Sheet Electron Beam Research Articles

Continuous-wave Y-band planar BWO with wide tunable bandwidth

A high performance continuous-wave (CW) backward wave oscillator (BWO) with planar slow wave structure (SWS) and sheet electron beam in Y-band is presented in this paper. The mode selection is discussed by studying the dispersion curve of SWSs, distributions of the electric field, and particle-in-cell simulation results, showing that the designed BWO operates in the fundamental mode TM11. The planar SWSs are fabricated by using the UV-LIGA technology with the processing error less than 0.003 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed BWO can operate in the fundamental mode TM11 and generate the state-of-art output power of 182 mW at the frequency of 0.3426 THz with a large frequency tuning range from 0.318 THz to 0.359 THz.

Design of mm-wave slow-wave devices with sheet and hollow electron beams

The frequency increase of the slow-wave electron devices is accompanied by inevitable increase of the electron current density and ohmic losses which strongly restricts the attainable power. In recent years, the use of the spatially-developed sheet electron beams is considered as the major way to develop the medium-power slow-wave devices at mm and sub-THz waves. Hollow electron beams is another configuration which could be used for this purpose. The designs of the oscillators and amplifiers in Ka-band and W-band with both sheet and hollow electron beams are considered and compared.

Моделирование электронно-оптических систем со сходящимся ленточным пучком для лампы бегущей волны терагерцевого диапазона частот

AbstractA converging sheet electron beam with a cross section of 0.05 × 2 mm and current density of 200 A/cm^2, 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 340 GHz phase‐velocity‐taper travelling wave tube

Staggered double-vane slow wave structure as the core part of the travelling wave tube (TWT) has been more popular in recent years. However, the electron efficiency of this structure is not enough high for higher frequency, especially THz. In this study, phase-velocity-taper method is utilised for the improvement of TWT's efficiency at 340 GHz. The reflection and transmission coefficients of the whole tube with attenuator show good propagation characteristics over the wide frequency range from 330 to 345 GHz. The particle-in-cell simulation results indicate that the output power can increase about 32% at 340 GHz with respect to that of the without-taper structure. The corresponding electron efficiency is improved from 2.8 to 3.5% by phase-velocity-taper. However, the simulation results also show that the tube can produce over 30 W output power in the frequency range from 330 to 343 GHz with an operating voltage of 21.3 kV, a current of 0.043 A, and an input power of 10 mW. In addition, a sheet beam electron gun with a beam current of 43 mA, a beam voltage of 21.3 kV, and beam waist cross-sectional dimension of 0.3 mm × 0.08 mm is also designed as the particle source of the sheet-beam TWT.

Design of W‐band sheet beam travelling wave tubes based on staggered double vane slow wave structure

In this study, a complete and viable plan about a W-band sheet beam travelling wave tube based on a staggered double vane slow wave structure is drawn up. The dispersion characteristics, transposition characteristics of high-frequency system, sheet electron beam gun, vacuum window, periodically cusped magnetic focusing system and beam–wave interaction are analysed by CST Microwave Studio, CST Particle Studio and HFSS. An attenuator is used in this device to suppress oscillation. A phase velocity taper is used to increase output power. The operation voltage is 20.6 kV and the current is 80 mA. With a 10 W input power, the output power is 1100 W versus the gain is 20.41 dB at 95 GHz. The peak amplitude approaches 1200 W versus the gain approaches 20.79 dB at 99 GHz.

0.85 THz truncated sine waveguide traveling‐wave tube with sheet beam tunnel

A sine waveguide (SWG) traveling-wave tube with sheet electron beam tunnel is proposed to amplify the high-frequency terahertz wave. In this study, the slow wave characteristics including the dispersion properties and interaction impedances have been investigated by using the eigenmode solver in the 3D electromagnetic simulation software Ansoft HFSS. The truncated SWG slow wave structure possesses the relatively large average coupling impedance. The beam–wave interaction characteristics of truncated SWG with sheet electron beam tunnel are calculated by high-frequency simulation software CST. From the particle-in-cell simulation results, this beam–wave interaction circuit can produce >490 mW ranging from 0.845 to 0.855 THz with a corresponding gain over 22 dB.

