  Erosion of copper target irradiated by deuterium ion beam with ultimate
fluence is studied. The target originally destined for neutron generation
represents bulk copper substrate covered by 3-\mum titanium layer. The target
was irradiated by deuterium ion beam generated in Bayard-Alpert type ion source
with energy of ions 17.5 keV/nuclear. Maximal fluence in the center of the
target achieves 2.5x10^23atoms/cm^2. Measurements of the profile of irradiated
target and estimation of fluence shows that physical sputtering is a dominating
process that determines the target erosion Most interesting feature is growth
of \mum-size tadpole-shaped structures, localized in the cracks of the surface.
RFA analysis of these structures showed extremely large (up to 60%at.) carbon
content.
