Warm Dense Matter

Warm dense matter is broadly defined as the parameter space for materials with densities between standard density and 10 times this value, and temperatures ranging from 0.1 eV to 100 eV (103 to 106s K). This defines the boundary between condensed matter physics and plasma physics. It is a region where both types of material models break down, such that at present there is no capability to predict accurately the behaviour of matter under such conditions. One of the main purposes of studying warm dense matter is to understand planetary interiors in terms of equation of state (EOS) and other material properties.  Only through such understanding can we hope to predict planetary formation and evolution.

Pre-compressed material (e.g. using diamond anvil cells) under well known pressure conditions can be heated using high power lasers, providing access to pressure-temperature conditions unobtainable by either technique alone. By studying hydrogen, strongly correlated degenerate plasmas can be produced and provide information about many body quantum physics and the EOS of giant planets and brown dwarfs.


Shock compressing matter using lasers has been used for many years to study EOS. In the past, shock and fluid velocities have been used to measure the thermodynamic properties of the material. These experiments however have been extremely restricted in their scope and accuracy. HiPER will provide a unique tool to study these parameters with far greater flexibility and precision.

Of direct interest to the HiPER energy mission is the need to understand the behaviour of the compressed fusion fuel, which is Fermi degenerate. Analogous problems exist in many astrophysical objects.  HiPER can both create such states and provide quantitative means of interrogating their behaviour.  For example, when ultra-high intensity laser beams interact with a material they produce bright sources of protons and X-rays and these can be used to probe the dense matter. X-rays can be Thomson-scattered by the dense plasma, yielding a technique which provides a direct measurement of the electron distribution function of high density material. These situations are hard to model and experimentally measure using current techniques and so using this diagnostic is fundamental to the success of laser fusion.