Interferometric Diagnosis of Warm Dense Matter

Matter at extreme pressures and temperatures provides an exciting field of research in both fundamental and applied physics. The basic physical properties of these "High Energy Density" (HED) states – for instance the equation of state (EOS) – are of great importance from an experimental as well as theoretical point of view. Under laboratory conditions such extreme states can be reached only in dynamic experiments using extremely powerful drivers. The GSI Helmholtzzentrum für Schwerionenforschung (GSI), with its unique heavy ion accelerator SIS-18 and high energy petawatt laser PHELIX facilities offers ideal conditions for the investigationof these states of matter. The aim of this work is to apply interferometric methods for studying thermophysical properties of metals within the warm dense matter (WDM) region of the phase diagram, characterized by temperatures of 1-50 eV and densities close to the solid state one. At the "High Temperature" (HHT) experimental area of GSI, pressure and temperature measurements of metals heated by intense uranium ion beams to regions near the critical point were performed. Sub-microsecond intense uranium ion beams were focused on a sub-millimetre spot on solid metallic targets, achieving both high energy density deposition and uniform volumetric heating. The expanding material got compressed against a sapphire window and temperature measurements were taken at this interface with a fast multi-channel pyrometer, while spatial velocity profiles were recorded on the free surface by the imaging displacement interferometer allowing for the determination of temporal pressure profiles. At the Z6 experimental area of GSI isentropic compression experiments of iron were conducted using PHELIX as driver. Free surface velocity measurements on the order of km/s were performed using two imaging VISARs (Velocity Interferometer System for Any Reflector) from which pressure profiles up to 0.25 Mbar were derived. The behaviour of iron during the alpha-epsilon transition at different compression rates was studied. Besides the interferometric set-ups, work was performed on the data acquisition system for the heavy–ion beam driven experiments at the HHT area