Electron Number Density Research Articles

Influence of energy transfer processes on the rovibrational characteristics of CO2 in low-temperature conversion plasma with Ar and He admixture.

The influence of argon and helium on the rovibrational kinetics of carbon dioxide (CO2) and CO in low-temperature conversion plasma is investigated. With this objective, a combined experimental and computational study is conducted, applying quantum cascade laser infrared absorption spectroscopy to a pulsed DC CO2 glow discharge with varying noble gas admixture and modeling it with a two-term Boltzmann solver. Time-resolved rovibrational temperatures and dissociation fractions are presented, exhibiting an increase in rotational-vibrational non-equilibrium and an increasing CO2 conversion with argon (Ar) and helium (He) admixtures. Results are discussed in the context of energy transfer processes for collisions involving electrons, corroborated by electron-kinetic modeling, and heavy particle collisions. With noble gas addition, an increase in the electron number density, promoting excitation, and the high-energy tail of the electron energy distribution function are found. Penning ionization processes are proposed as an explanation for the increase in conversion, showing higher conversion for Ar due to the lower excitation thresholds and, therefore, larger state population. In the context of rovibrational kinetics, processes leading to the gain or loss of vibrational energy of CO2 are analyzed, pointing out subtle differences in, for example, relaxation rate coefficients between Ar and He. However, the cooling of the gas through conductive heat transfer is identified as the most important influence of the Ar and He admixture, as it keeps the relaxation rate for vibrational quenching low.

Experimental study of electron bombardment ion electric propulsion based on a CO2/Xe mixed working medium

An experimental study was carried out on the use of a mixture of CO2 and Xe as the propellant for an electron bombardment ion thruster. The working performance parameters of the ion thruster under different flow mixing conditions were investigated using measurements and diagnostics such as power supply electrical parameter measurements, thrust measurements, and plasma diagnostics. In-depth studies of the particle species and the main electron collision reactions in the discharge chamber were carried out. The results showed that the CO2 in the discharge chamber led to a significant increase in the mean anode voltage and voltage oscillation amplitude, and the direct participation of CO2 in the discharge reaction could effectively improve the beam current and thrust of the ion thruster. When 5 sccm of CO2 was injected into the discharge chamber, the maximum measured thrust was increased by approximately 31.8 % compared to the state without CO2 injection. The addition of Xe led to a significant decrease in the discharge voltage and hence an increase in the electron number density, which significantly promoted CO2 dissociation and ionization. The insights obtained from this work can provide ideas for subsequent research related to an ion thruster using a mixed propellant.

The dense and non-homogeneous circumstellar medium revealed in radio wavelengths around the Type Ib SN 2019oys

Context. Mass loss from massive stars, especially towards the end of their lives, plays a key role in their evolution. Radio emission from core-collapse supernovae (SNe) serves as a probe of the interaction of the SN ejecta with the circumstellar medium (CSM) and can reveal the mass-loss history of the progenitor. Aims. We aim to present broadband radio observations of the CSM-interacting SN 2019oys. SN 2019oys was first detected in the optical and was classified as a Type Ib SN. Then, ~100 days after discovery, it showed an optical rebrightening and a spectral transition to a spectrum dominated by strong narrow emission lines, which suggests strong interaction with a distant, dense, CSM shell. Methods. We modelled the broadband, multi-epoch radio spectra, covering 2.2 to 36 GHz and spanning from 22 to 1425 days after optical discovery, as a synchrotron emitting source. Using this modelling, we characterised the shockwave and the mass-loss rate of the progenitor. Results. Our broadband radio observations show strong synchrotron emission. This emission, as observed 201 and 221 days after optical discovery, exhibits signs of free–free absorption from the material in front of the shock travelling in the CSM. In addition, the steep power law of the optically thin regime points towards synchrotron cooling of the radiating electrons. Analysing these spectra in the context of the SN-CSM interaction model gives a shock velocity of 11 000 km s−1 (for a radius evolution of ~∆t0.8, where ∆t is the time since optical discovery) and an electron number density of 4.1 × 105 cm−3 at a distance of 2.6 × 1016 cm. This translates to a high mass-loss rate from the progenitor massive star of 10−3 M⊙ yr−1 for an assumed wind of 100 km s−1 (assuming a constant mass-loss rate in steady winds). The late-time radio spectra, 392 and 557 days after optical discovery, show broad spectral peaks. We show that this can be explained by introducing a non-homogeneous CSM structure.

