Axial Injection Research Articles

Conditioned dissipation and average consumption maps in a turbulent nonpremixed flame using planar laser-induced fluorescence of O 2

Planar laser-induced fluorescence of O 2 has been performed in a turbulent nonpremixed flame using a broadband argon-fluoride source. For a given oxygen concentration, laser absorption and subsequent fluorescence emission increase strongly with temperature. The reverse configuration of the investigated flame with an axial injection of liquid oxygen in a fast coflow of hydrogen at ambient temperature is particularly well suited to this laser diagnostic. The liquid dart is quickly vaporized and no fluorescence is emitted from the liquid phase making it possible to investigate the concentration field of oxygen vapor in the flame. In addition, the laser irradiance has not been altered by cumulative absorption when it reaches the reaction zone where the hot and the weak amounts of O 2 are quantitatively detected with a maximum sensitivity. Assuming a fast direct reaction, the conditioned dissipation rate is derived from the gradient of the fluorescence signal at the stoichiometric surface. A two-dimensional map of the average rate of reaction is obtained showing a bimodal structure in the early stages of the flow development where the conditioned dissipation reaches high levels. These conditioned data have been spatially integrated to provide the cumulative oxygen consumption as a function of the distance to the injector. The results indicate that about 40% of the injected oxygen is consumed before the turbulent flame reaches the walls of the burner. To our knowledge, these are the first experimental data on quantitative reactant consumption in such a turbulent flame. The technique opens promising perspectives for detailed investigation of scalar dissipation and reaction rate in turbulent jet flames.

Measurements of OH and H2O for reacting flow in a supersonic combusting ramjet combustor

Mixing and combusting high-enthalpy flows, similar to those encountered in supersonic combusting ramjet engines, were investigated using a shock tunnel to produce the flow in conjunction with nonintrusive optical diagnostics that monitored the performance of two injector configurations. The shock tunnel was configured to produce Mach 3 flow and stagnation enthalpies corresponding to flight equivalent Mach numbers between 7— 11. A pulsed hydrogen injection capability and interchangeable injector blocks provided a means of examining high-speed, high-enthalpy reacting flows. Planar laser induced fluorescence of OH radicals in the near-injector region produced images that show the combusting and mixing zones for the reacting flow. Line-of-sight exit plane measurements of water concentration and temperature were used to provide a unique method of monitoring exit plane products. Near-injector mixing dynamics and exit plane compositions were compared for wall jet and axial injection systems. In addition, exit plane measurements indicated that a quasi-steady-state condition was achieved during the 1- to 2-ms test times.

Confinement and Heating of FRC Plasma

Confinement times of particle and trapped magnetic flux in FRC plasmas were simulated using a one dimensional transport modal and classical (Spitzer`s) resistivity. Comparing the simulation results and experimental results indicated that a transport in the plasmas was basically classical and deviations of experimental results from classical values (so-called anomaly) might attribute to a plasma geometry effect, by which the deviation was larger for fat plasmas and smaller for prolate ones. In order to verify this indication, a plasma electron heating with an axial injection of pulsed and intense ion beams was proposed for the plasmas in current FRC experiments. Possibility of this heating were examined by estimating an energy deposit rate of a beam ion in the plasmas. The energy deposit rate is a few% to about 100% for a plasma of 12cm in diameter and 80cm in length with a plasma parameter range of current experiments. 6 refs., 7 figs., 1 tab.

Numerical analysis of nitrogen-mixed argon plasma characteristics and injected particle behavior in an ICP torch for ultrafine powder synthesis

A numerical model is presented for the analysis of plasma characteristics of an ICP torch and gas mixing effects on the plasma when a nitrogen gas is added into the argon plasma as a carrier or sheath gas at the torch inlet, The fluid equations describing the plasma flow and temperature fields and the diffusions between two different gases are solved along with a magnetic vector potential equation for electromagnetic fields. The trajectory and the temperature change with time for a particle injected into the plasma are also investigated by a plasma-particle interaction model to find out optimum injection conditions for the synthesis of ultrafine nitride ceramic powders, It is found from the calculations that the nitrogen-mixed argon plasma with a nitrogen sheath gas is more favorable than the plasma with a nitrogen carrier gas for the reaction kinetics of nitride synthesis. It is also found that the radial injection through the holes of the tube wall Is preferable to the axial injection at the torch inlet for the complete evaporation of injected particle and the effective chemical reaction of reactant vapor with nitrogen. For the radial injection in an ICP torch of 20 cm in axial length, the optimum injection locations and initial velocities of 50 /spl mu/m aluminum particles are found for synthesizing aluminum nitride are in the range of 6/spl sim/12 cm apart from the torch inlet and over 15 m/s, respectively. >

Trapped metal cluster ions

An overview is given of experiments with stored metal cluster ions in a Penning trap system. The setup allows axial injection of clusters produced in an external source and a time-of-flight mass analysis of the reaction products after axial ejection. The system's options include the selection of stored ions, the manipulation of their orbits, addition of reactant and buffer gases and axial optical access for laser spectroscopic studies. As described by various examples, investigations have been made with respect to the development of trapping techniques and the characterization of metal clusters in terms of their physical and chemical properties.

