Effects of long-line reflection on the instantaneous tunability of gyrotron backward-wave oscillators

Summary form only given. The gyrotron backward-wave oscillator (gyro-BWO) is a coherent microwave/ millimeter wave radiation source based on the electron cyclotron maser instability. The backward wave oscillation occurs in a non-resonant structure, therefore, the continuous and instantaneous frequency tuning can be achieved by varying the beam voltage or the magnetic field. However, the discontinuous tuning was observed in previous experiments due to the lone-line reflection induced by the external circuit. In this study, the effects of long-line reflections on the tunability of gyro-BWO were examined by using the stationary code and the Particle-In-Cell simulation code. The numerical results show that the dynamical behavior of the gyro-BWO is sensitive to the distance of the reflection point to the oscillator (Lext). As Lext is increased, the discontinuity in frequency tuning becomes more severe and the instantaneous tunability of the gyro-BWO is deteriorated due to the hysteresis phenomenon. The details will be presented in the paper.