Dynamic compression of hydrogen for probing the molecular-atomic phase transition

Low-entropy, cylindrical implosion of cryogenic hydrogen is simulated to explore the equation of state (EOS) close to the transition from molecular to atomic structure. The simulations are based on the Los Alamos EOS library. Concerning isentropic compression, optimum time-shaped pulses are derived analytically and are used in numerical simulations. Small cylinders of cryogenic hydrogen, suitable for laser experiments, are considered with 100 μm radius and about a millimeter long; the energy to be invested into such cylinders to reach the transition is about 1 J. Multiple-shock compression by an imploding liner is also considered; the liner velocity has to be close to 1 km/s. Liner compression produces more uniform compressed configurations with longer lifetime (about 10 ns), though at somewhat higher entropy. Rarefaction shocks occur in the expansion stage and might be useful as a diagnostic.