There is a wide interest in the basic properties of dense, strongly interacting plasmas.   Interest in these kinds of exotic plasmas is driven, for example, by the desire to understand the structure of stars and giant planets, predict various aspects of inertial confinement fusion dynamics, and to understand the physics of solid density terrestrial materials when they are heated and/or shocked.  Even the most basic fundamental properties of these exotic states of matter such as equation of state, electrical and thermal conductivity, and particle transport, are difficult to calculate from first principles.  The transition region between the domains of condensed matter physics and classical dense plasmas is of particular interest.  A number of factors complicate the description of matter under these conditions.  These dense states are very strongly coupled plasmas, to the point where classical plasma models, which build from the assumption that kinetic energy dominates particle interactions and collision kinetics are purely two-body, break down.  For example, the number of electrons in a Debye sphere falls to the order of unity, invalidating the concept of Debye shielding. 

Debye sheaths in such plasmas, a concept that is the foundation for much of modern plasma physics.  In cooler plasmas, quantum degeneracy effects begin to play a significant role.  Atomic electronic structure is highly distorted; the proximity of ions in the plasma can lower ionization potentials or grossly broaden transition lines. 

We have used the Texas Petawatt laser to generate an ultrafast burst of protons (typically by Target Normal Sheath Acceleration, TNSA, from a thin sheet target) which then isochorically (or “flash”) heat a solid.  This concept is depicted in figure 1 and the states reached are shown on the density-temperature diagram of figure 2.  The burst of protons promotes the solid density target material up in temperature.  With the TPW beam alone we have produced solid density states in materials like copper with temperature up to 50 eV, and a pressure of the order of 100 Mbar using the Texas Petawatt Laser[1].  The temperature of the heated target is diagnosed by optical pyrometry or x-ray spectroscopy; EOS and conductivity are measured by looking at expansion rate and reflectivity respectively.

Figure 1:  Schematic illustration of how shock compression followed by ultrafast proton heating with a petawatt laser can be used to produce dense, high temperature plasmas.

Figure 2:  Plot of states in an Al plasma in density-temperature space.  A fast proton pulse heats up from solid density while the addition of a shock driver first compresses the target to higher density states before the proton pulse isochorically heats up the sample.