Axial Injection Research Articles

Electromagnetic modeling of axis-symmetric microwave devices

This paper presents calculations of electromagnetic field distributions with different microwave-driven devices. Results are obtained by using a two-dimensional numerical simulation tool that solves Maxwell's equations for an axis-symmetric TM mode, by considering a harmonic time description. The tool is applied to a coaxial waveguide, a circular waveguide with a shortening plate at the top, and a plasma reactor operated by an axial injection torch. This reactor consists of a circular cavity powered by a coaxial waveguide assembled to a nozzle, and creates a micro-plasma that affects only very locally the electric field distribution. We compare the solutions obtained for the three devices. We also carry out a simulation benchmarking in terms of accuracy, by using the analytical solution to the problem (in cases where it is available), or in terms of precision, by using the numerical calculation of the average power absorbed (in the presence of plasma).

A Study on Arc Instability Phenomena of an Axial Injection Cathode Plasma Torch

Axial injection in plasma gun through the cathode has clear benefit of longer particle residence time and optimum particle trajectory in the plume; however, accelerated wear of the cathode seem to be the major issue in this approach. This study investigates the arc instability phenomena in an axially injecting single cathode plasma torch design. Gun voltage measurements were used to evaluate the arc behavior. For comparison purpose, arc fluctuations with a standard solid cathode torch design under identical operating parameters have also been studied. A comparison of different internal hardware configurations is also done to understand and establish the important factors in the design of the axial injection and solid cathode systems. Further, this study presents the influence of plume elongation and accelerated gas velocities on the arc behavior in different configurations under low pressure environment.

Performance Modeling of a Thrust Vectoring Device for Hall Effect Thrusters

The ability to control the thrust vector direction on electric propulsion devices opens new possibilities for mission optimization. The addition of an external magnetic steering system and the nonsymmetric localized injection of propellant have been proposed to deviate the ion beam of a PPS®1350 Hall effect thruster. A two-dimensional hybrid model has been used to evaluate the preliminary design. Simulated results suggest the ion beam angular distributions may be varied in the range of 10 deg by changing the current in the external steering coils. However, a magnetic topography with field lines directly connected from the outer steering pole to the anode leads to a reduction of the Hall effect thruster performance. The erosion of the walls increases drastically as a function of the magnetic lens orientation (6 mm for 1000 h of thruster operation for high coil currents in the external coils). A localized axial injection of atoms has a positive effect on the steering angle of the ion beam (a few degrees), but exhibits additional erosion of approximately 10―15%. Qualitative comparisons with experimental results confirm the simulated trends.

Physics design of CYCAIE-100

The design and construction of Beijing Radioactive Ion-beam Facility (BRIF) was started at China Institute of Atomic Energy -CIAE) in 2004. In this project, a 100 MeV high intensity cyclotron, CYCIAE-100, is selected as a driving accelerator for radioactive ion beam production. It will provide a proton beam of 75–100 MeV with an intensity of 200–500 μA. The scheme adopted in this design, i.e., stripping the accelerated H−, makes the structure more compact and construction cost much lower. At present, the design for each system has been accomplished. This paper depicts the basic physics design of the machine, including its major structure and parameters, beam dynamics and each relevant system, e.g. basic structure of the main magnet, numerical simulation of the RF resonant cavity, axial injection system, central region, and study on crucial physics problems concerning the extraction and beam lines. The major problems encountered during the design of CYCIAE-100 are also summarized in this paper.

Deposition of Thin SiOx Films by Direct Precursor Injection in Atmospheric Pressure Microwave Torch (TIA)

AbstractAn axial injection torch (TIA, Torche à Injection Axiale) contained in an open air deposition chamber has been exploited to deposit thin silicon oxide films. The organosilicon precursor, tetramethylsilane (TMS), was injected directly in the plasma gas. A parametric study was carried out to study the effects of microwave power, precursor quantity and torch to substrate distance on the film deposition process. Inorganic films were obtained without the addition of oxygen in the system as the oxygen got incorporated in the plasma from the open air, as shown by optical spectroscopic studies on the plasma. The deposited films were characterised using different techniques like Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), elastic recoil detection analysis (ERDA), Rutherford backscattering spectroscopy (RBS) and nuclear resonance analysis (NRA). These analyses helped understanding the factors affecting the film deposition process. Results show that at short processing time, low microwave plasma power and precursor quantity at an optimised torch to substrate distance, thin non‐porous hydrogenated silicon oxide‐like films can be deposited at low substrate temperatures of around 370 K using this technique.

