Investigation On Novel Transit-time Oscillators

The three-cavity transit-time oscillator (TC-TTO) is a promising HPM source based on the axial transit-time effect. The span of any modulating cavity in the TC-TTO is uniform. The systematical theoretical investigation of the nonuniform TC-TTO (NTC-TTO) was not reported in the world, and there was no the experimental research on the NTC-TTO.By the use of theoretical analysis, particle simulation, and numerical calculation, the NTC-TTO has been investigated systematically. Furthermore, a successful experiment of the NTC-TTO has been accomplished, and the high power microwave (HPM) with an expected mode is stably produced. A series of new conclusions and new laws are presented. A new method for increasing the beam-to-microwave power conversion efficiency is obtained.We have investigated the electron beam transit-time effect in the π -mode standing wave electric field in the nonuniform two-cavity and three-cavity oscillator under the small signal condition. Mathematical expression of the beam-to-microwave power conversion efficiency has been obtained.The high frequency features of a nonuniform three-cavity resonator have been investigated numerically. The laws that a span change influences on TM0102 π/3-like mode and the corresponding frequency have been obtained. Furthermore, the laws that a span change influences on the z-axial component of the electric field and its radial distribution have been given.By employing a 2.5D particle-in-cell code, which involves the space-charge-effect and the nonlinear beam-wave interaction, the NTC-TTO and TC-TTO have been simulated, and the simulation results accord with the theoretical analysis.The e-beam's modulation and bunch in the NTC-TTO and TC-TTO have been investigated by nonlinear theory, and the e-beanrs modulation coefficient and kinetic energy spread in the NTC-TTO have been calculated and compared with those in the TC-TTO by a code written by myself. The calculations are consistent with the simulation results.The structure of extraction and output microwave has been optimized. The experimental study has been performed on the NTC-TTO designed with the help of simulation. The microwave frequency, the microwave power and its corresponding angular distribution have been given in the experiment, and the relation between the output power efficiency and the voltage of diode has been presented. The typical experimental data have been compared with the simulation results under the same parameters condition. The representative experimental results are as follows. The microwave output power of the uniform TC-TTO is 198.6 MW with the initial electron energy of 400 keV and the electron beam current of 3.28 kA. The microwave frequency is 4.58GHz.The beam-to-microwave power conversion efficiency is 15.13%. When the first the second and the third span of the NTC-TTO are 1.0cm, 1.4cm and 1.8cm. respectively, the microwave output power of the NTC-TTO is 246.6 MW with the initial electron energy of 468 keV and the electron beam current of 2.92 kA. The microwave frequency is 4.49GHz.The beam-to-microwave power conversion efficiency is 18.06%. When the first, the second and the third span of the NTC-TTO are 1.2cm, 1.4cm and 1.6cm, respectively, the microwave output power of the NTC-TTO is 246.6 MW with the initial electron energy of 434 keV and the electron beam current of 2.87 kA. The microwave frequency is 4.49GHz.The beam-to-microwave power conversion efficiency is 19.82%. The experimental results accord with the conclusions of theoretic analysis and simulation. It is shown that the power produced by certain NTC-TTOs is higher than that of the uniform TC-TTO under the same condition.The conventional HPM source based on the axial transit-time effect usually has a higher diode impedance, which in turn makes the power of the electron beam much lower, consequently the microwave output power is limited to a lower level. It has become the "bottle-neck" that influences the development of the conventional axial transit-time devices. In this dissertation one novel low diode impedance HPM sour...