RF breakdown experiments in “cold” slow wave structures under experimental circumstances of high power microwaves

Abstract

RF breakdown tests in “cold” slow wave structures (SWSs) are executed under experimental circumstance of high power microwave (HPM). All the SWSs under tests are made of stainless steel and are designed as traveling wave structures, which operate at π/2 mode of TM01 wave. The “cold” SWSs are fed by an X-band overmoded relativistic backward wave oscillator, which generates TM01 mode at 9.46 GHz with power around 1.8 GW, pulse duration about 100 ns, and repetition rate of 30 Hz. In the tests, the variances of peak surface electric field (Es-max, 0.53 MV/cm–1.79 MV/cm), number of periods (2–6 periods) of SWSs, and external magnetic field (Bext, 0–2.5 T) versus RF breakdown effects are recorded. The tests results indicate that the input microwave energy is mainly absorbed, not reflected by the RF breakdown process in traveling wave SWSs. Both larger magnitude of Es-max and more numbers of periods of SWSs aggravate the microwave absorption in the breakdown process and bring about shorter transmission pulse width. However, little correlation between RF breakdown effects and Bext is observed in the tests. Further theoretical and experimental studies would be helpful for understanding of the effects of Bext on RF breakdown and breakdown mechanisms under the experimental circumstances of HPM sources.