Sheet Electron Beam Research Articles

The development of W waveband diffraction radiation oscillator

This study presents the development of a continuous wave diffraction radiation oscillator utilizing a sheet electron beam. The oscillator comprises a slow-wave system formed by double-comb gratings, an open resonant cavity consisting of a spherically curved mirror and a cylindrically curved mirror, and a sheet electron beam generated by a diode gun. A permanent magnetic focusing system stabilizes the transmission of the sheet electron beam within the slow-wave system. Through a combination of mechanical and electronic tuning, the oscillator generates stable signal output in the TEM00q mode. The oscillator's frequency tuning range spans from 87 to 97 GHz, achieving a maximum output power of 13.5 W.

Design and development of a sheet-beam electron gun with large current for a THz traveling-wave tube

Design and development of a sheet-beam electron gun with large current for a THz traveling-wave tube

The New Approach to Focus High-Current-Density Sheet Electron Beam by Rotated Reversed Magnetic Field

The New Approach to Focus High-Current-Density Sheet Electron Beam by Rotated Reversed Magnetic Field

Study of a 0.3-THz Extended Interaction Oscillator Based on the Pseudospark-Sourced Sheet Electron Beam

Study of a 0.3-THz Extended Interaction Oscillator Based on the Pseudospark-Sourced Sheet Electron Beam

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.

A Modified Double Staggered Grating Waveguide Slow Wave Structure for Sub-THz Traveling Wave Tubes

A modified double staggered grating waveguide (DSGW) slow wave structure (SWS) is proposed for millimeter-wave and sub-THz traveling wave tubes (TWTs). Gratings with a cross section outline of exponential curves are applied instead of the traditional rectangular cross section. The proposed SWS owns a higher interaction impedance compared to DSGW, resulting in higher output power and gain. With proper design and optimization of the input–output couplers, the proposed SWS can have a wide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 15 dB impedance bandwidth, extending from 192 to 230 GHz. Particle-in-cell (PIC) simulations are carried out for a TWT with sheet electron beam (SEB) and the main SWS having 70 periods. Such a TWT provides a maximum power of 116.64 W which indicates a significant improvement compared with the traditional DSGW.

Theoretical Study of a Novel G-Band Sheet Beam Slots-Loaded Coupled-Cavity Traveling Wave Tube

In this article, the design of a novel symmetrical double slots coupled-cavity (SDSCC) traveling wave tube (TWT) 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">$\textit{G}$</tex-math> </inline-formula> -band is presented. The novel slow wave structure (SWS) suits sheet electron beam and has a large sheet beam channel and high coupling impedance. The novel structure shows great potential in high-power terahertz amplifier field. The dispersion characteristics are studied by both theory and simulation. An equivalent circuit of SDSCC SWS is built. The coupling impedance and electric field of operating mode are simulated. A suitable input–output structure is designed for this novel SWS. The transition characteristics are exhibited. The beam-wave interaction process is also simulated. The peak output power arrives at 384 W at 218 GHz by the usage of a sheet beam with 26.2 kV and 300 mA. The average dc current density in the sheet beam tunnel is around 160 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> . The spectrum of the output signal is pure, and the risk of mode competition is very low.

Design and testing of a high perveance sheet beam electron gun

This paper presents the design, prototype engineering, and initial testing of a relatively low-voltage, high aspect ratio electron gun for versatile pulsed power applications. The sheet beam, diode electron gun is designed for (23–25) kV voltage and 6 µA/V1.5, as is required for x-band klystron, as a part of a compact Klylac delivering electron beam energy in the MeV range. The gun prototype was engineered, built, and tested using a Scandinova M1-0.5 modulator. Beam loss on the anode aperture is evaluated from transient waveforms and equivalent circuit modeling.

