Coaxial disk-loaded waveguide has been widely used in magnetically insulated transmission line oscillators. Although the TM00 mode is its main mode, the asymmetric mode might be excited by a slight asymmetry of the structure, asymmetric emission of the beam, or both. Therefore, research on the asymmetric mode in coaxial disk-loaded waveguide is necessary. The general dispersion equation of the coaxial disk-loaded slow-wave structures is obtained using the field match theory for the first time. Numerical calculation is carried out based on the dispersion function. The theoretical calculated results agreed well with the simulated results of the MAFIA code and experiment.

Investigation of Dispersion Characteristics in Coaxial Disk-Loaded Slow-Wave Structures With Both Symmetric and Asymmetric Modes

An all-metal disk-loaded coaxial waveguiding structure, for its application in a magnetically insulated line oscillator (MILO), as a slow-wave interaction structure, excited in the TM mode, has been field analyzed. In the analytical model, modal matching technique has been used considering all the space harmonics generated due to the structure axial periodicity in the free-space region inside the structure and stationary modal harmonics caused by the reflections from the disk walls in the disk-occupied region of the structure. The dispersion relation of the structure is obtained considering the continuity of the fields at the interface between these two regions. A system of homogeneous equations is formed in the Fourier components of the field constants. The condition for the nontrivial solution of the equations gives the dispersion relation of the structure in the form of a determinantal equation. The analysis is further extended for the interaction impedance, which has direct relevance with the temporal RF signal growth in the device. The derived dispersion characteristic has been validated as special cases for the known results and has been also validated with those results published in the literature. Furthermore, the structure has been simulated using commercial code “CST Microwave Studio” for the dispersion as well as the interaction impedance characteristics. The simulated values have been found to be in agreement with the theoretically derived results. The dispersion characteristics and the axial interaction impedance of the structure have been plotted for a wide range of structure parameters. Furthermore, the desired operation of the MILO device, the method of structure parameter selection, and the effect of parameter variation have been also discussed. This study would help the design engineers in understanding the physics and in selecting the coaxial disk-loaded structure parameters for their successful use in MILO devices having reasonable RF growth rate in synchronism with the electron beam.

Electromagnetic Analysis of a Disk-Loaded Coaxial Waveguiding Structure for MILO

The existing studies about the dispersion characteristics of the sinusoidal rippled wall cylindrical waveguides mostly center on one-dimensionally (1-D) corrugated waveguides. Sometimes two-dimensional (2-D) corrugated waveguides are needed to provide better selective and resonance properties not achievable with 1-D periodic structures. The authors of this paper improve the method of calculating the waveguide axially periodic by expanding the slow-wave structure's boundary function in Fourier series, so that it can be adopted in periodic waveguides with axial and azimuthal corrugations. In addition, the general dispersion equations for the investigation of 2-D periodic waveguide are presented in this paper. The advantage of the method lies in its universality, providing solution to the dispersion characteristics for most of the periodic waveguides with axial and azimuthal corrugations. By the method suggested here, the paper analyzes the dispersion characteristics and coupling impedance of a new rib-loaded disk-loaded waveguide and other periodic waveguides.

An investigation of periodic waveguides with axial and azimuthal corrugations

A nonlinear self-consistent simulation code is employed to investigate the behavior of the outer-slotted-coaxial waveguide gyrotron traveling-wave amplifier (gyro-TWA). The influences of the velocity pitch, frequency, and input power of the electron beam on efficiency, output power, and saturated gain are simulated and discussed in detail. It is predicted that this design with 95 GHz, TE/sub 3,1/ will yield a peak output power of 264.3 KW, a peak efficiency of 33.7%, and saturated gain of 44.2 dB.

