Electron Optical System Research Articles

Electron-optical system for a high-current Ka-band relativistic gyrotron

An electron-optical system for a high-current relativistic Ka-band gyrotron was developed and experimentally tested. The system consists of a coaxial magnetically insulated diode forming a rectilinear hollow beam and an additional short coil (kicker) pumping the transverse electron velocities. An electron beam with a particle energy of 500 keV, a current of 1.5–2 kA, and a pitch-ratio of up to 1 has been produced. The beam is intended for a gyrotron with the output power of 200 MW. The measured beam characteristics are in good agreement with the results of calculations. The influence of the beam and gyrotron cavity axis misalignment on gyrotron operation is analyzed using PIC simulations.

Miniaturized Electron Optic Tracking System On Aerostat

In this paper, a miniaturized electron optic tracking system (EOTS) is proposed to improve the disturbance suppression performance when attached to near space aerostat. The electron optic tracking system, widely used in moving platforms can isolate the movement of the carrier and has high stability accuracy. However, the payload weight is limited for near space aerostats. The miniaturization of EOTS can effectively improve load distribution. To satisfy the demand of lightweight, micro-electro-mechanical system (MEMS) accelerometer is used in EOTS instead of fiber-optic gyroscopes (FOG). This paper employs position and acceleration double close-loop control method with MEMS linear accelerometer to improve the system performance especially in medium frequency. Meanwhile the disturbance observer (DOB) is introduced to suppress the measurably external disturbance. Furthermore, the disturbance performance of the EOTS is verified by MATLAB/Simulink. The results show that the improved miniaturized system can increase the payload of the aerostat effectively when the total load is limited.

Three-dimensional nonadiabatic electron- optical gyrotron systems with inhomogeneous current density

The results of a numerical study of the effect of threedimensional perturbations of the space charge density distribution in a nonadiabatic electron-optic systems of gyrotrons are presented. Data of direct numerical simulation using the 3-D program CST Studio Suite are described.

Performance improvement of a sub-THz traveling-wave tube by using an electron optic system with a converging sheet electron beam

Abstract Many applications, such as high-data-rate wireless communications, spectroscopy, high-resolution radar, biomedical imaging, security, etc. require compact high-power sources of sub-THz radiation. Traveling wave tube (TWT) amplifiers are the most promising candidates for such sources combining 10–100 W power and wide bandwidth. Here we present the results of design and simulation of a 0.2-THz TWT with a grating slow-wave structure (SWS) and electron-optical system (EOS) with a converging sheet electron beam. The designed EOS provides substantial improvement of the amplifier performance as compared with the EOS with straight beam immersed in a uniform magnetic field. In particular, it facilitates beam focusing and allows reduce of the focusing magnetic field and cathode current density. The latter allows increase of lifetime and makes possible operation in a continuous-wave mode. In addition, decrease of the beam thickness allows reduce of the beam tunnel height accordingly, which leads to nearly 2.5-times increase of the Pierce coupling impedance resulting in increase of gain and decrease of the required driving power. The simulation predicts small-signal gain over 30 dB in 180–200 GHz frequency band and over 80 W saturated power.

Synthesis of Electron-Optical Systems with Compression of Sheet Beam for Terahertz TWTs

Electron-optical systems are synthesized to form a converging sheet electron beam with a compression of 15 and 20, a cross section of 0.05 × 2 mm, and a current density of 100 A/cm2 in the presence of complete magnetic shielding of field-emission cathode. Deformation of low-perveance flux in the presence of magnetic field in the drift tunnel of slow-wave structure is analyzed with the aid of 3D computer simulation of the electron-optical system with the sheet electron beam.

Electron-Optical Systems with a Shielded Cathode and an Elliptical Ribbon Beam

Abstract—Based on the theory of high-density electron flows with the elliptical current tubes, a model of a ribbon beam from a shielded cathode in the case of emission in the ρ mode has been built. Algorithms of formation of high-compression flows passing into the Brillouin mode without oscillations with preserved elliptical cross section not rotated or strained have been developed.

