  Small parts of the electronic wavepacket of a multiple charged ion may still
tunnel through the high Coulomb barrier for a sufficiently intense laser field
of $10^{15}W/cm^2$ and higher. Solving numerically the corresponding
Schr\"odinger equation we find that the periodic recollisions of such a
wavepacket in the oscillating high power laser field will give rise to coherent
X-ray radiation in the multiple keV regime, i.e. substantially higher than
predicted or observed before.

Atomic Physics