The instability in the radially non-uniform electron beam-ion channel system

Abstract

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.