Hybrid Bulk-Surface Modes Excited by a Sheet Electron Beam in THz Cherenkov Oscillator

It was shown that a spoof surface plasmon polariton (SSPP) with the uniform RF field distribution compatible with a sheet electron beam is resonantly excited by a bulk wave of an open cavity containing a nonuniform (bi-periodic) grating. This provides an efficient interaction of a wide sheet electron beam with a hybrid bulk surface mode (HBSM) in the THz Cherenkov oscillator that has been demonstrated by 3-D PIC simulations. The presented simulation results showed the excitation of oscillations in the range from 0.628 to 0.648 THz with watt level of output power and output efficiency up to 1% for the 100-mA 17.2–23.2-kV electron beam. The conditions for the suppression of the competing modes having variations across a grating width have been discussed.