On the clinotron effect in a backward-wave tube

The results of a theoretical study of the clinotron effect in a clinotron model, which takes into account static electron trajectories in the focusing magnetic field and the initial spacing between the lower beam boundary and the surface of the slow-wave structure, are presented. Physical processes of interaction between a thick electron beam with transverse dimensions comparable with the length of the slow wave and the RF field at its oblique incidence onto the structure are considered. It is demonstrated that, as the current is increased from the starting to the working value, a beam tilt is necessary to reduce the nonlinear effects of interaction between the beam and the RF field and prevent the complex self-oscillation dynamics in the clinotron; in the small amplitude mode (start), the beam tilt is related to optimization of the beam supply into the interaction space, which ensures the minimum starting current. In addition, it is shown that, in the presence of the initial spacing between the beam and structure, the reduced clinotron efficiency η/С increases and, at the optimum tilt angle, is no less than the normalized efficiency of classical backward-wave tubes with a thin electron beam.     

A nonlinear clinotron theory

A model and a system of equations for investigation of the nonlinear regime of a clinotron are presented. Calculations are performed and physical interpretation of obtained results and specific features of manifestation of the clinotron effect for different sheet beam thicknesses and inclination angles to the surface of the slow-wave system is given. The universal dependence of the maximum efficiency and optimal inclination angle in the clinotron on the beam thickness is found. It is demonstrated that, for the optimal beam thickness and inclination angle, the clinotron efficiency considerably exceeds the efficiency of a standard backward wave tube (BWT) for the same electron beam parameters.     

Self-modulation of the output signal in clinotron

It is demonstrated that the self-modulation of the output signal in clinotron results from a delayed response of the distributed system of clinotron to the action of nonlinearity in the interaction of layers of a thick electron beam and high-frequency field. The effect differs from the self-modulation in a conventional O-type BWT, which is determined by the beam as a whole.     

Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.     

The oscillation adjustment in clinotron

Linear and nonlinear stages of the oscillation adjustment in a model of a source of millimeter-wavelength radiation (clinotron) are analyzed using the nonstationary theory of interaction in a system consisting of a thick electron beam and a backward wave. The duration of the transient process is studied as a function of the ratio of the working and starting currents and an angle of incidence on the surface of a slow-wave structure. It is demonstrated that the minimum duration of the process is reached in the vicinity of the optimal regime in which the beam is completely deposited on the surface of the slow-wave structure.     

具有正交直流场的边廊模(TEm11)回旋脉塞的研究

本文给出了具有正交直流场的边廊模回旋脉塞的线性和非线性分析。对模型的小信号起振,同轴腔内导体对模式的截止频率和分割度的影响以及外加电压对电子回旋频率,起振束功率和互作用效率的影响作了较详细的研究。计算表明,对m=2,互作用效率可达41%。我们还将其结果与相同条件下圆柱腔情况作了比较。这些分析有益于工程设计。     

Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.     

A nonstationary theory of the clinotron

Nonlinear equations for the analysis of the nonstationary operating mode of the clinotron are formulated. The linear stage of the transition to steady-state oscillations in the clinotron and the stability of the operating modes, which are found in the framework of the stationary single-mode theory, are considered. Complex dynamics of self-excited oscillations in the clinotron is revealed.     

Diffraction of an electromagnetic beam by infinite planar periodicmetal-strip grating

An hybrid angular spectrum method-Galerkin moment procedure has been developed to analyze the diffraction of an electromagnetic beam incident obliquely on an infinite planar periodic metal-strip grating. The integral expression obtained for the scattered field is expanded by means of an asymptotic method for determining the diffracted far-field. Some numerical examples show the decomposition of the incident beam in several beams corresponding to the propagating Floquet harmonics excited in the grating. The propagation directions of these beams show deviations with respect to the directions predicted by the Floquet theorem. The profile of the scattered far-field is analyzed as a function of the geometrical and electrical parameters     

Mode scattering by a nonlinear step-discontinuity in dielectricoptical waveguides

The scatter of an incident TE₀ mode at a step-discontinuity separating linear and nonlinear waveguides is studied. Under certain conditions the self-focusing nonlinearity is shown to strongly modify the scattered field in comparison with the linear counterpart. The stronger effects are shown to occur when the nonlinear waveguide is operated in the cut-off condition at low power while supporting a nonlinear guided mode at high power. The method of lines is used in modeling the structure     

Theory of the clinotron: A grating backward-wave oscillator withinclined electron beam

A nonlinear theory of the clinotron, which is a modification of the backward-wave oscillator (BWO), is presented. The problem of electron-wave interaction is treated in a self-consistent formulation. Theoretical results are presented on starting conditions, steady-state oscillations, and temperature regimes. Potentials of the clinotron for further upgrading of efficiency and output power are examined     

斜角入射沉积TiO_2薄膜的光学特性和表面粗糙度

采用电子束热蒸发技术在K9玻璃基底上以不同的沉积入射角沉积了单层TiO2薄膜,研究了不同入射沉积角沉积的TiO2薄膜的光学特性、填充密度和表面粗糙度,并比较了不同膜层厚度下薄膜表面粗糙度与入射沉积角之间的关系。研究结果表明,随着入射沉积角的增加,TiO2薄膜的透射率增加,透射峰值向短波移动,薄膜的填充密度从入射沉积角0°时的0.801降低到入射沉积角为75°时的0.341;薄膜的表面粗糙度随着入射沉积角的增加而增加,当入射沉积角为75°时,薄膜的表面粗糙度略高于基底的表面粗糙度。在沉积入射角不变时,随着膜层厚度的增加,膜层的表面粗糙度降低。     

