[1] Univ Aachen, Inst Phys 2, D-52056 Aachen, Germany
[2] European Synchrotron Radiat Facil, F-38043 Grenoble, France
[3] IBM Deutschland Speichersyst GmbH, D-55131 Mainz, Germany
[4] Forschungszentrum Julich, Inst Pytosphare ICGIII, D-52425 Julich, Germany