In this paper, we discuss the results from the computational investigation of the effect of a metal grounded target, metal target at a floating potential and dielectric targets (conductive and nonconductive) on the plasma bullet propagation and reflection. We show that the intensity of the primary ionization wave (IW) is the highest for the metal target, while it is significantly lower for the non-conductive dielectric. For the conductive dielectric, the wave intensity is greater than that for the non-conductive dielectrics, but lower than for a metal target. After the primarily forward IW touches the target, the reflected waves are observed for all the targets under investigation. For a metal target the reflected IW changes its direction and transforms into the secondary forward wave. We did not observe secondary forward IWs for dielectric targets. For dielectric targets, the reflected waves gradually decayed without changing their direction. The 'stopping' path for the reflected wave is introduced and the increase/decrease of this path is discussed in dependence on the target properties.

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In this paper, we investigate pre-breakdown and breakdown phenomena in gas-liquid systems. Cavitation void formation and breakdown in bubbles immersed in liquids are studied numerically, while complete breakdown of bubbled water is studied in experiments. It is shown that taking into account the dependence of water dielectric constant on electric field strength plays the same important role for cavitation void appearance under the action of electrostriction forces as the voltage rise time. It is also shown that the initial stage of breakdown in deformed bubbles immersed in liquid strongly depends on spatial orientation of the bubbles relative to the external electric field. The effect of immersed microbubbles, distributed in bulk water, on breakdown time and voltage is studied experimentally. At the breakdown voltage, the slow 'thermal' mechanism is changed by the fast 'streamer-leader' showing a decrease in breakdown time by two orders of magnitude by introducing microbubbles (0.1% of volumetric gas content) into the water. In addition, the plasma channel is found to pass between nearby microbubbles, exhibiting some 'guidance' effect.

In this paper, we discuss results from an experimental and computational study of the properties of a single jet and two-tube jet arrays operating in argon and helium. The jets are positioned horizontally. It was shown in experiments that the helium plasma plume bends upward and the plumes in the two-tubes jet array tend to divert due to the jet-jet interaction. To investigate these potential interactions, a computational study was performed of one- and two-tube argon and helium jet arrays having variable spacing. The effects of buoyancy forces on the jet-to-jet interaction of the plasma plumes are also investigated. Velocities of ionization waves inside and outside the tubes are estimated and compared for the argon and helium ionization waves. We show that in helium jet-jet interactions primarily depend on the spacing between the tubes and on the buoyancy forces. The helium plumes tend to merge into one single stream before dissipating, while the argon plasma plumes are less sensitive to the spacing of the jet tubes.

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