Positive System Of N2 Research Articles

Electrical and optical characteristics of a nanosecond pulsed electrical discharge in air in contact with a water droplet for various electrical conductivities

Abstract Interactions between pulsed electrical discharges and liquid dielectric materials is a growing research field with interests in fundamental discharge physics as well as in applications. Herein, we present an experimental study on the dynamics of nanosecond discharges in air with the presence of a water droplet with various electrical conductivities (EC) and at different applied voltages (Va). The discharges are characterized optically, by employing time-resolved ICCD imaging and optical emission spectroscopy, as well as electrically, by acquiring the current-voltage waveforms for every discharge. The results show that three modes of discharges can be obtained: i) streamer discharge between the cathode and the droplet, ii) streamer discharge between the cathode and the droplet as well as between the anode and the droplet, and iii) spark discharge that connects the two electrodes and propagates over the droplet. We find that the probability to obtain one of the three discharge modes is strongly related to the droplet’s EC as well as to Va. Although the ignition of the streamer is relatively insensitive to EC, its transition to a spark can be finely controlled by the droplet’s EC. The time-resolved ICCD images show that the discharge initiates in the gap between the cathode and the droplet, followed by ignition between the anode/ground electrode and the droplet. Then, an extinction phase is observed before the ignition of a secondary streamer, and depending on the conditions, the discharge may transition to a spark, i.e. a channel with high emission intensity. We find that the duration of each stage of discharge propagation as well as the corresponding emission (path and intensity) are sensitive to droplet’s EC. Finally, emissions from streamers (primary and secondary) as well as from sparks are analyzed using optical spectroscopy. We find that the emission from the streamers is dominated by the second positive system of N2, and that the droplet’s EC does not significantly influence the emission spectra nor the estimated rotational temperature of N2.

Characteristics of Merging Plasma Plumes for Materials Process Using Two Atmospheric Pressure Plasma Jets

Atmospheric pressure plasma jets (APPJs) have attracted significant attention due to their ability to generate plasma without vacuum systems, facilitating their use in small areas of plasma processing applications across various fields, including medicine, surface treatment, and agriculture. In this study, we investigate the interaction between two helium plasma jets, focusing on the effects of varying flow rate, voltage, and directional angle. By examining both in-phase and out-of-phase configurations, this research aims to elucidate the fundamental mechanisms of plasma plume merging, which has critical implications for optimizing plasma-based material processing systems. We demonstrate that while increasing voltage and flow rate for the in-phase condition leads to an extended plasma plume length, the plumes do not merge, maintaining a minimal gap. Conversely, plasma plume merging is observed for the out-of-phase condition, facilitated by forming a channel between the jets. This study further explores the impact of these merging phenomena on plasma chemistry through optical emission spectroscopy, revealing substantial differences in the emission intensities of OH, the second positive system of N2, and the first negative system of N2+. These findings offer valuable insights into controlling plasma jet interactions for enhanced efficiency in plasma-assisted processes, particularly where plume merging can be leveraged to improve the treatment area and intensity.

Streamer-induced kinetics of excited states in pure N2: II. Formation of N2(B 3Πg,v=0–21 ) through analysis of emission produced by the first positive system

Vibrational distributions of electronically excited states of N2 obtained through dipole-allowed radiative transitions provide an important tool to study the kinetics of non-equilibrium plasmas under various discharge conditions. In this work, we report, for the first time, streamer-induced visible/near-infra-red emission spectra developing during the first hundred nanoseconds after the initiation of the discharge. Emission through the first positive system of N2 was acquired in 500–1100 nm range, which allows a complete analysis of the N2(B 3Πg,v = 0–21) vibrational manifold. The investigated evolution of the vibrational distribution of the N2(B 3Πg , v = 0–21) state at the centre of the gap corresponds to the transition of the streamer head and the subsequent decay of the streamer channel. We show that the vibrational distribution characterising streamer head is determined by Franck–Condon factors, while during streamer relaxation, it is influenced by the complex interaction between triplet excited states of N2. Additionally, the observed N2(B 3Πg , v = 13–21) vibrational levels are likely produced by the interaction of high vibrational levels of N2(W 3Δu , B’ 3Σu− , B 3Πg) with N2(C3Πu) state. We also provide a detailed kinetic scheme for modelling vibrationally-resolved N2(B 3Πg ) state and compare model results with experimental outcomes.

