Glow Dynamics Research Articles

Formation of Miniature Analogs of Bead Lightning in Nitrogen and Air during Pulsed Discharge in Nonuniform Electric Field

The discharge glow dynamics during a nanosecond breakdown of air and nitrogen initiated by runaway electrons in a point–plane gap is studied with an ICCD camera. The formation of plasma bunches forming a structure analogous to a bead lightning is observed. It is shown that the number of bright plasma bunches in the gap (individual beads) increases with pressure. Up to four individual beads of equal size have been recorded in nitrogen at a pressure of 0.4 MPa.

Breakdown features of a high-voltage nanosecond discharge initiated with runaway electrons at subnanosecond voltage pulse rise time

In the wide pressure range of the pure nitrogen and sulfur hexafluoride with small admixture of nitrogen (2,5%) the development of the breakdown during the formation of diffuse discharges initiated by runaway electrons and X-Ray was investigated. Nanosecond voltage pulses of both polarities with an amplitude up to ~300 kV and risetime of ~0.5 ns applied across the discharge gap did provide sharply nonuniform electric field distribution. Estimations of average propagation velocity of the ionization wave in the nitrogen and mixture sulfur hexafluoride with nitrogen were performed on the basis of data on dynamics of radiation intensity of the second positive (2+) nitrogen system from various regions along of the longitudinal axis of interelectrode gap. Interrelation between the glow dynamics and the local value of the electric field strength has been defined. The results showed that the breakdown is developed in the form of the ionization wave propagating from the potential electrode with the highest concentration of the electric field to the flat-grounded one. In the regions near the grounded electrode practically simultaneous increasing of radiation intensity is registered, that indicates on a possible change of the breakdown mechanism in this part of the discharge gap.

Auroral glow equatorward from the auroral oval

On the basis of observations for the IGY period (visoplots) it is shown, that during magnetic storms diffuse glow is detected at all latitudes between the lowest latitude of the visually observed auroral glow at the zenith and the auroral oval. The diffuse glow region spatially coincides with the region of soft electron precipitation extending equatorward from the boundary of the oval to the latitude of the plasmopause projections along the magnetic force lines to the ionosphere. Using published materials on the diffuse glow dynamics and SAR arcs at the Yakutsk meridian, as well as simultaneous measurements of the DMSP F9 satellite, we discuss the contribution from low-energy electron precipitation transfered via convection toward Earth from the magnetosphere’s plasma sheet to excitation of 630.0 nm emission in low-intensity (<1.0 kR) SAR arcs.

Study of the glow dynamics in a laser-produced plasma jet expanding across the magnetic field

Results are presented from experimental studies of the glow dynamics of a plasma jet generated during the irradiation of a plane aluminum target by an iodine laser pulse with the wavelength 1.315 μm. The laser pulse energy was 330–480 J, the pulse duration was 0.5 ns, and the focal spot diameter was 3 mm, the laser intensity on the target surface being ∼1013 W/cm2. The jet expanded across an external magnetic field with the strength ∼1 kOe. The residual air pressure in the vacuum chamber was ∼10−5 Torr. The spatiotemporal behavior of the jet glow was investigated using a nine-frame camera in two mutually perpendicular directions (along and across the magnetic field). The results of measurements indicate azimuthal asymmetry of the jet expansion.

Plasma creation by terahertz electromagnetic radiation

The results of experiments aimed at the study of the discharge in a focused beam of terahertz waves in argon under near-atmospheric pressures are presented. The range of electric fields and gas pressures, at which a breakdown occurs, is determined. The study of the discharge glow dynamics showed that the discharge starts at the maximum of the terahertz wave beam field and its front moved towards the radiation with the speed of about 105 cm/s into the region of the fields being significantly weaker than the breakdown value. Measurements of the ratio of wave transmission through the discharge allow one to conclude that the density of the plasma produced in the discharge exceeds 1015 cm−3. Some features of the terahertz discharge are discussed.

Glow dynamics of the spark channel and detached shock wave at high gradients of the magnetic field pressure

The dynamics of the electric spark channel and the detached shock wave at high gradients of the magnetic field pressure between them are studied. The absorption coefficient of optical radiation at a given wavelength with allowance for stimulated radiation is determined from the ratio of the measured intensity per unit thickness of the radiation source to the radiation intensity of a reference Planckian source.

Transition of an atmospheric-pressure glow discharge from the diffuse to spark phase

The dynamics of glow and the electrical characteristics of a nanosecond glow discharge in the course of a transition from the diffuse to spark phase have been studied in a rod-plane electrode geometry in air at atmospheric pressure. For this purpose, a sequence of alternating-polarity voltage pulses with an amplitude decaying from 135–170 kV was applied to the interelectrode gap with a length of 5–6 cm. It is established that the spark channel formation is preceded by the stage of diffuse glow and that the spark parameters are correlated with the statistical features of the stage of gap shortage (bridging) preceding the diffuse glow. This analysis also revealed the important role of thermal processes in the dynamics of glow discharge development.

Pink splash of active nitrogen in the discharge afterglow

Results are presented from experimental studies of the glow dynamics of active nitrogen in the stage of its excitation by a current pulse and during the discharge afterglow. The mechanism is proposed for the generation of a light splash in a highly activated nitrogen after the end of its pulsed excitation. The key role in the generation of this splash is played by the D-V processes, by which the dissociation energy is transferred to the vibrational degrees of freedom in the course of recombination of nitrogen atoms, and the V-E processes, by which the vibrational energy of highly excited molecules N2(X, v ≥ 25–27) is transferred to the emitting electronic states N2(B, v) after the V-V delay. Results of simulations based on the mechanism proposed are also presented.

A survey of streamer and diffuse glow dynamics observed in sprites using telescopic imagery

While the fine structure in sprites can assume a wide variety of shapes, sizes, and timescales, certain patterns such as upward branching, downward branching, beading, columns, bidirectional streamers, and propagating large‐scale diffuse glow regions are repeatedly observed. Example cases of these streamer and diffuse glow dynamics observed in sprites are presented using video data obtained by a telescopic imaging system in July–August 1998 and are compared to predictions of current sprite and streamer theories. The previously unreported propagating diffuse glows move slowly (∼104 m/s) and are broader than that predicted for a streamer formation at the same altitude. Sudden brightening of slowly developing negative streamers may be indicative of a return stroke process in which the streamers connect with charge in a lowered ionosphere. Meteoric dust particles in the upper atmosphere may be responsible for the fine beading that exists in many negative streamers and may cause plasma enhancements that initiate double‐headed streamers. Beads at the base of columns can glow for over 100 ms while slowly drifting upward (∼104 m/s). Columns may initiate from downward branching positive streamers. Faint positive streamers are observed at the base of and/or preceding large bright sprite events. Some sprites may initiate as double‐headed streamers formed in localized regions of enhanced electron density. A transition between the streamer formation region and the diffuse glow region is observed at ∼80‐km altitude. No fine structure is observed in telescopic images of the diffuse glow region also referred to as the “sprite halo” [Barrington‐Leigh and Inan, 2001].