The reaction of arc discharge parameters to the selection of electrons from the emission plasma in an electron accelerator with a grid plasma cathode

In the electrode system of an electron source with a plasma cathode, which allows the generation of a pulse-periodic electron beam of a large cross section from vacuum to the atmosphere through the outlet foil window, investigations have been made of the effect of electron extraction from the emission plasma on the parameters of a low-pressure arc discharge in which this plasma is generated. The work of the plasma cathode in different modes of electron beam generation is compared, namely, with the use of both a wide-aperture two-electrode electron-optical system (EOS) characterized by high beam current losses on the ribs of the support grid and a multi-aperture two-electrode EOS, when a metal mask is installed on the emission mesh with a configuration of holes that repeats the configuration of the holes in the support grid, and the electron beam is a superposition of electron beamlets formed by separate emission structures, the plasma boundary of which is also stabilized by a fine-structure metal mesh. Under the experimental conditions, the selection of electrons from the emission plasma leads to an increase in the voltage in the interelectrode gap between the cathode and the hollow anode of the plasma emitter, whose “voltage-addition” depends on the conditions of generation of the emission plasma (pressure and type of working gas, the ratio of the anode area of the discharge to the emission area), the area of the emission structures and the cell size of the used emission grid.

Numerical model of EOS with large-area plasma cathode with mesh stabilization of the emission plasma boundary

The source of electrons that generates a beam of a large cross section (BLCS) with the beam release into the atmosphere through a thin metal foil has been developed in the IHCE SB RAS. The electronic BLCS in this case is a superposition of elementary beams formed by separate emission structures. Their plasma boundary is stabilized by a fine-grained metal mesh, covered by a mask with round holes. The configuration of holes repeats the configuration of the holes in the support grid of the outlet foil window having a slightly larger diameter. In preliminary experiments, the maximum current-to-atmosphere output coefficient reached ∼70% of the current in the accelerating gap. The objective of this paper is to select a numerical model of the electron-optical system (EOS) for computer simulation and analysis of the characteristics of the formed elementary beams for further optimization of the source and increase the efficiency of beam extraction into the atmosphere.

Analysis of the Methods of Discrete and Smooth Frequency Tuning in Gyrotrons for Spectroscopy, on the Example of a Generator Operated in the 0.20–0.27 THz Frequency Range

We consider the main features of a low-power frequency-tunable gyrotron with an oversized cavity, which is designed for the purposes of nuclear magnetic resonance spectroscopy and other applications and operates in the 0.20–0.27 frequency range producing an output power of 200 W. We study the possibilities of wideband output frequency tuning by exciting a sequence of modes with similar caustics using magnetic-field variations and smooth tuning due to the excitation of modes with a great number of longitudinal variations. Aiming at widening the frequency tuning range, we also analyzed the possibility of smooth frequency tuning determined by controlled variations of the cavity temperature. Specific features of the electron-optical system of such a gyrotron is discussed, along with the possibility of increasing its efficiency by means of single-stage recovery of the residual energy of the electron beam.

Modeling of an Electron-Optical System with Converging Sheet Beam for a Traveling Wave Tube of Terahertz Frequency Range

A converging sheet electron beam with a cross section of 0.05 × 2 mm and current density of 200 A/cm2, which is formed by an electron gun, is modeled using the synthesis and analysis methods at the condition of magnetic shielding of the cathode. The deformation in the cross section of the beam in the focusing magnetic field is analyzed based on a computer three-dimensional model of an electron optical system with a sheet electron beam. The current-voltage characteristic of an electron gun is studied experimentally in the pulse mode. A collector current of 200 mA is obtained with the beam thickness being 70 μm.