Passive Control of Pressure Oscillations in Solid Rocket Motors: Cold-Flow Experiments

Cold-gas experiments are used to study the pressure oscillations occurring in solid rocket motors and the performance of different ways of passive control of these oscillations. Previous studies stated that flow-acoustic coupling is mainly observed for nozzles including a cavity. The nozzle geometry has an effect on the pressure oscillations through a coupling between the acoustic fluctuations induced by the cavity volume and the vortices traveling in front of the cavity entrance. An important reduction of pressure oscillations (1 order of magnitude) is obtained, both for the axial and radial flow injection configurations, by removing the cavity located around the nozzle head. However, the nozzle integration cannot be avoided and this solution then cannot be implemented on a real flight. A permeable membrane (with holes to allow the combustion gas to pass through) placed in front of the cavity allows a reduction by a factor 1.5. The Helmholtz resonator shows a small attenuation of the pressure oscillations; however, its design could be optimized to maximize the acoustic damping. The three-dimensional-shaped inhibitors show a good attenuation of the pressure fluctuations, especially when the opening cross section is increased. This increase results in a shift of the Mach number associated with excitation. For a similar cross section, the asymmetric inhibitor (crenel-shaped) provides a reduction of pressure oscillations by a factor of 2 compared with an axisymmetric inhibitor. Therefore, the asymmetry of the inhibitor seems to be the best candidate for reducing the pressure oscillations.

Experimental and Theoretical Investigation of Droplet Dispersion in Venturi Scrubbers with Axial Liquid Injection

AbstractDroplet dispersion in a Venturi scrubber with axial liquid injection was investigated both experimentally and theoretically. The main objective of this study was to develop a mathematical model to predict droplet dispersion in a Venturi scrubber with axial liquid injection. The effects of the Peclet number and droplet size distribution on droplet dispersion were studied using the developed model. Sampling of the droplets was carried out, isokinetically, in 16 positions at the end of the throat section. The experimental data were used to find the parameters of the developed model, such as the Peclet number. From the results of this study, it was found that the Peclet number was not constant across the cross section of the scrubber channel. In order to achieve a better agreement between the results of the model and the experimental data, it was required to consider Peclet number variations across the Venturi channel. It was also revealed that the parameter representing the width of the Rosin‐Rammler distribution of droplet size could not be considered constant and it was influenced significantly by the operating parameters such as liquid flow rate and gas velocity.

Modeling of an axial injection torch

This paper presents simulation results for a microwave (2.45 GHz) plasma reactor, operated by an axial injection torch (AIT). The study gives a two-dimensional description of the AIT-reactor system, based on an electromagnetic model (that solves Maxwell's equations adopting a time-harmonic description, yielding the distribution of the electromagnetic fields and the average power absorbed by the plasma), and a hydrodynamic model (that solves the Navier-Stokes' equations for the flowing neutral gas, yielding the distribution of mass density, pressure, temperature, and velocities). Comparison between model results and experimental measurements reveal common variation trends, with changes in the reactor height, for the power reflected by the system, and yield a qualitative agreement for the axial profile of the gas rotational temperature. Model results, such as the power transmission coefficient and the gas temperature, are particularly dependent on the reactor dimensions, the electron density and temperature, and the gas input flow, which indicates that simulations can be used to provide general guidelines for device optimization.

Experimental investigation of nanofluids in confined laminar radial flows

This paper presents an experimental investigation of heat transfer enhancement capabilities of coolants with suspended nanoparticles (Al 2O 3 dispersed in water) inside a radial flow cooling device. Steady, laminar radial flow of a nanofluid between a heated disk and a flat plate with axial coolant injection has been considered. An experimental test rig was built. Results show that heat transfer enhancements are possible in radial flow cooling systems with the use of nanofluids. In general, it was noticed that the Nusselt number increases with particle volume fraction and Reynolds number and decreases with an increase in disk spacing.

Fundamentals of rotating detonations

A rotating detonation propagating at nearly Chapman–Jouguet velocity is numerically stabilized on a two-dimensional simple chemistry flow model. Under purely axial injection of a combustible mixture from the head end of a toroidal section of coaxial cylinders, the rotating detonation is proven to give no average angular momentum at any cross section, giving an axial flow. The detonation wavelet connected with an oblique shock wave ensuing to the downstream has a feature of unconfined detonation, causing a deficit in its propagation velocity. Due to Kelvin–Helmholtz instability existing on the interface of an injected combustible, unburnt gas pockets are formed to enter the junction between the detonation and oblique shock waves, generating strong explosions propagating to both directions. Calculated specific impulse is as high as 4,700 s.

