Gain and bandwidth of a gyrotron amplifier with tapered rectangular waveguide

Abstract

The linear dispersion equation for the rectangular TE10 mode is obtained using the Maxwell-Vlasov approach with a lorentzian velocity distribution. The resultant dispersion relation is used to find the distributed gain of a tapered gyro-TWT operating in rectangular waveguide. In order to examine bandwidth limitations, a synchronization parameter is introduced. This parameter is defined by the ratio of the local magnetic field to the synchronous magnetic field. The synchronous field ia defined is that which makes the beam mode tangent to the waveguide mode in the ω– K2 dispersion graph. By varying the synchronization parameter along the tube axis, a 40% bandwidth (3 dB) has been predicted for the TE10rectangular gyro-TWT with the linear wall taper. The total gain was 30 dB. A similar bandwidth can also be achieved by holding the synchronization parameter constant and imposing an appropriate non-linear variation on the waveguide dimensions.