Path integral calculation of shock Hugoniot curves of precompressed liquid deuterium

Abstract

Abstract. Path integral Monte Carlo simulations have been used to study deuterium at high pressure and temperature. The equation of state has been derived in the temperature and density region of 10 000 ≤ T ≤ 1 000 000 K and 0.6 ≤ ρ ≤ 2.5 g cm −3 . A series of shock Hugoniot curves is computed for different initial compressions in order to compare with current and future shock wave experiments using liquid deuterium samples precompressed in diamond anvil cells. The equation of state of dense deuterium has been the topic of intense discussions since Nova laser shock wave experiments [1] measured the Hugoniot curve up to megabar pressures in 1997 and predicted an unexpectedly high compressibility. Four years later, Knudson et al. measured a significantly smaller compressibility using magnetically driven flyer plates [2]. This controversy continues to initiate new efforts to determine the EOS in different regions of the high temperature phase diagram. In a new approach to reach higher densities, G.W. Collins and P. Cellier use a diamond anvil cell (DAC) to precompress samples of liquid deuterium and then launch laser shock into them. The focus of this article is to use path integral Monte Carlo (PIMC) results to determine Hugoniot curves for precompressed samples in order to make a prediction for comparison with current and future experiments.The two series of shock wave experiments using the Nova laser [1, 3] reached pressures of up to 340 GPa and predicted a 50% higher compressibility than previously estimated. The results provided the first experimental data in a regime of extreme pressure and temperature, in which our understanding had so far been primarily based on analytical models and computer simulations. The experimental findings suggested that standard EOS models such as Sesame [4] were too stiff, predicting a maximum compression of about 4-fold the initial density. Instead the measured EOS was found to be closer to softer models like [5] that predicts a maximum compression ratio of about 6. Such a difference in the EOS of dense hydrogen and deuterium would have significant consequences for our understanding of Jovian planets, brown dwarfs, and low mass stars as well as for the design of the inertial confinement fusion strategies. § militzer@llnl.gov

First Principles Calculations of Shock Compressed Fluid Helium

“…The principal shock Hugoniot curves for deuterium [24] and helium are shown for samples that were precompressed to different initial densities. For both materials, the precompression reduces the maximum compression ratio ρ/ρ0 that can be reached.…”

“…225000K 300000K (1) ρ 0 =0.400 g/cc (2) ρ 0 =0.300 g/cc (3) ρ 0 =0.250 g/cc (4) ρ 0 =0.171 g/cc (a) ρ 0 =0.4941 g/cc (b) ρ 0 =0.3706 g/cc (c) ρ 0 =0.2470 g/cc (d) ρ 0 =0.1235 g/cc FIG. 3: The principal shock Hugoniot curves for deuterium [24] and helium are shown for samples that were precompressed to different initial densities. For both materials, the precompression reduces the maximum compression ratio ρ/ρ0 that can be reached.…”

“…In Fig. 3, we use our first principles calculations to predict how the static precompression will affect the Hugoniot curves of helium and deuterium [24]. For helium, a precompression to 4-fold the cryogenic liquid density at 1 bar, ρ 0 = 4ρ .…”