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.     

Transmission properties of microwave in rectangular waveguide through argon plasma

To study the impact of plasma generated by microwave breakdown on the propagation properties of microwave in high power microwave(HPM) devices, a three-dimensional(3-D) fluid model of argon plasma slab in rectangular waveguide is established and calculated by the finite-difference-time-domain(FDTD) method. A rectangular waveguide with a breakdown chamber filled with argon is set as the physics model, and HPM with frequency of 3–50 GHz propagates through this physics model. The time evolutions of the breakdown process are investigated, the reflection, transmission, and absorption coefficients of HPM are calculated, and the influences of some important parameters, including the thickness of the plasma slab and the microwave frequency on the propagation properties of the microwave are shown. Results of this work can offer theoretical instructions for suppressing the influence of breakdown to the performance of HPM devices, and for the use of microwave breakdown, such as the design of plasma limiter or absorber in HPM devices.     

Transition radiation of surface electromagnetic waves by electron bunches in a cylindrical waveguide

Transition surface electromagnetic radiation from electron bunches that cross a metal-insulator-semiconductor structure in a perfectly conducting semi-infinite cylindrical waveguide is studied. It is shown that, using a periodic sequence (train) of electron bunches, a particular surface waveguide eigenmode can be amplified by bringing its frequency to resonance with the bunch repetition frequency in the train. Those eigenmodes are amplified most efficiently whose frequency falls into the range occupied by the first maximum of the geometric factor of one bunch.     

Excitation of microwave by an annular electron beam in a plasma-filled dielectric lined waveguide

An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper an excitation of Cherenkov radiation by a thin annular relativistic electron beam in a plasma-filled dielectric-lined waveguide is analysed by use of the self-consistent linear theory. The effect of the thin annular electron beam on the beam-wave interaction is completely described by a jump condition. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. Finally, the growth rate of the wave is obtained, and the effect of the background plasma density and the electron beam radius on the growth rate of the wave are presented.This work is supported by National Natural Science Foundation of China.     

波导管中微波波长测量方法的研究

基于微波测量线中驻波分布公式,采用测量驻波强度沿着 x轴分布的数据,拟合得到了波导管中微波的波长,不仅误差得到减小,而且可以绕过驻波比测量,用拟合参量计算微波反射率。     

Photonic-crystal waveguide for the second-harmonic generation

The possibility of efficient second-harmonic generation in the optical range in a planar dielectric waveguide with the active region in the form of a one-dimensional photonic crystal has been theoretically shown. The true phase matching can be achieved by controlling wave dispersion in the photonic crystal. The dispersion equations for the photonic crystal and three-layer waveguide have been self-consistently solved. It is shown that the coherence length may exceed 10 mm.     

Numerical analysis of radiation by a relativistic electron beampropagating parallel to a reflection grating

Two-dimensional radiation by a relativistic sheet electron beam propagating parallel to a reflection grating composed of a sinusoidally corrugated conducting surface is studied rigorously using the mode-matching method. Accurate dispersion curves for the eigenmodes that govern the Smith-Purcell radiation and the instability of the electromagnetic surface wave are presented. The imaginary parts of the eigenwavenumber and eigenfrequency give the leakage coefficient of space-charge waves and the growth rate of electromagnetic surface waves. Their dependences on the dimensions of the radiating structure are discussed. Optimum parameters for achieving the maximum leakage coefficient and the growth rate are determined. The method is general and can be applied to any two-dimensional system of electron beam coupled to an open periodic structure of arbitrary profile     

Natural electromagnetic modes in cylindrical waveguide junctions and their use for nondestructive microwave measurements of electromagnetic characteristics of materials

On the basis of mathematical analysis of electromagetic modes in cylindrical and radial waveguide junction an automatic nondestructive complex allowing to measure electromagnetic parameters of materials (ferrites, leucosapphires, etc.) was developed. Complex is characterized by high sensitivity to variations of parameters and small error of measurements, confirmed by comparison of received data with ones of certified materials.     

