Sheet Beam Research Articles

A High-Power Sheet Beam Slow-Wave Structure of Traveling Wave Tubes

In future electronic devices, the trade-off between power capacity and thermal management will be a severe challenge. In this letter, a sheet beam slow-wave structure (SB-SWS) has been proposed to realize high-power output while taking into account cooling design inside the traveling-wave tubes (TWT). The design of the modified structure ensures a sufficient axial electric field component to realize efficient interaction, meanwhile expands the width of the metal vanes by 327% to design micro-channel cooling. The power load capacity for electronic interception increased by 25%. Utilizing all-period optimization technology, the maximum output power can reach 4 kW, corresponding 18.8% electronic extraction efficiency. Also presented further is a proof-of-concept design model of Ka-band for practical test. The consistency between experiment and theory shows that this SWS is not only suitable for microwave frequency band, but more suitable for future miniaturized devices in sub-millimeter wave and terahertz bands.

Electron-optical system for dual radial sheet beams for Ka-band cascaded angular log-periodic strip-line traveling wave tube

A novel electron-optical system is proposed for dual azimuthally stacked radial sheet electron beams (ARSEBs). The two sheet beams are emitted from curved surfaces of two cathodes and are focused by a focusing electrode, which is carefully designed to produce a symmetric field distribution for the two beams and to avoid interference between the beams. A common tunable periodic cusped magnetic focusing system is also designed to focus the two ARSEBs. The dual sheet beams are used in a traveling wave tube (TWT) consisting of a cascade of two azimuthally supported angular log-periodic strip-line (ASALS) slow-wave structures (SWSs). The transmission efficiency in the presence of beam–wave interaction is 93%. The particle-in-cell simulation results show that for a beam voltage of 4400 V and a current of 0.39 A, the proposed cascaded TWT has a maximum gain of 32.5 dB at 35 GHz and a maximum output power of 180 W; this is a significant gain improvement over a TWT using a single ASALS SWS.

Stability Analysis of 300-GHz Sheet Electron Beam Transport in a Periodic Rectangular Quadrupole

A novel periodic magnetic focusing system is proposed. The stability of elliptical sheet beam transport in the magnetic field of a periodic rectangular quadrupole (PRQ) is studied and compared with that in the magnetic field of periodically cusped magnets (PCMs). Theoretically predicted matching conditions are verified by numerical simulations. An 11.7- kV, 35-mA, 0.32 mm $\times $ 0.06 mm elliptical sheet beam is confined in a 0.53 mm $\times $ 0.08 mm beam tunnel and transported over a distance of 30 mm. Both the PCM and PRQ have similar characteristics of electron beam distribution change, beam emittance, and beam transmission. The results of the initial stability analysis indicate that PCMs are preferable to PRQs because of their ability to confine the beam with a long magnet period.

Bond durability of epoxy and cement- bonded CFRP reinforcement to concrete interfaces subject to water immersion

Durability is a critical concern for concrete structures externally bonded with fiber-reinforced polymer reinforcement. This paper presents the results from an experimental study which compared the bond durability of epoxy-bonded CFRP sheets and cement-bonded CFRP grids to concrete interfaces subjected to water immersion. Totally twelve groups of CFRP sheet or grid-strengthened concrete beams with a notch at their midspan were carefully fabricated through epoxy- and cement-based bonding systems and tested under monotonic loading before and after water immersion exposure, respectively. The cement binder included polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC). The CFRP grids and sheets were designed with the similar tensile stiffness. The duration of water immersion ranged from 0 to 6 months. The test results indicated that debonding in concrete adjacent to the concrete-adhesive interface in accompany with a diagonal concrete crack near the notch was the main failure mode of the beams strengthened with epoxy-bonded CFRP sheet and ECC-bonded CFRP grid, while the tearing off of CFRP grids from the PCM matrix was the main failure mode of the beams strengthened with PCM-bonded CFRP grids. After water immersion exposure, the ultimate loads of the beams with cement-based CFRP grids were at least 50% higher than their epoxy-bonded counterparts, confirming the superior moisture durability of cement based bond to epoxy-bonded ones. The interfacial fracture energy was found to exhibit an exponential decline trend with water immersion duration.

