Sheet Electron Beam Research Articles

Замедляющая система меандрового типа на диэлектрической подложке для лампы бегущей волны миллиметрового диапазона

А novel planar microstrip meander-line slow-wave structure (SWS) on dielectric substrate for a miniature low-voltage millimeter-band traveling-wave tube (TWT) with a high-aspect-ratio sheet electron beam is proposed. Main electromagnetic parameters of the SWS were studied. Using of such a slow-wave structure may lead to increase of the gain and output power of the TWT-amplifier

Теоретическое и экспериментальное исследование миниатюрной планарной замедляющей системы на диэлектрической подложке для лампы бегущей волны W-диапазона

The research results of a miniature meander planar slow-wave structure (SWS) for W-band traveling wave tube are presented. 3D computer simulation of the electrodynamic parameters of SWS has been carried out. A new technology of manufacturing of planar microstrip SWS has been presented. An experimental research of the S-parameters of an SWS has been carried out. The results show good agreement with the results of 3D simulation. The output characteristics of the TWT with sheet electron beam and planar SWS on dielectric substrate were simulated.

Study of a 0.35 THz Extended Interaction Oscillator Driven by a Pseudospark-Sourced Sheet Electron Beam

A compact high-power extended interaction oscillator (EIO) driven by a pseudospark-sourced (PS-sourced) sheet electron beam (SEB) is presented at 0.35 THz. It combines the advantages of a planar interaction circuit and a SEB generated from the PS discharge, including a large beam cross-section, high gain per unit length, and high current density with the additional benefit of not requiring an external focusing magnetic field. Staying within what is achievable with microfabrication techniques, the influence of tolerance on the Q value, resonance frequency, and characteristic impedance was investigated. The effect of surface roughness caused by the manufacturing method on Ohmic loss of the material surface was studied. The advanced microfabrication techniques of Ultra Violet Lithographie, Galvanik, and Abformung (UV-LIGA) and Nano-computer numerical control (Nano-CNC), which are capable of realizing high precision and a metal surface of sufficient smoothness, were proposed to manufacture the planar structures. The effect of plasma density in PS-sourced SEB on the resonance frequency of the EIO circuit was investigated. The simulation results showed that the output signal had a slight frequency upshift and a decrease of the output power as the plasma density increased at 0.35 THz, which is consistent with the theoretical analysis. Beam–wave interaction simulations for this planar EIO predicted a peak output power of 1.8 kW at ~0.35 THz using an effective value of conductivity of ${1.1} \times {10}^{{7}}$ S/m to take into account the skin depth and surface roughness.

Design Approach for a Miniaturized Pseudospark-Based High-Current-Density Sheet Electron Beam Source

In this article, the design approach for a miniaturized high-current-density sheet electron beam (SEB) source has been reported. A study through simulation using COMSOL Multiphysics has been carried out to analyze the role of geometrical parameters of the hollow cathode in miniaturized SEB generation. These geometrical parameters play a very important role in defining the discharge inside the hollow cathode geometry and subsequent beam generation through a rectangular aperture. The hollow cathode diameter “D”, the length of the hollow cathode “L”, and the aspect ratio of the sheet beam defined by the aperture size in front of the hollow cathode region have been optimized for the generation of a SEB. The ratio of the length to the width of the rectangular aperture defines the aspect ratio of the SEB. It has been found that the beam aspect ratio plays an important role in the penetration of the accelerating field inside the hollow cathode geometry, which affects the transient behavior of the discharge. The hollow cathode dimensions have been optimized for the applied gap voltage varying between 15 and 25 kV, while the beam aspect ratio has been analyzed for the range between 5:1 and 12:1 keeping the fill factor constant.

Simulation of Electron-Optical Systems with a Converging Sheet Beam for Terahertz Traveling-Wave Tubes

A converging sheet electron beam with a cross section of 0.05 × 2 mm2 and a current density of 200 A/cm2 formed by an electron gun is modeled using the synthesis and analysis methods with partial and complete magnetic shielding of the cathode and a linear compression of 10 and 15. The cross-sectional deformation of the beam in a focusing magnetic field is analyzed based on the three-dimensional computer model of electron-optical systems with a sheet electron beam. The possibility of generation of a low-perveance flux with small deformation in the transit channel of a comb slow-wave structure up to 30 mm in length is demonstrated.