Optical emission spectroscopy and Langmuir probe studies of an intermediate pressure, supersonic microplasma jet deposition source

Optical emission spectroscopy and double Langmuir probe studies were conducted on the supersonic expansion plume of a flow-through, intermediate pressure (∼10 Torr) Ar/N2 microplasma source used for material deposition. Emission from the first positive system of N2 (B3Πg → A3Σu+) was used to determine the expanding gas rotational and vibrational temperatures; both were strongly dependent on plasma drive current, and the gas (rotational) temperature could be tuned from 300 to 800 K. The effects of drive current, plasma circuit configuration, and O2 addition to the gas feed on the local electron temperature (Te) were investigated using a miniature double Langmuir probe. Electron temperatures of 1–2 eV were estimated and decreased slightly with higher O2 content in the feed and increased distance from the capillary orifice. Te dependence on drive current was more complicated, falling into two regimes, namely, a nonuniform “predischarge” regime at low currents (<12 mA) where Te varied greatly, and the normal hollow cathode regime at higher currents (>12 mA) where Te remained nearly constant as plasma current was increased. These phenomena are discussed in light of the IV characteristics of the discharge drive circuit.

Ab initio study of the second positive system of N2 at high temperature

The potential energy-curves (PECs) and electronic transition dipole moment-curves (TDMCs) of the B3Пg and C3Πu states of N2 have been investigated by employing the multi-reference configuration interaction (MRCI) approach with the augmented correlation consistent polarized valence quintuple-zeta (aV5Z) set and active spaces 31103110. The calculated PEs of the two states (B3Πg, C3Πu) agree well with the Rydberg-Klein-Rees (RKR) potential energy, and the calculated TDMCs are more precise than those reported in previous literature studies. Calculation of the Einstein A coefficients, spectral parameters and wavelengths by using the exact potential energy and dipole moment are consistent with the recent experimental and literature values. For the first time, the intensities of eight bands of the second positive system (2PS) of N2 are obtained from the summation of their respective absorption spectral line intensities. The absorption spectral intensities of the 0–0, 0–1, 2–0, 2–1, 3–0, 3–1, and 4–0, 4–1 bands were computed in a wide temperature range, especially at high temperatures. For example, the 0–0 band intensities are 4.58 × 10−15 cm−1/(molecule cm−2), 2.50 × 10−15 cm−1/(molecule cm−2) and 9.47 × 10−16 cm−1/(molecule cm−2) at 300 K, 3000 K, and 6000 K, respectively. These results of spectral intensities can be utilized to predict spectral characteristics, and also definited as a theoretical reference value for high temperature astrophysics.

Effect of Dielectric Surface Morphology on Dielectric Barrier Discharge Mode in Air at Atmospheric Pressure

In order to study the effect of surface morphology of dielectric materials on features of dielectric barrier discharge (DBD) in air at atmospheric pressure (AP), electrical characteristics and optical emission spectrum are obtained in a 2-mm air gap with quartz glass and ceramic used as the dielectric layer (the capacitance of the used dielectrics is similar). The transition of discharge mode is observed for different dielectric material and surface morphology. Results show that with varying dielectric material and surface morphology, air atmospheric pressure dielectric barrier discharge (APDBD) presents three discharge modes, including a filamentary mode, a homogeneous mode, and a mixed mode of them. Further investigation reveals that the homogenous mode is in a Townsend discharge regime, which is realized in a proper surface morphology of 96% Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramic. Moreover, optical emission spectrum is obtained, which mainly consists of atomic lines of nitrogen and molecular bands originating from the second positive system of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> →B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ). From N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> →B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ), molecular vibrational temperature is investigated as a function of surface roughness (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) of the different dielectric materials. Result reveals that there is a minimal vibrational temperature when the discharge is in the homogeneous mode. With quartz glass used as the dielectric, the vibrational temperature decreases first and then increases with increasing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> . The minimum value appears at R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> of 215 nm. Besides, the discharge current is the most concentrated in time, and the discharge looks the most homogeneous under this circumstance.

Measurement of the first Townsend’s ionization coefficient for atmospheric pressure neon by a dielectric barrier discharge

Fast photography and optical emission spectroscopy are implemented in a 5 mm neon gap dielectric barrier discharge (DBD) at atmospheric pressure with quartz glass used as the dielectric layer. Results show that it starts with a Townsend discharge and ends at a sub-normal glow discharge in neon DBD. Based on the Townsend discharge, the first ionization coefficient of neon is measured. The measurements are consistent with those at low pressure. Optical emission spectroscopy indicates that the spectra are mainly composed of atomic lines of neon, molecular bands and molecular ion bands originating from inevitable gas impurities (mainly nitrogen). Moreover, spectral lines emitted from atomic neon corresponding to the transitions (2p5 3p → 2p5 3s) are predominant. Although the second positive system of N2(C3Πu → B3Πg) is observed, their intensities are too weak compared with neon’s spectrum. The molecular nitrogen ion line of 391.4 nm is observed. It reveals that Penning ionization between high energy neon excited states and the inevitable gas impurities plays an important role in the value of the α coefficient.

