Search

In this article, by substituting the dielectric tensor in Maxwell’s equations and using the boundary conditions in a longitudinally magnetized plasma-filled coaxial elliptical waveguide, the dispersion relation in the considered configuration is derived. We study the energy and dynamic of an injected external electron with initial energy using radiation of an electromagnetic source in the considered waveguide having the considered hybrid mode. The trajectory and kinetic energy of an injected electron in the considered waveguide along the propagating axis and hybrid field components are plotted. The obtained differential equations are numerically solved by the fourth-order Runge–Kutta method, and the results are graphically presented. The effects of different parameters on the trajectory and kinetic energy of injected electrons are investigated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A magnetically insulated line oscillator (MILO) was studied using the simulation software packages high-frequency structure simulator (HFSS) and Computer Simulation Technology-Particle Studio (CST-PS). HFSS was used to find dispersion characteristics of the slow-wave structure and predict resonant-mode frequencies. CST-PS was used to analyze the operation of the device with space charge included. At an applied voltage of 500 kV, CST-PS predicted 1.25-gigawatt (GW) microwave generation at 1.2 GHz while drawing 57 kA. These simulations are consistent with previously published experimental results for a similar MILO. The CST-PS model was used to predict MILO operation as a function of injected voltage, and a separate study was performed to evaluate the effects of an independent, externally applied axial magnetic field. These simulation efforts are in support of upcoming experiments at the University of Michigan, where the MILO investigated in this article will be tested on a new linear transformer driver facility. [ABSTRACT FROM AUTHOR]

This article presents a small-signal theory of a tape helix traveling-wave tube (TWT) with distributed cold tube loss, including the recently discovered space charge effects on the circuit mode that was obtained from the exact dispersion relation of the corresponding lossless tube. The classical values of Pierce’s parameter ${C}$ and ${Q}$ are modified in this new formulation, while the cold tube loss will enter in a similar way as in Pierce. Realistic examples are given, including tubes with uniform circuit loss and with a spatial sever, and compared with the Pierce’s classical theory. [ABSTRACT FROM AUTHOR]

Based on a kinetic model, a linear theory of the 2-D sheet beam metallic grating cyclotron maser has been derived and analyzed numerically. The TE mode dispersion relation and the periodicity of the normalized amplitudes of spatial harmonics of the cyclotron maser with rectangular gratings are obtained. Through numerical calculations, the dependence of the growth rate on the gap distance between the metallic grating surface and the beam, the external magnetic field strength, the beam current, the transverse-to-axial velocity ratio, the axial velocity spread, and the beam voltage are analyzed. This article presents an analysis of interaction using the fundamental TE mode in the 2-D metallic grating sheet beam system. The fundamental TE mode in the 2-D metallic rectangular waveguide grating structure is the fundamental TMx mode in the 3-D rectangular waveguide grating structure and this method can be extended to the practical 3-D interaction system that operates at other TMx modes and has a good potential for the study of the combined resonances in cyclotron masers with grating structures. [ABSTRACT FROM AUTHOR]

In this paper, the finite-element method (FEM) is applied for an exact solution of the dispersion of hybrid electromagnetic waves excited in a novel combined elliptical waveguide. This special configuration is included of an elliptical metallic waveguide filled with a dielectric material, whereas two axial hollows with circular cross section have been created in it. A hollow is placed in one of focuses of the elliptical waveguide and second hollow is located in another focus or shifted from it. Two straight relativistic electron beams with the same currents and velocities in opposite directions are injected inside the hollows. Here, we apply an accurate approach in which the electromagnetic fields described by the FEM and satisfies boundary conditions at the interfaces of different regions. Then, the time growth rate of slow waves amplified by the electron beam is numerically calculated. The excited waves are in microwave range. The effects of accelerating voltage and current density of electron beams, and geometrical parameters such as radius and location of electron beam, on the frequency spectra, the growth rate, and profiles of axial electric and magnetic fields of excited slow waves are studied. Our research shows, the novel waveguide studied in this paper is superior to other waveguide structures in wave amplification with applying minimum input electrical power. [ABSTRACT FROM AUTHOR]

