为了实现高功率微波发生器的小型化, 开展了S波段低磁场相对论返波振荡器工作特性的研究工作。由于S波段返波振荡器频率低, 对应的电子回旋共振磁场强度也很低, 因此低磁场条件下面临着电子束传输效率低和束波互作用效率低两大问题。为解决上述问题, 采取下列措施: 通过加大电子束与器件内壁的距离, 提高电子束传输效率; 采用较深的慢波结构作为提取腔, 实现高束波互作用阻抗; 提取腔前采用浅深度慢波结构, 使提取腔区域的电子速度与微波相速同步。粒子模拟证明, 以上措施有效, 在引导磁场强度仅为0.17 T、电子束电压435 kV、电流6.5 kA的条件下, 该返波管获得功率为670 MW、效率约为25%的输出微波。相对于常规S波段相对论返波振荡器的磁场系统(B=0.8 T), 适用于该返波管的0.17 T低强度磁场系统螺线管外半径下降了20%, 能耗下降了约93.8%。

In order to reduce the volume and weight of the high power microwave (HPM) system, an S-band relativistic backward wave oscillator(RBWO) operating at low guiding magnetic field is designed. The operation magnetic field of the RBWO is lower than that of the electron cyclotron resonance, which will decrease the electron beam transmission efficiency and beam-wave interaction impedance. By increasing the distance between the electron beam and the inner wall of the device, the transmission efficiency of the electron beam can be improved. The deep slow-wave structure is used as extraction cavity to enhance the efficiency of beam-wave interaction. The shallow slow-wave structure in front of extraction cavity is adopted to ensure synchronization of electron velocity and microwave phase velocity. The high power microwave is acquired under low guiding magnetic field. Simulation shows that 670 MW output power with 25% efficiency is generated under a guiding magnetic field of 0.17 T, electron voltage of 435 kV and beam current of 6.5 kA. Compared to the conventional magnetic field system (B of 0.8 T), the radius of solenoid of the 0.17 T low magnetic field system applied to the RBWO is reduced by 20%, and the energy consumption is reduced by about 93.2%.