Cooling of Relativistic Electron-Beams

A method of reducing the energy spread of an electron beam in a free-electron laser is suggested. The electron beam compression is based on a nonlinear mechanism of electron interactions with a ponderomotive wave in the presence of a constant and uniform magnetic field perpendicular to the electron motion. Due to this interaction the electrons slightly increase their energies; electrons with less initial energy are subject to a higher acceleration. As a result, the initial energy spread can be reduced several times.