Research on an Overmoded Ka-Band RBWO Operating in TM02 Mode With Low-Guiding Magnetic Field

A Ka-band relativistic backward-wave oscillator (RBWO) operating in the TM02 mode is researched theoretically and experimentally in this article. The RBWO can overcome the disadvantages of a traditional RBWO, such as small size and low-power capability, when the operating frequency goes to the millimeter-wave band and is more suitable for adopting a lower-guiding magnetic field. The mode-selection mechanisms in the RBWO ensure that the electron beam interacts with the negative first-harmonic wave of the TM02 mode efficiently. The particle-in-cell (PIC) simulation preformed the 490-MW output power at a frequency of 29.3 GHz. The experiment was done on the SINUS-881 accelerator, and with the diode voltage and current at 580 kV and 3.6 kA, respectively, at a guiding magnetic field of 1 T, the RBWO produced a microwave pulse with a power as high as 360 MW at a central frequency of 29.3 GHz. The dependence of microwave power on diode voltage coincides with PIC simulation. Pulse shortening as well as severe bombarding damage of the electron beam on the postcascaded resonators were observed. By increasing the guiding magnetic field to 1.26 T, the pulsewidth was evidently improved.