Coherent terahertz radiation from beam-driven upper hybrid wave in magnetostatic plasma

A scheme for generating tunable terahertz radiation using relativistic electron beam-induced upper hybrid wave immersed in a magnetized plasma is investigated. The ponderomotive force applied to the beam electrons because of electromagnetic radiation wave and pump wave generates the non-linear current density in the high-frequency regime. For an appropriate pump wave frequency, under the condition of phase matching the THz radiation wave is obtained. The enhancement in the radiation power occurs along the axial direction in the vicinity of Cerenkov resonance. Our analytical expression shows that the growth rate in the unstable modes of the THz radiation wave increases with beam density (beam current) and the modulation index. In addition, the growth rate of the instability decreases with an increase in radiation wave frequency and scales as the inverse cube root of radiation frequency. An interesting result obtained from our model is that an increase in cyclotron frequency causes the growth decrement in THz radiation emission, while the efficiency of THz radiation emission increases with the growth rate and the modulation index. Also, the emission of the THz radiation wave becomes larger as the modulation index approaches unity.