Electron Beam Power Research Articles

Classical scattering and stopping power in dense plasmas: the effect of diffraction and dynamic screening

AbstractIn the present work, classical electron–ion scattering, Coulomb logarithm, and stopping power are studied taking into account the quantum mechanical diffraction effect and the dynamic screening effect separately and together. The inclusion of the quantum diffraction effect is realized at the same level as the well-known first-order gradient correction in the extended Thomas–Fermi theory. In order to take the effect of dynamic screening into account, the model suggested by Grabowski et al. in 2013 is used. Scattering as well as stopping power of the external electron (ion) beam by plasma ions (electrons) and scattering of the plasma's own electrons (ions) by plasma ions (electrons) are considered differently. In the first case, it is found that in the limit of the non-ideal plasma with a plasma parameter Γ → 1, the effects of quantum diffraction and dynamic screening partially compensate each other. In the second case, the dynamic screening enlarges scattering cross-section, Coulomb logarithm, and stopping power, whereas the quantum diffraction reduces their values. Comparisons with the results of other theoretical methods and computer simulations indicate that the model used in this work gives a good description of the stopping power for projectile velocities $v\,{\rm \lesssim}\, 1.5 v_{{\rm th}}$, where vth is the thermal velocity of the plasma electrons.

Additive Manufacturing for Future Facades: The potential of 3D printed parts for the building envelope

The basic principle of '3D Printing' is the layer wise production of real parts from virtual data - be it with laser, with power glue, electron beam or UV light processing (Hopkinson, Hague, & Dickens, 2006). The professional application of '3D Printing' is 'Additive Manufacturing' (AM) and this opens a fascinating new world of engineering. It offers a selection of reliable building construction materials - done in concrete, aluminium, steel, high performance plastics or glass (Woodcock, 2011). No matter what applications can be found: to 'design for function', rather to 'design for production' turns our way of engineering of the last century upside down. As a result, AM opens the outlook to applications in our (built) future in combination with the available technologies of today (Straus, 2013). The tool-less production with AM allows for new shapes and functional parts in small batch sizes - down to batch size one. The parts performance can be re-interpreted based on the demands within the system, not based on the limitations of conventional manufacturing. AM offers new ways of materializing the physical part around its function. Advancements can for example be achieved in the semi-finished goods: fittings with less, but higher integrated parts could offer a better performance with lower material consumption. Solving the most critical part of a free-form structure and allowing for a smart combination with the approved standards has a great potential, as well. It leads toward customized and enhanced performance. This paper discusses the possible changes and influences those emerging technologies have on the development of building envelopes. To achieve today's demands of future envelopes, we have to find new solutions. Additive Manufacturing is one possible way to do so.

A three-dimensional transient thermal-fluid flow-compositional study of ingot casting during electron beam remelting of Ti–6Al–4V

Electron beam cold hearth remelting (EBCHR) is a consolidation and refining process capable of consolidating titanium scrap and sponge material into high quality titanium alloy ingots. During the final stage of casting in the EBCHR process, operators must balance the potential to form large shrinkage voids, caused by turning off the electron beam heating, against the tendency to evaporate alloying additions, which occurs if the top surface remains molten. A comprehensive understanding of the evaporation and fluid flow conditions occurring during the final stage of EBCHR is required in order to optimize ingot production. This research focused on developing a coupled thermal, fluid flow and composition model, capable of predicting the temperature, fluid flow and composition fields within an EBCHR cast, Ti–6Al–4V ingot. The physical phenomena of thermal and compositional buoyancy, mushy zone flow attenuation and aluminum evaporation were incorporated in the model formulation. Industrial scale experiments were carried out at the production facilities of a leading industrial producer of titanium to provide data and measurements for model verification. Model predictions for liquid pool profile, last liquid to solidify and composition fields are in good agreement with the industrially measured results. A sensitivity analysis was performed with the model to study the effects of variation of electron beam power input and hot top time duration on the evaporative losses and position of solidification voids. For the cases examined, there was a strong correlation between electron beam power and alloying element losses, while hot top duration variation results indicated a stronger dependence on last liquid to solidify than on alloying element losses. Therefore a classic optimization problem arises between balancing hot top duration with alloying element losses.

