Comparison of theory and simulation for a radially-symmetric transit-time oscillator

The transit-time effect in a coaxial structure has been used by Arman (1996) to design low impedance high power microwave devices that use no externally generated magnetic fields and have no confining foils. Luginsland et al. (1997) have developed simple one-dimensional (1D) nonlinear circuit equations that are solved numerically to estimate key device characteristics. This paper extends this approach to analytically estimate the values of the free parameters used in the circuit equations, compares the analytical values to similar values derived from two-dimensional (2D) particle-in-cell simulations, and compares the results of numerical solutions of the 1D circuit equations, 2D simulations, and initial experimental data. It is shown that the nonlinear relationship between voltage and current emission in a space charge-limited diode drives an RF oscillation whose frequency is determined by the resonant characteristics of the annular diode cavity. The results from the 1D analysis and 2D particle-in-cell simulation are shown to be in excellent agreement.