Spoof-Plasmon Instability in Terahertz Region Excited by Magnetized Electron Beam

Spoof plasmon is surface waves extended along corrugated surfaces and the terahertz equivalent of optical surface plasmon polaritons for metals. The spoof plasmon may be effectively excited by an electron beam. The beam is perturbed three-dimensionally during the interaction with the spoof plasmon. In this work, we present numerical analysis on the spoof-plasmon instability driven by a magnetized electron beam in a terahertz region. The slow cyclotron as well as Cherenkov instabilities of the spoof plasmon are excited due to the 3-D perturbation. The two instabilities grow large and merge by increasing the beam current and decreasing the magnetic field. The merged instability divides again into the two instabilities for an extremely high beam current. The spoof-plasmon instabilities are examined by revealing modes involved using the saddle-point analysis.