Phase Transition in a Strongly Nonideal Deuterium Plasma Generated by Quasi-Isentropical Compression at Megabar Pressures

High-explosive driven generators of cylindrical and plane shock waves in ${\mathrm{D}}_2$ and ${\mathrm{H}}_2$ were used for the generation of warm and dense strongly nonideal matter with an intense interparticle interaction and Fermi statistics. Highly resolved flash x-ray diagnostics were used to measure the adiabatic plasma compressibility. The thermodynamic measurements demonstrated the 20% increase of density at megabar pressure, just in the density range, where the electrical measurements indicated a sharp—5 orders of magnitude—increase of electrical conductivity due to pressure ionization in strongly coupled plasmas.

Figure 1

Experimental assembly for quasiadiabatic compression of deuterium plasma.

Figure 2

X-ray picture of experimental sample before (a) and during dynamic compression, after $43.04\mu \mathrm{s}$ from ignition (b); (c), (d)—optical density (D) of x-ray film (a) and (b) as a function of distance ($R$) from axis (0) of cylinder.

Figure 3

Trajectories of the experiments for quasi-isentropic deuterium compression up to $P=125\mathrm{GPa}$. Points—x-ray measurements; 1, 2—external and 3, 4—internal liners positions; solid and dashed lines—hydrodynamic simulation with different elastic-plastic models [25].

Figure 4

Isentropic compression of deuterium. Comparison of experimental data and theoretical predictions. Open circles—27; line with stars—present work; dashed line isentrope calculated by SAHA-D model [21, 26]; dotted line—isentrope calculated by model [10, 24]; hypothetical phase transitions: density gap at “plasma phase transition” (PPT) at $T=2000–10000\mathrm{K}$ [6]—up triangles; “dissociation driven” phase transition (DPT) at $T=1500\mathrm{K}$ [12]—down triangles with dashed line; anomaly at $T=3000\mathrm{K}$ and $\rho =1\mathrm{g}/{\mathrm{cm}}^3$ associated with DPT [13]—thick line; Insertion above. Electrical conductivity of compressed hydrogen: solid rhombus—data from experiments with liquid hydrogen [20, 21]; open circles and open squares—data from experiments with liquid and gaseous hydrogen accordingly [22, 23].