Synthesis of systems formation of converging sheet electron beams at partial magnetic shielding of the cathode

The synthesis method of electro-optical systems forming converging sheet electron beams at partial magnetic shielding of the cathode is developed. Equations of the inerior and exterior problems of the synthesis method and an equation for estimation of the deformation of the configuration of the sheet electron beam in the transit channel are obtained in the paraxial approximation. The proposed method is used to simulate electron guns forming converging sheet electron beams with the electrical parameters similar to the parameters of the uncompressed electron beam for terahertz radiation sources.

Investigation of a Ka-Band High-Power Sheet Beam Relativistic Extended Interaction Oscillator

The sheet beam relativistic extended interaction oscillator (REIO) is a very important high-power millimeter-wave source for many actual and potential applications. A Ka-band sheet beam REIO is designed by means of particle-in-cell (PIC) simulation. In the design, we adopt a sheet electron beam with dimensions of 45 mm × 1.5 mm to reduce the space charge effect and the extended interaction cavities to increase the power capacity. The results of the PIC simulation demonstrate the device can generate an output power of 404 MW at 30 GHz with an efficiency of 20%. In addition, we develop the experiment on a short-pulse accelerator. In the experiment, the oscillator generates a millimeterwave power of 125 MW with a beam current of 4 kA, a beam voltage of 500 kV, and guiding magnetic field of 1 T. The frequency of the output millimeter wave is 30.6 GHz and the pulsewidth is 16 ns. The experiment proves that millimeter wave of over 100 MW can be generated with the sheet beam REIO.

Nonlinear analysis of beam-wave interaction in a planar THz travelling-wave tube amplifier

Large-signal analysis is presented for analysing non-linear beam-wave interaction in a planar THz TWT with a sheet electron beam. The sheet beam within one RF beam wavelength is represented by uniform rectangular charged discs for confined flow of the beam, and the discs are tracked in small distance steps of forward integration. For a planar THz TWT, a staggered double-vane loaded rectangular waveguide slow-wave structure (SDVSWS) is used. Frequency-domain analysis is used to define the RF circuit field in the SDVSWS and the interaction of the RF circuit field with the electron beam is carried out for steady-state TWT operation. The RF circuit field is considered to be continuous as in a helix SWS and it is represented by transmission line theory at each integration plane. A large-signal analysis code of a helix TWT with pencil beam (SUNRAY-1D) was modified for a planar TWT with a sheet beam. The accuracy of the modified SUNRAY code was checked against the 3D e.m. field simulator (CST-PS) by comparing the output performance for a 0.22-THz planar TWT. The results for the gain and the output power over the operating band given by the two codes were found to be comparable. A significant advantage of the SUNRAY code is that it is very fast compared to the CST code. It takes less than a minute to simulate the RF performance of a typical THz TWT at a single frequency and drive power on a standard PC. The SUNRAY code can therefore, be used interactively for design a complete SWS with input/output couplers, sever, loss profiles and phase velocity taper for a high efficiency high gain THz TWT.