An analytical model is developed with the aim to investigate the propagation of dust-acoustic (DA) waves in a multicomponent thermal dusty plasma system including ion species as well. Dust particles are considered positively charged by electron and ion currents, thermionic and UV photo-ionic processes. The model is applied to laboratory plasma as well as Martian atmospheric plasma to explain the nature of dust potential variation as well as characteristics of DA propagation modes within the linear and nonlinear regimes for given plasma parameters. In the nonlinear regime, the KdV equation is derived, and the equation is seen to support the propagation of compressive solitons in laboratory plasma system and rarefactive solitons in the case of Martian atmospheric plasma. The inclusion of ion species in the system is seen to have an important role in determining the propagation speed, the amplitude, and the corresponding width of solitons. The thermionic work function W, photon yield factor Y, and low value of flux density of UV photon beam $J$ do not have an appreciable impact on dispersion relation and DA soliton structures. On the contrary, noticeable changes occur in the case of the dust surface potential obtained in both laboratory and Martian plasmas. [ABSTRACT FROM AUTHOR]

As it is well known that the simplified classical Pierce’s three-wave theory can provide scaling insights into traveling-wave tube (TWT) operation for its close-form solutions, and thus becomes a useful guide for TWT design. However, the classical Pierce’s three-wave theory shows poor agreement with Lagrangian theory, so determining how to achieve a more accurately Pierce’s three-wave theory from Pierce’s four-wave theory becomes an open problem. In this paper, a more accurately revised Pierce’s three-wave dispersion relation is deduced by using an approximate treatment on the nonlinear term of the dispersion relation of Pierce’s four-wave beam-wave interaction theory. Meanwhile, the boundary conditions of classical Pierce’s three-wave theory are revised by theoretical analysis. Thus, the revised Pierce’s three-wave theory is established. The Pierce small-signal theories are compared to each other and Lagrangian theory on a set of TWT parameters which are based on a single pitch section of C- and Ku- bands TWTs. It is found that the revised Pierce’s three-wave theory agrees extremely well with Lagrangian theory and gains more accuracy than the classical Pierce’s three-wave theory in the small-signal beam-wave interaction region. Finally, the phase difference between Pierce’s four-wave theory and revised Pierce’s three-wave theory is discussed. [ABSTRACT FROM AUTHOR]

The propagation of ionic perturbations in a dusty plasma is considered through a three-species kinetic simulation approach, in which the temporal evolution of all three elements, i.e., electrons, ions, and dust particles are followed based on the Vlasov equation coupled with the Poisson equation. Two cases are focused upon: first, a fully electron-depleted dusty plasma, i.e., a plasma consisting of ions and dust particles. The second case includes dusty plasmas with large electron-to-ion temperature ratios. The main features of the ionic waves in these two settings, including the dispersion relation and the Landau damping rate, are studied. It is shown that the dispersion relation of the ionic waves perfectly matches the dispersion relation of Langmuir waves and hence is called Langmuir-like ionic waves and can be considered as Langmuir-like ionic waves. These waves can be theoretically predicted by the dispersion relation of the dust-ion-acoustic waves. The transition of ionic waves from dust-ion-acoustic to Langmuir-like waves is shown to be sharp/smooth in first/second case. The Landau damping rates based on simulation results are presented and compared with theoretical predictions wherever possible. [ABSTRACT FROM PUBLISHER]

In this paper, the electromagnetic properties of a beam free trapezoidally corrugated slow wave structure (TCSWS) are numerically and experimentally investigated. The dimensions of the TCSWS are selected so that it can be deployed in $X$ -band backward wave oscillators (BWOs). The theoretical dispersion characteristics for the axisymmetric TM01\--TM03 modes are obtained by solving the dispersion equation numerically. In order to verify the numerical calculation, a cold test is conducted using a 6-period TCSWS cavity and a vector network analyzer (VNA). The cavity is excited by a small needle-type antenna and frequency of the VNA is swept over the passbands. The dispersion characteristics are obtained from frequency values of the discrete resonant peaks of reflection measurement of each TM mode. Experimental results show an excellent agreement with numerical ones. The numerical and cold test results reveal that TCSWS can be used as an alternative to sinusoidally corrugated slow wave structure in BWO experiments with an advantage of ease of fabrication. [ABSTRACT FROM PUBLISHER]