Directed electron transport through a ballistic quantum dot under microwave radiation

Rectification of microwave radiation by asymmetric ballistic dot is studied at different frequencies (1-40 GHz), temperatures, and magnetic fields. Dramatic reduction of the rectification is found in magnetic fields at which the cyclotron radius of electron orbits at the Fermi level is less than the size of the dot. With respect to the magnetic field, both symmetric and antisymmetric contributions to the rectification are presented. The symmetric part changes significantly with microwave frequency omega at omegatau_{f}>/=1, where tau_{f} is the time of the ballistic electron flight across the dot. The results lead consistently towards the ballistic origin of the effect, and can be explained by strongly nonlocal electron response to the microwave electric field, which affects both speed and direction of the electron motion inside the dot.     

Phase constant peculiarities of cylindrical zero-index anisotropic metamaterial waveguide

Here, we present the phase constant dependencies of propagating eigenmodes of an open cylindrical anisotropic metamaterial waveguide when the metamaterial permittivity and permeability tensor components may accept values close or equal to zero. Dispersion characteristics of rod and hollow-core waveguides with the radii 0.5, 2.5, and 5 mm at the left-handed polarization of the microwave are shown here. There are unusual shapes of eigenmode dispersion characteristics and anomalous sectors of the characteristics at certain frequencies. The first eigenmode of the rod waveguide with the lowest cutoff frequency is a particularly important mode because it is a single one in the frequency range 1.0?C1.9 GHz, and some small variations on the frequency produce large changes in the phase constant. We can observe packages of dispersion characteristic branches when their cutoff frequencies closed to the metamaterial electric and magnetic plasma frequencies between 1.9 and 3.5 GHz. There are only three modes in the hollow core anisotropic metamaterial waveguide at the frequency range 1.4?C2.8 GHz.     

The efficient inject of high microwave powers into the overdense magnetoactive plasma in the waveguide

On the boundary vacuum — a dense magnetoactive plasma, an incident RHCP (right hand circularly polarized) wave is strongly reflected if ₀ ² / ² 1 and _ce/ > 1;, ₀, _ce are the ncident wave frequency, the plasma frequency and the electron cyclotron frequency, respectively. This reflection strongly lowers the efficiency of the plasma heating by microwaves. Our experimental study shows that a suitable matching system consisting of dielectric plates, placed in front of the plasma, can ensure practically complete transfer of the RHCP wave energy into a dense plasma. The experiment was carried out in the S band waveguide (=12·7 cm) with the power of the order of l kW.The authors wish to thank to the director of the Institute of Plasma Physics Dr. J.Váa for his interest in this work.     

Investigation of mechanism of free electron laser through spontaneous radiation spectrum

In this paper, the mechanism of free electron laser with a guide magnetic field is investigated by analyzing spontaneous radiation spectrum of electrons. The physical relation between spontaneous radiation and stimulated radiation in FEL with a guide magnetic field is studied. It is found that this relation in FEL is similar to that in quantum lasers. The spontaneous radiation spectrum is discrete. The frequency of stimulated radiation in FEL is oneselected and amplified in the radiation spectrum.     

The microwave Hall effect of a two-dimensional electron gas

The integer Quantum Hall effect has been recently observed in the Hall conductivity _xy at microwave frequencies. Here we present a calculation of the wave propagation in the crossed waveguide system used in the experiments. The field pattern is more complicated than in the case of a pure plane wave. The essential result, however, remains unchanged: The field strength in the second (crossed) waveguide is proportional to _xy of the two-dimensional electron gas. Dedicated to Professor Karlheinz Seeger on the occasion of his 60th birthday     

Efficient weak-light amplification through phase control in a quantum well waveguide with electron spin coherence

We propose and analyze a new scheme to realize efficient weak-light amplification via phase control in a GaAs quantum well (QW) waveguide when driven coherently by two orthogonally polarized optical fields (a σ-polarized probe field and a π-polarized control field). It is shown that the amplification and absorption properties of the system are very sensitive to the relative phase between these driving fields. By choosing the relative phase appropriately, the enhanced amplification of the weak σ-polarized radiated field can be achieved in such a QW waveguide. We support our results by numerical calculation and analytical explanation. These theoretical investigations may find applications in devising the QW waveguide amplifier at room temperature.