Thin Electron Beam Research Articles

EXCITATION OF TM MODE BY A RELATIVISTIC ELECTRON BEAM IN AN AZIMUTHALLY CORRUGATED WAVEGUIDE

The excitation of an electromagnetic TM mode by a relativistic electron beam in a waveguide with a sinusoidalcorrugated azimuth conducting wall in a constant uniform external guiding magnetic field is theoretically studied. We consider a thin annular electron beam moving along the waveguide axis and rotating at an equilibrium radius around its axis. In the approximation of a small corrugation depth, the analytical dependences of the growth rate of instability and resonant frequencies on the parameters of the beam and waveguide are determined.

Direct comparison of analytically derived “Fedosov” solution with experimental measurements and numerical simulations of relativistic thin annular electron beam generation and propagation in magnetically insulated coaxial diode of SINUS-6 high-current electron-beam accelerator

The analytically derived solution for a thin annular electron-beam generation in a magnetically insulated coaxial diode (MICD), also known as “Fedosov solution,” is validated by direct experimental measurements of current–voltage (I–V) characteristics of MICD driven by the high-current electron-beam accelerator SINUS-6 and numerical particle-in-cell (PIC) simulations of a thin annular electron-beam generation and propagation in computer model of MICD of corresponding geometry and initial/boundary conditions. The experimental measurements of I–V characteristics of MICD are performed by monitoring and analyzing a voltage applied to MICD and an electron-beam current generated by an explosive-emission cathode of MICD. Numerical simulations of MICD operation are performed using ICEPIC code. The comparisons of analytically derived “Fedosov” solution with experimentally measured I–V characteristics of MICD as well as with results of ICEPIC simulations of a three-dimensional computer model of MICD operation are analyzed, and a conclusion is made that all three measures are pretty much consistent with each other. The appliance of the analysis is purposed now in using SINUS-6 accelerator for designing, prototyping, and studying different variants of O-type slow-wave high-power microwave/millimeter-wavelength vacuum electronic devices.

Theoretical Analysis and Simulated Verification of Circular Beam Electron Optical System for Terahertz Vacuum Electron Devices

The micro-structure miniaturization of vacuum electron devices (VEDs) in terahertz band requires the high precision description of formation and transportation for the ultrahigh density electron beams with the novelty theoretical analysis and simulation. In this article, the 3-D spatial potential of circular electron beam formation is presented by adopting differential geometry and tensor analysis theory. The specific numerical solution of the circular electron beam potential can be obtained by establishing a moving coordinate frame, carrying out numerical calculation, series expansion with adopting of Riemann method. In order to verify the complex theory, a 0.34 THz vacuum electron tube using thin circular electron beam gun and corresponding optical system are designed and analyzed. The beam voltage and current are 23.8 kV and 0.28 A respectively, with beam channel radius of 0.16 mm and magnetic field of 5250 Gs. Using 3-D simulation of CST, the ultrahigh density electron beam can transport 30 mm with good stability. The spatial potential of numerical calculation with the obtained theoretical functions and the simulation model are compared to verify our theoretical description. Both the results are with good consistent which preliminary proves the effectiveness of the theoretical function. Furthermore, we combine the theoretical function potential with the electron beam envelope under the same coordinate frame, the detailed characteristics of ultrahigh density beam formation with the potential function can be directly understood easily, which will give the deep physical mechanics vision for the development of high power and high-efficiency terahertz tube in the future.

Electron beam-plasma discharge in GDT mirror trap: experiments on plasma start-up with electron gun

The paper describes experiments on the injection of an electron beam into a gas at the gas dynamic trap (GDT) and develops a technique for creating a starting plasma with parameters sufficient for its subsequent heating by neutral beams. It is found that a relatively thin electron beam is capable of ionizing plasma in the entire volume of the trap, and the plasma turbulence it excites is capable of accelerating some of the electrons to energies tens of times higher than the initial energy of the beam. It is shown that, in contrast to early experiments on tabletop open traps, collective beam relaxation under GDT conditions occurs in the vicinity of the entrance magnetic mirror. Since the electron cyclotron frequency in this region significantly exceeds the plasma frequency, it is necessary to study the mechanism of a beam-plasma discharge under these conditions. As a first step along this path, we measure the radial diffusion coefficient of fast particles, as well as the rate at which they gain energy.

