SOME STUDIES ON SPECIFIC GYROTRON MODULES

Abstract

Highfrequency gyrotron has potential application in the industrial and high-technology heating applications, including plasma heating system and military operation system such as Active Denial system. In view of the high demand of gyrotrons for different applica tions, the design studies of specific gyrotrons at component levels have become necessary to investigate. The topic of the thesis has been introduced in Chapter 1 with the statement of the problem taken up for investigation. Chapter 2 is devoted to providing underlying concepts of gyrotron interactions with relevant design tools for gyrotron development as necessary to appreciate the rest of the thesis. The development of megawatt class gy rotrons operating at higher frequencies is itself a major challenge. Out of all, to achieve proper beam emission in the form of annular electron beam is one of the serious concerns in the development of gyrotron electron gun. The magnetron injection gun is used as a source of beam generation in gyrotron devices and responsible to produce the homoge neous electron beam from a thermionic cathode in the presence of accelerating voltage and external magnetic field. The quality of the electron beam emitted from the thermionic cathode plays a key role in gyrotron performance and the emission inhomogeneity can de grade the performance of the gyrotron. In Chapter 3, the electron energy distribution from thermionic cathode has been investigated for a magnetron injection gun (MIG) taking the operational gun parameters of a typical 42GHz gyrotron. A theoretical model describing the electron emission characteristic in the vicinity of MIG cathode has been developed. The electron cathode emission model includes the coexisting effects of electric field emis sion, thermionic emission, as well as reduced Schottky barrier effect. The design optimization of gyrotron is carried out for the nominal values of acceler ating voltage and the beam current with respect to the optimum value of magnetic field supplied. The externally employed magnetic field plays a major role in the operation of gyrotron devices and the variation in magnetic field can be a reason of discrete modes ex citation. However, there are certain chances due to that the unexpected result can happen, such as the manufacturing faults, misalignments issues etc. Hence for the better under standing of the gyrotron behavior, magnetron injection gun (MIG) magnet system with due consideration to the variation in magnetic field profile. Chapter 4 presents the design simulation of single coil magnet system to get the optimum magnetic field required for the gyrotron devices. In addition, in this chapter the beam characterization study has been done for the appropriate magnetic field profiles. Chapter 5 dedicatedly presents the design investigation of magnetron injection gun (MIG) used for kW to MW Class gyrotron. In this chapter the design investigations have been reported for the frequencies 28GHz, 42GHz, 110GHz, 140GHz, 170GHz, and 250GHz at the operating modes TE0,2, TE0,3, TE22,6, TE28,8, TE28,12, TE6,2 respectively, for the delivery of RF power output from several kilowatt to Megawatts ranges. The design validation analysis with different beam optics codes, high voltage analysis and sensitivity analysis has also been reported in this chapter. Afeebly-tapered gyrotron cavity for a typical 42GHz, 200kW gyrotron has been fabri cated and measurementsonthecharacteristics of the fabricated cavity have been presented in Chapter 6. The destructive and non-destructive methods and a computational analysis have also been carried out to represent the comparisons between the measured and design values with respect to the ohmic quality factor, efficiency. Chapter 7 presents the initial design study of undepressed and depressed collector, the latter being a single-stage depressed collector (SSDC). The design simulation of unde pressed and single stage depressed collector has been carried out by using beam trajectory code EGUN. The design simulation has been performed with 30-90 beam rays and their energy has been taken at the remaining electron beam energy after the RF energy conver sion. The study of uniform beam distribution on collector wall at an optimized depressed voltage has been carried out with presence of an external magnetic field and results are compared in both cases. The breakdown analysis for collector geometry is also included in this chapter. Finally, Chapter 8 summarizes the contribution of this thesis in the development of kilowatt to megawatt class gyrotrons especially used for ECRH and DNP applications with the future scope of the present work.