Spatial and time resolved determination of the vibrational temperature in ignition sparks by variation of the dwell time

The ignition process initiates the combustion in spark-ignition engines. Therefore, understanding the ignition process is an important aspect in developing more efficient combustion engines. In this thesis, the vibrational temperature of an ignition spark in air under atmospheric pressure and room temperature is observed in spatial and temporal resolution. The temperature is determined by comparing simulated spectra with the measured spectra of the second positive system of N2 between 360 and 381 nm. Changing the dwell time had no significant effect on the vibrational temperature of the three spark phases. In the breakdown the vibrational temperature is about 3300 K. The vibrational temperature of the following arc discharge is in the range of 3750 K to 4350 K. The glow discharge is divided into the negative glow and the positive column. Both show similar vibration temperatures in the range of 3500 K to 3900 K.

Analysis of the Spatial Nonuniformity of the Electric Field in Spectroscopic Diagnostic Methods of Atmospheric Electricity Phenomena.

The spatial nonuniformity of the electric field in air discharges, such as streamers, can influence the accuracy of spectroscopic diagnostic methods and hence the estimation of the peak electric field. In this work, we use a self‐consistent streamer discharge model to investigate the spatial nonuniformity in streamer heads and streamer glows. We focus our analysis on air discharges at atmospheric pressure and at the low pressure of the mesosphere. This approach is useful to investigate the spatial nonuniformity of laboratory discharges as well as sprite streamers and blue jet streamers, two types of transient luminous events taking place above thunderclouds. This characterization of the spatial nonuniformity of the electric field in air discharges allows us to develop two different spectroscopic diagnostic methods to estimate the peak electric field in cold plasmas. The commonly employed method to derive the peak electric field in streamer heads underestimates the electric field by about 40–50% as a consequence of the high spatial nonuniformity of the electric field. Our diagnostic methods reduce this underestimation to about 10–20%. However, our methods are less accurate than previous methods for streamer glows, where the electric field is uniformly distributed in space. Finally, we apply our diagnostic methods to the measured optical signals in the second positive system of N2 and the first negative system of N2+ of sprites recorded by Armstrong et al. (1998, https://doi.org/10.1016/S1364-6826(98)00026-1) during the SPRITE's 1995 and 1996 campaigns.

Experimental study of the dynamics of fast gas heating in a low-pressure DC discharge in nitrogen

This paper discusses the experimental studies of the gas heating dynamics of a low-pressure DC discharge in nitrogen. The time evolution of the discharge current, the electric field, and the gas temperature in the positive column of a pulsed DC discharge in nitrogen for a gas pressure of 1.5 Torr and a current density of 0.1–6 A cm−2 were measured. The gas temperature in the discharge was equal to the rotational temperature in the and metastable electronic states of nitrogen. The rotational temperature in the state was found from the spectra of the first positive system of N2, which were recorded by using intracavity laser absorption spectroscopy. The rotational temperature in the state was determined from the VUV emission spectra of the Lyman–Birge–Hopfield system of N2. The gas temperatures obtained by these two spectroscopic methods were in good agreement. It was found that two phases with different gas heating rates exist during a discharge pulse. In the first phase, the gas heating was relatively slow. With increasing current density, the duration of the first heating phase decreased from 150 μs at 0.2 A cm−2 to 10 μs at 2.5 A cm−2. In the second phase, fast gas heating occurred. The gas heating rate in the second phase increased with increasing discharge current, and was equal to 10 K μs−1 for a current density of about 2 A cm−2. The relation between the rate of the fast heating and the density of deposited power obeyed a power law. In 300 μs, the gas was heated in the discharge up to about 400, 1500, and 3000 K for current densities of 0.2, 1, and 2.5 A cm−2, respectively. These experimental data can be the basis for verification of kinetic models for gas heating dynamics in a low-pressure discharge in nitrogen.

Broadening and shift of emission lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse in air

We study the broadening and shift of N I (λ = 746.8 nm) and O I ( λ = 777.4 nm) lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). It is shown that the dynamic Stark effect makes a major contribution to the broadening and shift of the N I line (λ = 746.8 nm). It is found that amplified spontaneous emission of a regenerative amplifier and post-pulses break the LS coupling for the O I 3p 5P energy level, lead to the generation of side bands related to the Rabi splitting of levels and result in pulsed emission of the first positive system of N2.