Two phase cluster model in riser reactors: impact of radial density distribution on yields

Recent cold flow data (Miller et al., 1994) have shown that the manner in which the oil and catalyst are initially contacted in fluid catalytic cracker risers has a major impact on the radial density profile at the riser bottom. These results show that circumferential oil injection has a much more uniform radial density distribution than the traditional axial oil injection. In order to assess the impact of the improvements in radial density distribution on conversion and product selectivity, a two-phase heterogeneous model for riser reactors operating in pneumatic transport has been developed. The model consists of a dispersed cluster phase which contains all the catalyst and is where the bulk of the catalytic reactions occur, and a continuous oil phase with mass transfer between the phases. A simple three- component kinetic model is used to describe the rates of reaction which occur in the cluster phase. The average concentration of any component at any axial or radial position in the riser is then determined by the density-weighted average of the cluster phase and the oil phase at that position using experimental values for the radial density distribution. The radial density distributions were obtained in a cold flow riser unit simulating FCC riser reactor hydrodynamic performance. The resulting model matches commercial radial and axial conversion and gasoline yield profiles. This model provides a basis to determine the incentives for improving the mass transfer between the two phases in the riser by making hardware modifications. For example, the model predicts that the circumferential feed nozzle configuration would increase conversion by about 3 wt% over the traditional axial configuration.

An atmospheric pressure waveguide-fed microwave plasma torch: the TIA design

We report theoretical and experimental investigations of an atmospheric pressure, microwave plasma torch with axial gas injection (torche a injection axiale design). It is a waveguide-based structure comprising both waveguide and coaxial elements serving the purpose of wavemode conversion and impedance-matching. The device includes features common to various waveguide-fed torches disclosed previously by other authors, but not yet modelled. Our paper provides a simple equivalent circuit description of the torch operation that accounts for its impedance-matching, power transfer to plasma and tuning characteristics, as verified experimentally. From the outcome of the model and using our experimental results, we introduce new features in the torch design that enable one to optimize its performance. We also examine ways of simplifying its structure and operation.

Comparison of Classical and Axial Injection Torches for Spraying Alumina Coatings

Abstract A conventional and a hollow cathode dc spraying plasma torch are compared by spraying fused and crushed alumina particles with two size distributions : −45, +22 μm and −90, +45 μm. The conventional plasma torch was studied for 3 nozzle internal diameters (internal diameter): 6, 7, and 8) mm. The characterization of the plasma jets has shown that the main effect of the arc current I or total gas flow rate [mdot]increase was to raise the gas velocity with a very little increase of the jet length, as confirmed by measurements of the velocity and surface temperature distributions of the particles in flight. Finally, the coatings sprayed with a 7 mm internal diameter nozzle, at P=35 kW, [mdot]=60 slm and 25 vol% H2 and a stand off distance of 100 mm correspond for the −45, +22 um powder to a deposition efficiency pD = 64%, a ratio a/(a+g) = 2% and a Vickers Hardness HV5=1040. For the −90, +45 μm powder;r pD= 47%, α/(a+v) = 9% and HV5 = 800 (where α and γ correspond to the equilibrium phase of alumina ...

Effect of a plasma sheath and ion injection on axial particle and energy confinement in a collisional mirror plasma

Continual scattering of particles into the loss cone of a simple magnetic mirror used to confine a collisional, fully Maxwellian plasma results in exceedingly large particle and energy loss rates. However, a considerable increase in confinement is found when a material wall is placed at the high field side of the mirror. A plasma sheath forms which reflects a large fraction of the electrons which pass through the mirror. Further, the sheath potential can be increased by axial ion injection. With optimized axial ion injection, the energy loss rate for a deuterium–tritium plasma decreases to 1.5% of its value without sheath reflection and near perfect electron confinement is obtained.

