The instability caused by the interaction among the electron beam, plasma, and electromagnetic (EM) waves in a radially non-uniform ion channel is studied. The dispersion relation of the interaction is derived in this paper. The study shows that the EM instability can be induced nearby the center of the beam through the coupling between the fast plasma wave and forward EM wave. On the other hand, the beam mode instability is found in the region relatively far from the center, which means the beam mode can couple with the slow plasma wave so that the electron beam can provide energy to the plasma wave. The distributions of the instability with radius and plasma density are given, respectively, by the numerical simulation, and the result shows that the instability frequency is increased exponentially with the increase of the plasma density. When the plasma density reaches 1×1024m−3, the scale of the frequency can be 10 THz, which provides a theoretical basis for developing the new kind of high-power terahertz radiation sources. Besides, the related physics mechanisms of the instability are also discussed.

This particle-in-cell simulation study finds that the system of a long relativistic electron beam passing through an overdense plasma can produce high harmonic terahertz electromagnetic radiation. In this process, the electron beam is self-modulated to create a periodic electromagnetic structure which will resonate with the plasma wakefield and excite the electromagnetic instability in the nonlinear stage of the self-modulation. The study also finds that when the radiation is achieved, the self-modulated electron beam will be destroyed due to the self-consistent interaction among the radiation, the electron beam, and the plasma. Meanwhile, the radiation will gradually attenuate, which also coincides with the physical explanation of the radiation.

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In this paper, a novel scheme of generating terahertz radiation is proposed, which considers a relativistic electron beam being modulated by its self-excited plasma wakefield in a plasma-filled slow-wave structure (SWS). Both the dispersion relation and the particle-in-cell simulation show that the self-modulation of the beam can act as a mode-selection method to excite the high-harmonics of the SWS and generate terahertz electromagnetic radiation. The present work gives a new thought for researching high-power and tunable terahertz sources.

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