A Planar Source of Atmospheric-Pressure Plasma Jet

In a single-barrier discharge with voltage sharpening and low gas consumption (up to 1 L/min), plane atmospheric pressure plasma jets with a width of up to 3 cm and length of up to 4 cm in air are formed in the slit geometry of the discharge zone. The energy, temperature, and spectral characteristics of the obtained jets have been measured. The radiation spectrum contains intense maxima corresponding to vibrational transitions of the second positive system of molecular nitrogen N2 (C3Π u → B3Π g ) and comparatively weak transition lines of the first positive system of the N 2 + ion (B2Σ + → X2Σ g ). By an example of inactivation of the Staphylococcus aureus culture (strain ATCC 209), it is shown that plasma is a source of chemically active particles providing the inactivation of microorganisms.

Glow of the Plasma of a Pulse Discharge Produced in Nitrogen by High-Power Terahertz-Wave Radiation

We studied the glow of the plasma of a pulse discharge ignited in nitrogen by high-power focused radiation of a terahertz-wave gyrotron (a radiation frequency of 0.67 GHz, a pulse duration of 20 μs, and a power of 40 kW). The pressure in the discharge chamber varied in the range 0.1–350 Torr. It was found that at high pressures (more than 50 Torr), long-term (about 1.0–1.5 ms), a non-monotonic afterglow exists after the end of the terahertz pulse, whose intensity can exceed the plasma glow intensity significantly (by several times) during the action of the terahertz radiation pulse on the plasma. At pressures below 50 Torr, the afterglow duration proves to be significantly shorter, specifically, about several tens of microseconds. The observed long-term afterglow is radiation in certain vibrational bands of the second positive system of N2 and is due, evidently, to the processes of associative excitation of electron levels in nitrogen molecules with the participation of long-living metastables $$ {\mathrm{N}}_2\left({\mathrm{A}}^3{\varSigma}_{\mathrm{u}}^{+}\right) $$ .

Cross-correlation spectroscopy study of the transient spark discharge in atmospheric pressure air

A streamer-to-spark transition in a self-pulsing transient spark (TS) discharge of positive polarity in air was investigated using cross-correlation spectroscopy. The entire temporal evolution of the TS was recorded for several spectral bands and lines: the second positive system of N2 (337.1 nm), the first negative system of (391.4 nm), and atomic oxygen (777.1 nm). The results enable the visualization of the different phases of discharge development including the primary streamer, the secondary streamer, and the transition to the spark. The spatio-temporal distribution of the reduced electric field strength during the primary streamer phase of the TS was determined and discussed. The transition from the streamer to the spark proceeds very fast within about 10 ns for the TS with a current pulse repetition rate in the range 8–10 kHz. This is attributed to memory effects, leading to a low net electron attachment rate and faster propagation of the secondary streamer. Gas heating, accumulation of species such as oxygen atoms from the previous TS pulses, as well as generation of charged particles by stepwise ionization seem to play important roles contributing to this fast streamer-to-spark transition.

Absorption and emission characteristics of femtosecond laser plasma filaments in the air

The digital images of plasmas induced by tightly focused Ti:Sapphire laser (1.1mJ, 48fs) in air reveal new fluorescent structures not observed for slightly focused beams earlier. The fluorescent structures arise because of lens aberrations. The energy absorbed by femtosecond laser plasma has nonlinear dependence on incident laser energy. The threshold peak power for filament formation is 5.2 GW. Time-resolved spectroscopy of plasmas shows short-time emission of molecular bands (up to 1ns) and long-time emission of atomic lines (up to 150ns). Initially, second positive system of N2 and first negative system of N2+ are observed. The atomic lines are formed with delay of 50-80ps relative to molecular ones. Lines of N2 and N2+ demonstrate different temporal behavior, while lines of N I and O I have the same intensity time dependence. Peak intensities of second positive system of N2 and first negative system of N2+ are separated by 50ps time interval.

Physical Parameters and Chemical Composition of a Nitrogen DC Discharge with Water Cathode

This paper reports the results of the experimental study and chemical composition modeling for a DC nitrogen discharge burning above water cathode in the pressure range of 0.1-1 bar and at discharge current of 40 mA. The gas temperature, vibrational temperatures, reduced electric field strength, cathode voltage drop, and emission intensities of some nitrogen bands were obtained from experiment. The modeling chemical composition of plasma was carried out on the basis of these data. At modeling, the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N2 ,O 2 ,H 2 Oa nd NO molecules, equations of chemical kinetics and plasma conductivity equation were used. The calculations agree with the measured bands intensities for the second positive system of N2 and vibrational temperatures of N2ðC 3 PuÞ. In the frame of the model proposed, the data of other studies were explained. The second kind collision of electrons with N2 vibration excited states was shown to affect strongly the electron gas parameters. The electron av- erage energy and electron density are given. The difference between the properties of the discharges in N2 and air at the same conditions are discussed as well.

