A three-dimensional time-dependent theory for helix traveling wave tubes in beam-wave interaction

This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beamwave interaction.The radio frequency electromagnetic fields are represented as the superposition of azimuthally symmetric waves in a vacuum sheath helix.Coupling impedance is introduced to the electromagnetic field equations’ stimulating sources,which makes the theory easier and more flexible to realize.The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations.The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included.The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields,focusing fields and space-charge fields.The numerically simulated results of a tube are presented.     

Field theory of a traveling wave tube amplifier with a tape helix

A self-consistent relativistic field theory for a helix traveling wave tube (TWT) is presented for a configuration in which a magnetized pencil beam propagates through a tape helix enclosed with a loss-free well. A linear analysis of the interaction is solved subject to the boundary conditions imposed by the beam, helix, and wall. The wave equation for the fields within the electron beam corresponds to the Appleton-Hartree magnetoionic wave modes that are of mixed electrostatic/electromagnetic polarization. Hence, the determinantal dispersion equation that is obtained implicitly includes beam space-charge effects without recourse to a heuristic model of the space-charge field. This dispersion equation includes azimuthal variations and all spatial harmonics of the tape helix. Solutions that correspond to both the extraordinary (X) and ordinary (O ) solutions for the Appleton-Hartree modes are found numerically     

Mode Coupling in a Partially Filled Plasma Waveguide With a Dielectric Liner

The stimulated Raman scattering of a perturbed TM mode in a dielectric loaded partially filled plasma waveguide is considered. The radiation is the result of the scattering of pump electromagnetic wave, which is an EH waveguide mode, off of a space-charge wave. A nonlinear wave equation for a three-wave interaction is used to investigate the coupling of the space-charge and waveguide modes. Dispersion relations for electromagnetic modes are solved numerically to study the frequency characteristics of the interaction of the EH waveguide modes with the space-charge modes. Formulas for the growth rates of the backscattered wave near the electron cyclotron frequency are derived, and the effect of a dielectric liner on the growth rates is investigated. Numerical studies show that the presence of the dielectric liner has an effect on the phase-matching condition and leads to rather larger growth rates close to electron cyclotron resonance.      

Parametric interaction of space-charge waves in thin-film semiconductor structures

The general theory of parametric coupling between space-charge waves and drifting charge carriers in thin-film semiconductor structures has been worked out. This theory is applicable, in particular, to n-GaAs and n-InP semiconductors with negative differential conductance due to intervalley electron transitions under high electric fields. We started from the electrodynamic theory of waveguide excitation by extraneous currents, which was extended for arbitrary waveguide structures with composite active media. Our theory makes it possible to study parametric interaction between space-charge waves in semiconductor films with regard for boundary conditions, diffusion, the anisotropy and the frequency dispersion of the differential electron mobility, as well as the multifrequency and multimode nature of a wave process in thin-film structures.     

Low frequency double electron muon resonance (Demur) in fused quartz

Double electron muon resonance was studied with comparable amplitudes of the static and rf magnetic fields. The experiments were carried out in fused quartz and employed a resonant linearly-polarized rf field and a small static field. For small amplitudes of the rf field a three-line frequency spectrum was obtained consisting of a central line at the rf frequency and two weaker lines of equal amplitude symmetrically positioned about the central line. A symmetrical three line spectrum is predicted for muonium using the rotating wave approximation (RWA). For large rf fields the amplitudes of the three lines were not symmetric and depended on whether positrons were observed parallel or perpendicular to the beam. For very large rf fields the total amplitude of all the lines was less than for lower rf fields. These results do not agree with the theory using the RWA and no satisfactory theory currently exists.     

