Velocity of initial propagation of positive nanosecond discharge in liquid water: dependence on high voltage amplitude and water conductivity

Abstract

This study deals with the effect of water conductivity and high voltage pulse amplitude on the initial velocity of nanosecond discharge in liquid water. As variable parameters, we used water solutions with three different conductivities (2 μS cm −1 , 100 μS cm −1 , 500 μS cm −1 ), and positive high voltage pulses with four different amplitudes (80 kV, 91 kV, 100 kV, 113 kV). The discharge reactor consists of metallic electrodes in a point-to-plane geometry, both immersed in liquid water. The discharge was generated by a commercial nanosecond pulse power generator with positive HV pulses of ∼6 ns pulse duration (FWHM) and ∼2.5 ns rise time. ICCD timeresolved imaging microscopy with high temporal resolution (∼ns) was utilized as a suitable diagnostic tool for the discharge dynamic propagation. It can be concluded that the discharge visual characteristics and behaviour are not significantly influenced by water conductivity and the length of the filaments increases with the increasing voltage amplitude and reaches the maximum value of ∼1.8 mm for 90 kV. The initial propagation velocity also depends on the voltage amplitude and increases with the voltage. The effect of water conductivity on the propagation velocity is negligible. As far as we know, this paper is the first to bring insight into the topic of the effect of water conductivity on the nanosecond discharge propagation in liquid water.

Demonstration of Dynamics of Nanosecond Discharge in Liquid Water Using Four-Channel Time-Resolved ICCD Microscopy

“…The time-resolved microscopic images of the luminous filament evolving during the primary HV pulse provide fundamental signatures reflecting the discharge mechanism, i.e., the expansion velocity of the luminous fronts, radial dimensions, and the branching dynamics of the luminous filaments. These parameters were recently investigated in [7,8] by employing single-channel ICCD microscopy. Basic outcomes related to the expansion velocity of the luminous front obtained by using 'one ICCD image per one discharge pulse' approach revealed an initial expansion characterised by a constant velocity of~2 × 10 5 m/s (i.e., 200 µm/ns).…”

“…The initiation and formation of micro-discharges in liquid water driven by nanosecond high-voltage (HV) pulses are conditioned by the ultrafast (fs/ps) response of the structure of the H-bonded matrix to very high (~GV/m) non-uniform transient electric fields. The physical processes behind very likely include the collective re-orientation of individual molecular dipoles and the subsequent disruption of the cohesion due to the ponderomotive electrostrictive forces followed by the formation of nanovoids and the multiplication of charged species [1][2][3][4][5][6][7][8][9][10]. Experiments performed using extremely short pulses (~100 ps) have shown that discharges in liquid water can be formed in the absence of formation of gas bubbles and with minimal thermal effects [3,11].…”

“…For example, in our recent studies, we employed time-resolved emission and shadowgraphic microscopy to reveal fundamental morphologic signatures and estimated the average propagation velocity of expanding dark and luminous filaments [7,8,12]. We established that the dark or non-luminous discharge event is initiated at a certain delay after the onset of the HV pulse through a few isolated, tiny tree-like structures emerging from the surface of the anode tip.…”

Experimental evaluation of methodologies for single transient cavitation bubble generation in liquids

“…A first rough categorization of high-voltage-induced bubbles can be by either coronalike or arc discharge. A very fast (sub-ns) HVD (highvoltage discharge) can in fact lead to corona-like discharge (considered a partial discharge (Bruggeman et al 2016)) without the formation of a bubble (Pongrác et al 2019), as the bubble growth is usually in the µs range and the dissipation energy in liquids is relatively quick. The pre-breakdown phase change is believed to originate from nanosized voids created by electrostriction effect of the local high electric fields needed to create and sustain an electronic avalanche in liquids.…”

“…Transient bubbles are important for studying, bubble-bubble, bubble-interface and bubble-solid interactions, relevant for disinfection studies of microbiological (Lajoinie et al 2016) and biological tissue interactions (Vogel and Venugopalan 2003), enhanced mixing at small scales (Hellman et al 2007), medical applications (Mohammadzadeh et al 2016), cavitation emulsification (Orthaber et al 2020), erosion (Dular et al 2019), cleaning (Song et al 2004) and thermal effects (Dular and Coutier-Delgosha 2013). Outside the cavitation field, they are interesting for plasma in liquids (Horikoshi and Serpone 2017), acoustic emitters (Buogo et al 2009), high-voltage breakdown of liquids (Pongrác et al 2019) and pulsed laser ablation in liquids (Reich et al 2017) studies.…”