Electron Optical System Research Articles

Electron gun with an auto-emission cathode based on carbon nanotubes for a powerful millimeter-range extended interaction klystron

The possibilities of using auto-emission cathode-grided module in an electron-optical system of extended interaction klystron of the millimeter wavelength range are investigated. The results of a theoretical analysis of the developed design of an electron gun with high compression ratio are presented. The limits of the angular spread of electrons on the grid, which ensures the complete electron beam transmission through the interaction system of the device, are determined.

A Novel Efficient Computational Method for the Electron Optics System in Multibeam Klystrons With Applications to Manufacturing Sensitivities

A Novel Efficient Computational Method for the Electron Optics System in Multibeam Klystrons With Applications to Manufacturing Sensitivities

Research on electronic optical monitoring technology and system design for vacuum electron beam welding process

Electron beam welding technology is increasingly used in industrial manufacturing due to its high power density and the purity of welded joints. In vacuum environments, traditional optical and machine vision monitoring methods are susceptible to contamination by metal vapors, which hinders the monitoring effect. Due to the limitations of optical monitoring methods, electronic optical imaging technology is a new alternative monitoring method that has been introduced into the electron beam processing in recent years, but the complexity of the industrial electron beam welding environment makes it relatively less studied in the field of electron beam welding. In this study, a YAG scintillator detector is proposed to collect the backscattered electron information generated by the interaction of electrons with the sample, and an FPGA real-time processing system is used to realize the weld quality monitoring in the industrial electron beam welding processes. The distribution law of backscattered electrons in space is simulated by Monte Carlo method, and the results show that the number of distribution in the 40°∼60° angle region is more, the backscattering coefficient increases with the increase of the incident angle of the electron beam, and the backscattering coefficient of the samples with large atomic numbers is relatively high. The field monitoring experiments show that the designed system exhibits good sensitivity to the characteristic morphology, and the imaging resolution reaches more than 200 μm, and the weld hole defects are clearly visible. A good linear correlation between the current change curve during scanning and the actual shape profile is shown, while the image resolution is better when the spot current is 1 mA.

Mathematical modelling of the emission characteristics of a field electron cathode in a scanning electron microscope under biosampling conditions

Currently, the use of electron microscopes in medicine is developing intensively, including scanning electron microscopes (SEM), which are designed to solve a huge number of problems in various fields with a wide range of electron accelerating voltages and electron beam energies. The development of an SEM with certain emission characteristics, with a range of lower beam energies for the study of biological samples, is an urgent task because modifying the SEM to solve problems in medicine, for example, would make it possible to obtain higher-quality images of biospecimens for diagnostics and monitoring the effectiveness of therapy. To develop new SEMs with certain characteristics, it is proposed to conduct less expensive research using numerical methods based on mathematical models of processes in electron-optical SEM systems. In this regard, this work sets the task of determining the size and shape of the beam, the main emission characteristics of the field electron cathode (FEC) of the SEM, which is under the influence of the electric field that excites electron emission and the external longitudinal magnetic field by studying the movement of the outermost electron of the beam, taking into account the influence of space charge beam electrons, external magnetic field. In the model, the FEC is approximated by a paraboloid of rotation, and the concept of a boundary “outermost” electron is introduced, the trajectory of which determines the shape and size of the beam. The problem of calculating the emission characteristics along the trajectory of the outermost electron of a FEC is solved using a mathematical model that includes the following equations: motion of the “outermost” electron, Maxwell outside and inside the beam, continuity of the current density, Fowler-Nordheim equation. As a result, a system of 18 first-order ordinary differential equations was obtained, the numerical calculation of which using the 4th order Runge-Kutta method allows us to obtain the emission characteristics of the FEC. As a result, it is suggested that it would be feasible to modify SEMs for more effective use in the medical field, taking into account their increasing use in disease diagnosis and the possible improvement of image quality through the development of FEC SEMs with more suitable characteristics.