Characterization of metal-supported axial injection plasma sprayed solid oxide fuel cells with aqueous suspension plasma sprayed electrolyte layers

A method for manufacturing metal-supported SOFCs with atmospheric plasma spraying (APS) is presented, making use of aqueous suspension feedstock for the electrolyte layer and dry powder feedstock for the anode and cathode layers. The cathode layer was deposited first directly onto a metal support, in order to minimize contact resistance, and to allow the introduction of added porosity. The electrolyte layers produced by suspension plasma spraying (SPS) were characterized in terms of thickness, permeability, and microstructure, and the impact of substrate morphology on electrolyte properties was investigated. Fuel cells produced by APS were electrochemically tested at temperatures ranging from 650 to 750 °C. The substrate morphology had little effect on open circuit voltage, but substrates with finer porosity resulted in lower kinetic losses in the fuel cell polarization.

The effect of solids and dispersant loadings on the suspension viscosities and deposition rates of suspension plasma sprayed YSZ coatings

Suspension plasma spraying (SPS) is a promising modification of traditional plasma spraying techniques that uses small (≤ 2 μm) particles suspended in a liquid to fabricate coatings with fine microstructures and controlled porosity rapidly and without the need for post-deposition heat treatments. These qualities make SPS an interesting new technique to manufacture solid oxide fuel cell (SOFC) active layers. However, in order to be able to manufacture layers with good microstructures, the properties of the feedstock suspension must be optimized to enhance particle dispersion and improve feedability. This study uses a pressurized gas delivery system to feed aqueous YSZ suspensions containing an organic dispersant to a Northwest Mettech Axial III axial injection suspension plasma spray system. Three different dispersant types (polyacrylic acid (PAA), polyethylene imine (PEI) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA)) were characterized and the effects of solid loadings, dispersant type, and dispersant concentration on suspension properties such as viscosity and feedability, and layer characteristics such as microstructure and deposited thickness were examined.

Magnet design and beam dynamics in computed fields for the DC-350 cyclotron

The DC-350 is an isochronous cyclotron designed in the Flerov Laboratory of Nuclear Reaction (FLNR). It is intended for accelerating ions with a mass-to-charge ratio A/Z within an interval of 5–10 and with an energy of 3–12 MeV/u at the extraction radius. These ion beams will be used in nuclear and applied physics experiments. The paper describes the results of a 3D magnet simulation. The cyclotron magnet and IM90 analiziting-bend magnet of the axial injection channel are studied here. The influence of correction coils on the cyclotron magnet is calculated. All magnet fields were calculated by MERMAID 3D code [1].

An IC100 cyclotron based facility for producing nuclear filters and for scientific and applied research

The cyclotron IC-100 station, based on the Laboratory of Nuclear Reactions (JINR, Dubna, Russia), provides the industrial construction of nuclear filters. During modernization, the cyclotron was equipped with a superconducting ECR-ion source and an axial injection system. The specialized beam channel with a two coordinate scanning system and equipment for irradiating polymer films was installed in the implantation part of the station. High intensity heavy ion beams of Ne, Ar, Fe, Kr, Xe, I, and W have been accelerated to 1 MeV/nucleon energy. The investigation into irradiated crystals features and irradiation of different polymer films is provided. Also, a few thousands square meters of track films with holes in the wide range of densities were produced. The cyclotron-based station is capable of solving different kinds of scientific and applied problems as well.

Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina-Zirconia Ceramics

Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.

