Free-electron laser with a plasma wave wiggler propagating through a magnetized plasma channel

Abstract

A plasma eigenmode has been employed as a wiggler in a magnetized plasma channel for the generation of laser radiation in a free-electron laser. The short wavelength of the plasma wave allows a higher radiation frequency to be obtained than from conventional wiggler free-electron lasers. The plasma can significantly slow down the radiation mode, thereby relaxing the beam energy requirement considerably. In addition, it allows a beam current in excess of the vacuum current limit via charge neutralization. This configuration has a higher tunability by controlling the plasma density in addition to the γ-tunability of the standard FEL. The laser gain has been calculated and numerical computations of the electron trajectories and gain are presented. Four groups (I–IV) of electron orbits have been found. It has been shown that by increasing the cyclotron frequency, the gain for orbits of group I and group III increases, while a decrease in gain has been obtained for orbits of group II and group IV. Similarly, the effect of plasma density on gain has been exhibited. The results indicate that with increasing plasma density, the orbits of all groups shift to higher cyclotron frequencies. The effects of beam self-fields on gain have also been demonstrated. It has been found that in the presence of beam self-fields the sensitivity of the gain increases substantially in the vicinity of gyroresonance. Here, the gain enhancement and reduction are due to the paramagnetic and diamagnetic effects of the self-magnetic field, respectively.

Electron trajectories and growth rates of the plasma wave pumped free-electron laser

“…Following Freund et al [4], we employ an analytical approach to drive the electron orbits and the dispersion relation of the whistler pumped FEL. For convenience, we introduce the wiggler frame as [4,17],…”

“…Conversion of a whistler wave into a controllable helical wiggler magnetic field has been studied by Kalluri [16]. Recently, a theory for laser gain in FELs with a plasma wave wiggler propagating through a magnetized plasma channel has been presented by Jafari et al [17]; in that study, the effects of cyclotron frequency and plasma density on gain have been illustrated. In addition, the effects of beam self-fields on gain have been analyzed.…”

Low-frequency wiggler modes in the free-electron laser with a dusty magnetoplasma medium

“…In addition, the radiation can be confined to some degree by dielectric guiding by the plasma since the dielectric constant in the beam is larger than that of the outside plasma due to the relativistic mass increase of its electron [3,19]. The plasma can significantly slow-down the radiation mode thereby relaxing the beam energy and beam quality requirements considerably [21,22]. The presence of plasma enables the possibility of employing the plasma modes as wigglers which have a very short period for the excitation of shorter wavelengths.…”