Inverse-free-electron-laser beat-wave accelerator.

Abstract

It has been proposed [J. L. Bobin, Opt. Commun. 55, 413 (1985)] that the presence of a plasma can, under certain conditions, enhance the accelerating electric field in an inverse free-electron laser. In this scheme, the beat wave generated by a laser and an undulator is expected to couple to the plasma oscillations generated by the electron beam streaming through the plasma. We have undertaken an analytical and numerical study of the proposed acceleration scheme. Our results show that the electric field is dominantly the self-field of the electron beam, and the plasma makes a negligible contribution to the electric field. Based on our analysis, we propose an alternative method of acceleration that employs a high-current electron beam to generate a beat wave that is subsequently used to accelerate a higher-energy beam. We show that an accelerating electric field \ensuremath{\sim}1 MeV/cm can be achieved with an electron beam of current density \ensuremath{\sim}20 kA/${\mathrm{cm}}^{2}$. The results of the analytical study agree well with numerical results from a two-dimensional computer code. The parameters of a proof-of-principle experiment are presented.