A nonlinear theory has been developed for the generation of perfect az
imuthal bunching on a beam with axial initial electron velocity by slo
w radiation fields generated by the interaction itself, under conditio
ns of the anomalous Doppler shift. The dynamics of the beam is formula
ted in the framework of a Hamiltonian analysis and the helical equatio
ns of motion are derived along with the two exact invariant quantities
of the system in hand. Utilizing time separation a simplified set of
equations is derived which compares favourably with the exact model at
least for small initial pitch ratios. The simplified model is then ut
ilized for calculating the properties of an electron beam buncher. The
latter is also optimized to maximize the generated transverse momentu
m.