Effect of boundary reflection on helix backward wave oscillator

Summary form only given, as follows. The operation of the PASOTRON (Plasma-assisted slow-wave oscillators) is studied in the BWO regime. The absence of the guiding magnetic field in this device allows for the 3D motion of beam electrons. Recent studies showed the possibility of obtaining high efficiency up to 50 %. This was realized due to not only 3D motion but also due to properly optimized reflections from the slow wave structure ends in the experiment. The effect of the boundary reflection on the PASOTRON BWO is investigated theoretically. A stationary solution for the backward wave field amplitude is obtained in a self-consistent treatment of the wave excitation in the helix BWO with beam electrons 3D motion inside. The device electron efficiency and the oscillation frequency were obtained given a certain boundary reflection coefficient. At each value of the reflection coefficient, a number of different modes can be excited depending on the beam current. The efficiency of each of these modes was calculated. The results of this study can be used to increase the device efficiency, through adjusting the boundary reflection coefficient to the proper value.