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.

Study on plasma‐photonic‐crystal‐like beam–plasma system

“…As for the radiation frequency of two types of plasma‐photonic‐crystal‐like beam–plasma systems, they are all the same. According to [5, 6], plasma density influences the radiation frequency of the beam–plasma system, and the plasma density of plasma section in the plasma‐photonic‐crystal‐like beam–plasma system is the same which leads to the same radiation frequency. By comparing the amplitude of electric field in Fig.…”

“…Observing the above system, if the system is full of plasmas, it is a beam–plasma system, which has been studied in [5–9].…”

Experiment on the electromagnetic radiation excited in an electron beam‐ion channel system

“…Such a system can be formed in an under‐dense plasma ( n b ≥ n p ) with all the plasma electrons expelled by the beam, where n b is the density of the beam and n p is the density of plasma. In this regime, the space charge wave in the beam will couple with the transverse EM wave and excite EM instability at around the plasma frequency . However, in fact, the difficulty of producing high‐density electron beams will limit the radiation frequency.…”

“…However, in fact, the difficulty of producing high‐density electron beams will limit the radiation frequency. For example, to reach high‐frequency THz radiation, it needs an electron beam with a density of 10 22 m −3 , which seems unpractical for common experiments and compact devices . To overcome this problem, we proposed a scheme in this preliminary experimental study, where the electron beam is formed by the plasma electrons driven by a high‐voltage pulse.…”

“…Specially, it attracts interests again in these years for the purpose of designing high‐power THz sources . Among the recent studies, many theoretical works are based on the physical model of a long‐pulse electron beam propagating through an ion channel . Such a system can be formed in an under‐dense plasma ( n b ≥ n p ) with all the plasma electrons expelled by the beam, where n b is the density of the beam and n p is the density of plasma.…”