Energy estimation of small-scale jets from the quiet-Sun region

Context. Solar jets play a role in coronal heating and the supply of solar wind. Aims. In this study, we calculate the energies of 23 small-scale jets emerging from a quiet-Sun region in order to investigate their contributions to coronal heating. Methods. We used data from the High-Resolution Imager (HRI) of the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter. Small-scale jets were observed by the HRIEUV 174 Å passband in the high cadence of 6 s. These events were identified by the time–distance stacks along the trajectories of jets. Using the simultaneous observation from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), we also performed a differential emission measure (DEM) analysis on these small-scale jets to obtain the physical parameters of plasma, which enabled us to estimate the kinetic and thermal energies of the jets. Results. We find that most of the jets exhibit common unidirectional or bidirectional motions, while some show more complex behaviors; namely, a mixture of unidirection and bidirection. A majority of jets also present repeated eruption blobs (plasmoids), which may be signatures of the quasi-periodic magnetic reconnection that has been observed in solar flares. The inverted Y-shaped structure can be recognized in several jets. These small-scale jets typically have a width of ∼0.3 Mm, a temperature of ∼1.7 MK, an electron number density of ≳109 cm−3, with speeds in a wide range from ∼20–170 km s−1. Most of these jets have an energy of 1023–1024 erg, which is marginally smaller than the energy of typical nanoflares. The thermal energy fluxes of 23 jets are estimated to be (0.74–2.96)×105 erg cm−2 s−1, which is almost on the same order of magnitude as the energy flow required to heat the quiet-Sun corona, although the kinetic energy fluxes vary over a wide range because of their strong dependence on velocity. Furthermore, the frequency distribution of thermal energy and kinetic energy both follow the power-law distribution N(E)∝E−α. Conclusions. Our observations suggest that although these jets cannot provide sufficient energy to heat the whole quiet-Sun coronal region, they are likely to account for a significant portion of the energy demand in the local regions where the jets occur.

Numerical study of plasma behavior in a disk‐shaped noble gas MHD generator

AbstractPlasma behavior in cesium‐seeded argon (Ar/Cs) and xenon‐seeded argon (Ar/Xe) disk‐shaped MHD generators are compared under almost the same working conditions using r‐θ two‐dimensional simulation. For both working gases, uniform plasma occurs at the optimum load resistance, and the power outputs are the same under an identical inlet ionization degree. For Ar/Cs, plasma is stable and uniform in the range of electron temperature of 4300–5800 K basically according to the linear perturbation theory. In the actual plasma in the MHD generator, however, the uniform plasma still can be maintained even at higher electron temperatures due to the low three‐body recombination coefficient of Ar. For Ar/Xe, on the other hand, uniform plasma is maintained when the characteristic time of the electron number density is longer than the residence time of the working gas where the electron temperature is around 4300–8600 K, even though unstable plasma is suggested from the linear perturbation theory.