Novel mechanism for terahertz radiation by oblique colliding of two electron beams in plasma

A new scheme for generating high power terahertz (THz) radiation by using two obliquely colliding electron beams in plasma is proposed. The particle-in-cell (PIC) simulation finds that a small beam intersection of high electron density is formed within a plasma wavelength when two thin electron beams collide. Meanwhile, the beam intersection can oscillate in a strong plasma wave driven by the two beams to produce THz radiation at double plasma frequency. A theoretical model is established showing that the radiation mechanism is the second-order current generated by the beam intersection oscillation. The angular distribution of the THz radiation is calculated by the theory, which agrees well with the PIC simulation. Compared with the existing high power THz sources, the scheme provided in this article has the advantages of a simple structure and no need for extreme parameter conditions, which is hopeful for applications in kilowatt-level coherent compact THz sources.

Electrostatic Cumulation at Relativistic Energies

The electrostatic cumulation of current density in relativistic vacuum diodes with ring-type cathodes is described theoretically and confirmed experimentally. The distinctive feature of the suggested cumulation mechanism is a very low energy spread of electrons. As a result of electrostatic cumulation, a thin relativistic electron beam with a current density of 1 kA/mm2 can be formed.

Crystallography characteristics of tetragonal nano-zirconia films under various oxygen partial pressure

ABSTRACTStructural features and surface morphology of ZrO thin films electron beam evaporation-deposited under various oxygen partial pressure were studied. It was indicated tetragonal phase for all samples by XRD pattern. The highest crystallite size calculated via Scherrer equation is observed at the oxygen partial pressure of mbar; that was in good agreement with the high-resolution surface images obtained by FE-SEM. The photoluminescence spectrum of t-zirconia films exhibits an intense peak at 351 nm, this emission decrease in intensity by elevation of oxygen partial pressures. Surface roughness profile and scaling analyses were made by surface measurements of atomic force microscopy with using the height-height correlation function. The roughness has the maximum value at the highest oxygen partial pressure. It has been found that with the increase of oxygen partial pressures, lateral correlation length of samples increased, and fractal dimension changed within the range of 2.20–2.26.

Nonlinear Stabilization of Resistive Instability of a Tubular Charged Particle Beam Moving above a Solid-State Plasma Cylinder

Nonlinear stabilization of instability of an infinitely thin tubular electron beam moving along the surface of a solid-state plasma cylinder is analyzed. It is assumed that the electron collision frequency in the plasma cylinder is much higher than the frequency of plasma eigenmodes (oscillations). The beam is assumed to be nonrelativistic, and, thus, the problem is solved in the electrostatic approximation. It is shown that the growth of the wave amplitude is stabilized nonlinearly due to the self-trapping of the beam electrons by the field of the electrostatic wave excited in the beam itself. It is found that the saturation time of instability and the maximum amplitude of the excited wave depend on the radius of the plasma cylinder. It is established that the larger the radius of the plasma cylinder, the later the nonlinear stage of instability begins and the larger the maximum amplitude of the excited wave.