非同轴多层介质椭圆柱体的电磁散射—任意方向斜入射电磁波

本文基于椭圆柱谐基函数展开，对非同轴任意多层介质椭圆柱体的电磁散射进行了严格地电磁场分析，利用Ｍａｔｈｉｅｕ函数及其加法定理，在各层边界面上进行场的匹配，获得了任意方面斜入射电磁波下电磁散射解析解。     

Diffraction of a Wave Beam by an Aperture

The diffraction field of a wave beam from a circular and a rectangular aperture is obtained in the Fresnel region by using the Huygens-Kirchhoff approximation. The diffraction field in the Fraunhofer region can be obtained simply by replacing a parameter. The diffraction field is then expanded into a series of beam mode functions. From the field distributions and the expansion coefficients, which represent the coupling of the incident beam to the various modes in the diffraction field, the effects of an aperture on the incident beam can be known. With this mode expansion method, the conditions for optimum coupling between fundamental modes are obtained and solved numerically.     

Nonlinear analysis of the ion-ripple laser with the longitudinal component of the ion-ripple field taken into consideration

Ion-ripple laser, which consists of a relativistic electron beam obliquely propagating through an ion-ripple in a plasma, is investigated by nonlinear numerical simulation. The influence of the component of the ion-ripple field parallel to the beam direction on beam-wave interaction is analyzed. The results show that the longitudinal component of the ion-ripple field has a considerable influence on ion-ripple laser. The operating parameters are also optimized.     

STUDY OF CROSSED FIELD GYROTRON OPERATING ON WHISPERING-GALLERY MODE

A linear and nonlinear analysis of crossed-field gyrotron operating on whispering-gallery mode TE_(m11) is presented. The detailed discussions are given for the starting oscillationcondition, the effect of the internal conductor in coaxial cavity on the cut-off frequency of modeand the spacing between adjacent modes as well as the effect of the applied voltage on thecyclotron frequency of electron, the starting oscillation beam power and the electron efficiency.It is shown that the efficiency of 41% can be attained for m=2. A comparison of these resultswith those in cylindrical cavity is made. The analyses are helpful for the engineering design.     

Theoretical and Numerical Investigation of a Four-cavity TE<Subscript>021</Subscript>-Mode Gyroklystron

Using self-consistent field theory and PIC simulation, the interaction of electron flow with HF fields in a four-cavity Gyroklystron with TE₀₂₁-mode has been analyzed. Self-consistent field theory includes both linear theory and nonlinear theory. Optimized parameters and their corresponding efficiency, gain and bandwidth of the optimized Gyroklystron have been found. Numerical investigation using PIC simulation is also given. Parameters of the cavities which are operating in TE₀₂₁ mode are optimized to minimize TE₀₁₁ mode and to suppress parasitic self-oscillations. The results of theory are in good qualitative agreement with PIC simulation.     

Characteristics and Optimum Operating Parameters of a Gyrotron Traveling Wave Amplifier

Characteristics and optimum operating parameters are determined for a new type of high-power high-efficiency generator of millimeter waves known as a gyrotron traveling wave amplifier. In the example consided, wave amplification results from the interaction of a TE/sub 01/ waveguide mode with the fundamental cyclotron harmonic of an electron beam. The parameter optimization involves the determination of the point of maximum device efficiency as a function of beam density, beam energy, beam positioning, and external magnetic field for the output power required. An analytical linear theory and a numerical simulation code form the basis of theoretical calculations. As a result of the extensive survey in parameter space, the peak efficiency in the beam frame has been found to exceed 70 percent. This result has been applied to the specific design of a 35-GHz amplifier with output power ~340 kW, a power gain of 2 dB/cm, and a laboratory frame efficiency of 51 percent.     

W波段斜注管高频结构的设计和注波互作用模拟

斜注管是返波管的一种,其基本原理是将电子注稍微倾斜于慢波结构表面,通过改变电子注的倾角来优化有效互作用长度,达到更高的输出功率和效率.本文论述了斜注管的基本原理,对其冷特性进行了研究,初步设计了W波段斜注管慢波结构,并利用3D电磁模拟软件,对其注-波互作用进行了模拟,模拟得到20W的输出功率以及15GHz的带宽.     

High-Power, Highly Efficient Second-Harmonic Generation in a Periodically Poled ${hbox {MgO}}{:}{hbox {LiNbO}}_{3}$ Planar Waveguide

We designed a single-pass quasi-phase-matched second-harmonic generation (SHG) device with a planar waveguide; the device comprised a Y-cut 5 mol% MgO-doped LiNbO₃ (MgO:LiNbO₃)crystal core that was 3 mum thick and SiO₂ cladding. The waveguide provided a high coupling efficiency of 95% between an incident Gaussian beam and the fundamental guided mode of a fundamental wave; it also provided high electric-field confinement in the case of both the fundamental and SHG waves in the core. Thus, a high overlap between nonlinear polarization and an SHG-guided mode was attained. The bonding of the device with the waveguide side positioned downward to a heat sink provided a large heat radiation area when pumping with a near-collimated Gaussian beam, which reduced the temperature rise and its gradient along the waveguide to minimize the phase mismatch. We demonstrated the green light generation of 1.6 W with 40% conversion efficiency using a 7-mm-long sample and 1.2-W SHG with 60% efficiency using an 18-mm-long sample.