초고출력 마이크로파 발생장치용 상대론적 클라이스트론 설계 연구

Abstract

In the first part, we show the design and the experimental result of a relativistic klystron amplifier (RKA). We designed and built an RKA that has an operational frequency of 2.856 GHz and a peak power of 600 MW. This RKA emits microwaves with a peak power of 530 MW using a pulse that has 2.0-GW peak power and 530-kV peak voltage

therefore the peak power efficiency is 26%. Each component of the RKA and the operation characteristics of the whole system were tested and compared to results of particle in cell (PIC) simulations. The measured and simulated emission characteristics of the cold cathode gun are very similar. We can conclude that, to increase peak power, inductive detuning is suitable when pulse power has broad pulse shape, but that capacitive detuning is suitable when pulse power has narrow pulse shape (< several tens of nanoseconds). Beam trajectory in the output cavity also affects the efficiency. When it was modified such that the electron beam was collected near the output cavity, we acquired higher efficiency than was not.In rest parts, we study principles on RKA analytically. Theory of electron beam bunching for an RKA is reviewed in the second part, comparing it for a conventional klystron. Because electrons in the drift tube suffers non-negligible potential, potential depression of energy of electrons should be considered to analyze beam bunching in an RKA. Linear beam bunching theory shows that the location where beam bunching is maximized does not depend on the driving power. In the thirt part, our studies on the interaction between beam and cavity are summerized, especially on beam loading in an input cavity. Because extremely high beam current over kA is used for an RKA, a dc beam loading effect in an input cavity is not negligible. We calculates dc beam loading using Vlasov equation and analyzed a transient behavior of microwave in an input cavity due to dc beam loading. Dc beam loading could be considered as ohmic loss in the cavity. Thus, the effect can be parameterized with a Q-factor of the cavity. Supported with PIC simulations, one can calculate Q of dc beam loading with obtaining the ratio of saturation voltage without beam to it with beam.In the last part, we propose spatial power combining for high power microwave application. Array antenna should be used to radiate high power microwave. Loss of combined power due to phase error is analyzed.