Regimes of enhanced electromagnetic emission in beam-plasma interactions

Abstract

The ways to improve the efficiency of electromagnetic waves generation in laboratory experiments with high-current relativistic electron beams injected into a magnetized plasma are discussed. It is known that such a beam can lose, in a plasma, a significant part of its energy by exciting a high level of turbulence and heating plasma electrons. Beam-excited plasma oscillations may simultaneously participate in nonlinear processes resulting in a fundamental and second harmonic emissions. It is obvious, however, that in the developed plasma turbulence the role of these emissions in the total energy balance is always negligible. In this paper, we investigate whether electromagnetic radiation generated in the beam-plasma system can be sufficiently enhanced by the direct linear conversion of resonant beam-driven modes into electromagnetic ones on preformed regular inhomogeneities of plasma density. Due to the high power of relativistic electron beams, the mechanism discussed may become the basis for the generator of powerful sub-terahertz radiation.

Simulations of electromagnetic emissions produced in a thin plasma by a continuously injected electron beam

“…Recent PIC simulations with periodic boundary conditions [14,16] showed that, if the plasma thickness is comparable with the radiation wavelength, the power of electromagnetic emission near the frequency of the most unstable beam-driven mode can constitute the significant fraction (about 7%) of total beam power. It was also shown that the main features of observed radiation can be explained by the mechanism of plasma antenna.…”

“…It has been experimentally found that reducing in plasma thickness down to the radiation wavelength is accompanied by the substantial increase in the radiation efficiency [13]. Recent PIC simulations [14] of the simplified temporal problem have shown that such a thin system with a longitudinal density modulation can radiate as a plasma antenna. Indeed, in a periodically perturbed plasma, the most unstable beam-driven wave generates superluminal satellites which are able to interact resonantly with the vacuum electromagnetic waves at the skin depth.…”

Theory of electromagnetic wave generation via a beam-plasma antenna

“…It has been experimentally found that the beam power converts to radiation power much more efficiently when the typical transverse size of the beam-plasma system becomes comparable to the radiation wavelength [1]. These experiments have motivated theoretical studies on the mechanism of EM emission in the thin plasma case [2]. The feature of this regime is that a thin plasma column actually acts as an antenna which can efficiently radiate EM waves if a superluminal wave of electric current is excited inside the plasma.…”

Particle-in-cell simulations of 100 keV electron beam interaction with a thin magnetized plasma

“…The main pecularity of this regime is that a 100 keV electron beam creates a thin plasma column with the diameter comparable to the radiation wavelength [1]. Theoretical studies [2,3,4] motivated by these experiments have shown that such a high level of radiation efficiency can be explained by the mechanism of beam-plasma antenna. This theory is based on the fact that, in a thin plasma with a longitudinal density modulation, the beam-excited mode can generate the superluminal satellite which can resonate with vacuum electromagnetic waves.…”