  Ion beam requirements for fast ignition are investigated by numerical
simulation taking into account new effects such as ion beam divergence not
included before. We assume that ions are generated by the TNSA scheme in a
curved foil placed inside a re-entrant cone and focused on the cone apex or
beyond. From the focusing point to the compressed core ions propagate with a
given divergence angle. Ignition energies are obtained for two compressed fuel
configurations heated by proton and carbon ion beams. The dependence of the
ignition energies on the beam divergence angle and on the position of the ion
beam focusing point have been analysed. Comparison between TNSA and
quasi-monoenergetic ions is also shown.
