Electron Beam Formation Research Articles

Development of the prototype for the SPARC hard X-ray monitor.

The SPARC tokamak will be equipped with a hard X-ray (HXR) monitor system capable of measuring the bremsstrahlung emission from runaway electrons with photon energies in excess of about 100keV. This diagnostic will detect the formation of runaway electron beams during plasma start-up and inform the plasma control system to terminate the discharge early to protect the machine. In this work, we present a 0D estimate of the HXR emission in SPARC during plasma start-up. Then we discuss the characterization of a prototype of the HXR monitor. The detector mounts a 1 × 1-in.2 LaBr3 inorganic scintillator coupled with a photomultiplier tube and has been tested with γ-ray sources to find its dynamic range. Finally, two possible modes of operation for spectroscopic and current mode measurements on SPARC are proposed.

Assessment of minimal aperture size for a plastic collimator for efficient formation of medical electron beams

Assessment of minimal aperture size for a plastic collimator for efficient formation of medical electron beams

Beam-Plasma Generator of the THz Radiation Based on an Induction Accelerator (LIA-PET Project)

BINP SB RAS together with RFNC-VNIITF carry out a research in the field of creating new sources of electromagnetic radiation in the THz range. Within the framework of this article, a project of the THz beam-plasma generator based on an electron beam generated by a linear induction accelerator is presented. The article provides generator scheme and describes the main elements of the electron beam formation system. In addition, the results of modeling the beam transport and its cross-section compression are presented. These calculations were performed under the current up to 1 kA and energy up to 1 MeV for the subsequent injection of the beam into the plasma section with plasma density up to 1015 –1016 cm–3. The article also contains the analysis of previous experimental studies results which are connected with the beam-plasma interaction for various beam and plasma parameters. Based on this analysis, a requirement for the ratio of the beam and plasma electron densities was formulated. This requirement should be satisfied for creation of the beam-plasma generator of EM radiation for the range of 0.1–1 THz with a pulse power of several MW.

Suprathermal Electron Transport and Electron Beam Formation in the Solar Corona

Electron beams that are commonly observed in the corona were discovered to be associated with solar flares. These “coronal” electron beams are found ≥300 Mm above the acceleration region and have velocities ranging from 0.1c up to 0.6c. However, the mechanism for producing these beams remains unclear. In this paper, we use kinetic transport theory to investigate how isotropic suprathermal energetic electrons escaping from the acceleration region of flares are transported upwardly along the magnetic field lines of flares to develop coronal electron beams. We find that magnetic focusing can suppress the diffusion of Coulomb collisions and background turbulence and sharply collimate the suprathermal electron distribution into beams with the observed velocity within the observed distance. A higher bulk velocity is produced if energetic electrons have harder energy spectra or travel along a more rapidly expanding coronal magnetic field. By modeling the observed velocity and location distributions of coronal electron beams, we predict that the temperature of acceleration regions ranges from 5 × 106 to 2 × 107 K. Our model also indicates that the acceleration region may have a boundary where the temperature abruptly decreases so that the electron beam velocity can become more than triple (even up to 10 times) the background thermal velocity and produce the coronal type III radio bursts.

Integrated Modeling of Runaway Electron Beam Formation in JA DEMO Post-Disruption Plasmas

Integrated Modeling of Runaway Electron Beam Formation in JA DEMO Post-Disruption Plasmas

Impact of Magnetic Focusing on the Transport of Energetic Electrons in the Solar Corona

Observations of Type III radio bursts discovered that electron beams with power-law energy spectra are commonly produced during solar flares. The locations of these electron beams are ~ 300 Mm above the particle acceleration region of the photosphere, and the velocities range from 3 to 10 times the local background electron thermal velocity. However, the mechanism that can commonly produce electron beams during the propagation of energetic electrons with power-law energy spectra in the corona remains unclear. In this paper, using kinetic transport theory, we find for the first time that the magnetic focusing effect governs the formation of electron beams over the observational desired distance in the corona. The magnetic focusing effect can sharply increase the bulk velocity of energetic electrons to the observed electron beam velocity within 0.4 solar radii (300 Mm) as they escape from the acceleration region and propagate upward along magnetic field lines. In more rapidly decreasing magnetic fields, energetic electrons with a harder power-law energy spectrum can generate a higher bulk velocity, producing type III radio bursts at a location much closer to the acceleration region. During propagation, the spectral index of the energetic electrons is unchanged.