Additive manufacturing of metallic components by selective electron beam melting — a review

Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.

Measuring the mechanical recoil impulse of a polymeric target upon impact of a high power electron beam

A method for measuring the mechanical recoil impulse of a target produced by the relativistic electron beam of the Calamary accelerator is described. A detector based on a piezoelectric sensor is used in measurements. Results of measurements are presented for the mechanical recoil impulse produced by the relativistic electron beam with an energy as high as 300 keV, a current of up to 30 kA, and a duration of ~100 ns that is incident on an epoxy target. The energy flux density on the target surface is varied in the range of 1–10 GW/cm2. The maximum measured impulse value is 0.32 N · s at an energy flux density of 10 GW/cm2 (an energy fluence of 810 J/cm2).

Electron Accelerator Shielding Design of KIPT Neutron Source Facility

Abstract The Argonne National Laboratory of the United States and the Kharkov Institute of Physics and Technology of the Ukraine have been collaborating on the design, development and construction of a neutron source facility at Kharkov Institute of Physics and Technology utilizing an electron-accelerator-driven subcritical assembly. The electron beam power is 100 kW using 100-MeV electrons. The facility was designed to perform basic and applied nuclear research, produce medical isotopes, and train nuclear specialists. The biological shield of the accelerator building was designed to reduce the biological dose to less than 5.0e-03 mSv/h during operation. The main source of the biological dose for the accelerator building is the photons and neutrons generated from different interactions of leaked electrons from the electron gun and the accelerator sections with the surrounding components and materials. The Monte Carlo N-particle extended code (MCNPX) was used for the shielding calculations because of its capability to perform electron-, photon-, and neutron-coupled transport simulations. The photon dose was tallied using the MCNPX calculation, starting with the leaked electrons. However, it is difficult to accurately tally the neutron dose directly from the leaked electrons. The neutron yield per electron from the interactions with the surrounding components is very small, ∼0.01 neutron for 100-MeV electron and even smaller for lower-energy electrons. This causes difficulties for the Monte Carlo analyses and consumes tremendous computation resources for tallying the neutron dose outside the shield boundary with an acceptable accuracy. To avoid these difficulties, the SOURCE and TALLYX user subroutines of MCNPX were utilized for this study. The generated neutrons were banked, together with all related parameters, for a subsequent MCNPX calculation to obtain the neutron dose. The weight windows variance reduction technique was also utilized for both neutron and photon dose calculations. Two shielding materials, heavy concrete and ordinary concrete, were considered for the shield design. The main goal is to maintain the total dose outside the shield boundary less than 5.0e-03 mSv/h during operation. The shield configuration and parameters of the accelerator building were determined and are presented in this paper.

Optimum target source term estimation for high energy electron accelerators

Abstract Optimum target for bremsstrahlung emission is defined as the thickness of the target material, which produces maximum bremsstrahlung yield, on interaction of electron with the target. The bremsstrahlung dose rate per unit electron beam power at a distance of 1 m from the target material gives the optimum target source term. In the present work, simulations were performed for three different electron energies, 450, 1000 and 2500 MeV using EGSnrc Monte-Carlo code to determine the optimum thickness. An empirical relation for optimum target as a function of electron energy and atomic number of the target materials is found out from results. Using the simulated optimum target thickness, experiments are conducted to determine the optimum target source term. For the experimental determination, two available electron energies, 450 MeV and 550 MeV from booster synchrotron of Indus facility is used. The optimum target source term for these two energies are also simulated. The experimental and simulated source term are found to be in very good agreement within ±3%. Based on the agreement of the simulated source term with the experimental source term at 450 MeV and 550 MeV, the same simulation methodology is used to simulate optimum target source term up to 2500 MeV. The paper describes the simulations and experiments carried out on optimum target bremsstrahlung source term and the results obtained.

