Sheet Beam Research Articles

Analysis of Dual-Frequency Radiation From a ${G}$ -Band Extended Interaction Oscillator With Double Sheet Beam

The dual-frequency radiation scheme of a ${G}$ -band extended interaction oscillator (EIO) has been proposed. The analytic estimates of structure, mode characteristics, and oscillation-starting condition of the overmoded double-sheet-beam oscillator have been presented. The counterstreaming beams and optimized parameters were employed to reduce the fundamental mode competition in a TM21 mode EIO, allowing the high-order transverse mode ( ${\text {TM}}_{{21}}^{+-}$ ) and the fundamental mode ( ${\text {TM}}_{21}^{++}$ ) to operate simultaneously. The analyses are verified by simulations using 3-D particle-in-cell codes. The newly designed EIO was simulated with copper as a background material, and the dual-frequency radiation power of ~517 W is achieved when a double electron beam with 0.4 A and 21.5 kV is injected.

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.

Effect of cyclotron resonance on ‘hot’ dispersion in a staggered double metallic grating sheet beam travelling wave tube

Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced. Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.

Stacked dual beam electron optical system for THz integrated wideband traveling wave tube

In this paper, a stacked dual beam electron gun and the associated electron optical system are proposed. The stacked dual beam electron gun includes two compact focusing electrodes which help to achieve dual sheet beams. As an application of this dual beam electron gun, a 340 GHz integrated dual beam traveling wave tube (TWT) based on the staggered dual vane slow-wave structure (SWS) is also put forward. In order to reduce the length of the TWT, a novel input/output coupler is introduced. The overall transmission characteristics of the SWS structure together with the input/output couplers show a wide bandwidth covering a frequency range of 306 GHz to 360 GHz. Based on the parameters obtained for the integrated TWT, a stacked dual-beam electron gun with dual focusing electrodes is designed to achieve a beam current of 43 mA, a beam voltage of 21.4 kV, and a cross-sectional size of each beam of 0.3 mm × 0.08 mm. A uniform magnetic field of 0.52 T is utilized to focus the dual electron beams, and a beam transmission efficiency of 97.1% is achieved over a length of 50 mm. Finally, particle in cell simulation results show that the integrated dual-beam TWT can generate an output power of 5 W over the frequency range of 315 GHz to 350 GHz, with the maximum output power of 24.5 W at 330 GHz.

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.

3-D Fast Nonlinear Simulation for Beam–Wave Interaction of Sheet Beam Traveling-Wave Tube

In this paper, a 3-D fast time-domain nonlinear algorithm (FTDNA-3-D) based on particle-in-cell method for the beam–wave interaction of the sheet beam slow wave structure (SWS) is presented. Calculation equations of the circuit electric field and the space charge electric field are given. Calculation approaches of the energy exchange and the particle mover are displayed. A simplified coupling impedance simulation approach for sheet beam SWS is indicated. The FTDNA-3-D takes the transverse electric field and the focusing magnetic field into consideration. The FTDNA-3-D could reach a high simulation speed. This novel algorithm gives a faster accurate choice for the design of sheet beam traveling-wave tube (TWT). It could be used to enhance the design efficiency of sheet beam TWT. A Ka-band staggered double vane TWT is used to verify the FTDNA-3-D. Simulation results of output power and gain versus frequency from FTDNA-3-D are compared with results from CST particle studio. The results of FTDNA-3-D are in accord with CST particle studio well.

