Radial Transit Time Oscillator

Radial Transit Time Oscillator (RTTO) is a promising novel high power microwave source based on the radial transit-time effect. It can operate under the condition of low impedance and without external guiding magnetic fields. There exists great importance in the investigation of both the physical mechanism and the internal rules. Presented in this dissertation are theoretical analysis, particle simulation, and experimental studies of the fundamental physics of RTTO. The results obtained in this dissertation may enrich and promote the research of RTTO.By employing one-dimension planar gap model, the physical mechanism of RTTO is studied by single electron theory approximately. Under the cylindrical coordinate, the transit-time effect of the radial gap in the resonance cavity of RTTO is studied by hydrodynamic theory. The equation describing the interaction between the electron beam and the high frequency field is obtained. Meanwhile by using numerical method, the beam's one-order current density, and the power exchange between the beam and the field are solved. Curves are given to illustrate the relations among the above solved parameters and the gap's transit angle in different electron velocity and number density. The results obtained from hydrodynamic theory coincide with those from single electron theory.By employing a 2.5D particle-in-cell code, which involves the space-charge-effect and the nonlinear beam-wave interaction, the microwave development process in RTTO is simulated. Firstly, the physical pictures of microwave production in RTTO are presented, and from these pictures the physical mechanism of RTTO is investigated. Then the relations among RTTO's frequency, output power, microwave mode, and parameters of both the device geometry and the electron beam are studied in detail. The simulation results show that to start the oscillation, the length of the resonance cavity must be well matched with the radial span of the cavity; Mismatch of them will greatly affect the microwave development; The output power of the microwave in RTTO is affected by the microwave mode obviously. Under the same conditions, the output power for TEMooimode is the highest, and its start and saturation time of oscillation are the shortest. The results also show that the output power will decrease with the increase of the size of the extract window; The operating state of RTTO has great close relationship with the operating current, and there exists an optimum current value. When the current is smaller, though the operation may be stable, the output power is lower. When the current is larger, the space-charge-effect of the electron beam will greatly affect the microwave production. The frequency and mode of microwave will change and the output power will decrease obviously. Under some optimum conditions, the simulated maximum output power of RTTO may reach 1.1 GW when the input voltage and current are 300kV and 15kA, respectively.The experimental study is performed on the RTTO designed with the help of simulation, and the microwave based on radial transit-time effect is obtained. The output power is measured by horn and electric probe and the frequency is measured by a wave-guide dispersion line. The whole system is calibrated carefully. A microwave with the peak power of above 30MW is obtained at frequency 3.66GHz while the input voltage and current are 330kV and 29.7kA, respectively. The result is reasonable and reliable when compared with the results from corresponding simulation. By varying the diode voltage and current, the relations among the microwave power, frequency and the diode voltage, current are obtained. The results show that the output power decreases with the increase of the diode voltage in the range of 330~425kV. The input current exist a start value and also an optimum one. They are in the range of 20~25kA and 28-31kA, respectively. When the current exceeds the optimum value, the microwave mode changes, the output power decreases obviously, and the frequency spectrum is bad. Finally, explanat...