Reactive high-rate deposition of titanium oxide coatings using electron beam evaporation, spotless arc and dual crucible

Abstract Results of investigations on thin films of titanium oxide are presented in which the layers were deposited at a very high deposition rate of approximately 50–100 nm/s. The high-performance coating process is based upon electron beam evaporation, a dual crucible, and a spotless arc that burns in the metal vapor and reactive gas between the evaporating titanium electrodes that are heated by the electron beam. Electron beam power, arc current and oxygen flow rate were varied and the resulting coatings investigated with regard to their composition, optical properties, and microstructure. Even at such high deposition rates, transparent and dense layers with a high refractive index (2.4) could be produced. Amorphous TiO2 coatings were obtained at a substrate temperature below 150 °C while crystalline layers of the anatase form could be deposited at a substrate temperature in the range of 200 to 300 °C. The data regarding the chemical composition of the titanium oxide layers are compared with a mathematical model of reactive vapor deposition. An estimate based on the model shows that the incorporation coefficient of oxygen, which gives its deposit probability in the coating, is approximately 0.25 for stoichiometric TiO2 layers. Possible applications of the PVD process presented are foreseen for large-area optical coating systems and large-scale application of photo-induced effects.

Welding of Mo-Based Alloy Using Electron Beam and Laser-GTAW Hybrid Welding Techniques

In the current study, welding of TZM (molybdenum-based alloy) plates in square-butt configuration was carried out using electron beam and laser-GTAW hybrid power sources. Microstructures of weld joint containing three zones—parent metal, heat-affected zone, and fusion zone—were clearly identified when examined through optical and scanning electron microscopy. The weld joints were found to be sound with very wide fusion and heat-affected zones. The microstructure of the fusion zone was coarse-grained. as-solidified microstructure, while the microstructure of heat-affected zone was the recrystallized microstructure with reduction in grain size as distance from the fusion line increased. Microhardness profile using Vickers hardness tester was obtained across the weld region, and the tensile properties of the weld joints were evaluated by performing room temperature tensile test and fracture was examined using scanning electron microscope. Joint coefficient of the weld joints were ~40 to 45 pct of that of the parent metals with nonmeasurable tensile ductility with predominantly transgranular mode of fracture indicating weakness along the grain boundary. Detailed orientation imaging and transmission electron microscopy were carried out to understand the most dominating factor in introducing weld joint brittleness.

The Effects of Drilling Parameters on Pore Size in Keyhole Mode Welding

The pore sizes affected by different drilling parameters during high power density laser and electron beam welding processes are theoretically determined in this study. The drilling parameters include incident energy absorbed by the mixture in the keyhole, radius, and Mach number at the base, drilling speed, and location of the shock wave or surrounding pressure. The factors affecting the pore sizes are still lacking, even though porosity often occurs and limits the widespread industrial application of keyhole mode welding. In order to determine the pore shape, this study introduces the equations of state at the times when the keyhole is about to be enclosed and when the temperature drops to melting temperature. The gas pressure, temperature, and volume required at the time when the keyhole is about to be closed are determined by calculating the compressible flow of the vapor–liquid dispersion in a vertical keyhole with varying cross sections, paying particular attention to the transition between annular and slug flows. It is found that the final pore size decreases as absorbed energy, radius, and Mach number at the base increase, and decreases axial location of the shock wave or higher surrounding pressure for the keyhole containing a supersonic mixture. For a subsonic mixture in the keyhole, the final pore size decreases as released energy, radius, and Mach number at the base increase. This work provides an exploratory and systematical investigation of the pore size during keyhole mode welding.

Radiative cooling properties of He-defected tungsten with fiber-form nanostructured surface

The radiative cooling capability of tungsten with a fiber-form nanostructure is evaluated precisely using an electron-beam power system. It is found that the total emissivity of black nanostructured tungsten is very close to 1.0, meaning an almost complete black body. The discrepancies in the determination of the total emissivity between the electron-beam method and a fixed biasing procedure are discussed in terms of the power transmission through the plasma sheath, focusing on the ion energy reflection and cooling associated with electron emission.