Self-consistent nonlinear investigation of an outer-slotted-coaxial waveguide gyroton traveling-wave amplifier

The dispersion relation of electromagnetic waves in a rippled-wall waveguide with a degenerate plasma column protected by an annular dielectric layer is theoretically investigated. By injecting a thin annular relativistic electron beam (TAREB) in the region between dielectric and metallic cylinders in the aforementioned configuration as an energy source, the excitation of terahertz (THz) electromagnetic waves is investigated. Also, the dependence of dispersion relation and time growth rate on the radius of the dielectric, the corrugation amplitude, and period is studied. Furthermore, it is found that the presence of the degenerate plasma rod in the rippled-wall waveguide leads to obtain high-frequency modes in the THz frequency region. Finally, the electric-field profiles in this waveguide are plotted.

The Rod Degenerate Plasma-Rippled-Wall Waveguide and Its Excitation by Relativistic Electron Beam Injection

Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). Although TM
01 mode is it's main mode, the asymmetry mode may be excited by slight asymmetry of the structure, misalignment of the beam, or the asymmetry associated with the input or output structure. So research about asymmetry mode of disk-loaded waveguide is necessary. The general dispersion equation and interaction impedance expression of disk-loaded waveguide is obtained with accurate field theory for the first time. Based on these results, a broadband and a narrowband disk-loaded waveguides are designed which can be used in the Ka band HPTWT. Moreover, the theoretical calculated results are compared with the simulated results from the HFSS (High Frequency Structure Simulator) code using finite element method. It is found that frequency domain overlapped by these two modes of the narrowband structure is very narrow, so the HEM
11 mode may be ignored when calculating Beam-wave interaction. In the other hand, the interaction impedance of HEM
11 mode is very low generally.

Rigorous Analysis of the Disk-Loaded Waveguide Slow-Wave Structures

The relativistic traveling wave tube is an important high power microwave source. The corrugated cylindrical waveguide is usually used as slow wave structure of this device. Starting from wave equation and using boundary conditions, dispersion relation is derived for the corrugated waveguide, in which an intense relativistic electron beam propagates along the axis. Two cases which are shorter period and longer period are discussed in this paper respectively. The small signal gain of the relativistic traveling wave tube is analyzed and some conclusions are drawn. The analysis method presented in this paper can be extended to other types of slow wave structures of relativistic traveling wave tube.

Analysis of the instability in relativistic traveling wave tube

Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). It has been shown in many experiments that the interaction efficiency and output power can be increased greatly by injecting plasma into the vacuum microwave device. Using field analysis, the dispersion characteristics and the interaction impedance of the disk-loaded waveguide filled with plasma are analyzed in a strong longitudinal magnetic field. In conclusion, the frequency of the TM01 mode increases as the density of the plasma increases. It also can be found when the plasma density increases to a large scale, the TM01 mode of the disk-loaded waveguide overlaps the TG mode, these two modes couple each other and form the new hybrid modes.

Study of Disk-Loaded Waveguide Filled with Plasma

A new type of mm-wave slow wave system, double staggered ladder circuit is analyzed in this paper, by means of “average cavity field method” and three-dimensional finite element method. The influence of the electron beam channel on the dispersion characteristics is discussed. An experimental research is made, the experimental results agree well with the theoretical one.

Analysis for the double staggered ladder circuit

The behavior of a two-stage slotted Gyro-TWT amplifier is evaluated with a self-consistent nonlinear slow-timescale simulation code. The effects of the sever position and the lengths of the first section, sever, and the second section on beam-wave interaction are discussed in this paper. And the influences of the magnetic field and the electron beam's velocity spread on efficiency, gain and bandwidth are also simulated and discussed in detail. The electron beam we employ encircles around the axis of the wave guide.

Xiaolan Zhou

Papers

Rigorous Analysis of the Disk-Loaded Waveguide Slow-Wave Structures

Analysis of the instability in relativistic traveling wave tube

Study of Disk-Loaded Waveguide Filled with Plasma

Analysis for the double staggered ladder circuit

Self-Consistent Nonlinear Simulation of a Severed Slotted Gyro-TWT