Highly efficient electromagnetic emission during 100 keV electron beam relaxation in a thin magnetized plasma

In this paper, electromagnetic emissions produced by a beam-plasma system are investigated using particle-in-cell simulations for the particular case when the typical transverse size of both the 100 keV electron beam and the produced plasma channel is comparable to the radiation wavelength. The interest in this regime of beam-plasma interaction is associated with highly efficient generation of electromagnetic waves near the plasma frequency harmonics that has been recently observed in laboratory experiments on the GOL-3 mirror trap. It has been found that the radiation power only from the vicinity of the doubled plasma frequency in these experiments can reach 1% of the total beam power. Subsequent theoretical and simulation studies have shown that the most likely candidate for explaining such efficient generation of electromagnetic radiation is the mechanism of a beam-driven plasma antenna based on the conversion of the most unstable plasma oscillations on a longitudinal density modulation of plasma ions. In this paper, we investigate how effectively this mechanism can work in a real experiment at the GOL-3 facility, when a thin subrelativistic electron beam gets a large angular spread due to compression by a magnetic field, and the gas into which it is injected has macroscopic density gradients.

Electrostatic cumulation of high-current electron beams for terahertz sources

The electrostatic cumulation of current density in relativistic vacuum diodes with ring-type cathodes is described theoretically and confirmed experimentally. The distinctive feature of the suggested cumulation mechanism is a very low energy spread of electrons. As a result of electrostatic cumulation, a thin relativistic electron beam with a current density of 1 kA/mm$^2$ can be formed. This quantity exceeds typical current density values in high-current Cherenkov sources by an order of magnitude. Such a beam can be used as an active medium in high-power terahertz sources.

Second harmonic electromagnetic emission in a beam-driven plasma antenna

Generation of electromagnetic (EM) radiation near the second harmonic of the plasma frequency during the injection of an electron beam into a rippled-density plasma channel is investigated using both analytical theory and particle-in-cell simulations. The generating scheme is based on nonlinear interaction of the most unstable beam-driven potential plasma wave with its satellite arising due to scattering on the longitudinal modulation of plasma density. Resulting superluminal oscillations of electric current in a finite-size plasma channel radiate EM waves via the same mechanism which has been recently studied for the fundamental harmonic emission and reffered as a beam-driven plasma antenna. It is shown that theoretical predictions for the optimal plasma width and modulation period are confirmed by simulation results and the power conversion efficiency of the second harmonic emission reaches several percent. Such an efficient mechanism opens the path to explanation of laboratory experiments with a thin electron beam at the GOL-3 mirror trap as well as to developing the scheme of terahertz generation at the gigawatt power level.

NONLINEAR THEORY OF INTERACTION BETWEEN A TUBULAR BEAM OF CHARGED PARTICLES AND POTENTIAL SURFACE WAVES OF PLASMA CYLINDER

Investigation of the generation mechanisms of electromagnetic waves by the motion of charged particles in various electrodynamic systems is an actual problem of modern radiophysics and electronics. Recently, much attention has been paid to the interaction between the streams of charged particles and solid-state structures that have dispersion properties. As a rule, such structures contain plasma-like media. The basis for the generation of electromagnetic waves is the system instabilities caused by perturbations in the streams of charged particles. The stationary mode of wave generation is provided by nonlinear interactions of a charged particle beam with eigenmodes of solid-state structure. In this paper, a theoretical study of the nonlinear stabilization effect of instability of an infinitesimally thin tubular electron beam propagating along the surface of a solid-state plasma cylinder has been carried out. Using Maxwell's equations and motion equation of plasma electrons based on an integrated approach (analytical and numerical), the nonlinear theory of instability of the tubular electron beam flying above the plasma cylinder has been constructed. The plasma of the cylinder was assumed collisionless. The calculations have been performed to an electrostatic approximation due to the nonrelativistic nature of motion of the beam. It is shown that the nonlinear stabilization of increase in the wave amplitude is realized due to the bunching of the beam electrons into clots and their subsequent capture by the wave field. The dependence of the instability rise time and the wave maximum amplitude on the plasma cylinder radius has been found out. It is established that the nonlinear stage of instability begins earlier in an electro-dynamic system with a smaller radius of the plasma cylinder. At that in such a system, the maximum magnitude of the slow amplitude has a greater value. The research results broaden our understanding about the physical properties of systems with plasma-like media and systematize our knowledge about the excitation mechanisms of potential surface waves in the electrodynamic systems that form the basis of microwave oscillators.