The role of the ion sources in the EXCYT facility

A superconducting electron cyclotron resonance (ECR) ion source is going to be installed at the Laboratorio Nazionale del Sud (LNS) as an injector for the K-800 superconducting cyclotron in order to give high intensity light ion beams to be used for the exotics at the cyclotron Tandem (EXCYT) facility. The goal will be the production of some pμA beams of O7+, O8+, C5+, C6+, Ne9+, Ne10+, and 48Ca14+ at 70–80 MeV/n to be sent onto a thick target to produce recoils. The recoils will diffuse to a source located on the Tandem injector. Such a source will be a surface ionization source or a microwave discharge source followed by a charge exchange canal. The outcoming beams are then accelerated by the Tandem and transported to the experimental areas. The role of the negative sources for the secondary beams is fundamental, because efficiencies as high as possible are needed, and the beam emittance has to be matched with the mass separator, in order to get high mass resolution. The primary source and the axial injection beam line designed for intense beams as well as the secondary beam source are being described.

Mixing study of the induction plasma reactor: Part I. Axial injection mode

A systematic study of the gas-mixing pattern in an induction plasma reactor under atmospheric and low pressure conditions is reported. Different reactor configurations were investigated in which nitrogen is injected as an auxiliary gas either axially into an Ar/H2, discharge in the center of the induction coil region, or radially through multiple orifices, into the plasma jet at tire exit nozzle of the torch. Concentration mapping in the mixing zone was carried out, using a VG-Microniass-PC 300 D mass spectrometer at plasma power levels and reactor pressures, in the range of 13–24 k 6V and 35–93 kPa, respectively. Comparison of these results with cold-flow measurements underlined the substantial difference in the mixing pattern in each of these two cases. A considerably faster mixing of the gases is noted under cold flow conditions compared to that in the presence of the discharge. The results are discussed from the viewpoint of their use for optimum reactor design applied to tire vapor-phase synthesis of ultrafine ceramic powders, using induction plasma technology.

The computation of convective heat transfer in rotating cavities

In this paper, numerical solutions of the Reynolds-averaged Navier-Stokes equations are presented for convective heat transfer inside axisymmetric rotating disc cavities. The study involves the examination of three different disc-cavity configurations and the use of four different mathematical models of turbulence. The three configurations are a rotating cavity with flow entering axially at the center and leaving radially through the outer shroud, a rotating cavity with central axial throughflow, and a rotor-stator system with axial flow injection through the stator center and outflow through the annulus formed between the rotor disc and the outer shroud. Of the four turbulence models, three are based on the zonal modeling approach with the k- ε model in the main flow region and alternative low-Reynolds number treatments across the near-wall regions. These near-wall alternatives consist of two versions of the mixing-length hypothesis and a one-equation k-transport model. The fourth turbulence model is the mixing-length hypothesis applied over the entire cavity. Comparisons with available heat transfer measurements show that none of the models is successful in all cases examined. Considering overall performance, the k- ε model with the one-equation near-wall treatment is preferred.

Investigation of an injector with an arc multicharged ion source

An injector with a PIG ion source has been designed for the axial injection system of the U-200 cyclotron. An accel-decel electrode system and Wien filter are used for extraction of the ion beam. Some results of computer simulations of the ion trajectories in such an ion optical system and the experimental results of the ion beam formation and transport are presented.

RF induction plasma spraying: State-of-the-art review

Radio frequency (RF) induction plasma technology has gained wide acceptance for the preparation of plasma spray coatings and structural free-standing parts of metals, ceramics, and metal-matrix composites. Its principal advantages are the relatively large volume and low velocity of the discharge, which coupled with the ease of axial injection of the powder into the plasma allows for the melting of relatively large particles at high throughput. The absence of electrodes offers the added advantage of ease of operation under a wide range of conditions at atmospheric and low pressure, with an inert, reducing, or oxidizing atmosphere. Highlights of recent advances in induction plasma melting and deposition of materials are presented in this article. The first section deals with advances in induction plasma spraying technology including system and torch design. This is followed by a brief overview of mathematical modeling and diagnostic studies of the induction plasma deposition process. Examples of applications of induction plasma spraying for the preparation of protective coatings and fiber-reinforced metal matrix composites are presented in the final section.

Electron Trajectories and Gains in FELwith an Axial Guide Field

Electron trajectories and small signal gains have been evaluated for a FEL with a constant wiggler and strong axial guide field. Two different injections into the wiggler are considered in this paper. The first case is that the electron beam is injected into an ideal helical orbit. In the second case, the electrons are injected parallel to the axial guide field. At the Doppler upshifted wiggler frequency the magnitudes of gain for the two types of injection tend to become identical. At the upshifted Larmor frequency the FEL gain is feasible. In the case of axial injection, small gains at frequencies higher than those obtained with perfect beam injection are also found possible. Effects of space charge, including enhancement in gain are discussed.