A 0.34-THz High-Power, Slow-Wave Structure: Designing and Microfabricating an H-Plane Ridge-Loaded Folded Waveguide

High-power microvacuum electronic devices are one of the key technologies for the study of terahertz radiation sources. The traveling-wave tube (TWT) based on the folded waveguide slow-wave structure is the most promising terahertz device. This article designs the structural parameters of an H-plane ridge-loaded folded waveguide to improve the maximum output power of TWTs in the atmospheric window at 0.34 THz. The results predicted by a theoretical model and by electromagnetic (EM) simulation indicate the interaction impedance of the slow-wave structure is significantly increased. The simulation results show that the design is capable of raising the maximum output power to more than 50 W at 0.34 THz, with sheet electron beam parameters of 16.8 kV and 50 mA. The power gain, the 3-dB bandwidth, and the electronic efficiency of the folded waveguide can reach 30.5 dB, 10 GHz, and 6%, respectively. Finally, the designed slow-wave structure is microfabricated using multistep UVLIGA technology.

Mode Control Analysis and Large-Signal Design of a High-Power Terahertz Extended Interaction Oscillator

A high-power 200-GHz extended interaction oscillator (EIO) is designed by large-signal analysis. Analyzing different resonant modes, we calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure. From eigenmode analysis, it was predicted that the resonator-slow wave structure (SWS) coupling region has a considerable effect on resonant RF mode due to a ${L}_{{1}} \rightarrow {L}_{-{1}} $ mode transformation, where ${L}_{-{1}} $ is a parasitic low-output power resonant mode of the resonator. Using the eigenmode outcomes in addition to large-signal results, we found the optimum dimensions for the coupling region. The designed oscillator was then simulated by Particle-in-Cell (PIC) solver, leading to approximately the same results as those predicted by the mentioned procedure. The observed mode competition of different modes of the oscillator is analyzed and then removed by inserting a lossy layer at a proper location. By properly introducing a stub mode tuner near the output coupler, we could selectively excite the ${L}_{{1}} $ mode and maximize the RF output power to values even higher than those observed in the absence of mode tuner. Stable RF powers up to 2 kW are predicted to be obtainable by the sheet electron beams with beam densities lower than the state of the art.

Design and Millimeter-Wave Measurement of a Wideband Power Coupling Structure for Sheet Electron Beam Devices

Two power coupling structures based on a Y-type branch waveguide (YTBW) coupler for sheet electron beam devices are presented in this paper. The YTBW coupler is a good choice for the power coupling due to its broad bandwidth property and compact configuration. However, according to the previous studies, it is difficult for a YTBW coupler to obtain good isolation, small port reflection and, meanwhile, high transmission in a broad frequency band. To address this issue, the following two approaches were proposed: 1) introducing multiple branch slots between branch waveguide 1 and branch waveguide 3 of the YTBW coupler to cancel out the electromagnetic (EM) wave propagating toward the isolation port and 2) enlarging branch waveguide 1 at the junction of the three branch waveguides to achieve a port impedance matching and guide the EM wave to propagate to the port connecting with the slow-wave structure. The measured results demonstrated that the bandwidth of port reflection lower than -12.5 dB, isolation coefficient smaller than -12.0 dB, and meanwhile, the transmission higher than -1.0 dB, was 13.5 GHz (50.0-63.5 GHz), corresponding to a fractional bandwidth of 23.8%.

Compact high‐power millimetre wave sources driven by pseudospark‐sourced electron beams

This article presents the demonstration of several compact millimetre wave sources driven both by a pencil or sheet electron beam from a pseudospark (PS) discharge. The millimetre wave sources include two pencil beam extended interaction oscillators (EIO) in W-band (75-110 GHz), two sheet beam EIOs in W- and G-bands, two pencil beam backward wave oscillators (BWO) in W- and G-bands, and one pencil beam Cherenkov maser in Ka-band. These devices can generate up to kilowatts of output power, which are very attractive for many important applications.