The Effects of Entrainment on Pore Shape in Keyhole Mode Welding

This study theoretically investigates the effects of the entrainment accompanying mass, momentum, and energy transport on pore size during high power density laser and electron beam welding processes. The physics of macroporosity formation is not well understood, even though macroporosity often occurs and limits the widespread industrial application of keyhole mode welding. This work is an extension of a previous work dealing with collapses of keyholes induced by high intensity beam drilling. In order to determine the pore shape, this study, however, introduces the equations of state at the times when the keyhole is about to be enclosed and when the temperature drops to melting temperature. The gas pressure required at the time when keyhole collapses is determined by calculating the compressible flow of the two-phase, vapor–liquid dispersion in a vertical keyhole with varying cross sections, paying particular attention to the transition between annular and slug flows. It is found that the pore size increases as entrainment fluxes decrease in the lower and upper regions of the keyhole containing a supersonic mixture. The pore size also increases with decreasing total energy of entrainment and an increasing axial velocity component ratio between entrainment and mixture through the core region. With a subsonic mixture in the keyhole, the final pore size increases with entrainment fluxes in the lower and upper regions. This work provides an exploratory and systematical investigation of pore size induced by entrainment accompanied by mass, momentum, and energy transport during keyhole mode welding.

MODELING OF SURFACE HEATING OF METAL AFTER ELECTROEXPLOSIVE ALLOYING AT THE SUBSEQUENT ELECTRON-BEAM TREATMENT

A model of heating of titanium surface subjected to electroexplosive carburization at subsequent electron-beam treatment is considered. The model takes into account the pulse-periodic nature of treatment and allows to calculate the temperature field on the surface when accounting density of electron beam power, pulse duration and their frequency. The estimation of time of dissolution of particles of carbon fibers by electron-beam treatment is made for melted surface layer.

SIMULATION OF THERMAL STATE OF INTERMEDIATE TANK OF ELECTRONIC BEAM FURNACE

There was developed mathematical model of temperature pattern’s distribution in intermediate tank of electronic beam furnace. The model accounts for the power of electron beam, parametric sweep function of beam, parameters of water cooling, phase changes of treated material and convective current of melt from the delivery point to discharge of its into mold cup. There was developed computer software, allowing obtain quantity characteristics, as well as visualize the distribution of current of heat in the intermediate tank’s volume. There were showed examples of modeling of temperature pattern’s distribution, positions of boundary of hard and liquid phase in the intermediate tank under different power of electronic beam.

Ozone Generation in Air during Electron Beam Processing

Ozone, the triatomic form of oxygen, can be generated by exposing normal diatomic oxygen gas to energetic electrons, X-rays, nuclear gamma rays, short-wavelength ultraviolet radiation (UV) and electrical discharges. Ozone is toxic to all forms of life, and governmental regulations have been established to protect people from excessive exposures to this gas. The human threshold limit values (TLV) vary from 60 to 100 parts per billion (ppb) in air, depending on the agency or country involved. Much higher concentrations can be produced inside industrial electron beam (EB) facilities, so methods for ozone removal must be provided. Equations for calculating the ozone yield vs absorbed energy, the production rate vs absorbed power, and the concentration in the air of an EB facility are presented in this paper. Since the production rate and concentration are proportional to the EB power dissipated in air, they are dependent on the design and application of the irradiation facility. Examples of these calculations are given for a typical EB process to cross-link insulated electrical wire or plastic tubing. The electron energy and beam power are assumed to be 1.5 MeV and 75kW.