A Sheet Beam Electron Gun With High Compression Ratio and Long Transmission Distance Performance for W-Band TWT Applications

A sheet beam electron gun with high compression ratio and long transmission distance performance for $W$ -band traveling-wave tube (TWT) is presented. A beam focusing electrode (BFE) with two pairs of unequal length outstretched structures is designed to provide equal positions of beam waist in both horizontal and vertical planes, which is beneficial to obtain large compression ratio and keep the beam cross section shape over a long distance. The operational voltage is set as 30 kV. The beam current is 0.505 A, and the corresponding cathode current density is about 5.59 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The simulation results show that the electron gun can provide a stable sheet beam under a 0.85-T magnet field. The compression ratio of the obtained sheet beam can be over 35, and the sheet beam can be transported through a 126-mm beam tunnel without interception with a 0.6 fill factor. The parameter sensitivities of the gun are analyzed and discussed as well.

The High-Order Coalesced TM11-Like Mode Operation for 220 GHz Sheet Beam Traveling-Wave Tube

Sheet beam vacuum electron tubes are an attractive solution for high-power sources or amplifiers at millimeter-wave and terahertz range. In this article, a high-order coalesced TM11-like mode operation for 220 GHz sheet beam traveling-wave tube is proposed. The feasibility of coalesced TM11-like mode operation is investigated. The utilization of high-order mode expands the RF circuit power capacity, increases the beam current and reduces the cathode emission density. The self-consistent nonlinear code and three-dimensional particle-in-cell simulations are used to verify the 6.7% beam-wave interaction at 220 GHz without phase matching optimization. The maximum output power reaches 370 W. The results demonstrate this methodology is a good solution to build a high-power device for a wide region of terahertz.

Design of planar distributed three beam electron gun with narrow beam separation for W band staggered double vane TWT

A novel planar distributed three-beam electron gun with narrow beam separations is designed based on grids loaded sheet beam method. The dimensions of the three-beam gun in the y–O-z plane are determined using our basic theoretical design method developed for sheet beam gun. The results show that the profile of focusing electrode in the y–O-z plane is related to the beam width in the x-O-z plane. Then, the characteristics and parameters of three-beam array formation with their stability are analyzed thoroughly by adjustment of control grids in the x-O-z plane. Each of the beamlet obtained is with a small axial deviation of the two transverse waists. Based on the theoretical analysis and simulations, the planar three-beam electron gun is constructed with the beam voltage of 22 kV and the current of 3 times 0.15 A. The average radius of 0.08 mm at each beam waist is obtained with the compression factor of 4 for the 0.18 mm beam tunnel radius. The beam waist can be achieved at about 4.4 mm away from the cathode with the axis separation about 0.46 mm for each of beamlet. Thus, the design method can be generally used to construct such type of narrow beam separation and planar distributed multiple beam electron gun for the miniaturization and integrated vacuum electron devices in millimeter wave and terahertz band.

Electron-Optic System With a Converged Sheet Electron Beam for a 0.2-THz Traveling-Wave Tube

This article presents the results of a design study of an electron-optic system (EOS) for a sheet-beam ${G}$ -band traveling-wave tube. An electron gun providing a 0.1-A, 20-kV sheet beam emitted by a 0.8 mm $\times0.8$ mm curved cylindrical cathode is designed. The beam dimensions at waist position are 0.05 mm $\times0.8$ mm with a compression ratio of 16 in the vertical direction. A magnetic system providing 1.1 T magnetic field, which is nearly seven times higher than the Brillouin field, is designed, and beam transmission in the 0.1 mm $\times0.85$ mm beam tunnel is studied by 3-D particle-in-cell (PIC) simulation. It is demonstrated that the beam has a complex structure of particle distribution, i.e., a high-density central part (core) and a peripheral low-density part (halo). The effect of assembly tolerance on beam transmission is studied. The prototype gun is fabricated, which compresses the beam to 0.1 mm by electrostatic field only. The 135-mA current with 95% transmission through the 0.2-mm anode aperture is measured.

