External magnetic field effect on the growth rate of a plasma-loaded free-electron laser

Abstract

In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers’ efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.