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|Title:||Design and study of focusing structures in the transport of electron beam in linear beam microwave tubes|
|Abstract:||Microwave tubes are vacuum devices used for the generation or amplification of radio frequency signals in the microwave frequency range. Large size and weight are major drawbacks of microwave tubes, and this needs to be addressed. Often, the heaviest component in these devices is the focusing structure. The present work is on the growing need for reduction in size and weight of linear beam microwave tubes. This is achieved to a large extent by an improved design of the electron beam newlinefocusing structure. The improved design enhances the tubes performance towards higher power capability with better efficiency, better linearity and better noise performance. A majority of the modern linear beam tubes use the periodic permanent magnet (PPM)structure in focusing the electron beam and are preferred for their size and weight advantages. The available analytical design formulations for the PPM circuit are based on number of approximations and hence some empirical trimming of the design is often necessary. Finite newlinedifference method (FDM) and finite element method (FEM) have been used very successfully in the last four decades, for accurate design and optimisation of the PPM focusing structure. However, designs using analytical formulations provide several advantages like speed, flexibility newlineand user control. In the present work, the available analytical design formulations have been improved, and a more accurate analytical model for the design of the PPM focusing structure has been obtained. This has been achieved by considering the permeances in all possible flux paths in a newlinePPM structure. Magnetic saturation in pole-pieces, which is a critical design aspect of a PPM structure, has been addressed in this study. The end effects in a finite length PPM structure, not newlineaddressed earlier, have been done here by representing each PPM cell as equivalent solenoids and a method to obtain the equivalent solenoid parameters have been presented. A method to obtain a user defined axial magnetic field profile has been presented here.|
|Appears in Departments:||Department of Electronic Science|
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