Testing the Paraxial Model of Sheet Electron Beams

The paraxial model of a dense electron beam has been studied using analytical solutions that describe curvilinear sheet beams in a uniform magnetic field and without it. It is demonstrated how important it is to use, as a criterion for the accuracy of an approximate solution, the concept of a residual whose value is related to the error known for investigated reference flows.

Study on an X-Band Sheet Beam Meander-Line SWS

The miniaturized traveling wave tube (TWT) is a kind of high-efficiency, high-power, long-lifetime power amplifier which is an attractive choice for many applications, such as outer space exploration, phased array radar detection, unmanned aerial vehicle (UAV) communication, and on-chip application. In this article, a sheet beam miniaturized TWT with V-shaped meander-line slow wave structure (SWS) supported by two trapezoidal ceramic rods is designed. First, the dispersion characteristics, the impedance characteristics, and the S-parameters of the V-shaped meander-line SWS are analyzed in detail. Then, the particle-in-cell (PIC) simulation results predict that the TWT can produce 512-W output power driven by a 7.1 kV, 0.3-A sheet beam with a rectangular cross-sectional area of 3.5 mm $\times0.1$ mm. The TWT can cover the whole ${X}$ -band when the operation voltage shift from 7.1 to 9.1 kV. At last, the V-shaped meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and the measured ${S} _{\mathbf {11}}$ has been achieved and the mismatch between the simulated and the measured ${S} _{\mathbf {21}}$ has been discussed at the end.

Systematic Design Study of the Elliptical Sheet Beam Electron Gun for Terahertz TWT Applications

The design methodology of a sheet beam electron gun has been discussed and, subsequently, used for the design of a gun intended for use in a 0.3 THz traveling wave tube amplifier. The initial gun design parameters have been calculated analytically using a theoretical approach. Then, starting with these calculated parameters, the designed gun is then simulated using a commercial 3-D simulation code “CST Particle Studio” and optimized to get the target beam parameters. The circular-shaped cathode with an elliptically shaped beam-focusing electrode and elliptically shaped anode has been used to produce the good laminar elliptical sheet beam. The effect of varying the several parameters, such as height, width, and distance of focusing electrode, cathode-anode distance, and anode height have been studied to investigate their sensitivity on the target beam parameters. The simulation results predict that the designed sheet beam electron gun produces an elliptical beam with a desired beam cross section of 0.33 mm × 0.066 mm at a beam-waist position of 6.61 mm from the curved cathode emission surface corresponding to the beam parameters of 12 kV beam voltage and 55 mA beam current.

Design of G-band 500 W sheet beam extended-interaction klystron

High power generation in terahertz frequency band is limited by physical mechanism. A G-band sheet beam extended-interaction klystron was designed to demonstrate the power level and the physical factors that affect the performance of the klystron. An elliptical electron beam with a voltage of 24.5 kV, a current of 0.6 A and the dimension of 1 mm×0.15 mm was used. To match the size of the sheet beam and obtain high efficiency and high gain, the transverse-oversized barbell type multi-gap resonant cavity was used as the interaction circuit. The 3D PIC simulation results show that more than 500 W of power output can be obtained with the actual cavity loss considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency are largely restricted by the mode stability of the multi-gap cavity as well as the ohmic loss. The ohmic loss of the output cavity has a significant effect on the final output power which should be given special consideration in engineering design. The research in this paper has laid a good foundation for the development of high frequency sheet beam extended-interaction devices.