Spatial confinement offered by a blocker on the laser-induced breakdown spectroscopy of Ti plasma

Spatial confinement effects offered by a blocker on the laser-induced plasma parameters of titanium (Ti) are evaluated using the Optical Emission Spectroscopy technique. Nd:YAG (1064 nm, 10 ns) laser is used as an irradiation source. To observe the spatial confinement effects, an Al blocker at different distances of 4, 6, and 8 mm from the target is placed along the plume path. All the measurements are performed under the Ar environment at different pressures. It is observed that with increasing laser irradiance plasma parameters such as excitation temperature (Te) and electron number density (ne) increase, whereas it is vice versa true for increasing blocker distances. Without the blocker, the maximum values of Te and ne are about 7000 K and 1.4 × 1018 cm−3, respectively, at an Ar pressure of 50 Torr. A significant increase in emission intensity along with Te ≈ 9810 K and ne ≈ 2.2 × 1018 cm−3 is achieved in the presence of blocker. The results show that spatial confinement is responsible for the enhancement of Te and ne, which is attributed to the increased collisional frequency of plasma species after compression by shockwaves. The ablation pressure and shock pressure are also analytically evaluated and vary from 0.15 to 0.25 GPa and from 0.1 to 0.2 GPa, respectively, with increasing laser irradiance. With increasing blocker distances from 4 to 8 mm, the work done by reflected shockwaves to compress the plume varies from 0.02 to 0.002 mJ.

Zero-dimensional analysis of the effect of water vapor on reducing electrons in the plasma sheath

In this study, an air-water vapor ionization reaction model is developed within the quantum-kinetic (Q–K) model of the direct simulation Monte Carlo method to investigate the detailed mechanism of how water vapor reduces electrons. The zero-dimensional simulations of a typical non-equilibrium flow field downstream of a normal shock are designed, where the electron number density decreases by two orders of magnitude due to water vapor. We conclude that the introduction of water vapor reduces the mole fractions of oxygen atoms and nitrogen atoms through five pairs of reactions and enhances the reverse nitric oxide associative ionization reaction, leading to electron consumption. The phenomena and corresponding mechanisms under varying mole fractions of water vapor, air temperatures, and water vapor temperatures are investigated. Based on the mechanisms, we propose that the addition of hydrogen ions could improve the water's mitigation effect, which is then proven to be able to reduce the electron number density by another two orders of magnitude, not only at high air temperatures but also at lower air temperatures or lower mass injection rates.

The Temperature and Density of a Solar Flare Kernel Measured from Extreme-ultraviolet Lines of O iv

Previously unexplored diagnostics of O iv in the extreme-ultraviolet region 260–280 Å are used to derive a temperature and density for a solar flare kernel observed on 2012 March 9 with the Extreme-ultraviolet Imaging Spectrometer on the Hinode satellite. Seven lines from the 2s2p 2–2s2p3s transition array between 271.99 and 272.31 Å are both temperature- and density-sensitive relative to the line at 279.93 Å. The temperature, T, is constrained with the λ268.02/λ279.93 ratio, giving a value of log(T/K)=5.10±0.03 . The ratio λ272.13/λ279.93 then yields an electron number density, N e, of log(Ne/cm−3)=12.52 with a lower limit of 11.90 and an upper limit of 14.40. The O iv emitting volume is estimated to be 0.″4 (300 km) across. Additional O iv lines at 196, 207, and 260 Å are consistent with the derived temperature and density but have larger uncertainties from the radiometric calibration and blending. Density diagnostics of O v and Mg vii from the same spectrum are consistent with a constant pressure of 1017.0 K cm−3 through the transition region. The temperature derived from O iv supports recent results that O iv is formed around 0.10 dex lower at high densities compared to standard zero-density ionization balance calculations.

Laser-induced breakdown spectroscopy (LIBS) of animal fat (lard): Efficient sample preparation for onsite analysis and influence of sample temperature on the signal intensity and plasma parameters

