High-current Relativistic Electron Beam Research Articles

Characteristics of branched flows of high-current relativistic electron beams in porous materials

Branched flow is a universal phenomenon in which treebranch-like filaments form through traveling waves or particle flows in irregular mediums. Branched flow of high-current relativistic electron beams (REBs) in porous materials has been recently discovered [Jiang et al., Phys. Rev. Lett. 130, 185001 (2023)]. REB branching is accompanied by extreme beam focusing, up to a hundred times the initial value, at predictable caustic locations. The energy coupling efficiency between the beam and porous material surpasses that in homogeneous targets by two orders of magnitude. This paper examines REB branching, focusing on how beam parameters (e.g., Lorentz factor and density) and characteristics of the porous materials (e.g., pore size, skeleton thickness, and density) influence branching patterns. Analyses of the dynamics of individual beam electrons are also provided. The findings pave the way for further understanding REB branching and its potential applications in the future.

Optical Parameters of Aluminum Alloy Samples Irradiated by High Current Relativistic Electron Beams

The aluminum alloys D16, D16AT are widely used as construction materials in the aircraft industry. Questions connected with the enhancement of the properties of the construction elements made of the alloys through surface modification are of great interest now. The objects of the study in our paper are the samples of the aluminum alloy D16AT subjected to irradiation by high-current relativistic electron beams. Leaving aside the material science aspects, in this work we focused on modeling the optical properties of the samples. The problem is relevant because optical methods for surface analysis have become widespread due to their versatility and efficiency. Through the treatment of the preliminary measured ellipsometry data, we obtain the optical constants of the samples and their dispersion in the visible region of wavelength. The method used consists of an approximation of the reflection coefficient calculated from the ellipsometry data by finding the values of the parameters in the model. The last is performed by the least squares method. The reflection coefficient is assumed to correspond to the semibounded uniaxial medium with the optical axis perpendicular to the interface between the medium and the homogeneous and dielectric ambient medium. The dielectric function of the semibounded medium is approximated by the Drude-Lorentz model. The possibility of birefringence of the samples caused by the irradiation with electron beams is discussed.

THE SIMULATION OF EMERGENCY ACTION ON CONSTRUCTION MATERIALS BY HIGH CURRENT RELATIVISTIC ELECTRON BEAMS

Development of many innovative areas in energy, mechanical engineering, aircraft building and other industries is limited by the strength of materials under the action of temperature gradients. In this regard, the problem appears to find and justify technical means to model a complex of operating conditions. High-current relativistic electron beams reasonably belong to such instruments and means. As a result of their impact, pulsed electric and magnetic fields occur in the irradiated targets, temperature gradients are created, and shock waves are generated. The paper investigates the patterns of change in the internal structure of the blades of gas turbine engines and engineering materials, subjected to the action of an electron beam

Branching of High-Current Relativistic Electron Beam in Porous Materials.

Propagation of high-current relativistic electron beam (REB) in plasma is relevant to many high-energy astrophysical phenomena as well as applications based on high-intensity lasers and charged-particle beams. Here, we report a new regime of beam-plasma interaction arising from REB propagation in medium with fine structures. In this regime, the REB cascades into thin branches with local density a hundred times the initial value and deposits its energy 2 orders of magnitude more efficiently than that in homogeneous plasma, where REB branching does not occur, of similar average density. Such beam branching can be attributed to successive weak scatterings of the beam electrons by the unevenly distributed magnetic fields induced by the local return currents in the skeletons of the porous medium. Results from a model for the excitation conditions and location of the first branching point with respect to the medium and beam parameters agree well with that from pore-resolved particle-in-cell simulations.

Fractal analysis of fractograms of aluminum alloys irradiated with high current electron beam

The aluminum alloys D16 and AMg6 were irradiated using the high-current relativistic electron beam in vacuum. Intense electron irradiation of the materials modified their physical properties. The fractal character of the fracture surfaces’ images was studied. The change of the fractality is a distinguished descriptor of the materials modification. The characteristic ductile and brittle fractures are accompanied by the change of the fractal dimension.

Theoretical and experimental studies of W-band relativistic surface-wave oscillator of planar geometry

This paper presents the results of theoretical and experimental studies of a surface-wave oscillator (SWO) of planar geometry excited by a ribbon high-current relativistic electron beam. Within the framework of the quasi-optical approach and direct three-dimensional particle-in-cell modeling, we demonstrate the advantages of open transverse edged configuration against the closed one for effective mode selection at a fairly large oversize factor. In the experiments carried out on the basis of the SINUKI accelerator (Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, 1 kA/650 keV/17 ns), we form a magnetically guided ribbon electron beam with a cross-section of 0.3 × 20 mm2, which moves parallel to a slow-wave structure with a period of 1.75 mm. A planar W-band SWO both of open and closed edged configuration has been experimentally tested. In full agreement with modeling, the open configuration exhibits much more stable operation, where at a frequency of 75 GHz, we observe pulse generation with duration of about 7 ns. The output power measured by the calorimetric method reaches 25 MW.