Multicycle Surface Alloying of Aluminum with Titanium: Structure and Properties

Commercially pure A7 aluminum was surface alloyed with commercially pure titanium on COMPLEX equipment under unified vacuum conditions through vacuum arc evaporation and deposition of a thin Ti film and intense electron beam irradiation of the film–substrate system using a plasma-cathode pulsed electron source. The number of deposition–irradiation cycles was 20. The Ti film thickness in each cycle was 0.5 μm. After multicycle alloying, a modified surface layer of up to 60 μm thick was formed representing a multiphase structure of rapidly solidified submicro-and nanograins. The microhardness of the Ti–Al surface alloy (irradiation at 15 J/cm2, 50 μs, 10 pulses) was more than 8 times the microhardness of A7 aluminum, and its wear resistance and friction coefficient were respectively 45 times higher and 1.2 times lower than the values in the initial material. The chief cause for the improved mechanical and tribological properties of commercially pure A7 aluminum is the formation of an extended intermetallic layer.

Stability properties of a thin relativistic beam propagation in a magnetized plasma

A self-consistent nonlinear hydrodynamic theory is presented of the propagation of a long and thin relativistic electron beam through a plasma that is relatively strongly magnetized, $|\Omega_e|\sim\omega_{pe}$ and whose density is much bigger than that of the beam. In the regime when the parallel phase velocity in the comoving frame is much smaller than the thermal speed and the beam electrons are thermalized, a stationary solution for the beam is found when the electron motion in the transverse direction is negligibile and the transverse localization comes from the nonlinearity of its 3-D adiabatic expansion. Conversely, when the parallel phase velocity is sufficiently large to prevent the heat convection along the magnetic field, a helicoidally shaped stationary beam is found whose transverse profile is determined from a nonlinear dispersion relation and depends on the transverse size of the beam and its pitch angle.

The Effects of a Transverse Anisotropy Dielectric Rod in Excitation and Amplification Phenomena of Hybrid Electromagnetic Waves in a Cylindrical Metallic Waveguide

In this paper, a novel waveguide made of a hollow long metallic cylindrical column with a transverse anisotropy dielectric rod (TADR) is studied. The dispersion relation of hybrid electromagnetic waves is obtained in this structure, and its diagram variations will be investigated. The effects of dielectric permittivity coefficients of TADR on the dispersion relation of slow waves is studied. The mechanism of wave generation and its amplification phenomena by a thin annular relativistic electron beam are investigated for hybrid modes. Also, the graphs of operating frequency and the graphs of growth rate will be presented for the waves during the electron beam injection. The computations have done for terahertz hybrid waves.

Self consistent hydrodynamic description of the plasma wake field excitation induced by a relativistic charged-particle beam in an unmagnetized plasma

A self-consistent nonlinear hydrodynamic theory is presented of the propagation of a long and thin relativistic electron beam, for a typical plasma wake field acceleration configuration in an unmagnetized and overdense plasma. The random component of the trajectories of the beam particles as well as of their velocity spread is modelled by an anisotropic temperature, allowing the beam dynamics to be approximated as a 3D adiabatic expansion/compression. It is shown that even in the absence of the nonlinear plasma wake force, the localisation of the beam in the transverse direction can be achieved owing to the nonlinearity associated with the adiabatic compression/rarefaction and a coherent stationary state is constructed. Numerical calculations reveal the possibility of the beam focussing and defocussing, but the lifetime of the beam can be significantly extended by the appropriate adjustments, so that transverse oscillations are observed, similar to those predicted within the thermal wave and Vlasov kinetic models.