We report an efficient sample preparation method (freezing) for onsite fat and meat analysis via a specially designed thermoelectric cooling and temperature-controlling system. This investigation also focused on the effect of phase change on the sensitivity and reproducibility of LIBS emission signals and plasma parameters. The plasma emissions of animal fats (lard) were recorded when the sample was frozen (−2 °C), fluid (15 °C), and in a liquid state (37 °C) with a thermoelectric cooling system. At each temperature, the plasma emissions were acquired at laser pulse energy from 50 to 300 mJ and detector gate delay (DGD) from 0.5 to 5 μs. With increasing sample temperature, the DGD, where the optical emission intensity reached a maximum, decreased. At a laser pulse energy of 200 mJ and a sample temperature of −2 °C, the emission signals increased fourfold, the signal-to-noise ratio (SNR) improved tenfold, and the self-absorption in the emission lines decreased significantly. The repeatability of the emission signals and plasma parameters of frozen and liquid fat samples was determined using the relative standard deviation (RSD) of Se I (473.08 nm) and K I (766.48 nm) emission lines. The RSDs of the emission signals improved from 40 to 18 % and 37 to 16 %, whereas the shot-to-shot RSDs of the electron temperature and electron number density get improved from 11 to 6 % and 12 to 6.8 %, respectively.

Characterization of Atmospheric Electrical Discharge in Pin-water Configuration at Different NaCl Concentrations

The interaction between a pin-plate and plasma are representing an interest subject in plasma technology and applications. In this research, the influence of added NaCl to distilled water on the discharge characteristics that formed in the gap between pin-water surfaces was investigated in more details. Their electrical and optical characteristics serve as identifiers. It's found that all optical emissions intensity peaks as a results that detected are decreased with increasing of NaCl concentrations (300,400, and 500 mg). As well as, the emission intensity of neutral emission peaks are much higher than that of the ionic emission peaks. The addition of NaCl changes the liquid accessibility, which alters the kinetics of the discharge that forms in the pin-water surface gap. Also, its observed that the NaCl concentrations affected on the I-V characteristics. The data detected that the plasma frequency ((377.1176 - 279.1951)*1011 rad/sec), electron number density ((4.4519 – 2.4401)*1017 cm-3) and electron temperature (2.1537 – 1.663 eV) decreased with increases of NaCl concentrations except the Debye length ((1.6342 – 1.93989)*10-6 cm) shown a different behavior with increase of NaCl concentrations.

Two-dimensional investigation of characteristic parameters and their gradients for the self-generated electric and magnetic fields of laser-induced zirconium plasma

Two-dimensional diagnosis of laser-induced zirconium (Zr) plasma has been experimentally performed using the time-of-flight method by employing Faraday cups in addition to electric and magnetic probes. The characteristic parameters of laser-induced Zr plasma have been evaluated as a function of different laser irradiances ranging from 4.5 to 11.7 GW cm−2 at different axial positions of 1–4 cm with a fixed radial distance of 2 cm. A well-supporting correlation between the plume parameters and the laser-plasma-produced spontaneous electric and magnetic (E and B) fields was established. The measurements of the characteristic parameters and spontaneously induced fields were observed to have an increasing trend with the increasing laser irradiance. However, when increasing the spatial distance in both the axial and radial directions, the plasma parameters (electron/ion number density, temperature and kinetic energy) did not show either continuously increasing or decreasing trends due to various kinetic and dynamic processes during the spatial evolution of the plume. However, the E and B fields were observed to be always diffusing away from the target. The radial component of electron number densities remained higher than the axial number density component, whereas the axial ion number density at all laser irradiances and axial distances remained higher than the radial ion number density. The higher axial self-generated electric field (SGEF) values than radial SGEF values are correlated with the effective charge-separation mechanism of electrons and ions. The generation of a self-generated magnetic field is observed dominantly in the radial direction at increasing laser irradiance as compared to the axial one due to the deflection of fast-moving electrons and the persistence of two-electron temperature on the radial axis.