Design and preliminary experiment of radial sheet beam terahertz source based on radial pseudospark discharge

To satisfy the demands for compact, inexpensive terahertz (THz) sources with power of hundreds of watts, a radial sheet beam THz source which does not require an external magnetic field and is driven by a radial pseudospark discharge plasma electron gun (PSDP-EGUN) is proposed. Radial design has been used in pseudospark switches, but in this paper the design of a PSDP-EGUN to drive a radial THz source is presented for the first time. Being different from the latest reported axial quasi-rectangular sheet beam THz sources driven by an axial PSDP-EGUN, a new design consisting of a circular plate-shaped sheet beam that is directly generated by the radial PSDP-EGUN is reported. As compared to an axial system, the radial configuration may result in a larger beam current and a larger beam-wave interaction area together with a higher potential of THz output power. Theoretical analysis and particle-in-cell simulation have been employed in the design of the radial sheet beam THz source. Output powers in the kilowatt range have been observed in the simulation of this 0.22 THz source. Preliminary experimental results of the radial PSDP-EGUN are also presented.

Confined focused sheet beam flow of a thermionic linear electron source

A magnetically confined sheet beam has been designed and tested for its uniform transmission. The beam is fully immersed in a uniform magnetic field of 50 Gauss which bends and focuses the beam throughout in a uniform laminar flow at 180̂. A sheet beam of uniform cross section (0.35 cm × 12.5 cm) successfully has been tested; the width of the beam is many times the thickness. The gun is designed and simulated in CST software. The beam is uniform throughout with parameters; current density, emittance and perveance values; 1.04 A/cm2, 14 π-mm-mR and 5 μAV−3/2, respectively. The simulation and test results are in agreement. The first application is the evaporation of refractory metals for coating in the field of nanotechnology and also expected to be used in klystrons for advanced particle accelerators and colliders at higher acceleration potentials.

Theoretical analysis and simulation of W-band sheet beam extended interaction klystron amplifier

The sheet beam extended interaction klystron is an important kind of millimeter-wave and sub-millimeter-wave vacuum electron device, which has extensive applications such as in high resolution radar, imaging system, satellite communication and precision guided missiles. Compared with conventional pencil beam klystron, the sheet beam extended interaction klystron, in which a thin rectangular sheet beam is used, can generate higher power by obtaining higher current and reducing space-charge-effect of electron beam. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Electron flow oscillatory theory is a compromise between kinematical theory and space charge wave theory, which adapts to the bigger modulation of electron beam than space charge wave theory, while it is inaccurate in the case of big bunching parameter. Based on electron flow oscillatory theory under the small signal condition, the influence of electron beam on standing wave electric field of 2π mode in a three-gap cavity is analyzed, and the expressions of beam loading conductance and beam loading susceptance in a three-gap cavity are obtained. The influences of plasma frequency, transit angle of single gap and transit angle of drift on the interaction of beam and wave in a three-gap cavity are discussed. The results show that space-charge-effect of beam is unbeneficial to the interaction between beam and wave, otherwise beam loading conductance and beam loading susceptance fluctuate with the increasing of transit angle of single gap and transit angle of drift. A W-band sheet beam extended interaction klystron is designed by theoretical analysis and 3D PIC software. The output power of 5773 W at 94.47 GHz is obtained with an efficiency of 8.46%, a gain of 37.6 dB and a 3 dB bandwith of about 140 MHz, when beam voltage is 19.5 kV, current is 3.5 A and focus magnetic field is 0.85 T. This research is important for the engineering of the W-band sheet beam extended interaction klystron amplifier.

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.

3-D Nonlinear Theory for Sheet-Beam Folded-Waveguide Traveling-Wave Tubes

A 3-D frequency-domain nonlinear model for sheet beam (SB) traveling-wave tubes (TWTs) based on folded waveguides (FWs) is presented in this paper. The SB with finite thickness is a 3-D asymmetric system. To characterize such a system, an accurate description of the radio frequency (RF) fields and the space charge (SC) fields in the interaction gap in all three dimensions is required. An analytical expression for the interaction electric fields is derived. Beside of the interaction electric fields, a modified analytical model for the dispersion and interaction impedance is also imbedded in our code predicting the cold characteristics of the waveguide, which agrees with the results of the 3-D simulation code CST. As a result, the model provides a through predictive capability from the geometrical parameters to the device performance, such as saturation power and gain. Due to the short computing time, our code is very useful for the large-scale optimizations of TWTs. For the calculation of the SC field, a particle-in-cell method is used by solving the 3-D Helmholtz equation and the motion equation. Such analytical technology is much more preferable to interpret the complicated beam–wave interaction than the conventional electron beam models, which attributes to the ever-increasing computing capacity of the computers. These features have been incorporated in the development of our large-signal code SB-FWTWT-3-D. The validation of the model is performed and comprehensive results are presented.

