on Bessel functions is used to obtain the axial potential distribution of immersed accelerator electrodes in double-electrode field and it is then compared to the mentioned models by solving the final equation via the least square method. Finally, by using CST Studio software and the information we obtained from the axial potential, the column of electron accelerator with its energy distribution and its optimal electron output beam radius is designed and simulated.

Simple fabrication of micro time-of-flight mass spectrometer using a carbon nanotube ionizer

This paper demonstrates a time-of-flight mass spectrometer (TOFMS) fabricated using simple micro electromechanical system technologies. It consists of two components: a triode-type field emitter for electron-impact ionization and ion separator with a repeller, an acceleration electrode, and a flight tube. As a cold-cathode, the field emitter with carbon nanotube is a promising electron source and offers several advantages over conventional thermionic electron sources, such as compact size, low power consumption because of the absence of heating elements, excellent durability, and high electron emission density. Micromachined TOFMS successfully detects signals of Ar and CH3I. This is practically proved with preliminary experiments on ionization and mass spectrum tests with Ar and CH3I, ions, including finite element modeling and theoretical analysis.