Creating the Core Conditions of Extra-solar and Solar Giant Planets

Materials can be experimentally characterized at high pressures and densities by sending a laser-induced shock wave through a sample that is pre-compressed inside a diamond-anvil cell. This combination of static- and dynamic-compression methods has been experimentally demonstrated, and ultimately provides access to the 10-100 TPa (0.1-1 Gbar) pressure range that is relevant to planetary science. We report on dynamical measurements of the high pressure compressibility of helium, hydrogen and helium/hydrogen mixtures up to 230 GPa by combining laser shocks and static compression in diamond anvil cells. The initial density of samples in these precompressed targets has been varied by a factor of 3. The measurements on the principal He Hugoniot, i.e with the initial density of cryo-helium, is extended above 100 GPa and a maximum of compression ratio of greater than 5-fold of the initial density is observed. Also, a strong decrease in compressibility is observed by increasing the initial density. A similar data set has been produced for precompressed H{sub 2} and a mixture of He and H{sub 2}.