Wideband Power Combining of Four Microfabricated W-Band Traveling-Wave Tubes

Wideband power combining of four W-band microfabricated traveling-wave tubes (TWTs) is presented. The proposed TWTs are based on a planar helix slow-wave structure (SWS) with straight-edge connections (PH-SEC) that can be microfabricated with stripline input–output feed. A novel 1:4 WR-10 waveguide-to-stripline power divider–combiner is designed that covers the frequency range of 92–104 GHz. The simulation results show that ${S}_{{11}}$ is less than −20 dB and the magnitude and phase differences among the four output signals are less than 0.01 dB and 0.41°, respectively, indicating a power combining efficiency as high as 99.9%. The power divider, four PH-SEC SWSs, and the power combiner are assembled and the performance of the overall assembly is checked by simulation. The overall ${S}_{{11}}$ is better than −15 dB in the frequency range of 91.7–100.7 GHz and ${S}_{{21}}$ is better than −12.3 dB. Effects of power and phase variation of individual TWTs have also been considered. With four 5-kV and 10-mA sheet electron beams, particle-in-cell simulations show that the combined TWTs can give 25-W saturation peak power at 94 GHz with a gain of 18 dB.

A dielectric-embedded microstrip meander line slow-wave structure for miniaturized traveling wave tube

A modified microstrip meander line (MML) slow-wave structure (SWS) embedded with dielectric rod for miniaturized traveling wave tubes (TWTs) is presented in this paper. High-frequency characteristics, fabrication processes, and beam-wave interaction of the modified MML SWS are analyzed. Compared with conventional MML SWSs supported by dielectric substrate, the modified MML SWS possesses a wider cold bandwidth (about 53.5% increased) and larger interaction impedances (about 21.4% increased). Moreover, this modified MML has better connection with the dielectric, which may improve the slow-wave structure’s stability and reliability under thermal shock, stress impact, and electron bombardment. The beam-wave interaction simulation results indicate that TWTs using the modified MML SWS is capable of delivering 75.85 W saturated output power, corresponding a gain of 28.8 dB and an electron efficiency of 6.32% at the frequency of 35 GHz, with the sheet electron beam of 6000 V and 200 mA.

Study on Radial Sheet Beam Electron Optical System for Miniature Low-Voltage Traveling-Wave Tube

Angle log-periodic meander line microstrip radial sheet beam traveling-wave tube is one kind of novel minimized vacuum device with low beam voltage. To generate and focus the radial sheet electron beam, a novel radial divergent sheet beam electron optical system, including the tractable radial sheet electron beam gun and miniaturized and feasible radial small tunable periodic cusped magnetic focusing system, is proposed in this paper. The fan-shaped radial sheet beam is emitted from the cylindrical surface cathode, compressed in axial direction, and confined in azimuthal direction by the focusing electrode. Simulation results show that the total emission of the angular radial sheet beam gun is 51.2 mA with the dimensions of $0.26~\text {mm} \times 8$ ° under the voltage of 1.7 kV, and the fan-shaped radial sheet beam can totally pass through the fan-shaped drift tunnel under the magnetic field. The experimental results are good in agreement with the simulation results. The tested angular radial sheet beam transmission efficiency is >90% in an 18.8-mm-length beam tunnel with the fill factor of 50%.

Study on Ka-band sheet-beam, three-slot-staggered-ladder coupled-cavity traveling-wave tube in a small tunable periodic cusped magnet

A Ka-band sheet electron beam (SEB) traveling-wave tube (TWT) based on three-slot staggered-ladder (TSTL) coupled-cavity slow-wave structure (CC-SWS) is proposed. The high-frequency characteristics of TSTL SWS were analyzed in detail. A well-matched input/output coupling system that solves the problem of energy coupling between the SWS and the external circuit was designed. A new method of loading the distributed attenuator for TSTL SWS was investigated for suppressing backward wave oscillation effectively. In addition, a SEB gun which can produce the SEB conveniently was optimized. A small tunable periodic cusped magnet (STPCM) system was designed to focus the low voltage, high-current SEB, which decreases the whole dimension of the TWT sufficiently. Moreover, the special STPCM system is predicted to exhibit 100% beam transmission efficiency. Finally, the beam-wave interaction was studied. The results obtained by CST simulation show that the SEB TWT can produce output power over 5 kW within the bandwidth ranging from 31.5 to 35.5 GHz, and the maximum output power is 10.15 kW at 33 GHz, corresponding electron efficiency of 10.36%. The fabrication of the device is under way.

