High-power transit-time oscillator: onset of oscillation and saturation

A simple circuit model is used to investigate the transit time oscillator driven by a high current diode. A novel condition for the onset of oscillation is derived in terms of the diode impedance. The initial growth is calculated, and the saturation level is numerically computed using the 1D model. The 1D results are in excellent agreement with a full scale 2D particle-in-cell simulation. The success of the much simpler 1D model allows a close examination of the roles played by the convection current and by the displacement current, as well as the modification in the transit time due to the intense space charge within the gap.