Calculation of start-oscillationcurrent for lossy gyro-TWT using linear TWT parameter conversions

Summary form only given. The start-oscillation-current of a gyro-TWT determines the stable operating current level of the device. The amplifier is susceptible for oscillations when the operating current level is higher than the start-oscillation current. There are several ways of calculating the start-oscillation current, including using the linear theory of a gyro-TWT. In this paper, we present a simple way of determining the start oscillation current of lossy gyro-TWT. The linear TWT parameters that include the effects of synchronism, loss, and gain, were converted to gyro-TWT parameters to calculate the start oscillation-current. The dependence on magnetic field, loss, and beam alpha was investigated. Calculations were carried out for a Ka-band gyro-TWT for both operating and competing modes. Comparison with linear theory will be presented.