Microwave Generation due to Degenerate Interaction of Cherenkov and Cyclotron Beam Modes

对于磁化的电子束，存在三个不同的波束波，可以产生微波代。它们分别是慢速回旋波、快速回旋波和束流空间电荷波。在零磁场下，传统的切伦科夫和回旋共振相互作用简并。本课题提出了由于简并相互作用而产生的微波代，包括理论和实验研究。在零磁场下，应同时考虑光束的纵向和纵向摄动运动。在传统切伦科夫相互作用和回旋共振相互作用的简并束相互作用中，束真空边界处的表面电荷起着至关重要的作用。轴对称TM模和非轴对称HE和EH杂化模均存在简并相互作用引起的不稳定性。在100 A以上的大电流区和弱相对论能量区，简并相互作用优于传统的切伦科夫相互作用。这个BWO简单紧凑。在离子聚焦状态下，背景气体（氦或氮）自电离产生等离子体，电子束可以在没有引导磁场的情况下传播。观测到BWO微波代的气体压力，氮气和氦气分别为5-10 mTorr和100-160 mTorr。振动模态为轴对称TM模态和非轴对称TE模态，可以用简并相互作用来解释。TM模式的输出功率小于1kW，对应的电子效率小于0.004%。电子效率低的原因可能是由于大直径光束的轮廓控制不好。

For a magnetized electron beam, there exist three distinct beam waves, which can contribute microwave generations. They are the slow and the fast cyclotron waves and the beam space charge wave. At zero-magnetic field, the conventional Cherenkov and cyclotron resonance interactions degenerate. This research project has proposed microwave generations due to the degenerate interaction and includes theoretical and experimental studies.At zero-magnetic field, vertical as well as longitudinal perturbed beam motions should be taken into account. In the degenerate beam interaction of the conventional Cherenkov and cyclotron resonance interactions, surface charge at beam-vacuum boundary plays an essential role. Instabilities due to the degenerate interaction occurs for axisymmetric TM mode and non-axisymmetric HE and EH hybrid modes. In the high current region above 100 A and in the weakly relativistic energy region, the degenerate interaction is superior to the conventional Cherenkov interactionA large diameter backward wave oscillator (BWO) without guiding magnetic field is demonstrated experimentally. This BWO is simple and compact. Electron beam can propagate without guiding magnetic field due to generation of plasma in ion-focused regime by self-ionization of background gas (helium or nitrogen). The gas pressures, at which microwave generations of the BWO are observed, are 5-10 mTorr and 100-160 mTorr for nitrogen and helium, respectively. The oscillation modes are axisymmetric TM and non-axisymmetric TE modes, which can be explained by the degenerate interaction. The output power of the TM mode is less than 1kW, which corresponds to electronic efficiency less than 0.004 %. The low electronic efficiencies might be ascribed to poor profile control of the large diameter beam.