Amplification of a wake field generated by a charged bunch in a resonant medium

A bunch of electrons moving in an active medium excites a wake that is ampl ified by the medium. The intense radiation field generated in this process reduces the population inversion and, as a result, the held-medium interact ion reaches saturation. We show that the accelerating gradient at saturatio n may reach the 1 GV/m level before the medium is ionized. When ionization occurs, higher gradients may develop provided that we excite resonant sates of a partially stripped atom.