The circular orbit linear theory of the axial injection orbitron maser (AXIOM) oscillator

The linear theory of axial injection orbitron maser (AXIOM) oscillators is formulated analytically for circular electron orbits using the relativistic Vlasov equation and Maxwell’s equations. The theory treats transverse electric (TE) or transverse magnetic (TM) modes with sinusoidal axial field profiles. Owing to the simplicity of modeling circular electron orbits the theory is fully relativistic. The power transferred from the electron beam to the cavity fields is calculated in terms of a general distribution function and the cavity parameters. A cold beam distribution function is used to evaluate the theory. The results of the theory are presented in terms of the threshold value of the cavity Q times the electron beam current required for self-oscillation. The results show that TE modes with small azimuthal mode numbers have the strongest interaction and that modes with large azimuthal mode numbers resonate at lower electrostatic fields but require larger electron beam currents for self-oscillation.

GALOPR, a beam transport program with space charge and bunching

Abstract GALOPR is a first-order beam transport code including three-dimensional space-charge forces and the beam bunching process. It deals with usual optical devices (bending magnets, lenses, solenoids, drift spaces, bunchers) and can take into account any special optical device represented by its transfer matrix with space charge (the “Muller” and the “Pabot-Belmont” inflectors were recently introduced as one of these devices). The beam can be continuous, bunched or undergoing a bunching or debunching process. The beam-line parameters can be optimized to fit any elements of the 6 × 6 transfer and/or covariance matrices in order to obtain the maximum transmission efficiency. The results are presented with a complete set of printouts and graphical displays. This code has been used to optimize the 100 kV axial injection beam line at GANIL.

Trajectory calculations for axial injection of ions into a magnetic field: overcoming the magnetic mirror effect with an r.f. quadrupole lens

The magnetic mirror effect is one of the problems that must be overcome in order to perform Fourier transform mass spectrometry (FT-MS) experiments with an external ion source. Since the ion source is located outside of the magnetic field, about 1 m from the FT-MS analyzer cell, some type of focusing is needed to guide the ions through the fringing fields of the magnet. Several years ago, McIver and co-workers showed that a quadrupole lens operated in the r.f.-only mode was an effective means for accomplishing this. In this paper, the theory of ion injection by a r.f. quadrupole lens is developed and trajectory calculations are performed to determine how the mass range of the quadrupole lens depends on the frequency and low voltage of the signal that is applied to the rods. The calculations show that the quadrupole lens functions like a broadband filter with certain low mass and high mass cut-offs. By selecting the proper operating conditions, the mass range of the injection ions can extend over several thousand mass units and high mass ions ( m/z greater than 20 000) can be injected.

Helicity injection and diagnostics for orbitron millimeter wave source

Conventional orbitrons utilize the radially injected electrons for production of electromagnetic waves. In such a scheme, however, more than half of the electrons would not participate in the orbital motion around the anode due to the lack of acceleration. Only the electrons who did not suffer collisions till the radius 2/3 of the outer conductor (cathode) radius are possible to acquire the azimuthal velocity, via collisions, as large as the critical velocity with which the electrons can undergo circular equilibrium orbits. The axisymmetric injection is also a problem; 50% of electrons would be lost directly to the anode by the head-on collisions. This paper discusses various ways to enhance the efficiency and absolute power of an orbitron millimeterwave source. Experimental results are described on employment of a tapered metal-end, tangential injection of a thin electron beam, axial injection of rotating annular electron beams, and application of external magnetic fields. Further problem of conventional orbitrons is in its construction in which the potential-well is prematurely destroyed due to the shortening discharge current. Its diagnostics and consequence are discussed together with a new scheme leading towards the goal, an efficient injection of helicity (or helical electron-beam) into the potential-well conserved orbitron interation region.

Ecris development at GANIL

The realization of the ’’O.A.E.’’ project at GANIL (Fermi et al., 11th Conference on Cyclotrons and Their Applications, Tokyo, Oct. 1986) (modification of the stripping ratio between the two cyclotrons from 3.5 to 2.5) requires the use of an ECRIS producing an optimized current for ions such as Ar7+, Kr13+, Xe17+, Ta22+ Pb23+, and U24+. We describe the new ECR3 (Caprice source) built at GANIL and we show the last results with gaseous and metallic ions. With the O.A.I. project we plan to increase the beam current and the efficiency of the axial injection line by putting the source on a 100-kV insulated platform. ECR4 is a source with a maximum field corresponding to twice the resonance field for 14.5 GHz. The electrical power is 40 kW. The hexapole made of FeNdB has a field of 1.1 T on poles and weight of 22 kg. The UHF injection is coaxial.