Design of compact ultrafast microscopes for single- and multi-shot imaging with MeV electrons

Ultrafast high-energy electron microscopy, taking advantage of strong interaction of electrons with matter while minimizing space charge problems, can be used to address a wide range of grand challenges in basics energy sciences. However, MeV-electron lenses are inherently bulky and expensive, preventing them from acceptance in a broad scientific community. In this article, we report our novel design of a compact, low-cost imaging-lens system for MeV-electrons based on quadrupole multiplets, including triplet, quadruplet and quintuplet, both symmetric and asymmetric. We compare optical performance of quadrupole-based condenser, objective and projector lenses with that of the traditional round-lenses and discuss the strategy for their practical use in constructing MeV-electron microscopes for high spatial and temporal resolution single- and multi-shot imaging. Combining the compound electron-optical system with a photocathode radiofrequency (RF) gun, such a MeV electron microscope can be fit into a small-sized laboratory for ultrafast observations and measurements.

Development of Electron Optics System for "ETHOS" High-Performance FIB-SEM

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Possibility of Effective High-Frequency Generation in Low-Voltage Gyrotrons at the Second Cyclotron Harmonic

Despite the high theoretical values of the electron efficiency of the subterahertz gyrotrons working at cyclotron harmonics at low operating voltages, the achievement of acceptable output power levels in such devices is a significant challenge due to the mode competition, the necessity of producing an electron beam with a high current, high ohmic losses in the walls, and the required high accuracy of cavity manufacturing. To solve these problems, we analyze thoroughly variants of low-voltage gyrotrons with conventional cavities and the recently proposed variant of the sectioned cavity, and present a calculation of the electron-optical system for such cavities. It is shown that by ensuring micrometer accuracy of cavity manufacturing at a low operating voltage (5 kV), it is possible to achieve output efficiencies of up to 5% and a power of up to 100 W at frequencies of about 0.4 THz and higher at the second cyclotron harmonic.

OPTIMAL VOLTAGE PROFILE FOR HEMISPHERICAL DEFLECTOR ENERGY ANALYZERS USING GENETIC ALGORITHM

In this study, the genetic algorithm (GA) method is used to optimize the hemispherical deflector analyzer, which can analyze according to the energies of charged particles. The GA inspired by evolutionary codes consists of the population of individuals. At each step, the GA, selects the population individuals as parents and uses them to produce children for the next generation. Thus throughout generations, the population evolves to an optimal solution. The purpose of this study is to achieve the best voltage profile for the 180° hemispherical energy analyzers through the voltage equations of the energy analyzer. The best voltage values ​​for the 180˚ hemispherical deflector analyzer, which is the most used analyzer in experimental studies, are found with high accuracy in this study. Optimization of a complex electron optical system, such as an analyzer system with a GA, has been achieved using voltage equations and has been found to work very well given the difficulty of the problem. In contrast to other techniques in the literature, the best voltage profile is obtained in a short time by means of the proposed GA method.

Influence of Perturbations in the Axial Symmetry on Formation of Helical Electron Beams in a System with the Reversed Magnetic Field

We perform three-dimensional numerical simulation of the electron-optical system (EOS) with the reversed magnetic field, which is designed for a large-orbit gyrotron (GBO) operated in a wide frequency range of 0.26–0.65 GHz, within the framework of a static model and analyze the influence of perturbations in the axial symmetry of electrodes and the magnetic field on the parameters of the axis-encircling electron beam. It is shown that the most significant perturbation of the parameters of the helical electron beam (HEB) is determined by the radial displacement of the cathode and the tilt of the cathode coil, which ensures the reversal of the magnetic field. Analytical estimations are presented, which allow determining the corresponding margins for the development of such systems.

