Regime of capture of electron bunches by a backward electromagnetic wave in a longitudinal electrostatic field

The regime of capture of electron bunches is considered for the case in which the phase and the group velocities of the electromagnetic field are of opposite signs (backward wave field). It is also assumed that the electrons flow in the same direction as the phase of the synchronous spatial harmonic of the EM field. In the case of an accelerating electrostatic field the efficiency of energy conversion increases for smaller initial bunch phase width. In the case of a retarding electrostatic field the longitudinal decrease in the bunch phase width is noted as the primary benefit of the energy conversion mechanism described. Results are presented for an O-type BWT.