Suspension HVOF Spraying of Reduced Temperature Solid Oxide Fuel Cell Electrolytes

Metal-supported solid oxide fuel cells (SOFCs) composed of a Ce0.8Sm0.2O2−δ (SDC) electrolyte layer and Ni-Ce0.8Sm0.2O2−δ (Ni-SDC) cermet anode were fabricated by suspension thermal spraying on Hastelloy × substrates. The cathode, a Sm0.5Sr0.5CoO3 (SSCo)-SDC composite, was screen-printed and fired in situ. The anode was produced by suspension plasma spraying (SPS) using an axial injection plasma torch. The SDC electrolyte was produced by high-velocity oxy-fuel (HVOF) spraying of liquid suspension feedstock, using propylene fuel (DJ-2700). The emerging technology of HVOF suspension spraying was explored here to produce thin and low-porosity electrolytes in an effort to develop a cost-effective and scalable fabrication technique for high-performance, metal-supported SOFCs. In-flight particle temperature and velocity were measured for a number of different gun operating conditions and standoff distances and related to the resulting microstructures. At optimized conditions, this approach was found to limit material decomposition, enhance deposition efficiency, and reduce defect density in the resulting coating, as compared to previous results reported with SPS. Produced button cells showed highly promising performance with a maximum power density (MPD) of 0.5 W cm−2 at 600 °C and above 0.9 W cm−2 at 700 °C, with humidified hydrogen as fuel and air as oxidant. The potential of this deposition technique to scale-up the substrate size to 50 × 50 mm was demonstrated.

Numerical solution to an electromagnetic model with Neumann boundary conditions, for a microwave-driven plasma reactor

This work deals with the two-dimensional electromagnetic modelling of a microwave-driven plasma reactor, operated by an axial injection torch (AIT). The model solves Maxwell's equations, which are discretized using a finite difference scheme within staggered grids, adopting a time-harmonic description at fixed 2.45 GHz excitation frequency. The study focuses upon azimuthal axis-symmetric situations, which can be described by a single second-order Helmholtz-type differential equation for the transverse magnetic field. Perfect-conductor boundary conditions are imposed at metal walls, corresponding to zero derivatives for the magnetic field. In situations where convergence requires a more restrictive framework, these Neumann boundary conditions are better replaced by equivalent Dirichlet conditions, whose boundary values depend on the problem solution. Here, we propose a simple numerical algorithm to manage these situations, by tailoring the Dirichlet boundary values to satisfy the physical Neumann conditions. The algorithm is applied to an air-filled circular wave-guide (as a test system) and to the AIT-reactor device (in the presence of plasma). Solution benchmarking checks its accuracy with respect to the corresponding analytical solution (for the circular wave-guide), and analyses its numerical precision by using different integral expressions to calculate the power transmission coefficient (for the AIT-reactor). Results show a 99% accuracy and precision errors lower than 0.1%, for a mesh with 104 grid points.

Numerical simulation of the mixing kinetics of an iodine-containing flow and the oxygen flow excited in the electric-discharge oxygen-iodine laser

A parametric analysis has been carried out to discover how the concentration of atomic oxygen in the O2: O2 (1Δg): O flow and the degree of predissociation and concentration of molecular iodine in the I2: He mixture affect the temperature regime and the formation of the inverse population at the atomic iodine laser transition at elevated pressures of P = 5–10 Torr in a simulated system with the axial injection of an I2: He mixture in the EDSOG-excited oxygen flow.

Thermo-physical processes in cerium nitrate precursor droplets injected into high temperature plasma

The thermo-physical phenomena inside a droplet during its flight in a thermal plasma flow have been modeled for SPPS processes using cerium nitrate precursor. The different thermo-physical stages encountered during droplets' flight include aerodynamic breakup, rapid vaporization of solvent and precipitation, internal pressurization with shell rupture and rapid heating of volumetrically precipitated ceramic particle. The effects of injection type (transverse versus axial) and initial size of the droplets on the final deposit layer microstructure have been studied. The results show that for axial injection the heating process is very rapid and smaller droplets (< 10 µm) undergo full pyrolization resulting in favorable microstructure. On the contrary for transverse injection the heating process is slower as the droplets are injected in the outer shear layer of plasma where the temperature and velocity both are much lower than the core of the plasma. The larger droplets (> 20 µm) have better chances of getting pyrolized in the case of transverse injection. It was also observed that the angle of trajectory of the droplets after primary (first) precipitation does not have much effect on the final microstructure.

Transmission and directionality control of light emission from a nanoslit in metallic film flanked by periodic gratings

We investigate the transmission and directional properties of light emission from a nanoslit film flanked by periodic gratings, formed on a silver film, embedded in a high index dielectric medium. Using FDTD calculations it is demonstrated that the transmission has strong dependence on dimension of the dielectric film. The directional property of the emitted beam is controlled by tapering height of output grating elements and this effect is explained by standard theory of antenna array. We propose and examine the potential of such slit grating structure as a Plasmonic antenna in axial injection of light from single mode fiber to photonic crystal waveguide.