Formation and focusing of converging sheet electron beam based on field emission

The development of compact amplifiers with an average power of the frequency range 0.2–0.3 THz is related to the design of electron-optical systems using converging sheet beams that allow obtaining sufficiently high current densities with a lower current load on the cathode and with a lower value of the magnetic field. Based on the theory of synthesis the numerical simulation results for electron-optical systems for the formation of a converging sheet electron beam are presented. Reduction of the current load on the cathode allows the principle of transformation of a cylindrical electron beam into a sheet by employing electrostatic compression of the beam in one plane. A sheet beam electron-optical system with a field emission cathode with convergence of 10, and with the beam of 0.1 × 1.1 mm2 and current density of 45 A/cm2 has been performed. The electron gun employing the cathode–gate structure with diameter of 1 mm has an emitting current up to 10 mA in experiment. The modulation coefficient of the cathode current for a gun with a sheet electron beam has 0.3% of the anode potential.

Development of a 0.32-THz Folded Waveguide Traveling Wave Tube

A traveling wave tube amplifier operating above 300 GHz based on folded waveguide (FWG) slow-wave structure is presented in this paper. The design and test results of key components are presented, including FWG slow-wave structure, electron optic system, and RF windows. The FWG slow-wave structure of this prototype tube was fabricated by the high-speed precision milling technology; the dimension tolerance achieves $\pm 5~\mu \text{m}$ , and fabricated surface roughness achieves 300-nm Ra. This amplifier demonstrates over 130 mW of maximum output power and 19.6 dB of small-signal gain at 318.24 GHz from a 16.9-kV, 16-mA electron beam with a duty cycle of 10%. The operation voltage rising induced by fabrication errors is also discussed.

Automated electron-optical system optimization through switching Levenberg–Marquardt algorithms

In the current study, we demonstrate an automated optimization method based on the Levenberg–Marquardt algorithm for electron-optical systems, incorporating an adaptive merit function switching process that enhances minimization convergence. The algorithm is successfully applied to three energy spectrometer designs—a radial mirror analyzer, a parallel radial mirror analyzer, and a parallel magnetic sector analyzer—by first implementing practical modifications to the device geometries. We then optimize the key design parameters to yield good focusing optics. The robustness of the method towards starting configuration is also demonstrated. The procedure can greatly enhance efficiency in the design process of electron-optical systems.

2D imaging X-ray diagnostic for measuring the current density distribution in a wide-area electron beam produced in a multiaperture diode with plasma cathode

A simple and inexpensive X-ray diagnostic tool was designed for measuring the cross-sectional current density distribution in a low-relativistic pulsed electron beam produced in a source based on an arc-discharge plasma cathode and multiaperture diode-type electron optical system. The beam parameters were as follows: Uacc = 50–110 kV, Ibeam = 20–100 A, τbeam = 0.1–0.3 ms. The beam effective diameter was ca. 7 cm. Based on a pinhole camera, the diagnostic allows one to obtain a 2D profile of electron beam flux distribution on a flat metal target in a single shot. The linearity of the diagnostic system response to the electron flux density was established experimentally. Spatial resolution of the diagnostic was also estimated in special test experiments. The optimal choice of the main components of the diagnostic technique is discussed.

Electron diffraction covering a wide angular range from Bragg diffraction to small-angle diffraction.

We construct an electron optical system to investigate Bragg diffraction (the crystal lattice plane, 10-2 to 10-3 rad) with the objective lens turned off by adjusting the current in the intermediate lenses. A crossover was located on the selected-area aperture plane. Thus, the dark-field imaging can be performed by using a selected-area aperture to select Bragg diffraction spots. The camera length can be controlled in the range of 0.8-4 m without exciting the objective lens. Furthermore, we can observe the magnetic-field dependence of electron diffraction using the objective lens under weak excitation conditions. The diffraction mode for Bragg diffraction can be easily switched to a small-angle electron diffraction mode having a camera length of more than 100 m. We propose this experimental method to acquire electron diffraction patterns that depict an extensive angular range from 10-2 to 10-7 rad. This method is applied to analyze the magnetic microstructures in three distinct magnetic materials, i.e. a uniaxial magnetic structure of BaFe10.35Sc1.6Mg0.05O19, a martensite of a Ni-Mn-Ga alloy, and a helical magnetic structure of Ba0.5Sr1.5Zn2Fe12O22.