Examining the role of magnetic fields in plasma behavior and surface evolution of a Mg alloy with varied irradiances in a femtosecond laser treatment

This paper reports the effect of a magnetic field on plasma parameters and surface structuring of the Mg alloy after laser irradiation. Femtosecond pulses of a Ti:sapphire laser system (800 nm, 35 fs, 1 KHz) are employed as the source of irradiation at various irradiances ranging from 0.011PW/cm2 to 0.117PW/cm2 to generate ablated Mg-alloy plasma. A transvers magnetic field (TMF) of strength 1.1 Tesla is employed to confine laser generated Mg plasma. All the measurements are performed with and without TMF. The two plasma parameters, i.e., excitation temperature (Texc) and electron number density (n e ) of Mg plasma, have been evaluated by laser-induced breakdown spectroscopy (LIBS) analysis. It is observed that the values of Texc and n e of laser produced plasma (LPP) of the Mg alloy are higher in the presence of a magnetic field as compared to the field free case. Both show initially an increasing trend with increasing laser irradiance and after attaining their respective maxima a decreasing trend is observed with the further increase of irradiance. The magnetic confinement validity is confirmed by analytically evaluating thermal beta (β t ), directional beta (β d ), confinement radius (R b ), and diffusion time (t d ) for LPP of the Mg alloy. To correlate the LPP parameters of the Mg alloy with surface modifications a field emission scanning electron microscope (FE-SEM) analysis is performed. It was revealed that structures like laser-induced periodic surface structures (LIPSSs), agglomerates, islands, large sized bumps, along with channels and multiple ablative layers are observed. Distinct and well-defined surface structuring is observed in the presence of TMF as compared to the field free case. It is concluded that by applying an external magnetic field during laser irradiation, controlled material surface structuring is possible for fabrication of nanogratings and field emitters where spatial uniformity is critically important.

Surface engineering by rogue wave induced by energetic carbon clusters

Swift heavy ions are effective in nanostructuring material surfaces. The irradiation of lanthanum fluoride with 30 MeV C60 leads to the creation of surface nanohillocks of size larger than the ones produced by monoatomic heavy ions. The generation of the observed nano-sized hillocks is described here by a new approach that is based on ion-induced intensive electronic excitations that create localized rogue waves. Consequently, the induced nonlinear ion-acoustic rogue waves are considered a hallmark of nanohillock formation. Plasma hydrodynamic equations produce a relationship between normalised electron number density and crystal lattice spacing. Similarities to the hillock profile suggest the crucial primary role of electron density in the fabrication of surface nanostructures.

Sensitivity Analysis of Ionization in Two-Temperature Models of Hypersonic Air Flows

Plasma generation in hypersonic flows is analyzed using a two-temperature model of nonequilibrium air. The uncertainties in electron number density predictions are assessed for flow scenarios that correspond to both strongly shocked and strongly expanded flows, and the dependencies of the calculated uncertainties on individual input parameters are quantified. Ionization levels behind 5 and 7 km/s normal shocks are found to be most sensitive to the associative ionization reactions producing O2+ and NO+ in the region of peak electron number density, with nitric oxide kinetics dominating the uncertainty downstream. The higher levels of ionization behind a 9 km/s shock are found to strongly depend on the electron impact ionization of atomic nitrogen as well as the charge exchange between N2+ and N. Recombining flow scenarios depend on many of the same processes that influence the shocked flows, with the notable addition of the reassociation reaction O++N2↔NO++N, which is responsible for large uncertainties in electron number density in net recombining flows. The results provide valuable insight into the typical magnitude of uncertainty associated with plasma formation predictions in hypersonic flows and identify the parameters that should be targeted in efforts to reduce those uncertainties.

State-resolved modeling of electronic excitation in weakly ionized oxygen mixtures.