A staggered double-vane slow-wave structure with double sheet electron beams for 340 GHz traveling wave tube

ABSTRACTAn improved slow-wave structure (SWS) for a 340 GHz traveling wave tube (TWT) is proposed. The dispersion curve and transmission characteristics of SWS have been calculated and analyzed. The transmission and reflection of the RF structure are S21 > −7 dB and S11 < −16 dB, respectively. Two sheet electron beams with identical physical parameters are used to control the operation of a TWT. In addition, the output power, gain, and bandwidth of the TWT were studied using three-dimensional particle-in-cell (PIC) simulation method. A uniform constant magnetic field with the magnetic field density of 0.2 T is used to focus the sheet electron beam. The results of the PIC simulations show that the TWT achieves the maximum output power of 12 W and the 3 dB bandwidth of 25 GHz (328–353 GHz) at the input power of 10 mW. At 340 GHz, the output power of 12 W and the gain of 30.8 dB are obtained.

To the theory of gyrotrons with confocal resonators

In recent years, in addition to the development of traditional gyrotrons with an axially symmetric interaction space, there has been strong interest in developing gyrotrons, whose interaction space is not axially symmetric (e.g., gyrotrons with confocal resonators). The theory of such gyrotrons is presented in this paper. First, equations describing such gyrotrons in the cold-cavity approximation are formulated. Then, the linear theory is developed, which is followed by a simple, single-mode, nonlinear theory. After that, the theory describing the mode interaction in such gyrotrons is presented. Then, an alternative concept of gyrotrons with single and multicavity confocal resonators and sheet electron beams is proposed. This paper also includes the analysis of diffractive losses in confocal resonators and the estimates for curling of the ends of sheet beams of gyrating electrons caused by the space charge forces.

Design, Fabrication, and Cold Testing of a Ka-Band kW-Class High-Bandwidth Dielectric-Loaded Traveling-Wave Tube

This paper describes the design, fabrication, and initial testing of a Ka-band dielectric-loaded traveling-wave tube (TWT) with very high bandwidth. Applications for high-power mm-wave sources span radar (including imaging), biology, medicine, communications, national security, and other areas. Specifically, to achieve long-range, cm-scale imaging using synthetic aperture radar techniques, a radio-frequency (RF) source with an average power level of 1 kW and a bandwidth of 10 GHz will be required. We developed a novel Ka-band TWT architecture that approaches these requirements. To achieve a very wide bandwidth, we proposed to use a dielectric-lined waveguide slow-wave structure. A dielectric constant of larger than 13 is needed for the resonance with a 20-keV electron beam. In our design, we have used $\varepsilon = 20$ magnesium–calcium–titanate (MCT) ceramics. The two halves of the dielectric are shaped to ensure that the TM11-like mode has a flat electric field profile along the beam slot to accommodate transport of a 5-A sheet electron beam. The gain for the structure peaks at 33.25 GHz and is predicted to be 2.3 dB/cm with a total gain of 30 dB. The structure was fabricated and cold tested. Although the results of the cold test were inconclusive, we discuss possible reasons for discrepancies between simulations and measurements and propose simplifications to the tube’s geometry for future studies.

On Simulation of Sheet Electron Beams with Regard to the Initial Transverse Thermal Velocities of Electrons

A technique to take into account the initial transverse electron thermal velocities in converged sheet electron beams has been developed. This determines the main integral characteristics of a thermal beam in a gun and transportation region of the paraxial approximation via chosen characteristic electron trajectories. We have equations of characteristic electrons motion, initial conditions to solve equations, and formulas for the current density distribution in the thermal beam cross-section and current fraction in conventional boundary. The derived equations and formulas may be used in modeling electron-optical systems and choosing parameters in which the effect of heat electron motion on beam characteristics will lie within tolerable limits.

