  We report the observation of multiple ionization of Argon through
multi-XUV-photon absorption induced by an unprecedentedly powerful laser driven
high-harmonic-generation source. Comparing the measured intensity dependence of
the yield of the different Argon charge states with numerical calculations we
can infer the different channels -direct and sequential- underlying the
interaction. While such studies were feasible so far only with FEL sources,
this work connects highly-non-linear-XUV-processes with the ultra-short time
scales, inherent to the harmonic pulses, and highlights the advanced
perspectives of emerging large scale laser research infrastructures.