Efficient Heat Dissipation Study of High-Power <inline-formula> <tex-math notation="LaTeX">${W}$ </tex-math> </inline-formula>-Band Sheet Beam Extended Interaction Oscillator

The microchannel cooling structure, as an efficient heat dissipation technology, is applied to improve the power capacity of a W-band continuous-wave (CW) sheet beam (SB) extended interaction oscillator. Its configuration is designed and optimized to further enhance the heat flux handling. The results show that microchannel cooling technology can greatly enhance the heat transfer efficiency. Specifically, the maximum temperature of the cavity drops from 308.9 °C to 144.9 °C. The power capacity of CW increases to 7 kW with 2% (49-kV and 2-A SB) electronic interception, and the tolerable electronic interception rate increases to 4% with 3.6-kW CW output power and 2.3-kW ohmic power loss. The microchannel cooling technology enables compact devices with higher frequencies and higher power to work under CW conditions.

Multi-resonance interaction in rectangular waveguide grating structure

For developing millimeter and sub-millimeter wave devices, the rectangular waveguide grating sheet beam system is a very promising way to realize a high power operation. To further improve the interaction efficiency, we can substitute the cyclotron beam for the rectilinear one and utilize the multi-resonance effect. In rectangular coordinates, we rigorously derive the formulae to describe the Lorentz forces acting on the electrons and the coupling coefficients of each concerned resonance. The theoretical calculation demonstrates that the combined gain is evidently enhanced when the multi-resonance condition is satisfied, the occurrence of which is always caused by the coupling of two major resonances. The results also show that the multi-resonance effect will rapidly disappear if the beam voltage and the magnetic field deviate from their exact values. Although the parameters should be carefully sustained, the multi-resonance can be excited by using the fundamental TEx10 hybrid mode, which is beneficial for the stable operation. So, as an available mechanism to upgrade the future device performance, it is worth being particularly studied.

Non-destructive 2-D beam profile monitor using gas sheet in J-PARC LINAC

A beam profile monitor using interaction between the beam and the gas molecules distributed in sheet shape has been developed. Ions or luminescence generated by passing the beam through the gas sheet has the information of cross-section shape of the beam. The gas sheet beam monitor will become a useful tool to measure the profile of high power beams because it has no breakable element such as wires. Furthermore, 2-D beam profile can be obtained at a certain position of beam line. We applied the gas-sheet based beam profile monitor to J-PARC LINAC, where the negative hydrogen atoms are accelerated to the energy of 400 MeV. The vacuum system was carefully designed not to make an unacceptable pressure rise in nearby cavities when the gas was injected. The clear image of the beam profile was successfully obtained by detecting the ionized N2 gas.

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 a Microfabricated Planar Slow Wave Structure for a 0.22-THz TWT for Communication, Imaging and Remote Sensing

ABSTRACTA microfabricated planar 0.22 THz TWT is being investigated as a high power, broadband amplifier for ultra-broadband wireless communication, imaging and remote sensing. Planar staggered double-vane-loaded rectangular waveguide slow wave structure (SDV-SWS) is selected for the 0.22 THz TWT because of its wide bandwidth, high impedance and low loss, easy fabrication using MEMS technologies with high precision and surface finish, and inherent compatibility for operation with sheet electron beam. A simplified approach is presented for determining initial design parameters of the SDV-SWS of wide bandwidth and high impedance. The initial design parameters of the SDV-SWS are used for analytically determining the dispersion and the impedance characteristics of the structure which are found comparable with the simulated characteristics by the 3D e.m. field simulator CST code. The SDV-SWS is designed for a planar 0.22 THz TWT with a sheet beam of beam voltage 20 kV and beam current 100 mA. In-house developed large signal analysis code (SUNRAY-p) is used to analyse RF performance of the planar TWT over the band. The RF performance of the 0.22 THz TWT as determined using SUNRAY-p code is found comparable with the simulated results by the CST code over the frequency band.

