NONLINEAR-ANALYSIS OF A MULTICAVITY GYRO-TWYSTRON

To preserve high gain, high efficiency and high power merits of gyrokl ystron, a gyro-twystron is designed using an electron beam with alpha( v(perpendicular to)L/v(z)) greater than unity. With a multi-cavity sec tion of high gain, the length of the waveguide output section can be m ade shorter than the threshold length of the absolute instability with out losing total system gain. Numerical simulations are carried out to analyze a ka-band gyro-twystron consisting of three TE111 mode caviti es and an output section of a TE11 mode waveguide. Stability study is performed to ensure the tube without self-excited oscillations. With a lpha = 1.5, the 3-dB linear and saturated gain bandwidth in excess of 2% can be obtained by stagger tuning for an 80 kV, 3 A electron beam w ith 5% axial velocity spread. The maximum saturated gain is more than 55 dB at 33% efficiency. By tapering the magnetic field of the last 2 cm of the interaction region, the efficiency can be increased to 43% w ithout degrading the bandwidth, which corresponds to an output power o f 103 kW.