MEC Experimental Methods

Warm Dense Matter

Warm dense matter is a state of matter that is close to solid density, but with temperatures ranging from a couple of eV to tens of eV. In this state, standard plasma theories are not valid (as the matter is too dense and cold), and neither are solid state theories (since the thermal energy is of the same order as the interaction energies between atoms and perturbative approaches break down). Despite its transient character in laboratory experiments (e.g. inertial confinement fusion experiments), WDM is found abundantly in nature (e.g. cores of large planets [4], stellar accretion disks [3]).

The study of warm dense mater requires the generation of a sample that is uniformly heated to temperatures near and above melt. The method of production can vary from the direct irradiation of a sample by the LCLS [4] or a short pulse laser for thin (1 nm to 100 nm) samples, the irradiation of thicker samples by the LCLS or a long pulse laser on inertially confined samples, or the interaction of ion or electron beams produced by short pulse laser focused to high intensity (>10¹⁶ W/cm²). 

Hot Dense Matter

The creation of hot dense matter (matter of around solid density and 100s of eV temperature) requires long and/or short pulse lasers to irradiate solid or near solid density material at moderate optical laser intensities (10¹² to 10¹⁶ W/cm²). In the generic experiment a solid sample is irradiated by a long pulse laser to create a high energy density (HED) plasma, which has ablated from the surface, and a heat conduction wave that moves into the matter both along, and transverse to, the optical laser beam axis. The plasma plume formed in front of the sample varies in density from near solid to dilute plasma. To diagnose the plasma temperature and density one uses a variety of diagnostics, including Thomson scattering⁵, interferometry, and X‐ray spectroscopy. In addition, specific plasma absorption lines can be pumped to study plasma kinetics.

High Pressure Science

These experiments in their fullest will address a wide variety of topics in high‐pressure research including shocks , equations of state, shock induced chemical reactions, disorder (diffuse scattering), strength/kinetic issues, dislocation dynamics, coupling to large scale molecular dynamics (MD), high strain rate phenomena and shear modulus under compression, (phonon dispersion curves). The generic high pressure experiment has a long pulse laser focused to a target, to a spot size of 150 to 600 μm after having its wavefront smoothed with continuous phase plates. The rear of the target is diagnosed by the VISAR system, which measures the surface motion and the surface reflectivity. These diagnostics are complemented by the XUV spectrometer that measures the fluorescence induced by the LCLS.