Results of the Study of a New Generation Technological Gyrotron System With High Power and Efficiency

A series of work has been carried out to develop a new generation of technological gyrotrons on the first cyclotron harmonic with a radiation frequency of 28 GHz and a power beyond 20 kW. The generation efficiency reaches up to 55% at 6-kW power level without a system of recovery of residual electron energy. The efficiency of the entire setup is about 35% in the mode of maximum radiation power, which is achieved by using a magnetically shielded oil-cooled solenoid. The proper operation of the developed electron-optical system under conditions of a quasi-adiabatic magnetic field in the area of formation of a helical electron beam and a non-adiabatic one in the collector region is confirmed. The letter presents experimental data which is consistent with the results of numerical modeling. This allows us to further count on the implementation of generators up to the W-band frequency range using the magnetic system and high-voltage power sources.

Numerical simulation of cold emission in coaxial diode with magnetic isolation

Due to the emergence and active development of new areas of application of powerful and super-powerful microwave vacuum devices, interest in studying the behavior of ensembles of charged particles moving in the interaction space has increased. An example is an electron beam formed in a coaxial diode with magnetic isolation. Numerical simulation of emission in such a diode is traditionally carried out using particle-in-cell methods. They are based on the simultaneous calculation of the equations of motion of particles and the Maxwell’s equations for the electromagnetic field. In the present work, a new computational approach called the point macroparticle method is proposed. In it, the motion of particles is described by the equations of relativistic mechanics, and explicit expressions are written out for fields in a quasi-static approximation. Calculations of the formation of a relativistic electron beam in a coaxial diode with magnetic isolation are performed and a comparison is made with the known theoretical relations for the electron velocity in the beam and for the beam current. Excellent agreement of calculation results with theoretical formulas is obtained.

Influence of the Foucault Currents on Excitation of the Magnetic Field and Dynamics of Formation of Helical Electron Beams in Pulse Gyrotrons

Influence of the Foucault Currents on Excitation of the Magnetic Field and Dynamics of Formation of Helical Electron Beams in Pulse Gyrotrons

Low-energy electron beam deposition of coatings based on lignin and quercetin, their structure and properties

The peculiar features of electron-beam formation of lignin- and quercetin-based coatings in vacuum have been considered for the first time. Their molecular structure, morphology and antibacterial properties have been studied. Depositing a lignin + quercetin composite coating makes it possible to decrease significantly (more than 4 times) the rate of quercetin release into the aqueous medium. The antibacterial activity of the coatings against the test culture E. coli ATCC 25922 has been studied. The lignin-based coating has been found to have no antibacterial activity. There has been a statistically significant decrease in CFU/ml for a thin layer based on quercetin (more than 13 times) and for a lignin + quercetin composite coating (2 times).

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.

Development of Powerful Spatially Extended W-Band Cherenkov Maser of Planar Geometry With Two-Dimensional Distributed Feedback

A powerful spatially extended planar Cherenkov maser project operating in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band is under development in collaboration between Budker Institute of Nuclear Physics of the Russian Academy of Sciences (BINP RAS) (Novosibirsk) and Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) (Nizhny Novgorod). The ELMI accelerator (1 MeV/5–7 kA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \text{s}$ </tex-math></inline-formula> ) forms a sheet electron beam with the transverse size (width) of up to 18 cm, which serves to drive the oscillator. The electrodynamic system of this Cherenkov maser is based on doubly periodical structure, which combines the properties of a slow wave system that realizes conditions for an effective Cherenkov interaction with a high-current rectilinear sheet electron beam and a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> resonator that implements the mechanism of two-dimensional distributed feedback and provides selective excitation of the operating mode in the strongly oversized interaction space. In this article, the crucial elements and design parameters of the oscillator are discussed, and the results of simulations are presented to demonstrate the possibility of achieving a stable narrow-band generation regime for a transverse system size reaching about 50 wavelengths and a gigawatt output power level. To provide a single-directed output of radiation, a planar Bragg reflector is elaborated for installation at the cathode side of the interaction space. A mode converter formed by a slowly tapered waveguide section for transformation of the radiated wavebeam into a Gaussian-type wavebeam was designed to be installed at the oscillator output. In the electron-optical experiments, the formation of a large-width sheet electron beam with parameters acceptable to drive designed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band Cherenkov maser is demonstrated.

