Disk-loaded Slow-wave Structure Research Articles

Electromagnetic Analysis of an Axially Periodic Disk-Loaded Slow-Wave Structure With Low-Loss Dielectric Filling Between Disks for a Magnetically Insulated Line Oscillator

The partially dielectrically filled periodic disk-loaded co-axial structure as a slow wave interaction structure for magnetically insulated transmission line oscillator (MILO) has been electromagnetically analyzed using field matching technique. The slow wave structure (SWS) includes a periodic disk-loaded coaxial structure in which the low-loss dielectric material is partially filled between successive disks. In the analysis, the dispersion relationship and interaction impedance have been calculated taking into account all the harmonics generated inside the structure. The effect of the dielectric constant of the material on the dispersion characteristics and phase velocity has been investigated. Also, the effect of different structural parameters on the dispersion characteristics and the interaction impedance has been obtained. To validate the performed theoretical analysis, the analytically obtained dispersion results have been compared with previously known dispersion results and then also confirmed by the commercial code “Computer Simulation Tool (CST) Studio Suite.” The agreement between theoretical analysis and simulation with respect to the dispersion characteristics is within 5%.

Linear analysis of an X-band backward wave oscillator with a circular-edge disk-loaded cylindrical waveguide driven by an annular electron beam

An X-band backward wave oscillator (BWO) with a circular-edge disk-loaded periodic metallic slow wave structure (CDSWS) is proposed and studied numerically. The structure is the modified version of our previously modeled semi-circularly corrugated slow wave structure (SCCSWS). The CDSWS is energized by an intense relativistic electron beam (IREB) which is directed by a strong magnetic field. The electromagnetic (EM) wave of the slow wave structure (SWS) merges with the space charge wave of the beam under the guidance of the strong axial magnetic field. The inner wall contour of CDSWS is modeled by a finite Fourier series and the dispersion characteristics of different TM modes are solved by utilizing the linear Rayleigh-Fourier (R-F) technique, which is verified by a commercial EM solver. To study the temporal growth rate (TGR) for the fundamental TM01 mode, the dispersion equation is solved for the beam current of 0.1-1.0kA and the beam energy of 205-665kV. For the TM01 mode, the TGR that occurs at the unstable region, which provides a qualitative index of the strength of the microwave generation, is compared with those of the BWOs with sinusoidally corrugated SWS (SCSWS), disk-loaded SWS (DLSWS) and triangularly corrugated SWS (TrCSWS) for different beam parameters. The dimension of the CDSWS is determined by comparing the dispersion characteristics of fundamental TM01 mode with DLSWS and SCSWS. For the same set of beam parameters, an average of 3.5%, 7%, 1.5% and more than 50% higher TGR have been obtained with the proposed CDSWS than that of SCSWS, DLSWS, TrCSWS and SCCSWS respectively. Moreover, the presented structure also provides an advantage in the fabrication process and is less prone to RF breakdown since it has no sharp edges in the inner wall where the electric field intensity can be infinitely high.

High frequency characteristics of a magnetically insulated transmission line oscillator oscillating in HEM11 mode

Coaxial disk-loaded waveguide has been widely used in magnetically insulated transmission line oscillators (MILO). Although TM00 mode is assumed to be its main mode, the asymmetric mode might be excited by slight asymmetry of the structure, asymmetric emission of the beam, or both. So the research on asymmetric mode in coaxial disk-loaded waveguide is necessary. The general eigen equation with both symmetric and asymmetric modes in coaxial disk-loaded slow-wave structures is theoretically analyzed. Then, a HEM11 mode working MILO is designed and a tentative experiment is carried out to test its performance. Employing an electron beam of about 480 kV and 39 kA, HEM11 mode working MILO generates a high power microwave output of about 1.2 GW with 40 ns pulse duration at 1.98GHz. The power conversion efficiency is about 6.5% and the generated microwave mode is TE11 in the coaxial output region.

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

Coaxial disk-loaded waveguide has been widely used in magnetically insulated transmission line oscillators. Although the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> 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.

Analysis of Coaxial Ridged Disk-Loaded Slow-Wave Structures for Relativistic Traveling Wave Tubes

The coaxial ridged disk-loaded structure which is a new disk-loaded periodic system is presented and analyzed in this paper. As an all-metal slow-wave circuit, it has properties that can be used in high-power traveling wave tubes (TWT) and relativistic TWTs. The dispersion equation and coupling impedance of the structure are investigated in the first part of this paper. The results of numerical calculations of the dispersion relation and coupling impedance with different structure dimensions indicate that the interaction impedance of the ridged disk-loaded structure is higher than that of the disk-loaded structure without ridges in most frequency ranges. In the second part, the hot dispersion equation of this circuit with an annular electron beam is obtained according to a self-consistent linear theory. The influence of physical dimensions and beam parameters on the small signal gain is discussed.