Nonadiabatic effects in the electron-optical system of a relativistic millimeter-wave gyrotron

Gyrotrons based on relativistic electron flows generated by thermionic magnetron injection guns are promising pulsed sources of millimeter and submillimeter radiation with multi-megawatt output power. Obviously, to increase the output power of such devices, it is necessary to provide a high beam current of more than 100 A. At the selected emission density, this forces the use of an emitter with a sufficiently large area. As is well known, wide emitters produce beams with a large velocity spread, which reduces the efficiency of the electron-wave interaction. Therefore, it is necessary to increase the diameter and, accordingly, increase the distance from the cathode to the gyrotron cavity, which leads to an increase in the magnetization reversal coefficient. Thus, the magnetic field in the region of beam formation becomes weak, and the Larmor radius and the turn pitch of the electron trajectory become large compared to the geometry of the surrounding electrodes, which can cause nonadiabatic effects. In this work, we consider one of these effects, which consists in the emergence of a range of anode voltage values in which the monotonic growth of the pitch factor stops. The results of trajectory analysis using current tube and discrete source methods based on the ANGEL software package are presented, as well as an assessment of the influence of a magnetic lens on the properties of an electron beam based on a simple analytical model.

Measurement uncertainty analysis of centering error of pyroelectric infrared sensor module

Pyroelectric Infrared (PIR) Sensor Modules which are widely used in order to detect heating sources passing their field of views, are non-imaging electronic optical (EO) systems, in which the output is considered to be random signal over time. Specifying optical axis position of such system is certainly essential and challenging. This paper presents the uncertainty analysis of a measurement of centering error of the PIR sensor module that is conducted in a setup using a modulated infrared radiating source. The analysis helps point out specific parameters, such as, the difference between background temperature and heating source temperature; modulating frequency, etc., which have greatest effect on the measurement accuracy of such EO system.

Atomic-level imaging of beam-sensitive COFs and MOFs by low-dose electron microscopy.

Electron microscopy, an important technique that allows for the precise determination of structural information with high spatiotemporal resolution, has become indispensable in unravelling the complex relationships between material structure and properties ranging from mesoscale morphology to atomic arrangement. However, beam-sensitive materials, particularly those comprising organic components such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), would suffer catastrophic damage from the high energy electrons, hindering the determination of atomic structures. A low-dose approach has arisen as a possible solution to this problem based on the integration of advancements in several aspects: electron optical system, detector, image processing, and specimen preservation. This article summarizes the transmission electron microscopy characterization of MOFs and COFs, including local structures, host-guest interactions, and interfaces at the atomic level. Revolutions in advanced direct electron detectors, algorithms in image acquisition and processing, and emerging methodology for high quality low-dose imaging are also reviewed. Finally, perspectives on the future development of electron microscopy methodology with the support of computer science are presented.

Recent Development of Lens Array Fabrication: A Review

The lens array is a multi-functional optical element, which can modulate the incident light such as diffusion, beam shaping, light splitting, and optical focusing, thereby achieving large viewing angle, low aberration, small distortion, high temporal resolution, and infinite depth of field. Meanwhile, it has important application potential in the form, intelligence and integration of op-to electronic devices and optical systems. In this paper, the optical principle and development history of lens arrays are introduced, and the lens array fabrication technologies such as ink jet printing, laser direct writing, screen printing, photo lithography, photo polymerization, hot melt reflow and chemical vapor deposition are reviewed. The application progress of lens arrays in imaging sensing, illumination light source, display and photovoltaic fields is presented. And this paper prospected the development direction of lens arrays, and discussed the development trends and future challenges of new directions such as curved lenses, superimposed compound eye systems, and the combination of lenses and new op-to electronic materials.

Non-adiabatic Non-axisymmetric Electron-Optic Systems for Multi-mirror and Multi-barrel Gyrotrons

Non-adiabatic Non-axisymmetric Electron-Optic Systems for Multi-mirror and Multi-barrel Gyrotrons

First Experimental Studies of the High-Power Relativistic Ka-Band Gyrotron with Beam Compression in the Electron-Optical System

First Experimental Studies of the High-Power Relativistic Ka-Band Gyrotron with Beam Compression in the Electron-Optical System

Demonstration of a 263-GHz Traveling Wave Tube for Electron Paramagnetic Resonance Spectroscopy.

