On the cyclotron maser instability in a waveguide

The cyclotron maser instability is conventionally treated as a pure electromagnetic instability⁽⁵⁾. Waveguide modes can'be equivalent to plane waves reflected slantingly upon the two sides of the waveguide. According to the principles of plasma physics(⁶) the electromagnetic and the electrostatic modes can't be decoupled when the wave vector isn't strictly perpendicular or parallel to the d-c magnetic field. Therefore the conventional treatment is incomplete and invalid in the case of intense beams.Vlasov kinetic theory of the cyclotron maser instability taking into account the space-charge wave is presented. It is found that the respective couplings between the negative-energy cyclotron mode and the RHCP waveguide mode as well as the fast space-charge mode are responsible for the wave-guide maser instability.     

The microwave generation mechanism of arelativistic electron beampropagating through the dielectric-loaded cylindrical waveguide

The general dispersion relation is derived for the fundamental transverse magnetic modes driven by a cold relativistic electron beam in a dielectric-loaded cylindrical waveguide using the fluid Maxwell equations. It is then reduced to the algebraic equation for the space charge and cyclotron modes using a tenuous beam approximation. Solutions of the resulting equation are obtained by varying several parameters, such as the external magnetic field the dielectric constant and the thickness of the dielectric material. It is shown that the growth rate of the slow cyclotron instability is greatly increased for the region of B_o≲1000 G to the extent that it becomes comparable to the growth rate of a slow space-charge instability. In this region the magnetic-field effect on the slow space-charge mode is shown to increase the growth rate by up to 10%. In the limit of the critical external magnetic field defined as the field below which no beam equilibrium exists, it is found that two slow modes of cyclotron and space-charge modes become degenerate with a finite value of growth rate     

未磁化等离子体介质切连科夫脉塞的线性理论

利用线性自洽场理论，讨论了电子在扰动场作用下的三维扰动．在此基础上，对常用的薄环形相对论电子环束在填充未磁化等离子体的介质筒慢波波导中激励的切连科夫辐射进行了详细的分析，导出了此电子环束与慢波系统中任意波导模互作用的色散方程和波增长率，并对其进行了详细的分析和讨论．分析表明切连科夫辐射是由其波导模与电子注模耦合所致．最后详细计算和分析了等离子体密度对色散特性和波增长率的影响 关键词：     

Wave growth rate in a cylindrical metal waveguide with ion-channel guiding of a relativistic electron beam

This paper addresses the formulae and numerical issues related to the possibility that fast wave may be grown when a relativistic electron beam through an ion channel in a cylindrical metal waveguide.To derive the dispersion equations of the beam-wave interaction,it solves relativistic Lorentz equation and Maxwell’s equations for appropriate boundary conditions.It has been found in this waveguide structure that the TM 0m modes are the rational operating modes of coupling between the electromagnetic modes and the betatron modes.The interaction of the dispersion curves of the electromagnetic TM 0m modes and the upper betatron modes is studied.The growth rates of the wave are obtained,and the effects of the beam radius,the beam energy,the plasma frequency,and the beam plasma frequency on the wave growth rate are numerically calculated and discussed.     

Excitation of Electromagnetic Modes in a Dielectric-Loaded Waveguide via Cyclotron Resonance Interaction

An analytical treatment of the excitation of electromagnetic modes by an axial electron beam in a cylindrical waveguide partially loaded with a dielectric is presented. Equations describing the mode structure of the waves are obtained in cylindrical geometry. Using apropriate boundary conditions a dispersion relation is derived in the weak-beam approximation (?b >> ?). In addition to the conventional Cerenkov interaction, the slow-cyclotron resonance interaction (? ? ?V0 - ?c), which involves the coupling of the TM mode of the waveguide with the slow cyclotron beam mode, is also seen to be important. The growth rate of the instability scales as n01/2 (where n0 is the beam density), decreases with an increase in V0, and is rather insensitive to the variation in the magnetic field.     

