Displacement current during the formation of positive streamers in atmospheric pressure air with a highly inhomogeneous electric field

Abstract

This paper presents experimental data on the dynamics of positive streamers formation in a highly inhomogeneous electric field under threshold for the breakdown of the gap conditions as well as at high voltage. The glow of the streamer was registered with a four-channel intensified charge-coupled device camera with simultaneous recording of voltage and current characteristics per pulse. It was shown that the streamer appearance is accompanied by a displacement current pulse induced by a redistribution of the electric field strength in the gap. We call this current the dynamic displacement current (DDC). The DDC value changes during the streamer propagation in the gap. It reaches the maximum values when the streamer starts and when it is close to bridge the gap. The DDC was also registered with a collector placed behind the grid plane electrode which is usually applied for the registration of runaway electrons when a negative streamer is formed. It was shown that the DDC allows to study the features of the streamer formation.

Corona with Streamers in Atmospheric Pressure Air in a Highly Inhomogeneous Electric Field

“…1a at 2 kV is higher than 0.4 MV/ cm. This value is of the order of the electric field at pointed electrodes in nanosecond pulsed diffuse discharges formed by wide (ball) streamers [28,31,32] . Hence, similar mechanisms can be expected for discharges from sharp points at rates of voltage rise of <10 6 V/s and >10 12 V/ s. The rates >10 12 V/s correspond to diffuse discharges involving fast and runaway electrons at negative voltage polarity [33] and X rays at positive polarity [34] .…”

“…Typically, two main areas appear in this type of discharge: an ionization region near a pointed electrode where the electric field is high and a region remote from it where the field is low and the current is provided by charged particle drift. As has recently been proven [28] , the part of current in non-ionized region is contributed by dynamic displacement current due to fast plasma expansion by streamers from a pointed electrode. Corona discharges can be initiated by applying DC and AC voltages and by applying short voltage pulses which make them short-lived in a single form [5,7,13] .…”

“…The short duration of the current pulse is caused by a rapid decrease in the rate of ionization processes as the diameter of the streamer increases and the strength of the electric field at its front decreases. These features of current during the development of a streamer were studied in [28] .…”

“…When cylindrical streamers develop (Figs. 8 and 10), the pulsed current increases greatly (Table 4) due to dynamic displacement current [28,37] . As a cylindrical streamer moves from a pointed to a plane electrode kept in a low electric field, capacitive charging occurs between its front and plane electrode.…”

“…The current recorded during the formation of ball streamers is also contributed by dynamic displacement current. However, its amplitudes in corona discharges (due to small streamer sizes) are lower than its amplitudes in nanosecond diffuse discharges [28,[37][38][39][40] . Measurement data on electric fields at ionization wave fronts during breakdowns are reported elsewhere [41][42][43] .…”