The dispersion relation of electromagnetic waves in a rippled-wall elliptical waveguide with a degenerate plasma column protected by an elliptical annular dielectric layer is theoretically investigated. Using the linear field theory, the dispersion relation of electromagnetic waves in a rippled-wall elliptical waveguide with a plasma rod and an elliptical annular dielectric is obtained. In addition, by injecting a finite thick annular intense relativistic electron beam in this waveguide, the dispersion relation of these waves is investigated. In addition, a cold and uniform plasma-filled traveling wave tube with sinusoidally corrugated slow-wave structure is driven by a finite thick elliptical annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. Using the linear field theory, the dispersion relation for the elliptical relativistic traveling wave tube is derived. [ABSTRACT FROM PUBLISHER]

An improved small-signal theory of triaxial klystron amplifiers is proposed with a reduction factor and the beam coupling coefficient being taken into account. It may be concluded that the beam coupling coefficient amends the amplitude of the modulated current and the reduction factor mainly modifies the optimum drift distance, at which the modulated current is maximum. The modified theory is validated by means of PIC codes, which indicates that the improved theory predicts the first-order modulation current more accurately than the previous theory. [ABSTRACT FROM PUBLISHER]

The dispersion characteristics of electrostatic and electromagnetic modes of an electron tube, with ion channel guiding, in a cylindrical waveguide are presented. The analysis takes into account a relativistic hollow electron beam guided by an ion channel. Dispersion relations are derived and solved numerically to study the waveguide, betatron, and space charge modes. The effect of the annular electron beam thickness on frequencies of the electrostatic and electromagnetic waves is investigated. This paper reveals the strong dependence of the electromagnetic and electrostatic waves' frequencies on the electron beam thickness. The results of this paper are compared with previous works where an electron tube is guided with an axial magnetic field. [ABSTRACT FROM PUBLISHER]

The dispersion characteristics of a toroidal waveguide in the presence of a plasma column are considered. The solution of the wave equation in a toroidal waveguide is presented using an analytical approximation method. In this method, the curvature of the axis of the waveguide is considered as a disturbance parameter to the straight circular cylinder approximation. The perturbed torus field for both the plasma and the vacuum regions is expanded in terms of the eigenfunctions of the unperturbed quantities. The effect of the plasma column in the toroidal waveguide is considered as the second perturbation factor in MHD equations. The perturbed Maxwell's equations along with the perturbed momentum transverse and the continuity equations lead to dispersion relation. [ABSTRACT FROM AUTHOR]

A simple but reasonable approach to the cold dispersion analysis of a coaxial arbitrary-shaped groove cylindrical waveguide is presented in the fast-wave regime for potential application in wideband gyro-traveling-wave tubes (gyro-TWTs). The unified dispersion equation of this structure is obtained by using an approximate field-theory analysis, in which the profile of the groove is approximately replaced by a series of rectangular steps, and the continued relation of the fields between two adjacent steps and the matching conditions at the interface between the groove region and central region are investigated. The dispersion characteristics of the disk-loaded structure obtained by modifying above results have been validated against those reported by Kesari et al. Meanwhile, the dispersion characteristics of arbitrary-shaped groove, such as the triangle-groove-loaded one are proved to agree well with Computer Simulation Technology (CST) Microwave Studio simulation. The results of numerical calculations of the dispersion relation shows that the adjustment of structure parameters led to the possibility of widening the straight-line portion of ω-β dispersion characteristics, which is required for wideband TWT performance in view of widening the bandwidth of resonance between the beam-mode and the waveguide-mode. Comparison of several different shape groove-loaded structures shows that the coaxial inverted trapezoid groove one shows the most potential application in wideband gyro-TWT because its transverse electric field is the greatest so that can interact effectively with the electron beam. [ABSTRACT FROM AUTHOR]

Normal mode spectra of finite two-dimensional dust clusters of microspheres in a complex plasma have been measured and analyzed. The mode spectra have been obtained from the thermal Brownian motion of the microspheres. Here, small, medium, and large clusters have been investigated in view of the transition from the normal mode spectrum of finite clusters to the dispersion of waves in infinite systems. [ABSTRACT FROM AUTHOR]

A helicon-type discharge is realized in a curved magnetic field with end point launching of whistler waves by a flat RF antenna. Standing modes are observed by monitoring conditions of zero reflected power. There are indications of Landau damping, with the phase velocity matching the thermal velocity. [ABSTRACT FROM AUTHOR]