Etching with atomic precision by using low electron temperature plasma

There has been a steady increase in sub-nm precision requirement for many critical plasma etching processes in the semiconductor industry. In addition to high selectivity and low controllable etch rate, an important requirement of atomic precision etch processes is no (or minimal) damage to the remaining material surface. It has traditionally not been possible to avoid damage in conventional radio-frequency (RF) plasma processing systems, even during layer-by-layer or ‘atomic layer’ etch. To meet these increasingly stringent requirements, it is necessary to have an accurate control over ion energy and ion/radical composition during plasma processing. In this work, a new plasma etch system designed to facilitate atomic precision plasma processing is presented. An electron sheet beam parallel to the substrate surface is used to produce a plasma in this system. This plasma has a significantly lower electron temperature Te ~ 0.3 eV and ion energy Ei < 3 eV (without applied bias) compared to inductively and capacitively coupled RF plasmas. Electron beam plasmas also have a higher ion–to–radical ratio compared to RF plasmas, so this plasma etch system employs an independent radical source for accurate control over relative ion and radical concentrations. A low frequency RF bias capability that allows control of ion energy in the 2–50 eV range is another important component of this plasma etch system. The results of etching of a variety of materials and structures in this low-electron temperature plasma system are presented in this study: (1) layer-by-layer etching of p-Si at Ei ~ 25–50 eV using electrical and gas cycling is demonstrated; (2) continuous etching of epi-grown µ-Si in Cl2-based plasmas is performed, showing that surface damage can be minimized by keeping Ei < 10 eV. Also presented are the results of molecular dynamics modeling of atomic precision etching at low Ei.

Performance of a Nano-CNC Machined 220-GHz Traveling Wave Tube Amplifier

We report on hot test measurements of a wide-bandwidth, 220-GHz sheet beam traveling wave tube amplifier developed under the Defense advanced research projects agency (DARPA) HiFIVE program. Nano-computer numerical control (CNC) milling techniques were employed for the precision fabrication of double vane, half-period staggered interaction structures achieving submicrometer tolerances and nanoscale surface roughness. A multilayer diffusion bonding technique was implemented to complete the structure demonstrating wide bandwidth (>50 GHz) with an insertion loss of about −5 dB achieved during transmission measurements of the circuit. The sheet beam electron gun utilized nanocomposite scandate tungsten cathodes that provided over 438-A/cm2 current density in the 12.5:1 ratio sheet beam. An InP HBT-based monolithic microwave integrated circuit preamplifier was employed for TWT gain measurements in the stable amplifier operation region. In the wide-bandwidth operation mode (for gun voltage of 20.9 kV), a gain of over 24 dB was measured over the frequency range of 207–221 GHz. In the high-gain operation mode (for gun voltage of 21.8 kV), over 30 dB of gain was measured over the frequency range of 197–202 GHz. High-power tests were conducted employing an extended interaction klystron.

Observation of the reversed Cherenkov radiation

Reversed Cherenkov radiation is the exotic electromagnetic radiation that is emitted in the opposite direction of moving charged particles in a left-handed material. Reversed Cherenkov radiation has not previously been observed, mainly due to the absence of both suitable all-metal left-handed materials for beam transport and suitable couplers for extracting the reversed Cherenkov radiation signal. In this paper, we develop an all-metal metamaterial, consisting of a square waveguide loaded with complementary electric split ring resonators. We demonstrate that this metamaterial exhibits a left-handed behaviour, and we directly observe the Cherenkov radiation emitted predominantly near the opposite direction to the movement of a single sheet electron beam bunch in the experiment. These observations confirm the reversed behaviour of Cherenkov radiation. The reversed Cherenkov radiation has many possible applications, such as novel vacuum electronic devices, particle detectors, accelerators and new types of plasmonic couplers.

