Development of a Cryogenic Capability for Shock Compression of Liquid Helium on the Z machine

A cryogenic system has been developed to generate liquid helium (LHe) samples at 2.1 K for high precision equation-of-state (EOS) and isentropic compression measurements using the Z machine. Accurate data on He properties at Mbar pressures are critical to understanding gas giant planetary interiors and for validating first principles density functional simulations; however, limited high pressure He EOS data exist due to difficulty in condensing LHe samples (\textless 3.5 K) for gas guns, magnetic and explosive devices and laser facilities. To address this need, we have developed and demonstrated a cryogenic system to generate quiescent superfluid LHe samples (2.1 K). The cryostat system utilizes a conduction refrigerator with a pumped LHe reservoir to cool the cryocell. The cryostat design produces stable, controlled temperatures resulting in well-characterized initial states of liquid He samples, which is key for precision EOS measurements. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.