Energy efficiency of the high-current diode under the blow-up mode evolution in the anode

The results of experimental studies of energy fluxes released during the diode target blow-up initiated by a high-current relativistic electron beam are presented in the paper. The energy of target explosion products required for realization of the observed diode structural elements deformation is being estimated. Measurements of the target explosion products parameters and finite-element modeling of the mechanical deformation of the cathode system elements show an energy release during the target explosion that far exceeds the energy input.

75 GHz Relativistic Surface-Wave Oscillator of Planar Geometry

We present the results of simulations and experimental studies of a W-band surface-wave oscillator powered by a ribbon high-current relativistic electron beam produced by SINUKI accelerator (IAP RAS, Nizhny Novgorod, 1 kA / 650 keV / 17 ns). Planar geometry of the interaction space facilitates efficient mode selection over wide transverse coordinate by using open waveguide at fairly large oversize factor (the width of the waveguide is ~8 wavelengths). Stable oscillation regime is obtained at frequency of 75 GHz with a pulse duration of about 5 ns. The output power measured by the calorimetric method reaches 25 MW.

MICROSTRUCTURE AND PROPERTY MODIFICATIONS IN SURFACE LAYERS OF A AA6111 ALUMINUM ALLOY INDUCED BY HIGH-CURRENT PULSED RELATIVISTIC ELECTRON BEAM

The processing of the AA6111-T4 aluminum alloy by the high-current relativistic electron beams affects the forming of the surface layer with a modified structure and phase state. The depth of the modified surface layer achieves 200 μm. The changes in microstructure occurring both in the near-surface layer and in the modified layer can be distinguished with XDR, SEM, and EDS analyses. It is established that the aluminum-based supersaturated solid solution makes the main phase of the modified layer, whereas intermetallic phases that were present in the initial state of the alloy are not distinguished by the X-ray methods in the modified layer. There are some available microcracks and craters on the surface of the remelt layer. Discussion of the results of these observations gains a more sufficient understanding of the processes raised by the irradiation by a high-current relativistic electron beam.

Investigation of Transverse Instability of a High-Current Relativistic Electron Beam in a Linear Induction Accelerator

The article presents the results of studies on the transverse instability of a high-current relativistic electron beam developing in a linear induction accelerator LIA for 5 MeV electron energy, which is created at the BINP SB RAS together with RFNC VNIITF. These results were obtained using a software package that makes it possible to simulate the dynamics of the instability development, as well as to calculate the increment of this instability averaged over the accelerator length. The package consists of four main parts. The first of them, made on the base of a three-dimensional model of the accelerating module electrodynamic system of the LIA, allows calculating the main characteristics of electromagnetic dipole modes of such a module, the second and third parts are designed to find three-dimensional accelerating electric and focusing magnetic fields, respectively. In the last part of the package, a system of ordinary differential equations is solved that describes both the motion of beam macroparticles in electric and magnetic fields, including the eigenmode fields, and the excitation of the mode fields by the electron beam. The adequacy of the physical models used in the software package was tested by comparing the spectra of field oscillations in the accelerator modules obtained in calculations and recorded in the experiment. On the base of the data obtained, the main regularities of the transverse beam instability development in the frequency range ∆f = 0.3–1.1 GHz were revealed, and possible methods for suppressing this instability in the LIA were proposed.

Relativistic Sub-THz Surface-Wave Sheet-Beam Amplifier With Transverse Energy Input and Output

We propose a high-power extended interaction klystron (EIK) amplifier exploiting open gratings as surface-wave cavities driven by a relativistic high-current sheet electron beam. For in- and out-coupling of the radiation, an additional subharmonic corrugation with a period twice larger than the period of the grating is proposed. Simulations based on both averaged quasi-optical model and particle-in-cell (PIC) code demonstrate the feasibility of the 150-GHz amplifier with 20–40-MW output power and 20–30-dB linear gain in 1% bandwidth.

Excitation of high cyclotron harmonics in a high-current relativistic gyrotron in the frequency multiplication regime

Using the averaged equations supplemented with 3D particle-in-cells simulation methods, we have studied the frequency multiplication regime in a high-current relativistic gyrotron. The paper shows that the ratio between the output power of the higher (fifth or sixth) harmonics and that of the fundamental cyclotron resonance may be of about 0.1-0.3%. Accordingly, the nonlinear transformation coefficient is several orders of magnitude higher than the values achievable in gyrotrons with weakly-relativistic electron beams. Keywords: gyrotron, harmonic excitation, high-current relativistic electron beams.

Nanoscale Electrostatic Modulation of Mega-Ampere Electron Current in Solid-Density Plasmas.

Transport of high-current relativistic electron beams in dense plasmas is of interest in many areas of research. However, so far the mechanism of such beam-plasma interaction is still not well understood due to the appearance of small time- and space-scale effects. Here we identify a new regime of electron beam transport in solid-density plasma, where kinetic effects that develop on small time and space scales play a dominant role. Our three-dimensional particle-in-cell simulations show that in this regime the electron beam can evolve into layered short microelectron bunches when collisions are relatively weak. The phenomenon is attributed to a secondary instability, on the space- and timescales of the electron skin depth (tens of nanometers) and few femtoseconds of strong electrostatic modulation of the microelectron current filaments formed by Weibel-like instability of the original electron beam. Analytical analysis on the amplitude, scale length, and excitation condition of the self-generated electrostatic fields is clearly validated by the simulations.

