The pasotron: progress in the theory and experiments

Plasma-assisted slow-wave oscillators (pasotrons) are unique sources of microwave radiation, in which the beam propagation in the absence of external magnetic fields is provided by the ion focusing and the electron interaction with the RF field is essentially two-dimensional. This paper overviews the results obtained in the last several years and presents recent accomplishments in the theory and experimental performance of the pasotron. In particular, the 50% efficient operation at the 0.5-MW power level and more than 30% efficient operation at more than a 1-MW level are reported. Theoretical results of the analysis of nonstationary self-consistent processes in the beam focusing and transport agree with PIC simulations. The paper also contains the first results of the noise measurements in the pasotron. The paper is focused at describing the progress in the field, and explaining the interesting physical effects and improvements in the device performance without going into details of either the theoretical formalism or experimental parameters.