In this letter, a 263 GHz traveling wave tube for electron paramagnetic resonance spectroscopy is designed, fabricated and tested. A periodic permanent magnet focused pencil beam electron optical system is adopted. A folded waveguide slow-wave structure with modified serpentine bends is optimized to provide high-power wideband performance and stable operation. An experiment has been performed to verify the analysis results and confirm the amplifier stability. The device provides a maximum 11.9 W saturation output power and 25.5 dB saturation gain. Although the available solid-state signal source is unable to drive the amplifier to saturation beyond 260 - 264 GHz, 10 W output power over 5.6 GHz bandwidth has been measured.

Electron Flows Formed by Electron-Optical Systems Using Composite Field Emitters Made of Thermally Expanded Graphite and Diamond–Graphite Mixtures

Electron Flows Formed by Electron-Optical Systems Using Composite Field Emitters Made of Thermally Expanded Graphite and Diamond–Graphite Mixtures

2D calculation of parasitic fields in misaligned multipole electron-optical systems

The effects of geometrical imperfections in electron-optical components are usually evaluated in 3D simulations. These calculations inherently take a long time, require a large amount of memory, and do not directly produce the necessary axial field functions. We present a 2D perturbation method to calculate parasitic fields in misaligned multipole systems. Our method is based on finding an equivalent potential perturbation, similarly to Sturrock’s method, but does not rely on the potential being differentiable. The method is directly applicable to both electrostatic and non-saturated magnetic problems. It does not require any 3D data and it is fully compatible with existing finite element method codes such as EOD. The proposed method produces axial field functions with an accuracy of units to a few tens of percents, depending on the number of unperturbed multipole field components used and the geometry. The results can then be used, for instance, to determine the parasitic imaging aberrations of the misaligned optical system using standard methods, in order to evaluate the effect of mechanical design tolerances.

Ultracoherent Single-Electron Emission of Carbon Nanotubes.

A single-electron emitter, based on a single quantized energy level, can potentially achieve ultimate temporal and spatial coherence with a large emission current, which is desirable for atomic-resolution electron probes. This is first developed by constructing a nano-object on a metal tip to form a quantized double barrier structure. However, the single-electron-emission current can only achieve a picoampere level due to the low electron tunneling rate of the heterojunction with large barrier width, which limits the practical applications. In this study, carbon nanotubes (CNTs) serve as a single-electron emitter and a current up to 1.5nA is demonstrated. The double barrier structure formed on the CNT tip enables a high tunneling rate (≈1012 s-1 ) due to the smaller barrier width. The emitter also shows high temporal coherence (energy dispersion of ≈10meV) and spatial coherence (effective source radius of ≈0.85nm). This work represents a highly coherent electron source to simplify the electron optics system of atomic-resolution electron microscopy and sub-10nm electron beam lithography.

Design and Experimental Demonstration of a Circular Beam Electron Gun and a PPM System for D-Band TWTs

In this article, we present a design scheme of an electron-optical system (EOS) for terahertz vacuum electron amplifiers. The performance characteristics are studied by simulation, and the feasibility is verified by transmission experiment. Based on the Pierce design method, an electron gun with an isolated beam focus electrode (BFE) is designed, which has been simulated and confirmed by CST particle tracking solver and OPERA charged particle solver. A periodic permanent magnet (PPM) system including dual D-magnets of RF signal coupling port is utilized for focusing beam transportation in the 0.15-mm-radius tunnel. The experimental results of the magnetic field are in good agreement with the simulation results. The simulation results show that the beam-focusing system with the axial peak magnetic field of 5.2 kGs can confine the electron beam within the beam tunnel. Additionally, the EOS is successfully developed and used in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> -band folded waveguide traveling-wave tube (TWT). The experimental results of electron transmission show that the thermionic cathode with a cathode load of 5 A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> can provide a beam current of 56 mA, and 90% beam current is transmitted through the beam tunnel to the collector.

