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.

In this article, we present the results of numerical design and modeling of an electron gun with an impregnated thermionic cathode producing a triple elliptic-shaped electron beam of $0.1\ \text{mm}\times 0.6\ \text{mm}$ dimensions of each beamlet. Such a beam interacts with a higher-order TE30 mode of the dual-grating staggered slow-wave structure (SWS). The 0.2-THz SWS with dielectric absorbers to prevent backward-wave excitation of lower-order transverse modes is designed and simulated.

Design and simulation of a sub-THz traveling-wave tube amplifier with a grating slow-wave structure (SWS) is discussed. A Pierce-type electron gun with a converging sheet electron beam emitted from a cylindrical curved cathode is designed. Beam focusing by the uniform and reversal magnetic field is compared. The results of gain and output power calculations are presented.

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.

This paper contains the results of experimental investigations of electron-optical system, forming convergent sheet electron beam for perspective THz amplifiers. The model of an electron gun consisting of a rectangular cathode with a size of 0,5×0,8 mm 2 , focusing electrode and anode was created. Measurements of current-voltage characteristics were carried out in pulsed mode, the current density distribution was measured using a pinhole method. Thus the beam current is about 130 mA and a beam thickness not exceeds 100 μm.

The results of simulation of electron-optical systems with sheet electron beam with compression are presented. Electron gun is considered with thermionic and field emission cathodes with 2.1 0.8 mm 2 . The result of modeling the electron gun at linear compression of 14, the beam of current 0.1 A has dimension of 0.15 0.8 mm 2 are performed. The electric field on the cold cathode is 0.16· 10 5 V/cm at anode voltage 20000 V.

0.2-THz traveling-wave tubes (TWT) with a grating slow-wave structure (SWS) are studied. The results of design and simulation of sheet-beam and multiple-beam electron-optical systems are reported. Electromagnetic parameters of SWSs are calculated. The results of small-signal and large-signal gain analysis are presented. According the simulations, for 0.l-A 20-kV sheet beam, peak small-signal gain and saturated power are about 39 dB and 80 W, respectively.

We present an analysis of the current state and development of pulsed amplifying traveling-wave tubes for terahertz radiation operation at frequencies of at least 200 GHz, as well as the development prospects of the principles of creating electron-optical and magnetic systems. The possibility of using field emission cathodes based on carbon nanotubes for constructing an electron-optical system with the compression of a sheet beam is discussed. A numerical simulation of a field emission electron gun forming a sheet electron beam for traveling-wave tubes of the terahertz range is carried out.

This report presents a design of an electron-optical system (EOS) with triple electron elliptical beams. A current of each beam is 31 mA and a dimension is 300×600 ¼m 2 . A magnetic field of 0,55 T is used for focusing of electron beams. A technology of fabrication and assembly of a model of EOS that contains a dispenser cathode, anode, collector and magnetic system is presented. In the course of experimental investigation of a model in impulse mode total current of 93 mA was obtained at cathode temperature of 1100°C and grid potential 900-1000 V. The realized design of a model with elliptical beams demonstrates the feasibility of creating of THz TWT on the basis of a similar EOS.

Особенности разработки электронно-оптических систем для импульсных терагерцовых ламп бегущей волны (Обзор)

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.

Microfabricated vacuum-tube millimeter- and THz-band sources are of great interest for numerous applications such as communications, radar, sensors, imaging, etc. Recently, miniaturized sheet-beam traveling-wave tubes for operation at sub-THz and THz bands have attracted a considerable interest. In this paper, we present the results of modeling and development of slow-wave structures (SWS) for medium power (10-100 W) traveling-wave tubes (TWT) amplifiers in near-THz frequency band. Different types of SWSs are considered, such as double-vane SWS for TWT with a sheet electron beam, folded-waveguide SWS, and novel planar SWSs on dielectric substrates.

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.

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 x 1.1 mm(2) and current density of 45 A/cm(2) 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.

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/cm 2 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.

This report presents the results of 3D modeling of an electron optical system with low perveance electron elliptical beams. The comparison of triple elliptical beams with continuous sheet and elliptical beams has been conducted. The studied systems have a triode design with an anode potential of 20 kV and a grid potential of 950 V. The total current of electron beams is a 93 mA. Results of 3D modeling show that using of electron optical system forming triple elliptical beams in THz devices permits to achieve a high current transmission through a beam tunnel of a slow-wave structure with a dimension of 140×2500 ¼m 2 and provide interaction with the higher transverse mode of three RF field variations.

The results of modeling by synthesis and analysis a convergent sheet electron beam with a cross section of 0.05 2 mm 2 and a current density of 200 A/cm 2 with magnetic shielding of the cathode are presented. Experimental investigations of the current-voltage characteristic of an electron gun in a pulsed mode are conducted, where collector current is 200 mA, and the measured beam thickness is 70 μm.

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.

We study a 0.2-THz traveling-wave tube (TWT) with a grating slow-wave structure (SWS) and sheet electron beam focused by reversal magnetic field. Change in the direction of the guiding magnetic field causes change in the direction of beam curling and can suppress the diocotron instability, which is a main problem for sheet beam focusing. Electron gun with a converging sheet beam is designed and fabricated. Over 100 mA current was measured. The results of small-signal and large-signal TWT gain analysis are presented.

Синтез электронно-оптических систем с компрессией ленточного пучка для ламп бегущей волны терагерцевого диапазона© А