Design and Non-Uniform Current Analysis of a 0.35-THz Extended Interaction Oscillator Based on Pseudospark-Sourced Multiple Sheet Electron Beams

A novel method, which combines a multiple-beam extended interaction oscillator (EIO) with pseudospark-sourced (PS) sheet electron beams, is applied to generate high-power terahertz sources. For a multiple-beam EIO, the beam cross-section is significantly improved by replacing the commonly used pencil electron beams with sheet electron beams. The PS electron beams have the advantage of high current density and operate without a focus magnetic field. The volume of the cavity is larger when the EIO operates in the TM31-3π mode than in the conventional TM01-2π mode at the same operating frequency. The EIO operating at the terahertz frequency has a larger cavity volume, which means greater power capacity and lower manufacturing difficulty. For a PS multiple-beam EIO, the non-uniformity of electron beam currents is a common problem. In order to study this problem, an original high-order mode EIO driven by PS multiple sheet electron beams is presented with enhanced output power at 0.35 THz. The authors analyze electron beams with different currents through particle-in-cell (PIC) simulations. Simulation results show that the EIO can operate stably even in the case of non-uniform PS electron beam currents. When each current is 1.4 A, simulation results show the EIO’s output power of 4.9 kW at 0.35 THz. Considering the low conductivity of 1.1 × 107 S/m, the efficiency is still 1.42%.

Research on Folded Double-Groove Waveguide With Two Sheet Beams Operating on High-Order TE20 Mode for High-Power Terahertz TWT

In this article, a folded waveguide with two coupling grooves is proposed for high-power and high-frequency traveling wave tubes (TWTs). The structure allows a modified TE20 high-order mode interact with two sheet electron beams. The transmission characteristics of this novel structure were simulated and measured. A good <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{21}}$ </tex-math></inline-formula> of −10 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> of less than −15 dB were achieved in the 218–230-GHz range. Moreover, simulations of the beam–wave interaction in this structure predicted an output power of 930 W at 220 GHz, with a small signal gain of 58 dB and a 3-dB bandwidth of 1.3 GHz.

Electrical Characterization of Plasma-Assisted Electron Beam Source With Sub-mm Sheet Aperture

In this article, the electrical characterization of a plasma-assisted electron beam source with a sub-mm sheet aperture has been performed. The developed sheet electron beam source comprises a hollow cathode cavity, two floating anodes, and one ground potential anode with a sheet aperture of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times0.3$ </tex-math></inline-formula> mm. The source has been characterized under varying applied gap potential range, i.e., 10–30 kV in self-breakdown operating mode. The breakdown parameters and resultant beam parameters, such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} - {I}$ </tex-math></inline-formula> characteristics, electron beam current density, duration to reach the conductive phase, and the energy transformation efficiency of the developed source, have been analyzed. The successive breakdown phenomenon has also been presented in the profile of the developed electron beam source.

A 0.34-THz Standing Wave Enhanced Sheet Electron Beam Traveling-Wave Tube

A 0.34-THz standing wave enhanced sheet electron beam traveling-wave tube (SWE-SEB-TWT) is proposed in this article. The high-frequency structure is composed of two sections of staggered double-vane slow wave structures (SDV-SWSs) and two multigap resonant cavities that fall in between. A sheet-beam optical system, which shows a 100% flow rate over 50 mm in simulation, is designed to provide the required electron beam. By means of particle-in-cell (PIC) simulations, the output power of the 0.34-THz SWE-SEB-TWT reaches 25 W with the voltage of 19.5 kV and the current of 60 mA, corresponding to a gain exceeding 40 dB. The test results of the high-frequency structure fabricated by computer numerical control (CNC) milling show that the high-frequency characteristics are consistent with the expectation.

