Abstract
Pulsed plasmas in liquids exhibit complex interaction between three phases of matter (liquids, gas, plasmas) and are currently used in a wide range of applications across several fields, however significant knowledge gaps in our understanding of plasma initiation in liquids hinder additional application and control; this area of research currently lacks a comprehensive predictive model. To aid progress in this area experimentally, here we present the first-known ultrafast (50 ps) X-ray images of pulsed plasma initiation processes in water (+25 kV, 10 ns, 5 mJ), courtesy of the X-ray imaging techniques available at Argonne National Laboratory's Advanced Photon Source (APS), with supporting nanosecond optical imaging and a computational X-ray diffraction model. These results clearly resolve narrow (~10 micron) low-density plasma channels during initiation timescales typically obscured by optical emission (<100 ns), a well-known and difficult problem to plasma experiments without access to state-of-the-art X-ray sources such as the APS synchrotron. Images presented in this work speak to several of the prevailing plasma initiation hypotheses, supporting electrostriction and bubble deformation as dominant initiation phenomena. We also demonstrate the plasma setup used in this work as a cheap ($<$US\$100k), compact, and repeatable benchmark imaging target (29.1 km/s, 1 TW/cm$^2$) useful for the development of next-generation ultrafast imaging of high-energy-density physics (HEDP), as well as easier integration of HEDP research into synchrotron-enabled facilities.
Highlights
Nanosecond-pulsed plasma processes attract significant interest for their broad applicability in fields such as nanochemistry [1,2], medicine [3,4], three-dimensional (3D) printing [5], and aerodynamic flow manipulation [6], among many others
Light-emitting plasma channels propagate across the full field of view within the first captured frame of the event, implying a lower bound of 630 m/s for propagation speed
This propagation speed is of the same order as that reported in Ref. [26], as well as in analysis of equivalent x-ray imaging results discussed later in this work [11.7 km/s, from Fig. 5(c)]
Summary
Nanosecond-pulsed plasma processes attract significant interest for their broad applicability in fields such as nanochemistry [1,2], medicine [3,4], three-dimensional (3D) printing [5], and aerodynamic flow manipulation [6], among many others. Along with its merit as a phenomenon of primary interest to the fields of plasma physics and engineering, the plasma diagnosed in this work shows potential for application in the development of new nanosecond imaging systems. This is due to the inherent hypersonic phenomena involved (29.1 km/s), as well as low turnaround time between events (less than 1 s) compared with other benchmark imaging targets of similar power density (such as exploding wire, which unlike water requires manual reloading). In this work we demonstrate the operation of such a device for well-timed interrogation of the water plasma initiation process itself, while highlighting its value as a repeatable nanosecond imaging target
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