Self-consistent field theory of a helix traveling wave tubeamplifier

A self-consistent relativistic field theory of a helix traveling wave tube (TWT) is presented for a configuration in which a thin annular beam propagates through a sheath helix enclosed within a loss-free wall. A linear analysis of the interaction is carried out, subject to the boundary conditions imposed by the beam, helix, and wall. A detrimental dispersion equation is obtained which implicitly includes beam space-charge effects without recourse to a heuristic model of the space-charge field. The equation is valid for arbitrary azimuthal mode number and is solved numerically for the azimuthally symmetric case. The coupled-wave Pierce theory is recovered in the near-resonant limit. Numerical comparisons between the complete dispersion equation and the Pierce model are described. A discrepancy is found between the Pierce and the field theory even for low currents in the nominally ballistic regime, owing to the dielectric effect of the beam on the helix modes     

自由电子激光中空间电荷波的单电子分析

从单粒子模型理论出发,对考虑空间电荷的自由电子激光进行了分析,并提出了迭代计算方法,计算结果表明,自由电子激光中三波耦合的一次迭代解与已有结果一致,二次迭代解显示了空间电荷波有更复杂的结构. 关键词：     

Nonlinear behavior of localized space-charge waves in space-charge dominated electron beams

We present experimental observations of the abnormal growth of localized nonlinear space-charge waves in space-charge dominated electron beams passing through a resistive channel. The energy width of the space-charge waves is measured on both ends of the channel. Previous experiments had shown that, for small initial perturbations, the energy width of the slow waves increases, while the energy width of the fast waves decreases, in agreement with linear theory. We report that in the nonlinear regime (large initial perturbations), the energy width of the fast wave increases, which is unexpected, and, to the best of our knowledge, no theory exists that would predict this phenomenon.     

多次聚束的空间电荷波理论

本文采用空间电荷波的观念,讨论了包括电子相互作用的多次聚束问题。所得结果,在电流接近以零为极限时,简化成费恩柏格(E.Feenberg)由运动学观点出发的结果。但是空间电荷效应的包括,显示了多次聚束系统一些不能由运动学方法得到的特徵。本文的分析,可以应用在一系列的微波电子器件上。文中对这方面,也提供了一些具体的方向。     

Resonance excitation of polaritons and plasmons at the interface between a uniaxial crystal and a metal

A resonance is theoretically predicted in which a plane electromagnetic wave in a transparent optically uniaxial crystal, reflected from its metallized surface, creates a wave field at the interface whose intensity is considerably higher than the intensity of the incident wave. In the crystal, a high-intensity (bulk or surface) polariton is excited, whereas, in the metal, a large-amplitude localized plasmon is excited. The structure of the fields created in the crystal is close to that of the fields of bulk polaritons at the boundary with a perfectly conducting surface. The nonideality of the metal is taken into account in the Leontovich impedance approximation. Conditions are found under which the resonance is accompanied by a full transformation of the incident wave into a polariton-plasmon localized near the interface. This coupled wave can be considered as a pumped eigenmode. The intensity of the wave field localized at the boundary can amount to 10–15 times the intensity of the incident wave in the visible range. The resonance half-width with respect to the angles of incidence amounts to a few degrees. In the infrared range, the excitation factor can be an order of magnitude higher, while the resonance half-width sharply decreases down to about 0.1° for a wavelength of 5 μm. Conditions are obtained for the resonance excitation of high-intensity bulk polaritons that arise as reflected modes propagating at a small angle to the boundary. The phenomena investigated are completely attributed to the anisotropy of the crystal.     

Vector Approach to Calculating Space-Charge Fields in Crystals withntrast Light Interference Pattern

A new method for calculating space-charge fields in photorefractive crystals with shallow-lying traps illuminated by a light interference pattern of arbitrary contrast and shape is suggested. A space-charge field in a BSO:Cd crystal with shallow-lying traps illuminated by a sine light interference pattern with the high contrast m = 0.99 is calculated.     

Surface-acoustic-wave-induced space-charge waves in electron-hole systems

Space-charge waves in an electron-hole system are studied, which are excited by a moving grating provided by a surface acoustic wave (SAW). The SAW induces a constant current that may change its sign, when a constant electric field is applied opposite to the wave propagation direction. Current resonances are predicted to appear, when the SAW wavelength and frequency match the ones of the space-charge wave.     