Non-thermal electron velocity distribution functions due to 3D kinetic magnetic reconnection for solar coronal plasma conditions

Magnetic reconnection can convert magnetic energy into kinetic energy of non-thermal electron beams. Those accelerated electrons can, in turn, cause radio emission in astrophysical plasma environments, such as solar flares via micro-instabilities. The properties of the electron velocity distribution functions (EVDFs) of those non-thermal beams generated by reconnection are, however, still not well understood, in particular, properties that are necessary conditions for some relevant micro-instabilities. We aim at characterizing the EVDFs generated in 3D magnetic reconnection by means of fully kinetic particle-in-cell code simulations. In particular, our goal is to identify the possible sources of free energy offered by the generated EVDFs and their dependence on the strength of the guide field. By applying a machine learning algorithm on the EVDFs, we find that (1) electron beams with positive gradients in their 1D parallel (to the local magnetic field direction) velocity distribution functions are generated in both diffusion region and separatrices. (2) Electron beams with positive gradients in their perpendicular (to the local magnetic field direction) velocity distribution functions are observed in the diffusion region and outflow region near the reconnection midplane. In particular, perpendicular crescent-shaped EVDFs (in the perpendicular velocity space) are mainly observed in the diffusion region. (3) As the guide field strength increases, the number of locations with EVDFs featuring a perpendicular source of free energy significantly decreases. The formation of non-thermal electron beams in the field-aligned direction is mainly due to magnetized and adiabatic electrons, while in the direction perpendicular to the local magnetic field, it is attributed to unmagnetized electrons.

Multi-layer structure formation of relativistic electron beams in plasmas

A two-dimensional electromagnetic particle-in-cell simulation model is proposed to study the density evolution and collective stopping of electron beams in background plasmas. We show here the formation of the multi-layer structure of the relativistic electron beam in the plasma due to the different betatron frequency from the beam front to the beam tail. Meanwhile, the nonuniformity of the longitudinal wakefield is the essential reason for the multi-layer structure formation in beam phase space. The influences of beam parameters (beam radius and transverse density profile) on the formation of the multi-layer structure and collective stopping in background plasmas are also considered.

Influence of the Foucault Currents on Excitation of the Magnetic Field and Dynamics of Formation of Helical Electron Beams in Pulse Gyrotrons

Influence of the Foucault Currents on Excitation of the Magnetic Field and Dynamics of Formation of Helical Electron Beams in Pulse Gyrotrons

DYNAMICS OF AN ELECTRON BEAM FORMED BY MAGNETRON GUN WITH THE SECONDARY EMISSION CATHODE IN THE DECLINING MAGNETIC FIELD OF SOLENOID: EXPERIMENT AND SIMULATION

The article presents the results of research and calculations on the formation of a radial electron beam by a magnetron gun with a secondary emission cathode in the electron energy range 35...65 keV and measuring its parameters during transportation in the total decreasing magnetic field of thesolenoid and the stray field of permanent magnets. The beam was transported in a system consisting of copper rings with an inner diameter of 66 mm,located at a distance of 85 mm from the exit of the magnetron gun. The dependence of the beam current on the amplitude and gradient of the fielddecay has been studied. The studies carried out have shown the possibility of stable formation of a radial electron beam with an energy of tens of keVin the decreasing magnetic field of the solenoid. By optimizing the distribution of the magnetic field (created by the solenoid and ring magnets) and itsdecay gradient, it is possible to achieve an increase in the incident of electrons on one ring (up to ~72% of the beam current). On the basis of themathematical model of the movement of the electron flow, a software tool has been synthesized that makes it possible to obtain and interpret thecharacteristics of the resulting flows. The obtained numerical dependences are in satisfactory agreement with the experimental results for a magneticfield with a large decay gradient. Various configurations of the magnetic field are considered. Solutions to the direct problem of modeling electrontrajectories for given initial conditions and parameters are obtained. Various configurations of the magnetic field are considered. It is shown that forthe selected initial conditions for the electron beam and the distributions of the longitudinal magnetic field along the axis of the gun and the transportchannel, the electron flux falls on a vertical section, the length of which is on the order of a millimeter. Thus, by changing the amplitude anddistribution of the magnetic field, it is possible to control the current in the radial direction along the length of the pipe, and, therefore, the place of theelectron irradiation.

Suppression of parasitic secondary emission in a magnetron-injection gun of a 24-GHz technological gyrotron

This article analyzes the ways of reducing the parasitic emission current in the electron beam formation system of a technological gyrotron. The operation of the magnetron-injection gun in the quasi-critical mode and the profiling of the cathode can significantly reduce the space charge of electrons captured in a magnetic trap between the gun and the entrance to the gyrotron working space. The calculated electron-gun configurations improve the beam quality, especially in the regimes with a high pitch factor.