Electronic excitation and ionization in oxygen-argon mixtures are analyzed using a three-temperature electronic state-resolved model and evaluated using recent experimental data from reflected shock experiments. A detailed description of the model formulation and parameter selection is provided. Excellent agreement is obtained between model predictions and experimental measurements of O_{2} number density during dissociation in mixtures of 2%-5% O_{2} dilute in argon. Next, electron number density measurements are leveraged to infer a rate constant for the heavy particle impact excitation of argon, facilitating improved modeling of net ionization and a clearer understanding of the electronic excitation kinetics of oxygen. The electronic state-resolved model is then assessed using measured data for three electronic states of atomic oxygen. The model successfully reproduces the multistage behavior observed in the measured time histories and yields new insights into the multistage behavior that revises previous interpretations. For several experiments, the modeling choices involved in the calculation of escape factors significantly influence the predicted time histories. A global sensitivity analysis considering nearly 300 parameters is then conducted to identify which model parameters most sensitively influence the predicted excited state populations. Excitation of the measured states from the metastable levels and collisional excitation between the three measured states are important across all conditions. The excited state populations demonstrate complex sensitivities involving a large number of collisional and radiative processes, highlighting the importance of adopting a detailed modeling approach when interpreting excited state measurements.

Effect of desorbed gas on microwave breakdown on vacuum side of dielectric window

The gas desorbed from the dielectric surface has a great influence on the characteristics of microwave breakdown on the vacuum side of the dielectric window. In this paper, the dielectric surface breakdown is described by using the electromagnetic particle-in-cell-Monte Carlo collision (PIC-MCC) model. The process of desorption of gas and its influence on the breakdown characteristics are studied. The simulation results show that, due to the accumulation of desorbed gas, the pressure near the dielectric surface increases in time, and the breakdown mechanism transitions from secondary electron multipactor to collision ionization. More and more electrons generated by collision ionization drift to the dielectric surface, so that the amplitude of self-organized normal electric field increases in time and sometimes points to the dielectric surface. Nevertheless, the number of secondary electrons emitted in each microwave cycle is approximately equal to the number of primary electrons. In the early and middle stages of breakdown, the attenuation of the microwave electric field near the dielectric surface is very small. However, the collision ionization causes a sharp increase in the number density of electrons, and the microwave electric field decays rapidly in the later stage of breakdown. Compared with the electromagnetic PIC-MCC simulation results, the mean energy and number of electrons obtained by the electrostatic PIC-MCC model are overestimated in the later stage of breakdown because it does not take into account the attenuation of microwave electric field. The pressure of the desorbed gas predicted by the electromagnetic PIC-MCC model is close to the measured value, when the number of gas atoms desorbed by an incident electron is taken as 0.4.

Hypersonic boost-glide systems: Flight mechanics and plasma parameters evaluation through aero-thermo-chemical computational fluid dynamics

Currently, the conception, design, and development of hypersonic space-borne systems is a central topic of discussion among researchers and industrial stakeholders. In the design phase of a hypersonic manoeuvrable vehicle, it is essential to characterise the thermal heating and manage the problem of the communication blackout, in addition to other challenges concerning guidance, navigation and control, and propulsion. The interference of electromagnetic waves propagating in plasma affects the datalink and the radar detection of hypersonic targets. This work aims to provide valuable information about the aero-thermo-chemical behaviour of the fluid in the region around a hypersonic glider. Launch and re-entry phases of boost-glide systems have been modelled to perform trajectory predictions and assess range and flight paths under the effect of different manoeuvres, defining their possible performances. The resulting flight conditions are used to study the flow field surrounding a glider geometry similar to the Hypersonic Technology Vehicle-2. The thermodynamic and chemical fields around the body have been determined, and plasma parameters for novel electromagnetic interaction studies have been evaluated. Computational fluid dynamics simulations have been carried out to solve the averaged Navier-Stokes equations with the k−ω model for turbulent flows, coupled with the energy equation. Chemical non-equilibrium phenomena involving electronic energy relaxation as well as ionisation reactions have also been included. A gas mixture potentially composed of 11 species has been considered, namely oxygen and nitrogen derivatives. The electron number density is computed to evaluate the electron plasma and collision frequencies, essential parameters to characterise the electromagnetic interference caused by the plasma sheath. Among other results, high temperatures are reached at the nose region of the body in specific conditions of velocity and altitude, and non-negligible dissociation or ionisation of chemical species occurs. Plasma frequencies up to tens of GHz are reached in a region close to the body surface, while lower interference characterises the extended ionised wake.