Enhanced efficiency of C‐band sheet beam driven backward wave oscillator guided by periodic magnetic field

AbstractIn this article we present the effect of periodic magnetic field on the efficiency of a sheet beam driven C‐band backward wave oscillator (operational in Megawatt power regime) through MAGIC3D PIC simulation. At 90 kV beam energy, 200 A beam current, and 0.6 T average magnetic field, our results depict an efficiency of nearly 70% due to improved electron beam confinement and electron bunching. A qualitative comparison is shown for efficiency through the same slow wave structure, guided by a uniform axial magnetic and the proposed periodic magnetic field. Efficiency enhancement of nearly 20% is observed in case of periodic magnetic field.

Investigation on a Ka Band Diamond-Supported Meander-Line SWS

The microstrip meander-line traveling wave tube (TWT) is a kind of small sized, low voltage, low cost, and easy to fabricate TWT. It is an attractive choice for many applications, such as communication systems, phased array radars, security detectors, and electronic counter measure (ECM) instruments. In this paper, a Ka band U-shape meander-line slow wave structure (SWS) supported by a diamond rod is presented. The dispersion characteristics of this meander-line SWS are analyzed using CST MW Studio. The S-parameter simulation results show that the reflection is below − 15 dB between 32 and 38 GHz, and the particle-in-cell (PIC) simulation reveals that this meander-line TWT can produce 57 W output power at 36 GHz, when it is driven by a 8.1 kV, 0.04 A sheet beam with rectangular cross-sectional area of 1.0 mm × 0.12 mm. This meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and measured S11 has been achieved and the mismatch between the simulated and measured S21 has been discussed at the end.

Analysis of the Combined Cyclotron and Cherenkov Resonances in Metallic Grating Structures

The metallic grating structure is usually used in the Cherenkov maser. In order to further improve the gain and bandwidth of the sheet beam metallic grating waveguide system, the beam can be with initial transverse and axial velocity instead of pure axial velocity. In this situation, the sheet helical beam will interact with several space harmonics waves simultaneously, and then, the combined cyclotron and Cherenkov resonances can be utilized. Based on the linear theory, the “hot” dispersion equation of the sheet beam metallic grating cyclotron maser is derived and calculated. Through the numerical calculations, the contribution of each resonance, and the influence of beam voltage, the magnetic field and transverse to axial velocity ratio on the gain and bandwidth are analyzed. Besides, the effects of the beam voltage and magnetic field on the growth rate are also simulated, which can further verify the accuracy of the theoretical calculations. This analysis shows the potential of the sheet helical beam with a metallic grating waveguide system, which can be further studied and applied in the future.

0.2-THz Traveling Wave Tube Based on the Sheet Beam and a Novel Staggered Double Corrugated Waveguide

A novel slow wave structure (SWS), named staggered double corrugated waveguide (SDCW), is proposed for the development of wideband high-power terahertz (THz) traveling wave tubes (TWTs). The SDCW-SWS not only has the wideband characteristic of staggered double grating (SDG) but also has the high interaction impedance characteristic of symmetrical double grating. In addition, its tunnel width is independent of the lower cutoff frequency and can be further increased. Numerical Eigen mode calculations show that, under the same dispersion, the passband of SDCW-SWS is increased by more than 10 GHz compared with SDG-SWS, and the average interaction impedance at 195 GHz is increased by about 62%. A particle-in-cell simulation analysis confirms that the average output power, saturated gain, and electron efficiency of SDCW-TWT at 195 GHz are ~110 W, ~20.34 dB, and ~5.46%, respectively, when the operating voltage is 20 kV and the beam current is 100 mA. Therefore, SDCW is a promising slow wave circuit of wideband high-power THz traveling wave amplifier.