Design and Experiment of 4 MW Ka Band Sheet Electron Beam TWT

High-power vacuum electron devices (VEDs) are attractive, because of their broad applications, such as advance radars, electromagnetic warfare, and plasma reactors. In this paper, a Ka band mega-watt sheet electron beam traveling wave tube (TWT) is reported. A two-staged rectangular waveguide grating slow wave structure (SWS) driven by a sheet electron beam (20 mm × 1 mm, 164.8 kV, 850 A, 20 ns) is used in this TWT. In order to suppress the self-excited oscillation, a rectangular BeO attenuator is inserted between the two-staged SWSs. The experimental results show that the TWT can produce more than 2 MW output power from 34.2 to 35.5 GHz. And the maximum output power is 4.24 MW at 35 GHz, corresponding to the gain of 25.9 dB. In the future, the TWT will be used to perform research on biomedical effects and imaging.

Planar THz FELs Based on Intense Parallel Sheet Electron Beams and Intracavity Wave Scattering

A design for a planar FEL operating in the terahertz frequency range at the multimegawatt power level is being jointly developed at the ELMI accelerator by the Budker Institute of Nuclear Physics and the Institute of Applied Physics. The FEL oscillator is driven by parallel intense sheet electron beams of moderately relativistic energy, and transitions to the above frequency range via a two-stage cascade scheme. The first beam generates a powerful millimeter pump wave, which then travels through special waveguides to the parallel channel and is scattered by the second beam into a wave of terahertz radiation. Various possible arrangements of the FEL scheme are discussed, and results from their simulation are presented. The results from cold tests of the FEL’s electrodynamic system are reported.

Умножитель субтерагерцевого диапазона на основе лампы бегущей волны с ленточным электронным пучком

AbstractIn this paper, we present the results of the study of a multiplier based on a traveling wave tube with a sheet electron beam and slow-wave double-grating structures. Device configurations with the possibility of obtaining an output power above 60 W at the second harmonic frequency of 190 GHz with an input power of about 10 W at the first harmonic frequency were determined.

Моделирование лампы бегущей волны суб-ТГц диапазона с многолучевым ленточным электронным пучком

Моделирование лампы бегущей волны суб-ТГц диапазона с многолучевым ленточным электронным пучком

Threshold-less and focused Cherenkov radiations using sheet electron-beams to drive sub-wavelength hole arrays.

Cherenkov radiation (CR) was one of the most famous discoveries in the last century and still has broad applications in modern physics. Recently, threshold-less and reversed CRs have attracted even more attention thanks to their unique characteristics and application prospects. Here we illustrated a threshold-less CR in vacuo by using a sheet free-electron beam (FEB) to excite an oblique-lined sub-wavelength hole array. It is achieved by setting the effective velocity of emitters-resonant modes successively excited by the sheet FEB-to be greater than the speed of light in vacuo. By letting the sub-wavelength holes line up along a designed curve, we further demonstrated a focused CR with radiation being convergent to specific focusing spots, which can be located at any designed positions in space, achieving backward (reversed) as well as forward (normal) CRs in effect. This focused CR does not have the conventional Cherenkov cone, and its intensity at the focusing spot is greatly enhanced. These newly revealed threshold-less and focused CRs may lead to broad interest and attractive applications, especially for developing integrated and focused light sources in the terahertz region.

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.

Development of the sheet electron beam focusing system based on thermionic and field emission cathodes

Synthesis method has been developed for modeling the electron-focusing systems formed compressed sheet electron beam with a field emission cathode. The results of modeling by synthesis of a convergent sheet electron beam with a cross section of 0.15·0.8 mm2 and a current of 100 mA with magnetic shielding of the thermionic and field emission cathodes are presented. The estimated electric field on the cathode is 0.2·105 V/cm at the anode voltage of 20 kV. Experimental investigations of the current-voltage characteristic of an electron gun with impregnated flat cathode in a pulsed mode are conducted, where the collector current is 100 mA.