Determination of Spectroscopic Temperatures and Electron Density in Rotating Gliding Arc Discharge

The spectroscopic characteristics of rotating gliding arc (RGA) discharge, codriven by a magnetic field and tangential gas flow, have been investigated by optical emission spectroscopy. In argon gas, the electron density of the atmospheric RGA plasma was measured, while the vibrotatinoal temperatures were measured in nitrogen discharge. By simulating the spectral line profile determined by the joint effects of Lorentzian (Stark, van der Waals, and natural) and Gaussian (Doppler and instrumental) broadening, the electron density fluctuated in the range of 1.32×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> -4.56×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 4.06×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> -5.74×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> within the variation of argon flow rate and applied voltage, respectively. The rotational temperature in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> discharge was obtained by comparing the modeled optical emission spectrum with the experimental measurements. The vibrational temperature was derived from a Boltzmann plot by analyzing the spectral bands of the second positive system of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> → B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Π <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ). The vibrational and rotational temperatures varied in the range of 0.1-0.13 eV and 0.42-0.44 eV, respectively, under the same operating condition, indicating that the RGA discharge is a nonequilibrium plasma. By analyzing the fundamental spectroscopic parameters of the discharge, a comprehensive understanding of RGA plasma was achieved, facilitating its application in practical industry processes.

Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N2(C3Πu) and N2+(B2Σu+) emissions and fundamental streamer structure

Theoretical analysis of ultra-short phenomena occurring during the positive streamer propagation in atmospheric pressure air is presented. Motivated by experimental results obtained with tens-of-picoseconds and tens-of-microns precision, it is shown that when the streamer head passes a spatial coordinate, emission maxima from N2 and N2+ radiative states follow with different delays. These different delays are caused by differences in the dynamics of populating the radiative states, due to different excitation and quenching rates. Associating the position of the streamer head with the maximum value of the self-enhanced electric field, a delay of 160 ps was experimentally found for the peak emission of the first negative system of N2+. A delay dilatation was observed experimentally on early-stage streamers and the general mechanism of this phenomenon is clarified theoretically. In the case of the second positive system of N2, the delay can reach as much as 400 ps. In contrast to the highly nonlinear behavior of streamer events, it is shown theoretically that emission maximum delays linearly depend on the ratio of the streamer radius and its velocity. This is found to be one of the fundamental streamer features and its use in streamer head diagnostics is proposed. Moreover, radially resolved spectra are synthesized for selected subsequent picosecond moments in order to visualize spectrometric fingerprints of radial structures of N2(C3Πu) and N2+(B2Σu+) populations created by streamer-head electrons.

Temporal evolution of temperature and OH density produced by nanosecond repetitively pulsed discharges in water vapour at atmospheric pressure

We report on an experimental study of the temporal evolution of OH density and gas temperature in spark discharges created by nanosecond repetitively pulsed discharges in pure water vapour at 475 K and atmospheric pressure. The plasma was generated by 20 kV, 20 ns pulses, at a repetition frequency of 10 kHz. The temperature was measured during the discharge by optical emission spectroscopy of the second positive system of N2, and between two discharges by two-colour OH-planar laser induced fluorescence (OH-PLIF) using two pairs of rotational transitions. Between two successive discharges, the relative density of OH was measured by OH-PLIF and was found to decay very slowly, with a 1/e decay time of about 50 µs. With the use of a chemical kinetics model, the OH density was placed on an absolute scale.

Experimental investigation of nanosecond discharge plasma aerodynamic actuation

In this paper we report on an experimental study of the characteristics of nanosecond pulsed discharge plasma aerodynamic actuation. The N2 (C3Πu) rotational and vibrational temperatures are around 430 K and 0.24 eV, respectively. The emission intensity ratio between the first negative system and the second positive system of N2, as a rough indicator of the temporally and spatially averaged electron energy, has a minor dependence on applied voltage amplitude. The induced flow direction is not parallel, but vertical to the dielectric layer surface, as shown by measurements of body force, velocity, and vorticity. Nanosecond discharge plasma aerodynamic actuation is effective in airfoil flow separation control at freestream speeds up to 100 m/s.