Multioutput Circuit for Low Voltage Ultracompact W-Band Klystron

In this article, the design, characterization, and manufacture of a circuit for a ${W}$ -band, ultracompact continuous wave sheet beam klystron are described. This klystron, aiming to produce more than 1.5-kW output power, operates at a comparatively low voltage benefiting the device size and extending its application space. However, a lower operation voltage adversely affects the beam-gap interaction efficiency. Two multigap output cavities have been employed to achieve a higher beam interaction efficiency without introducing additional competing modes or shrinking the interval between the operation mode and competing mode. Inspired by the resynchronization technology, the second output cavity can be optimized for the spent beam from the first output cavity. Comprising a single cavity output structure, the circuit efficiency of this double output cavity circuit is increased from 2.37% to 4.96%. In this circuit, electromagnetic modeling and design have been optimized to avoid complicated structures which are constrained by current mechanical design and manufacturing techniques. The MAGIC simulation shows that, driven by a 1-W RF signal, this circuit can extract more than 1.7-kW output power from a 35-kV, 1-A beam. A prototype single output cavity circuit has been designed and manufactured to determine the required machining tolerances for the final double output cavity circuit.

Shear stops forces distribution analysis in combined floors of multi-storey buildings

Combined flooring is the most frequent and affordable floor disks constructive solution in steel frame buildings. Vertical load is the main load perceived by the overlap. The horizontal loads become necessary to take into account with the store’s number increasing and depending on the construction area. Flexible anchors combine the work of profiled sheet (fixed formwork) and floor beams. The problem is that according to Russian standards the studs setting is governed mainly by design requirements. However, flexible anchors calculation for horizontal load showed that their forces exceed maximum permissible, so the structure cans failure.The forces in the studs change depending on the floor slabs supporting design solution and the aspect ratio. The correction factor derived in the article allows take into account the real efforts distribution in shear stud without losses in calculation accuracy in buildings and structures design. This issue’s study will clarify the combined overlap’s calculating methods and will allow using the material in the most rational way.

Design and Cold Test of Dual Beam Azimuthal Supported Angular Log-Periodic Strip-Line Slow Wave Structure

A novel Ka-band azimuthal supported angular log-periodic strip-line (ASALS) slow wave structure (SWS) is proposed for a miniature radial sheet beam traveling wave tube (TWT). In the proposed SWS, two dielectric rods are employed to support the ASALS at both azimuthal sides. The strip-line is made of high-melting metal; thus, the ASALS SWS has a higher power capacity than microstrip SWSs. The high-frequency characteristics of that proposed SWS are investigated by using simulation software. The ASALS SWS is then fabricated and assembled for cold test. The measured transmission loss and reflection loss are better than − 2.5 dB and − 10 dB, respectively. The hot performance of the proposed is studied based on particle-in-cell (PIC) simulation. It is shown that when the operating voltage is 5700 V, the ASALS TWT can give a maximum output power of 320 W at the frequency of 39 GHz, corresponding to a gain of 14.9 dB and electron efficiency of 9.12%.

Design and Analysis of the Staggered Double Grating Slow Wave Circuit for 263 GHz Sheet Beam TWT

The complete design process of a high-frequency circuit for a 263 GHz staggered double grating, sheet beam traveling wave tube is presented in this article. This device, for use in a pulsed electron paramagnetic resonance spectrometer instrument, requires >30 dB gain and a 20 GHz bandwidth centered at 263 GHz. In addition to the standard Pierce gain analysis and point by point particle in cell (PIC) simulation, a novel fast pulse response analysis technique was utilized to determine the accurate synchronization voltage and test the ``hot” feature of the high-frequency circuit. Since this new method can evaluate the entire bandwidth in a single simulation, it can significantly reduce the computational resources normally required for the conventional PIC analysis while also illustrating the potential instabilities near the band edge. Good agreement between the fast pulse response and PIC simulation results validate the accuracy of this novel method. According to the analysis results and given the manufacturing limits of nano/micro-computer numerical control (CNC) machining, an appropriate SWS, coupler, and sever designs were chosen to complement the simulated design. Finally, a prototype circuit was manufactured and cold tested to verify the design and inspect the machining tolerances.