Landau damping effects on dust ion-acoustic solitary waves in a nonthermal pair-ion plasma

The Landau damping effects on the nonlinear propagation of dust ion-acoustic solitary waves (DIASWs) are studied in an electron-free unmagnetized collisionless dusty pair-ion plasma. The two species of nonthermal ions (positive and negative) are described by the kinetic Vlasov equations, whereas the massive charged dust grains form only the background plasma. Using the multi-scale reductive perturbation technique generalized for the applications to the Vlasov equation, we derive a modified Korteweg–de Vries (KdV) equation that governs the evolution of DIASWs with the effects of linear resonance, in particular, linear Landau damping. The properties of the phase velocity and the Landau damping rate of DIASWs are studied with the effects of positive and negative-ion nonthermality parameters ( α p , α n ), the ratios of the positive to negative ion masses (m) and temperatures (T) as well as the dust to negative-ion number density ratio (δ). It is found that, depend on the degree of positive to negative ion mass ratios (m), both of damped and growing oscillations occur in a collisionless dusty pair-ion plasma due to the resonance phenomena between the wave and the nonthermal particles of the system. The properties of the decay rates of the amplitude of the KdV soliton with a small effect of Landau damping are also studied with the above system of parameters. The results may be useful for understanding the localization of solitary pulses and associated resonance damping and/or growing oscillations of the wave in laboratory and space plasmas, in which the number density of free electrons is much smaller than that of ions and highly charged heavy, micron seized dust grains.

Effect of trapping of electrons and positrons on the evolution of shock wave in magnetized plasma: A complex trapped K-dV burgers’ equation

Our research demonstrates that positive and negative ions, along with trapped electrons and positrons, propagate as small-amplitude electrostatic shock waves in a magnetized collisions-less plasma. The trapped Korteweg-de Vries Burger's (T-KdVB) equation was derived by the widely recognized standard reductive perturbation technique (RPT), employing two separate scales of standard coordinates. The study examines the impact of temperature ratio on the shock wave characteristics of positive and negative ions, as well as positrons with electrons. The analysis and discussion focus on the impacts of negative ion number densities, as well as the number densities of electrons and positrons. The T-KdVB equations are responsible for governing rarefactive shock waves. Additionally, it is important to acknowledge that nonlinearity and dissipation play a key role in controlling the amplitude of the shock.

Application of emission spectroscopy in plasma-assisted NH3/air combustion using nanosecond pulsed discharge

This work investigates the effects of atmospheric-pressure nanosecond (ns) pulsed plasma discharges on NH3/air flames using optical emission spectroscopy (OES). Firstly, spatially-resolved OES in the 200–800 nm range of NH3/air flames with and without discharges are presented to identify the plasma-induced excited species (such as N2* and H*). Then, time-resolved OES with ns timescale resolution are achieved to illustrate the discharge dynamics using a statistical imaging strategy, which is specifically designed to overcome the timing jitter of the discharge. From the time-resolved spectra of excited N2, the first and second emission events in NH3/air flames with a time interval of 80 ns are revealed, and each exhibits a profile with two exponential decays. Furthermore, spatial- and time-resolved rotational and vibrational temperatures are derived from the spectral fitting of N2(C→B) to quantify the thermal effects of ns plasmas, thus revealing the ultrafast and slow gas heating processes. In addition, the electron number density along the flame is obtained from the intense Hα line, which locally reaches up to 1 × 1017 cm−3. Besides, the spatial-resolved Hα line intensity suggests that the flame chemistry does not directly affect, but the discharge dominates the production of the atomic hydrogen. It provides insight into the kinetic effects of ns pulsed discharge on NH3 combustion enhancement.