An electromagnetic particle-in-cell simulation code is used to
investigate particle
density effects on the nonlinear amplification of inverse-bremsstrahlung
electron
acceleration, according to the schemes proposed by Kawata et al.
and by Hussein
and Pato. It is shown that although the space-charge self-consistent field
does not
modify the basic results obtained with the one-particle model, the electromagnetic
fields produced by the transverse particle current play a substantial role
for large
beam densities.