填充等离子体的介质同轴波导中的切伦科夫辐射

 利用自洽线性场理论，导出了薄环形相对论电子注通过填充等离子体的介质同轴波导中的注波互作用色散方程，得到了注波互作用产生切伦科夫辐射的同步条件和波增长率。分析了填充等离子体后的波与电子注之间的能量交换及等离子体密度对色散特性、波增长率和注波能量交换的影响。分析结果表明：切伦科夫辐射是由沿介质同轴波导传播的慢波与沿薄环形相对论电子注传播的负能空间电荷波耦合所致，且其耦合强度与电子注的密度成正比；输出频率和波增长率随着填充等离子体密度的增大而提高；保持一定的输出频率，增大电子注的束流可得到高的微波输出功率。     

Excitation of slow EM waves in a waveguide having a thin, annularplasma sheet

A thin, annular plasma sheet in a waveguide slows down the phase velocity of electromagnetic modes in a plasma density window for frequencies below the electron cyclotron frequency via Cerenkov interaction. At lower densities, the plasma is not effective enough to reduce the phase velocity of the EM wave below c. At higher densities the plasma expels the radiation field, leading to enhancement of phase velocity. The lowest mode having azimuthal number l=0 is most unstable. The radial mode having amplitude maximum at r=a, viz the plasma boundary, has the largest growth rate     

Effect of longitudinal space-charge waves of a helical relativisticelectron beam on the cyclotron maser instability

The influence of the longitudinal space-charge waves of a coherently gyrophased helical relativistic electron beam on the cyclotron maser instability is investigated in a cylindrical waveguide configuration using a three-dimensional kinetic theory. A dispersion relation that includes waveguide effects is derived. The stability properties of the cyclotron maser interaction are examined in detail. It is shown that, in general, the effects of space-charge waves on a coherently gyrophased beam are suppressed in a waveguide geometry, in comparison with an ideal one-dimensional cyclotron maser with similar beam parameters     

Collinear interaction of optical waveguide modes with an increasing space-charge wave

Collinear interaction of optical modes in a thin-film semiconductor waveguide with a space-charge wave increasing along its propagation direction has been investigated. Analytical solutions to the equations of coupled unidirectional and counterpropagating waveguide modes at their phase matching are obtained for the first time, and the dependence of the mode conversion efficiency on the space-charge wave amplification level, the coupling coefficient, and the length of the interaction region of optical modes is analyzed.     

Linear analysis of cyclotron-cherenkov and cherenkov instabilities in dielectric-loaded coaxial waveguides

We present, based on the cold fluid theory, linear analysis of the Cherenkov and cyclotron-Cherenkov instabilities which are driven when a linear electron beam is injected into a dielectric-loaded waveguide immersed in an axial magnetic field. In the analysis we consider azimuthally symmetric TM_0n modes. We derive dispersion relations for three types of waveguide, and compare computationally obtained linear growth rates of both instabilities. For the type A, which consists of a metallic cylinder with dielectric liner on its inner surface, the growth rate of the Cherenkov instability is larger than that of the cyclotron-Cherenkov instability. For the type B, which consists of a dielectric core and an outer metallic cylinder, both growth rates are comparable. And for the type C, which consists of a metallic core with dielectric liner on its surface and an outer metallic cylinder, the growth rate of the latter instability is higher than that of the former instability. Finally, for the type C, obtained are dependences of the oscillation frequency and the growth rates of both instabilities on the following parameters: the beam energy, the beam current, the axial magnetic field, the dielectric constant, and the thickness of the dielectric.     

Field theory of dielectric Cherenkov maser

The effect of three-dimensional perturbed velocity and three-dimensional perturbed current density on the beam-wave interaction of dielectric Cherenkov maser is analysed by use of the self-consistent linear field theory. Three distinct cases are considered. First, the propagation of the electron beam in an annular dielectric liner enclosed by a loss-free conducting wall is investigated. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. It's clearly shown that the instability of the interaction results from the coupling of the TM mode in the dielectric lined slow-wave waveguide to the beam mode via the electron beam. And the coupling is proportional to the density of the beam. The growth rate of the wave produced by the electron beam are obtained. Then, the case of a relativistic electron beam guided by a longitudinal magnetic field in the same slow-wave structure is examined. The motion of electrons could be approximated to be one-dimensional when the simultaneous condition of the beam-wave interaction of dielectric Cherenkov maser is satisfied. Finally, the effect of the background plasma on the instability of the beam-wave interaction is studied.This work is supported by National Natural Science Foundation of China.     

Stimulated raman scattering from plasma modes in magnetoactive semiconductors

Stimulated scattering off electron plasma mode is investigated analytically for the case when the pump wave is an intense circularly polarised electromagnetic wave propagating parallel to a homogeneous dc magnetic field in an isotropic semiconductor-plasma. The threshold electric field of the pump necessary for the stimulated Raman scattering and the growth rate of the parametrically unstable mode have been obtained for two cases (i)B ₀=0 and (ii) B₀ ≠ 0. It is seen that the magnetic field does not significantly affect the threshold electric field as well as the growth rate provided the cyclotron frequency is small compared to the frequency of the pump wave. The threshold conditions are also found to be insensitive to the electron thermal velocity.     