The Research on the High-Current-Density Shielded Sheet Electron Beam Matching Focusing Magnetic Field

Increasing beam current density is a very effective approach to boost the output power in millimeter wave and terahertz vacuum devices. However, the current density of sheet electron beam (SEB) is severely limited, due to instabilities in the SEB transport, especially in the case of high current density. To overcome this limitation, a new approach for stably transporting a high-current-density SEB, named shielded SEB matching focusing magnetic field (shielded SEB-MFM), is presented in this article. This new focusing magnetic field consists of a small transverse magnetic field and a conventional shielded uniform magnetic field (shielded UM). Compared with the conventional shielded UM, about double the maximum beam current density can be transported by the shielded SEB-MFM, in the same strength as the magnetic field. In addition, an implementable scheme of an electron optical system based on the shielded SEB-MFM is designed and calculated to verify the feasibility of the shielded SEB-MFM. The results indicate that the SEB with a 636-A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> current density can be well focused by a 0.8-T shielded SEB-MFM in a 40-mm tunnel. To achieve the same expansion degree of thickness, the conventional shielded UM must be around 1.5 T.

Digital Fabrication and Reliability Evaluation Method for G-Band TWT Electron Optical System

Terahertz traveling wave tubes (THz-TWTs) electron optical system (EOS) has strict fabrication accuracy requirements. The low reliability of traditional manual assembly always is the direct problem hindering the development of TWT to high frequency, high power, high efficiency, and high reliability. In this article, a digital fabrication and reliability evaluation method for THz-TWTs EOS was presented. First of all, through improving the gun shell structure and sealing molds, developing automatic and semi-automatic assembly methods, writing automatic geometric measure programs, measuring the thermal deformation of cathode and focusing electrode (FE) under working temperature, etc., the implementation of digital fabrication technology was completed, which promoted the fabrication accuracy (1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma \text{)}$</tex-math> </inline-formula> to 3–10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> m and 0.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> –0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> . Then, in order to find the tolerance limit to keep the electronic trajectory stable and the balance between design reliability and fabrication reliability, the CST particle solver single and multi-parameter sweep function was used to analyze the EOS of a 0.22 THz-TWT. Based on the digital fabrication technology process capability, 6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma $</tex-math> </inline-formula> quality management theory, and equal proportion compress single parameter tolerance limit method, we defined four independent sensitive parameters, and calculated the reliability of THz-TWT EOS digital fabrication was not less than 72.47% by MINITAB software. This method can be used as a quantitative calculation of whether the TWT EOS design and fabrication are matched, and give appropriate tolerance and compensation range in the actual TWT fabrication process.

Research on a Highly Overmoded Slow Wave Circuit for 0.3-THz Extended Interaction Oscillator

Here, we present the complete design process of a highly overmoded slow wave circuit (SWC) stably operating in the quasi-TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{04}}$</tex-math> </inline-formula> mode for terahertz (THz) extended interaction oscillator (EIO). The developed interaction circuit emits THz frequency electromagnetic radiation through structural size of the engineered millimeter-wave (MMW) circuits, which provides a new technological horizon for overcoming the engineering challenges caused by the limitation of circuit size. Through careful engineering of the electron optical system, a cylindrical beam with a diameter of 0.38 mm and a current of 0.25 A is obtained at a bias of 14.8 kV. Through the particle-in-cell (PIC) simulation, these new design approaches have been shown to achieve an output power of 250 W at 0.3 THz in a cylindrical cavity with an inner diameter of 4.16 mm.

Experimental Study on Measuring Petzval Image Plane of Streak Tube with Single Image

In the process of image reconstruction of compressed sensing algorithms, building a measurement matrix related to the parameters of the imaging system is necessary to improve its imaging quality. Additionally, building a compressed ultrafast imaging system based on a streak camera, which includes aberrations in the imaging system, is necessary. However, the aberration coefficient of the streak tube can be obtained only by numerical calculation based on the known internal structure of the streak tube, and it does not apply to a tube with an unknown structure. Based on the Lagrange–Helmholtz relation, which is widely established in electronic optical imaging systems, this study proposes a method to obtain the Petzval image plane of a streak tube by measuring only a single image without considering the internal structure of the streak tube. This method provides a reference for the construction of the measurement matrix in the application of the compressed sensing algorithm; additionally, it provides a test scheme for the performance index of the streak tube after assembly in commercial production to further optimize the assembly process and improve the yield of production.

Improvement of accuracy degree of electron optical imaging system

Improvement of accuracy degree of electron optical imaging system