Modeling the complete prevention of disruption-generated runaway electron beam formation with a passive 3D coil in SPARC

The potential formation of multi-mega-ampere beams of relativistic ‘runaway’ electrons (REs) during sudden terminations of tokamak plasmas poses a significant challenge to the tokamak’s development as a fusion energy source. Here, we use state-of-the-art modeling of disruption magnetohydrodynamics coupled with a self-consistent evolution of RE generation and transport to show that a non-axisymmetric in-vessel coil will passively prevent RE beam formation during disruptions in the SPARC tokamak, a compact, high-field, high-current device capable of achieving a fusion gain Q > 2 in deuterium–tritium plasmas.

Influence of electron emission on operation of a constricted arc discharge in a pulsed forevacuum plasma-cathode electron source

The research of influence of electron emission and processes associated with the formation of a pulsed large-radius electron beam on operation of a constricted arc discharge, which forms emission plasma in a forevacuum plasma-cathode electron source, is presented. Processes, occurring in case of generation of the electron beam at forevacuum pressure range 3–20 Pa, provide lower operating voltage of the constricted arc discharge. The constricted arc voltage decreases with increasing pressure and increasing accelerating voltage. However, at pressure more than 15 Pa, the arc voltage decreases until a certain minimum value is reached, and then arc voltage is almost independent on pressure and accelerating voltage. This minimum value of the constricted arc voltage is on average 1.5–2 times higher as compared with voltage of the cathodic arc at the same discharge current. The observed decrease of operating voltage of the constricted arc is most likely caused by accelerated back-streaming ions, which move toward the emission electrode from beam-produced plasma. These accelerated ions partially penetrate into the hollow anode of discharge system through the mesh emission electrode and facilitate formation of the arc plasma, and thus provides lower voltage of the constricted arc.

LONGITUDINAL TRAP OF ELECTRON BEAM IN POTENTIAL PIT MAGNETIC SOLENOIDAL FIELD

A two-mode cylindrical magnetic field is considered, the potential of which has a minimum. The object of this work is the study of the parameters of an electron beam when it moves in a solenoid field with the longitudinal trap formed by the magnetic field, and the construction of the computational model of the motion of an electron beam. The problem is posed of the stability of the motion of electrons in such solenoid magnetic field. The possibility of obtaining oscillatory modes of particle motion has been studied. It was found that for oscillations of particles with an energy of tens of kiloelectronvolts in the potential well in a well, the field with the amplitude of tens of thousands of Oersteds is required. For the solenoid magnetic field of the solenoid, the formation of electron beam with an energy of 55 keV in the longitudinal and radial directions during its transportation is studied. A section of a magnetron gun was used as the physical object. One possible direction is to combine the two matched magnetic systems of the gun to create the potential magnetic field well. It is shown that, for the chosen conditions, the motion of electrons can be associated with the model of three-dimensional oscillations. In this work, on the basis of the Hamiltonian formalism of the motion of electrons in a magnetic field and an algorithm for numerically finding solutions to the differential equations of dynamics, a software tool is constructed that allows one to obtain arrays of values of particle trajectories in the volume. The use of the software made it possible to simulate the main dependences of the motion of the electron beam in a given two-mode solenoid magnetic field. The results of numerical simulation of electron trajectories in the gradient magnetic field with the point secondary emission cathode located in the middle of the system are presented. The formation of the beam with energy of 55 keV in the radial and longitudinal directions during its transportation in a solenoid magnetic field with a large gradient is considered. For significant time intervals, the possibility of three-dimensional oscillations is shown and the operating modes of the magnetic system are obtained, in which the particle undergoes stable three-dimensional oscillations. The influence of the initial conditions during emission on the occurrence of the reciprocating oscillatory effect has been studied. It is shown that for a given electron energy and fixed magnetic field, the parameter that determines the reflection of a particle, is the polar angle of entry relative to the axis of the cylindrical magnetic field. The dependence of the formation of the final distribution of particles on the amplitude and gradient of the magnetic field along the axis of the system is investigated. The results of numerical simulation on the motion of the electron flow are presented. The characteristics of the resulting electron beam are considered on the basis of a model of electron flow motion. The obtained simulation results show that it is possible to establish the phenomenon of oscillatory-return longitudinal motion under experimental conditions.&#x0D; Keywords: electron beam, magnetron gun, three-dimensional oscillations, electron dynamics, gradient magnetic field, mathematical modeling.