Features of interferometry of small-sized plasma channels obtained during nanosecond discharge

The initial stage of the fast electrical breakdown of an air gap with a pin-to-plane electrode geometry is studied on a nanosecond time scale using multi-frame laser probing with an exposure time of 70ps and spatial resolution as high as 3-4μm. We find that the gap breakdown is associated with the fast (1 ns) formation of a micron-sized (∼10 μm) cathode spot that appears as a plasma with an electron density of » n 10 cm e 19

mentioning

confidence: 99%

Mechanisms responsible for the initiation of a fast breakdown in an atmospheric discharge

Parkevich

Ivanenkov

Medvedev

et al. 2018

“…It should be noted that in a number of works [33,34], it is assumed that the discharge constriction is the result of magnetic compression of plasma channel. The magnetic pressure P m is a function of the discharge current I and of the filament radius R f :…”

Section: Synchronized Electron Temperature and Electron Density Measumentioning

confidence: 99%

Filamentary nanosecond surface dielectric barrier discharge. Plasma properties in the filaments

Shcherbanev

Ding

Starikovskaia

et al. 2019

100

Streamer-to-filament transition is a general feature of nanosecond discharges at elevated pressure. The transition is observed in different discharges by different groups: in the nanosecond surface dielectric barrier discharges (nSDBDs) in a single shot regime at high pressure (2-15 bar), in the point-to-point or point-to-plane open electrodes discharges at high repetitive frequency (so-called nanosecond repetitive pulsed discharges, NRPDs) at atmospherics pressure. The present paper contains experimental analysis of plasma properties in the filamentary nSDBD: the electrical current, the specific deposited energy, the electron density and the electron temperature were measured for a wide range of pressures and voltages. A model explaining plasma properties in filamentary nanosecond discharges and the role of excited species in streamer-to-filament transition is suggested and discussed.

“…The gap between the wire and the plane copper anode was 3 mm. Notably, it was essential to reduce the deviation of the evolving spark channel from the focal depth (∼200 μm) of the optical system since this deviation results in diffraction of the probing radiation ('defocusing' effect), thus complicating the procedure for interferogram processing [33]. Owing to the gap geometry, the studied spark channel originated at a particular region of the point cathode and propagated almost along the gap axis.…”

Section: Diagnosing Setupmentioning

confidence: 99%

Fast fine-scale spark filamentation and its effect on the spark resistance

Parkevich

Medvedev

Ivanenkov

et al. 2019

Formation of a millimeter-sized spark discharge in ambient air is traced on a nanosecond time scale using multi-frame laser probing with an exposure time of 70 ps and spatial resolution of 3-4 μm. The discharge is initiated by a 25 kV voltage pulse with a rise time of 4 ns, with the pulse applied to the gap formed by a point cathode and flat anode. It is demonstrated that the gap breakdown is accompanied by the fast (∼1 ns) formation of a highly ionized homogeneous spark channel originating from the point cathode. We discover that the fast fine-scale filamentation of the homogeneous spark channel arises several nanoseconds after the breakdown and at some distance from the cathode, which results in a complex filamentary structure of the channel. We find that the growing spark channel, in fact, develops in the form of multiple (N  10) rapidlyevolving filaments that constitute micron-sized (∼10-50 μm) plasma channels with an electron density of -ñ 10 10 e 19 20 cm −3 and subnanosecond characteristic evolution time. First filaments appear at the top of the developing homogenous spark channel. Further, the growing filaments are split themselves, and their number is increased over time up to several tens. Our findings indicate that the fast fine-scale filamentation is one of the important mechanisms governing the spark channel resistance after the breakdown.