Dynamics of an electron bunch accelerated by a wakefield

The energy characteristics of an electron bunch accelerated by a wakefield are largely determined by the initial bunch dimensions. Present-day injecto rs are still incapable of ensuring the initial spatial parameters of the bu nches required for their acceleration without increasing the energy spread of the bunch electrons. in connection with this, the possibility is studied of improving the energy characteristics of an accelerated bunch by precomp ressing it in the longitudinal direction in the stage of trapping by a wake field. Analytic formulas are derived that describe the one-dimensional dyna mics of the spatial and energy characteristics of a short (much shorter tha n the wakefield wavelength) electron bunch in both the trapping and acceler ation stages. The analytical results obtained are shown to agree fairly wel l with the results from one-dimensional and three-dimensional simulations, provided that the electrons are injected into the region that is optimum fo r acceleration. The possibility is discussed of forming compressed bunches so as to ensure the high quality of the bunch in the course of its accelera tion to high energies. (C) 2001 MAIK "Nauka/Intterperiodica".