A continuous-wave clinotron at 0.26 THz with sheet electron beam

A high performance continuous-wave (CW) clinotron with a sheet electron beam at 0.26 THz is presented in this paper. The mode selection is discussed by studying the dispersion curve of the high frequency structure, distribution of the electric field, coupling impedance, and particle-in-cell simulation result, showing that the designed clinotron operates in the fundamental mode TM10. The planar comb gratings are fabricated by using the wire electrical discharge machining technology with the processing error less than 0.005 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with a maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed clinotron can operate at the fundamental mode TM10 and generate an output power of 820 mW at a frequency of 0.26 THz with a large frequency tuning range from 0.25 THz to 0.262 THz.

Analysis of Experimental Results on Pseudospark Discharge-Based Electron Beams With Simulation Model

In this paper, simulation studies have been performed to analyze the role of plasma for sheet-electron beam propagation inside a drift space region filled with argon gas using particle-in-cell simulation code VSim6.2. The sheet-electron beam has been propagated inside the drift space of size 100 mm $\times100$ mm $\times200$ mm. A beam emitter of size 7 mm $\times1$ mm, which is equal to size of anode aperture, has been taken at the entrance of the drift space with identical operating conditions to the experiments, i.e., beam voltage 17 kV, beam current 156 A, and argon gas pressure 11 Pa. The transversal and longitudinal distribution of the sheet-electron beam is mainly dependent on beam voltage and current and also on gas pressure inside the drift space. The simulated images of the sheet-electron beam inside the drift space region have been compared with the experimental ones under these conditions. A good agreement has been found between the experimental and simulation results. This analysis has helped in obtaining transient plasma parameters, such as ion density, space charge neutralization time, and secondary electron temperature, simultaneously. These parameters are also analyzed at different operating conditions in the drift space region for sheet-beam stability. The operating condition at which a sheet-electron beam propagation up to 80 mm without any external magnetic field and instability has been obtained and the same has been explained on the basis of charge neutralization factor.

Gain analysis of the gap-groove folded-waveguide travelling-wave tube

In this paper, a Pierce-type analysis for the novel gap-groove folded-waveguide (GGFW) sheet electron beam traveling-wave tube is presented. The introduced analysis effectively reduces the required time for the initial design and optimization procedure of these kinds of tubes. Using equivalent circuit of the slow-wave structure, the one-dimensional linearized Pierce theory is applied to calculate the amplifier gain. Furthermore, the obtained results of the analysis are compared with those of PIC simulations. Good agreement between these results verifies the correctness and accuracy of the presented analysis.

Two Novel Kinds of the $G$ -Band Travelling-Wave Tubes With Multiple Gap-Groove Folded-Waveguides

In this paper, two kinds of the travelling wave tubes (TWTs) with multiple gap-groove folded-waveguides are investigated. In these kinds of tubes, the sheet electron beam passes through the small gap between a bed of nails and the folded groove, realized in a metallic plate. The bed of nails and the metallic plate form a high impedance structure-perfect electric conductor parallel plate waveguide, which prevents the fields from leaking transverse to the propagation direction. Therefore, multiple GGFWs can be placed near each other with no need to any separator. First, a simple G-band TWT with two GGFWs is designed, and the electromagnetic properties of the propagating even and odd modes, versus the distance between two grooves, are studied. Meanwhile, the PIC simulation performed by the particle studio of computer simulation technology indicates that the optimum performance of the tube will occur when the distance between two GGFWs is 0.51 mm, and the odd mode is propagated. In this case, each circuit of the proposed double slow wave structure TWT can deliver 278 W, which is corresponding to maximum gain and efficiency of 43.6 dB and 18.3%, respectively. Afterward, according to these obtained results, a low voltage, relatively high efficiency and miniature log-periodic GGFW TWT with 30 circuits, is presented. The PIC simulation shows that this kind of TWT can deliver 36 W, which is corresponding to the efficiency of 9%.