About background plasma effects on excitation and generation of the waves in a cylindrical metallic waveguide with anisotropic dielectric rod

In this work, the dispersion relation of hybrid electromagnetic waves propagating in a novel plasma cylindrical waveguide with a cold collisionless unmagnetized plasma column and a transverse anisotropy dielectric rod (TADR) is investigated. The dispersion diagram of the hybrid waves in this configuration is obtained. The effects of dielectric permittivity coefficients of TADR on the dispersion relation of slow waves are studied. Excitation of the waves by a thin annular relativistic electron beam (TAREB) will be presented. Furthermore, the diagrams of the operating frequency and time growth rate are obtained. In continuation, the accelerating voltage, the current density of TAREB, and the radius of the plasma column on the growth rate will be discussed.

Water Sorption in Electron-Beam Evaporated SiO2 on QCM Crystals and Its Influence on Polymer Thin Film Hydration Measurements

Spectroscopic ellipsometry (SE) and quartz crystal microbalance (QCM) measurements are two critical characterization techniques routinely employed for hydration studies of polymer thin films. Water uptake by thin polymer films is an important area of study to investigate antifouling surfaces, to probe the swelling of thin water-containing ionomer films, and to conduct fundamental studies of polymer brush hydration and swelling. SiO2-coated QCM crystals, employed as substrates in many of these hydration studies, show porosity in the thin electron-beam (e-beam) evaporated SiO2 layer. The water sorption into this porous SiO2 layer requires correction of the optical and mass characterization of the hydrated polymer due to changes in the SiO2 layer as it sorbs water. This correction is especially important when experiments on SiO2-coated QCM crystals are compared to measurements on Si wafers with dense native SiO2 layers. Water adsorption filling void space during hydration in ∼200-260 nm thick SiO2 layers deposited on a QCM crystal resulted in increased refractive index of the layer during water uptake experiments. The increased refractive index led to artificially higher polymer swelling in the optical modeling of the hydration experiments. The SiO2-coated QCM crystals showed between 6 and 8% void as measured by QCM and SE, accounting for 60%-85% of the measured polymer swelling in the low humidity regime (<20% RH) and 25%-40% of the polymer swelling in the high humidity regime (>70% RH) from optical modeling for 105 and 47 nm thick sulfonated polymer films. Correcting the refractive index of the SiO2 layer for its water content resulted in polymer swelling that successfully resembled swelling measured on a silicon wafer with nonporous native oxide.

On the clinotron effect in a backward-wave tube

The results of a theoretical study of the clinotron effect in a clinotron model, which takes into account static electron trajectories in the focusing magnetic field and the initial spacing between the lower beam boundary and the surface of the slow-wave structure, are presented. Physical processes of interaction between a thick electron beam with transverse dimensions comparable with the length of the slow wave and the RF field at its oblique incidence onto the structure are considered. It is demonstrated that, as the current is increased from the starting to the working value, a beam tilt is necessary to reduce the nonlinear effects of interaction between the beam and the RF field and prevent the complex self-oscillation dynamics in the clinotron; in the small amplitude mode (start), the beam tilt is related to optimization of the beam supply into the interaction space, which ensures the minimum starting current. In addition, it is shown that, in the presence of the initial spacing between the beam and structure, the reduced clinotron efficiency η/С increases and, at the optimum tilt angle, is no less than the normalized efficiency of classical backward-wave tubes with a thin electron beam.

Phased Array Ultrasonic Testing of Thin DP Steel Electron Beam Weld Joints

Duplex steels are an important group of materials which are generally used for applications where resistance to corrosion, or high strength and creep resistance at elevated temperatures, are required. They are used extensively in nuclear plant. Although ultrasonic inspection methods have been routinely used in industry for some three decades, it is well known that cast or welded austenitic components can be difficult, or even impossible, to examine ultrasonically. Development of ultrasonic techniques is therefore in progress in several countries to provide improvements which are being sought on safety and economic grounds.The aim of this paper is a brief description of the relevant metallurgical characteristics given before a consideration of the physical properties of the weld metal and the current theoretical models used to describe ultrasound propagation in it. The paper deals with the steps taken to improve the capabilities of ultrasonic inspection and includes a discussion of the problems of flaw location and sizing.