The cyclotron autoresonance maser with a large-orbit electron ring in a dielectric-loaded waveguide

The cyclotron autoresonace maser with a large-orbit electron ring in a dielectric-loaded waveguide has been analyzed. The stability properties are investigated self-consistently on the basis of the linearized Vlasov-Maxwell equations. The numerical results show the growth rate increases when the electron rotating ratio increases. And the dielectric liner can greatly reduce the energy of the electron beam.     

Wave dispersion, growth rates, and mode converter analysis for asheet beam, hybrid-mode Cerenkov amplifier

The hybrid-mode dispersion relation and resonant growth rates are solved for a finite-thickness sheet electron beam propagating through a rectangular guide with a thin dielectric slab. Analytic results for the growth rates, bandwidth and mode competition for an infinite magnetic field in the limit of a dilute beam are then presented. To properly couple to the desired EH₁₀ hybrid amplifier slow wave mode, the coupled waveguide mode equations are solved for a dielectric taper to accomplish the TE₁₀ to EH₁₀ mode transition. A piecewide linear taper which suppresses the competing EH₁₁ mode and other hybrid modes is developed and the overall amplifier system is discussed     

Waveguide interaction between light and an amplified space-charge wave

The collinear interaction of optical waveguide modes is considered in a thin semiconductor layer containing an optical inhomogeneity (space-charge wave) growing along the wave-propagation direction. Coupled-mode equations are solved for the case where interacting waves propagate in the same direction or in opposite directions. The mode conversion efficiency is shown to depend substantially on the space-charge wave amplification with allowance for the detuning from the phase matching condition. The incident and the oppositely propagating modes can be “degenerate,” in which case the modes have the same power over the entire disturbed region.     

Linear Theory of Plasma-Filled Coaxial Cylindrical Cherenkov Maser

Injection of background plasma into the beam-wave interaction region can greatly enhance the beam-wave interaction efficiency and the microwave output power of the device. In this paper, a new type of plasma-filled slow-wave structure, i.e., plasma-filled, dielectric-loaded coaxial cylindrical waveguide with a dielectric ring enclosing tightly the inner conductor, is developed. The Cherenkov radiation excited by the beam-wave interaction in the slow-wave structure is examined by use of the self-consistent linear field theory. The dispersion equation and the synchronized condition of the beam-wave interaction are derived. It's clearly shown that the Cherenkov radiation excited by the beam-wave interaction results from the coupling between the slow electromagnetic wave, TM-modes, propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam. And the wave growth rate is solved, and the beam-wave energy exchange in the presence of the background plasma is discussed. Finally, the effects of the background plasma density on the dispersion characteristics, the distribution of the longitudinal fluctuating electric field, the wave growth rate and the beam-wave energy exchange are calculated and discussed.     

Scattering from an eccentric system,including a dielectric rod placed in a thin annular magnetized relativistic rotating electron beam (TAMRREB)

The electromagnetic wave scattering from a dielectric rod placed in a non-coaxial thin annular magnetized relativistic rotating electron beam is simulated. The resonance frequency shift and the effective factors on it are investigated. In addition, the dependencies of pattern of scattering to the plasma frequency, the rotating frequency, geometrical dimensions and dielectric constant of dielectric rod have been investigated. The eccentricity effect on the resonance frequencies is studied.     

X-band dielectric Cerenkov maser amplifier experiment

An X-band dielectric Cerenkov maser amplifier experiment is reported. The amplifier system consisted of a solid, thermionically generated electron beam propagating through a cylindrical waveguide partially filled with an annular, dielectric liner. The input signal was provided by a tunable (9-10.3 GHz) magnetron with power up to 10 kW. Electron beam voltages and currents of up to 250 kV and 100 A could be generated for 1 μs pulse durations. The system was configured to operate in the TM₀₁ mode of the dielectric-lined waveguide. In this experiment the gain of the system with respect to the length of the dielectric liner was studied at a fixed input frequency of 10.3 GHz. At electron beam parameters of 160 kV and 60 A, a power gain of 24 dB over 56 cm of interaction length was measured for an input power of 4.5 kW, corresponding to a maximum RF amplified power of 1.15 MW and 12% efficiency