The influence of magnetic field on the beam quality of relativistic electron beam long-range propagation in near-Earth environment

In recent years, it has been proposed to use satellite-mounted radio-frequency (RF) accelerators to produce high-current relativistic electron beams to complete debris removal tasks. However, when simulating the long-range propagation (km-range) process of the electron beam, it is difficult to directly use the particle-in-cell method to simultaneously consider the space charge effect of beam and the influence of the geomagnetic field. Owing to these limitations, in this paper, we proposed a simplified method. The ps-range electronic micropulses emitted by the RF accelerator were transmitted and fused to form a ns-range electron beam; then, combined with the improved moving window technology, the model was constructed to simulate the long-range propagation process of the relativistic electron beam in near-Earth environment. Finally, by setting the direction of movement of the beam to be parallel, perpendicular and at an inclination of 3° to the magnetic field, we analyzed and compared the effects of the applied magnetic fields in different directions on the quality of the beam during long-range propagation. The simulation results showed that the parallel state of the beam motion and magnetic fields should be achieved as much as possible to ensure the feasibility of the space debris removal.

Emittance Variation of a High-Current Relativistic Electron Beam in a Bend Magnet

The article presents the investigation results on the main angular divergence sources of a high-current relativistic electron beam when it passes through a real 12° bend magnet of the transport system in the linear induction accelerator (LIA), being developed by collaboration of Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia, and Russian Federal Nuclear Center—Zababakhin All-Russia Research Institute of Technical Physics (RFNC-VNIITF). The main results of the work are the calculated trajectories of the beam electrons, the shape of its cross section, as well as the change in the normalized emittance of the beam as it passes through the region of the bend magnet. It was shown that at typical beam parameters—electron energy of 20 MeV, beam current of 2 kA, and beam radius of 2 cm—the emittance of a high-current relativistic electron beam with uniform current and charge densities after the bend element is determined mostly by the magnet aberrations and much less by the beam self-fields. Optimization of the dipole magnet geometry made it possible to achieve a substantial decrease in the beam emittance with geometric expansion of the magnet in the median plane of the beam.

HIGH-CURRENT RELATIVISTIC ELECTRON BEAM FOCUSING IN PLASMA

The analysis of the envelope equation for high-current relativistic electron beam propagation in plasma in an external uniform magnetic field is presented. The envelope equation is obtained in a Hamiltonian form with an effective potential, which depends from electron beam and plasma parameters, and external magnetic field. Hamiltonian aproach allows fully analyze the behavior of the beam envelope as a function of the beam current, beam energy, plasma density and conductivity, as well as on the external magnetic field and the initial beam angular momentum.

Research on Solenoidal Permanent Magnet for Guiding and Focusing Annular Electron Beams

The vacuum oscillators generally utilize high current annular relativistic electron beams to generate high-power microwaves. The annular electron beams are usually guided and focused by strong axial magnetic fields. A permanent magnet is developed for the application of annular electron beams. The configuration of the permanent magnet is based on the Halbach structure. A new method is proposed to design this solenoidal permanent magnet. The permanent magnet flux source can generate a 0.88 T axial magnetic field at the interaction region and a peak field of 0.94 T. The diameter of its clear bore is 50 mm. The total weight of the permanent magnet is 320 kg. The design, fabrication, and test results are presented in this article.

The features of the structural state and phase composition of the surface layer of aluminum alloy Al-Mg-Cu-Zn-Zr irradiated by the high current electron beam

The structural and phase changes in the surface layer of the 1933 aluminum alloy caused by the irradiation of a high-current relativistic electron beam are studied. The impact of the electron beam leads to the formation of a remelted surface layer with surface relief and microcracks. The structural phase state of this layer is determined by the complex impact of the electron beam and the kinetics of melt crystallization under ultrafast cooling. Via X-ray diffraction studies and the results of energy dispersive X-ray microanalysis it became possible to make a conclusion that submicron sizes of magnesium oxide are present in the remelted layer. MgO inclusions are distributed homogeneously in the remelted layer. The presence of MgO inclusions leads to hardening of the surface layer of the alloy. The nature of formation of MgO during the impact of a pulsed electron beam are discussed

Shadow streak methods for studying the interaction of relativistic electron beams with polymer targets in the high-current generator diode

When a high-current relativistic electron beam interacts with the polymer surface, plasma forms. The results of a plasma dynamics study in vacuum diode using laser shadow photography, including the effect of atypically rapid propagation of the glow, are presented. Experiments were carried out on the high current generator «Calamary». Series of the experiments to study the plasma propagation along the diode axis and in the transverse direction in different cross sections were performed. The results were discussed and possible ways to continue research were considered.

Generation of Terahertz Superradiance Pulses under Stimulated Scattering of Laser Radiation by an Associated High-Current Relativistic Electron Beam

Generation of Terahertz Superradiance Pulses under Stimulated Scattering of Laser Radiation by an Associated High-Current Relativistic Electron Beam