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The group "Experimental Physics II - Reactive Plasmas" at the faculty of physics and astronomy at Ruhr University Bochum.

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Propagation of nanosecond plasmas in liquids—Streamer velocities and streamer lengths

Nanosecond plasmas in liquids are often generated by applying a short high voltage pulse to an electrode immersed in a liquid for biomedical or environmental applications. The plasmas appear as streamers that propagate through the liquid. The understanding of the ignition of these nanosecond plasmas in liquids, however, is an open question. The occurrence of any traditional gas phase ignition mechanism is unlikely, because the formation of a gas bubble prior to ignition is suppressed by the inertia of the liquid. Therefore, either electron multiplication inside nanopores that are induced by an electric field pressure gradient or field effects at the tip and at the ionization front of the liquid streamer may act as electron generation mechanisms. A deeper understanding can be achieved by comparing the velocity and dynamic of the plasma propagation with modeling, where the individual mechanisms and transport coefficients can be analyzed. Here, we are using intensified charge-coupled device imaging to investigate the time dependence of the streamer dynamic and compare this with a 1D fluid code for negative voltages. It is shown that the maximum streamer length scales with the applied electric field, indicating that an electric stability field in the liquid streamer channel is important, as known for gas streamers. The 1D fluid code can reproduce the proper streamer velocities, if transport coefficients for hydrated electrons are chosen. The model suggests that the propagation of liquid streamers is dominated by the local ionization rate at the ionization front rather than by advection or diffusion of electrons as in gases. This also explains the finding that positive and negative streamers exhibit almost identical electron densities.

Release Date
Permanent Identifier (URI)
Is supplementing
Plasma Source Name
Plasma Source Application
Plasma Source Specification
Plasma Source Properties
Rise time of 2–3 ns and a pulse width of 10 ns. Frequency of 1Hz. Voltages between -18 and -22kV
Plasma Medium Name
Plasma Medium Properties
distilled deionized water with an electrical conductivity of 1 μS/cm and a pH of approximately 5.5
Contact Name
von Keudell, Achim
Contact Email
Plasma Diagnostic Properties
ICCD: iStar DH734-18U-03 camera with a gate width of 2 ns and a resolution of the CCD chip of approximately 77 px/mm Simulation: one dimensional drift diffiusion fluid model
Public Access Level
Plasma Diagnostic Name
Funding Agency