Samuel J.P. Stafford

Observations on the nucleation of ice VII in compressed water

Water can freeze upon multiple shock compression, but the window material determines the pressure of the phase transition. Several plate impact experiments were conducted with liquid targets on a single-stage gas gun, diagnosed simultaneously using photonic doppler velocimetry (PDV) and high speed imaging through the water. The experiments investigated why silica windows instigate freezing above 2.5 GPa whilst sapphire windows do not until 7 GPa. We find that the nucleation of ice occurs on the surfaces of windows and can be affected by the surface coating suggesting the surface energy of fused silica, likely due to hydroxyl groups, encourages nucleation of ice VII crystallites. Aluminium coatings prevent nucleation and sapphire surfaces do not nucleate until approximately 6.5 GPa. This is believed to be the threshold pressure for the homogeneous nucleation of water.

A new pulsed power facility for isentropic compression experiments

Summary form only given. A new pulsed power facility has been commissioned at Imperial College as part of the Institute for Shock Physics. The facility, based around the MACH-Mega Ampere Compression and Hydrodynamics-generator, is dedicated towards exploring ramp loading of material samples with pressures up to ~100KBar.

Plastic formers as a z-pinch driven radiative shockwave platform

Summary form only given. The use of plastic formers coated in a thin film of Aluminium for the purposes of tailoring pulsed power driven radiative shock waves is discussed.

Interaction of radiatively cooled plasma jets with collimated, supersonic gas flows

Summary form only given. A supersonic (Mach∼3–5), radiatively cooled plasma jet is produced by the ablation of plasma from a radial foil1, a metallic disk subjected to a ∼1.4 MA, 250 ns current pulse from the MAGPIE generator. The ablated plasma converges on axis, producing a steady and collimated jet with a typical axial velocity of ∼100 km/s.