Single-Cycle Terahertz Pulse Generation via Superimposed Diffraction With Cherenkov Effect

The ultrashort terahertz (THz) pulse with a broad frequency spectrum has important applications in THz spectroscopy and imaging. Previous THz-pulse generating methods are restricted by either low power or high cost. Here, we propose a novel scheme for generating ultrashort THz pulses, which uses a low-energy sheet electron beam to drive an inclined array of size-graded grooves. The diffraction radiation (DR) from each groove is successively generated and coherently superimposed at a specified direction via the Cherenkov effect. A single-cycle THz pulse with a spectrum band covering the region from 0.1 to 1 THz can be realized. In addition, using several arrays of grooves, a train of ultrashort THz pulses can be further obtained. The radiation power, which depends on the beam current, reaches as high as several kilowatts by using available electron beams. It affords an effective way of generating ultrashort THz pulses with broad application prospects.

Study of Beam–Wave Interaction in a Sub-THz Traveling Wave Tube with a Converging Sheet Electron Beam Focused by a Uniform Magnetic Field

A traveling-wave tube (TWT) with a sheet electron beam and staggered double-grating slow-wave structure (SWS) is a promising high-power, wideband terahertz amplifier. In such tubes, electron-optical systems (EOSs) with a converging sheet beam are mostly used, which allow a reduction of the cathode load, increase the lifetime, and enable operation in a continuous-wave (CW) mode. This paper presents the results of a 3D particle-in-cell (PIC) simulation of the 0.22 THz TWT driven with a converged sheet beam, which is compressed to less than 100 μm thickness in the EOS with a magnetically shielded cathode. The beam with high compression has a significant transversal velocity spread and essentially non-uniform current density distribution over the cross-section. These factors significantly affect the beam–wave interaction. We compare the performance of the TWT driven by the compressed sheet beam and by an idealized initially rectilinear beam without any velocity spread.

Investigation of a Modified Flat-Roofed Sine Waveguide Slow-Wave Structure for Wideband 220-GHz TWT

In this letter, the modified flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed for the wideband high-power sub-terahertz traveling-wave tube (sub-THz TWT), which possesses the advantages of wide operating bandwidth, low loss, minimal reflection, and ease of fabrication. The simulation results demonstrate that the transmission parameter is more than −5.0 dB in the frequency range between 210 and 250 GHz. The beam–wave interaction results indicate that the modified FRSWG can provide over 50 W of output power and 30 dB of gain from 205 to 250 GHz with sheet electron beam with a voltage of 20.8 kV and a current of 150 mA. Finally, we use high-speed milling to fabricate the modified FRSWG by the nano-Computer Numerical Control (CNC) technology. The cold test results demonstrate that the modified FRSWG has low loss and good reflection characteristics.

High-order mode interaction structure for a W-band CW sheet beam extended interaction klystron

To solve the problem of mode competition in high-order working modes, this paper presents a fast design method based on the TM31-2π mode for the dumbbell shaped extended interaction cavity. Based on the equivalent circuit theory, the high-frequency characteristics of the structure are studied. In addition, we propose a W-band continuous wave sheet beam extended interaction klystron high-frequency circuit. The circuit was driven by a 20 kV and 0.85 A sheet electron beam, with a 3.2 × 0.3 mm2 section. The beam was focused by a 0.8 T permanent magnet system. The high-frequency system adopts five dumbbell shaped five-gap cavities, and the output system adopts a symmetrical output waveguide. The 3D particle-in-cell simulation shows that more than 1.5 kW power can be obtained at an input power of 0.12 W, and the electron efficiency and gain are 9.2% and 41.2 dB, respectively.