Numerical investigations on hatching process strategies for powder-bed-based additive manufacturing using an electron beam

This paper investigates in hatching process strategies for additive manufacturing using an electron beam by numerical simulations. The underlying physical model and the corresponding three-dimensional thermal free-surface lattice Boltzmann method of the simulation software are briefly presented. The simulation software has already been validated on the basis of experiments up to 1.2kW beam power by hatching a cuboid with a basic process strategy, whereby the results are classified into porous, good, and uneven, depending on their relative density and top surface smoothness. In this paper, we study the limitations of this basic process strategy in terms of higher beam powers and scan velocities to exploit the future potential of high power electron beam guns up to 10kW. Subsequently, we introduce modified process strategies, which circumvent these restrictions, to build the part as fast as possible under the restriction of a fully dense part with a smooth top surface. These process strategies are suitable to reduce the build time and costs, maximize the beam power usage, and therefore use the potential of high power electron beam guns.

Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing-wave linac and RF photoinjector powered by a single ultrastable RF transmitter at x-band RF frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire accelerator is approximately 1 meter long and produces hard x-rays tunable over a wide range of photon energies. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is $5 \times 10^{11}$ photons/second in a 5% bandwidth and the brilliance is $2 \times 10^{12}\mathrm{photons/(sec\ mm^2\ mrad^2\ 0.1\%)}$ in pulses with RMS pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.

Synthesis of copper nanopowders using electron-beam evaporation at atmospheric pressure of inert gas

This work is devoted to the description and analysis of the technique used to obtain copper nanopowder by substance evaporation with the help of a powerful electron beam. The method possesses the following features: high yield, the possibility of obtaining nonoxidized copper, it works at atmospheric pressure, and the possibility of varying the parameters of the powders to be obtained directly in the process of synthesis. The possibility of efficiently obtaining nonoxidized copper using a closed cycle of inert gas circulation has been implemented. Copper nanopowders of a spherical shape with a diameter from 15 to 700 nm have been obtained. The dependences of the performance and specific surface area of the powders on the parameters of the production process for various evaporation modes are obtained. The factors affecting the size of the particles to be obtained (modes of boiling and cooling and configuration of the vaporization region) are analyzed. The peculiarities of the process used to obtain copper nanopowders are revealed. This allowed us to create a system for monitoring and controlling the parameters of the process, which made it possible to increase its performance and broaden the range of varying nanopowder properties.

An analytical study on the diffraction quality factor of open cavities

Open cavities are often employed as interaction structures in a new generation of coherent millimeter, sub-millimeter, and terahertz (THz) radiation sources called the gyrotron. One of the open ends of the cavity is intended for rapid extraction of the radiation generated by a powerful electron beam. Up to the sub-THz regime, the diffraction loss from this open end dominates over the Ohmic losses on the walls, which results in a much lower diffraction quality factor (Qd) than the Ohmic quality factor (Qohm). Early analytical studies have led to various expressions for Qd and shed much light on its properties. In this study, we begin with a review of these studies, and then proceed with the derivation of an analytical expression for Qd accurate to high order. Its validity is verified with numerical solutions for a step-tunable cavity commonly employed for the development of sub-THz and THz gyrotrons. On the basis of the results, a simplified equation is obtained which explicitly expresses the scaling laws of Qd with respect to mode indices and cavity dimensions.

Breakdown Process of Pseudospark Discharge Using the Various Discharge Module

A argon Pseudospark discharge is studied and modelled with our developed simulation program. The structure of our code is flexible and transparent. The modular structure is divided into three main parts: electromagnetics module which forms the heart of the model, the neutral gas module, and the chemical reaction module. The above three parts with the plasma module are controlled by the user. The strong modularity makes the code easy to handle and easy to adjust or expand. This project will do in-depth numerical simulation for the study of the inception of breakdown characteristics via a electrostatic particle-in-cell plus Monte-Carlo collision method. The model tracks the trajectories of both electrons and ions, including ionizing collisions in the gas phase by electrons and ions, and secondary electron emission by ions on surfaces. The result indicated the pseudospark discharge breakdown process mainly induced by field emission.The peak discharge current is found to be dependent on gas pressure,electrode borehole diameter. The effect of these design parameters on the peak anode current has been analysed. Simulate the discharge breakdown physical processes for the Pseudospark in order to lay the theoretical foundation for the optimize and improve the pulse power electron beam.