Design of a 0.22THz, 100W Planar TWT for Ultra Wide Band Wireless Communication

Development activities addressed to 0.22THz centre frequency is of significant importance for ultra wideband communication and remote sensing because of the available atmospheric spectral window over a band from 0.20THz to 0.30THz. 0.22THz planar TWT of output power more than 100W, gain more than 30dB, and bandwidth more than 30GHz is designed for high data rate wireless communication, imaging and remote sensing. Planar TWT is designed using a rectangular sheet electron beam of beam voltage 20kV and beam current 100mA, and of beam size 100m (thickness) x 600m (width). A planar staggered double vane loaded rectangular waveguide slow-wave structure (SDV-SWS) of broad bandwidth, high impedance and low circuit loss is designed for the 0.22THz TWT. Planar structure is used because it is compatible for sheet beam operation and it is also easy to fabricate using MEMS technologies. Large signal analysis code SUNRAY-P, developed to determine RF performance of a planar TWT with sheet beam, is used to design the 0.22THz 100W TWT with sever, couplers and phase velocity taper. WR-3 rectangular waveguide of size 864m x 432m is used for the input and the output couplers.

Start current study of a THz sheet beam extended interaction oscillator

This paper presents a theoretical study on a start current of a 0.378 THz sheet beam extended interaction oscillator (SB-EIO), and the design of this device driven by thermionic cathode stands a chance to realize a compact and powerful THz coherent continuous radiation sources. After theoretical study, the SB-EIO with eleven gaps is designed to operate at 2π mode. The coupling and interaction abilities are optimized to meet the synchronization conditions and thus improve the output power and efficiency. The start current analysis is preliminarily accomplished, and the advantages are: (1) At the operation frequency of 0.378 THz, the start current and current density of the device are optimized to 20 A/cm2 and 8.4 mA, and the output power is 14 W. (2) It works in the condition of smooth copper plane in simulation, and the output power is still about 20 W when an electron beam with 252 mA and 41 kV is injected. The research gives an estimation of up to 3.5 times decline in output power when the surface roughness emerges. (3) The results of the simulation show that a relatively high efficiency of ∼13% in particle-in-cell (PIC) was observed, and a stable output power range from 98 W to 234 W is found when the injected electron beam (0.35 mm × 0.12 mm) is 16.8–42 mA and 42 kV. Moreover, the reliability of PIC results is verified in this paper.

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.

On-Wafer Microstrip Meander-Line Slow-Wave Structure at Ka-Band

A novel configuration for a Ka-band V-shaped microstrip meander-line slow-wave structure (SWS) is reported. The SWS is designed to work at a voltage less than 4 kV and provide a wide bandwidth. Coplanar waveguide (CPW) input–output feed lines and a shielding structure are incorporated to enable fast on-wafer cold test measurements on a CPW probe station without requiring dicing or a metal enclosure. Simulated dispersion characteristics and coupling impedance for the optimized design are presented. The simulated S11 of the entire structure is better than −15 dB over 25–36 GHz. The proposed configuration is fabricated using $4^{\prime \prime }$ Si wafers and standard microfabrication processes. The measured S11 of the entire structure is better than −10 dB over 20–40 GHz. The observed high insertion loss has been explained in detail, and alternative approaches that can reduce the loss have been proposed. The PIC simulation results show that for a 3.6-kV, 50-mA sheet beam, the output power can potentially reach 14.5 W at 34 GHz with a gain of 21.6 dB. A 3-dB bandwidth of about 25% centered at 32 GHz is also indicated.