Theoretical Analysis of Sheet Beam Electron Gun for Terahertz Vacuum Electron Devices

In the terahertz band, the vacuum electron devices with planar and miniaturized structures require the ultrahigh-precision description of high-density electron beams for formation and transportation with the theoretical analysis and simulation. Thus, the absence of the available theory for the sheet beam electron is put forward to investigate the 3-D spatial potential using a differential geometry and tensor analysis. The equation of electron beam potential can be derived by establishing a moving coordinate frame, carrying out the numerical calculations, and doing series expansion. To solve the complex sheet beam description of the existence of four corner singularities, the Riemann method and conformal mapping are adopted to overcome this difficulty. Then, a 0.22-THz vacuum electron tube using a sheet beam electron gun and corresponding optical system are designed. The beam voltage and current are 16.5 kV and 0.5 A, respectively, with a beam channel size of 1.4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.14$ </tex-math></inline-formula> mm and a uniform magnetic field of 5980G. With the 3-D simulation, the high-density sheet electron beam can transport 18 mm successfully. The spatial potential of numerical calculation with the obtained sheet beam theoretical function and the simulation model are compared to verify the theoretical description. Both the results are with good consistency, which preliminarily proves the effectiveness of the theoretical function. This work will give the deep physical mechanics vision for the development of high-power and high-efficiency sheet beam terahertz tube in the future.

Design, Simulation, and Cold Test of a W-Band Double Nonparallel Staggered Grating Backward Wave Oscillator

A novel double nonparallel staggered grating (DNPSG) slow wave structure (SWS) is proposed to enhance the coupling impedance in a <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 backward wave oscillator (BWO) driven by a pseudospark-sourced sheet electron beam. The DNPSG SWS has been shown a broadband of 72–125 GHz and a higher coupling impedance compared with the traditional double staggered grating (DSG) SWS in simulation. The DNPSG BWO structure consisting of ten SWS units and a broadband output structure is designed and fabricated. In the cold test of the DNPSG BWO, the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{11}$ </tex-math></inline-formula> (double of the losses in the DNPSG BWO) is above −10 dB in most of the band, which is satisfactory in the pseudospark-driven high-power device. The hot-test performance of the DNPSG BWO is analyzed by particle-in-cell (PIC) simulation in a beam voltage range of 14–90 kV and a current density range of 1.5– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times10$ </tex-math></inline-formula> 7 A/m2, obtaining a high output power (max. 190 kW) over an ultrawide tuning band of 38 GHz (75–113 GHz) due to enhanced coupling impedance.

Microfabrication, Characterization, and Cold-Test Study of the Slow-Wave Structure of a Millimeter-Band Backward-Wave Oscillator with a Sheet Electron Beam

In this paper, the results of the microfabrication, characterization, and cold-test study of the previously proposed truncated sine-waveguide interaction structure with wideband-matched output couplers for the millimeter-band backward-wave oscillator (BWO) driven by a high-current-density sheet electron beam are presented. Computer-numerical-control (CNC) micromilling was used to fabricate the designed interaction structure. The first sample was microfabricated from an aluminum alloy to test the milling process. The final sample was made from oxygen-free copper. Scanning electron microscopy (SEM) and optical microscopy were used to investigate the morphology of the microfabricated samples, and stylus profilometry was used to estimate the level of the surface roughness. Cold S-parameters were measured in Q- and V-bands (40–70 GHz), using a vector network analyzer (VNA). Using the experimentally measured phase data of the transmitted signal, the dispersion of the fabricated interaction structure was evaluated. The experimentally measured dispersion characteristic is in good agreement with the numerically calculated.

Sheet Electron Optical System for a 1.03-THz Traveling-Wave Tube

The electron optical systems (EOS) play a vital role in vacuum electron devices (VED). This letter reported the design and experiments of the sheet EOS for the 1.03 THz traveling wave tube (TWT). A high-current-density sheet electron beam (SEB) electron gun generating up to 20.3-mA at 22.4-kV is designed, based on the requirements of this TWT. Due to the very high operating frequency, more than 1 THz, the miniature tunnel and beam waist with a dimension of 0.05 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> 0.148 mm and 0.025 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> 0.114 mm, respectively, will lead to a very high beam current density (906.9 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Therefore, a 1-Telsa uniform magnetic system is designed, to ensure such a high-current-density SEB passes through the 27-mm tunnel. Finally, the primary experiments indicate that 7.56-mA current reaches the collector.