Double period slow wave structure for long pulse operation of a high-power backward wave oscillator

Summary form only given. Linear dispersion relations for an axisymmetric metal-wall slow wave structure (SWS) with double period corrugations have been analyzed numerically. The double period SWS is proposed to improve the performance for long pulse operation high-power backward wave oscillators (BWOs) that can sustain stable oscillation despite the energy depression of the driving relativistic electron beam. High efficiency oscillation near the entrance of the SWS results in an instantaneous exhaustion of beam energy, and beam-microwave interaction changes to stop. In order to avoid such harmful intermission, the size parameters of the SWS must be designed carefully to vary gradually to respond to the variation of the beam energy from upstream to downstream. We consider an infinitely long double period SWS with inner wall radius; R(z)=R0+hlcos(Klz)+h2cos(K2z). The 1st, the 2nd and the 3rd terms are, respectively, the mean radius, the short period corrugations and the long period variation to reduce the mean radius to fix the oscillation frequency against the energy decrease.