毫米波自由电子激光的空间电荷效应

本文编制了三维数值模拟程序,考虑了电子在摇摆器(Wiggler)内纵向速度β^z=υ^z/c<1的影响,考虑了电子在有质动力势阱中因"群聚"而引起的纵向空间电荷力的影响,考虑了电子束内静电波和激光场、Wiggler静磁波的三波相互作用对电子位相的影响等。对因"群聚"而引起的纵向电场满足的方程求出了近似的二维解析解,用4096个电子模拟求解了电子运动方程和光场方程。数值模拟的结果和Livermore实验室的实验结果进行了比较。结果表明,由于上述几项因素的考虑,我们的数值模拟结果和实验位基本一致,消除了文献[1,2,3]中出现的失谐曲线(detuning curve)峰值磁场漂移300-500高斯的差距。     

等离子体波在喇曼自由电子激光中的作用

本文用参量放大器模型,分析了喇曼型自由电子激光中等离子体波的作用。结果表明,在忽略电子束初始横向速度的情况下,慢等离子体波与散射波耦合的必要条件为k_wv₂₀>ω_c,即电子的平衡态运动应处于第一组轨道。文中还求出散射波的色散特性和增益公式,以及散射波与等离子体波的相位匹配关系。 关键词：     

Linear Theory of Radially Inhomogeneous, Unneutralized, Relativistic Electron Beams

A set of four, coupled, first-order differential equations describing the normal modes of a cylindrically symmetric, cold fluid, unneutralized, relativistic electron beam of arbitrary radial profile is derived. Effects of beam rotation and equilibrium fields are treated exactly. The differential equations are found to have singular points for a radially inhomogeneous beam wherever the eigenfrequency equals the cyclotron or Doppler resonance frequencies. The resulting branch cuts in the dispersion function give rise to secularly decaying contributions to the initial value problem. The rate of decay and the character of the eigenmode near the singularity are determined from the solution of the corresponding indicial equation. Discrete eigenmodes also exist and are obtained by numerical solution of the differential equations and boundary conditions. For realistic solid-beam equilibria, only one slow cyclotron-mode exists for any given pair of axial and azimuthal wavenumbers, and that mode is localized at the beam edge. Under identical conditions several slow space-charge modes exist and are not so distorted. However, even at the space-charge limit, the phase velocity of long-wavelength slow space-charge waves does not decrease to zero. These results are relevant to the Autoresonant and Converging Guide collective ion acceleration proposals.     

Theory of self-focusing in photorefractive InP

We present a theory of self-focusing and solitons in photorefractive InP, including the previously unexplained intensity resonance and the resonant enhancement of the space-charge field.     

Linear Cold-Fluid Theory of a Free-Electron Laser

The linear cold-fluid theory of a free-electron laser is given where the laser field must be in the two-mode operation. The ration between the two modes of laser field is obtained. The dispersion relation is discussed in the Raman- and Compton-regimes and the space-charge wave theory is worked out.     

A small signal theory of gyro-devices using the concept ofspace-charge waves

The linear theory of the interaction between a thin annular beam of gyrating electrons and a traveling electromagnetic wave is developed. This theory is very close in its methodology to the classical small signal theory of O- and M-type devices. Just this fact makes it possible to consider a number of issues in the theory of gyro-devices, namely, space-charge wave propagation in drifting electron beams, noise and parametric phenomena, effects of input signal suppression (Kompfner dip) in gyro-traveling-wave-tubes, and gyro-backward-wave-amplifiers     

Spin-polarized transport in inhomogeneous magnetic semiconductors: theory of magnetic/nonmagnetic p-n junctions

A theory of spin-polarized transport in inhomogeneous magnetic semiconductors is developed and applied to magnetic/nonmagnetic p-n junctions. Several phenomena with possible spintronic applications are predicted, including spin-voltaic effect, spin valve effect, exponential and giant magnetoresistance. It is demonstrated that only nonequilibrium spin can be injected across the space-charge region of a p-n junction, so that there is no spin injection (or extraction) at low bias.     

Steady-State Spatial Solitons in Low-Amplitude Regime in Biased Photorefractive-Photovoltaic Crystals

A theory of the space-charge field is improved in biased photorefractive-phorovoltaic crystals. Steady-state spatial solitons are obtained in the low-amplitude regime in biased photorefractive-photovoltaic crystals. When photovoltaic effect is neglected, these solitons are screening solitons, and their space-charge field is the space-charge field of screening solitons. When the external field is absent, these solitons are photovoltaic solitons for the closed or the open circuit and we also predict that gray solitons exist in photorefractive-photovoltaic crystals, and their space-charge field is the space-charge field of photovoltaic solitons.