New Raman Spectroscopy Results of Single-electrode Pulsed Plasma Branches in Water for Interrogation of High-Pressure Liquid-Solid Phase Transition

Pulsed plasmas in liquids are broadly useful phenomena, already employed for chemical conversion and sterilization among other applications. However, these plasmas exhibit complex multiphase behavior over short timescales ($<$20 ns) which is not well-described by conventional plasma theory. Using a low-jitter laser-triggered voltage pulse (30 kV, 5 mJ), resulting plasmas achieve high instantaneous power density ($\sim$1 TW/cm$^2$), which in liquids causes local isotropic and isochoric behavior. In water, phase transitions which exist at pressures above 1 GPa (Ice VI and VII) are achievable via such thermodynamic processes. Prior results provided tentative evidence of this type of local phase transition during pulsed plasmas in water, using time-resolved Raman spectroscopy of the O-H stretching mode of H$_2$O. Here we present updated imaging and Raman spectroscopy results at higher time resolutions and larger sample sizes, further investigating the local presence of a transient high-pressure solid phase. Such a phase may limit achievable energy densities, which has ramifications across several fields interested in producing high-energy-density plasma processes in liquids.