Diffuse Glow Research Articles

Modeling the Effect of Ionospheric Electron Density Profile and Its Inhomogeneities on Sprite Halos

Sprite halos are diffuse glow discharges in the D-region ionosphere triggered by the quasi-electrostatic (QES) fields of lightning discharges. A three-dimensional (3D) QES model is adopted to investigate the effect of ionospheric electron density on sprite halos. The electron density is described by an exponential formula, parameterized by reference height (h’) and sharpness (β), and the local inhomogeneity has a Gaussian density distribution. Simulation results indicate that the reference height and steepness of the nighttime electron density affect the penetration altitudes and amplitudes of normalized electric fields, as well as the altitudes and intensities of the corresponding sprite halos optical emissions. A comparison of the daytime and nighttime conditions demonstrates that the daytime electron density profile is not favorable for generating sprite halos emissions. Furthermore, the pre-existing electron density inhomogeneities lead to enhanced local electric fields and optical emissions, potentially offering a plausible explanation for the horizontal displacement between sprites and their parent lightning, as well as their clustering.

Gamma-ray line emission from the Local Bubble

Deep-sea archives that include intermediate-lived radioactive 60Fe particles suggest the occurrence of several recent supernovae inside the present-day volume of the Local Bubble during the last ~10 Myr. The isotope 60Fe is mainly produced in massive stars and ejected in supernova explosions, which should always result in a sizeable yield of 26Al from the same objects. 60Fe and 26Al decay with lifetimes of 3.82 and 1.05 Myr, and emit γ rays at 1332 and 1809 keV, respectively. These γ rays have been measured as diffuse glow of the Milky Way, and would also be expected from inside the Local Bubble as foreground emission. Based on two scenarios, one employing a geometrical model and the other state-of-the-art hydrodynamics simulations, we estimated the expected fluxes of the 1332 and 1809 keV γ-ray lines, as well as the resulting 511 keV line from positron annihilation due to the 26Al β+ decay. We find fluxes in the range of 10−6–10−5 ph cm−2 s−1 for all three lines with isotropic contributions of 10–50%. We show that these fluxes are within reach for the upcoming COSI-SMEX γ-ray telescope over its nominal satellite mission duration of 2 yr. Given the Local Bubble models considered, we conclude that in the case of 10–20 Myr-old superbubbles, the distributions of 60Fe and26 Al are not co-spatial - an assumption usually made in γ-ray data analyses. In fact, this should be taken into account however when analysing individual nearby targets for their 60Fe to26 Al flux ratio as this gauges the stellar evolution models and the age of the superbubbles. A flux ratio measured for the Local Bubble could further constrain models of 60Fe deposition on Earth and its moon.

Plasma-droplet interaction study to assess transport limitations and the role of ⋅OH, O⋅,H⋅,O2(a 1Δg),O3, He(23 S) and Ar(1s 5) in formate decomposition

Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of ⋅OH as well as non-⋅OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O⋅ and H⋅ atoms, singlet delta oxygen (O2(a 1Δg)), O3 and metastable atoms of He and Ar, besides ⋅OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase ⋅OH flux at lower H2O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to e−/ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous ⋅OH concentrations. The formate decomposition in He/O2 plasma was similar, although with an order of magnitude higher O⋅ radical density than the ⋅OH density in the corresponding He/H2O plasma. Using a one-dimensional reaction–diffusion model, we showed that O2(a 1Δg) and O3 did not play a significant role and the decomposition was due to O⋅, and possibly ⋅OH generated in the vapor containing droplet-plasma boundary layer.

Study on water treatment effect of dispersion discharge plasma based on flowing water film electrode

To improve the utilization rate of plasma active species, in this study, a closed non-uniform air gap is formed by a flowing water film electrode and a sawtooth insulating dielectric layer to realize the diffuse glow discharge in the atmosphere. Firstly, the electric field distribution characteristics of non-uniform air gap in the sawtooth dielectric layer are studied, and the influence of aspect ratio on the characteristics of diffuse discharge plasma is discussed. Subsequently, the effects of wire mesh, the inclination angle of the dielectric plate, and liquid inlet velocity on the flow characteristics of the water film electrode are analyzed. The results show that the non-uniform electric field distribution formed in the sawtooth groove can effectively inhibit the filamentous discharge, and the 1 mm flowing water film is directly used as the electrode, and high-active plasma is formed directly on the lower surface of the water film. In addition, a plasma flowing water treatment device is built to treat the methyl orange solution and observe its decolorization effect. The experimental results show that after 50 min of treatment, the decolorization rate of the methyl orange solution reaches 96%, which provides a new idea for industrial applications of wastewater treatment.

Controlled plasma–droplet interactions: a quantitative study of OH transfer in plasma–liquid interaction

Plasmas in contact with liquids are a rich source of OH radicals and have been extensively studied in the last decade to leverage the ability to generate chemically reactive species in gas phase plasmas to decompose organics. Multiphase transfer of OH radicals is highly transport limited and to overcome transport limits, the plasma activation of aerosols, small liquid droplets, interspersed in the plasma has been proposed. In this work, we report a combined experimental and modeling study of a controlled plasma–droplet interaction experiment using a diffuse RF glow discharge in He + 0.2% H2O with detailed plasma diagnostics, ex situ analysis of the plasma-induced chemistry in the droplet containing formate, droplet trajectory and size measurements. This enables a quantitative study of the reactivity transfer of OH from the gas phase plasma to the liquid phase and how its diffusion limitations impact formate decomposition in the water droplet. For a droplet with a diameter of 36 μm, we observed 50% reduction in formate concentration in the droplets after plasma treatment for droplet residence times in the plasma of ∼10 ms. These short droplet residence times in the plasma allow in some cases for droplet size reductions of ∼5% in spite gas temperatures of 360 K. A one-dimensional reaction–diffusion model was used to calculate the OH transport and formate oxidation inside the droplet and was able to predict the conversion of formate by plasma in a droplet without any fitting parameters. The model further shows that formate conversion is dominated by near-interfacial reactions with OH radicals and is limited by diffusion of formate in the droplet. The results show that a controlled plasma–micro-droplet reactor as reported in this study might be an excellent tool for detailed quantitative plasma–liquid interaction studies.

Runaway Electrons Emitted by Electron Avalanches in Nanosecond Discharges in Air

Nanosecond electric discharges in atmospheric air at high overvoltages are considered. Plasma channels and diffuse plasma glow simultaneously exist in these discharges. Channels are created by subnanosecond streamers formed in the cathode region. Diffuse glow is caused by runaway electrons emitted by electron avalanche heads. The necessary electric field enhancement is created due to the plasma configuration in the avalanche head and body.

The nature of the diffuse light near cities detected in nighttime satellite imagery

Diffuse glow has been observed around brightly lit cities in nighttime satellite imagery since at least the first publication of large scale maps in the late 1990s. In the literature, this has often been assumed to be an error related to the sensor, and referred to as “blooming”, presumably in relation to the effect that can occur when using a CCD to photograph a bright light source. Here we show that the effect seen on the DMSP/OLS, SNPP/VIIRS-DNB and ISS is not only instrumental, but in fact represents a real detection of light scattered by the atmosphere. Data from the Universidad Complutense Madrid sky brightness survey are compared to nighttime imagery from multiple sensors with differing spatial resolutions, and found to be strongly correlated. These results suggest that it should be possible for a future space-based imaging radiometer to monitor changes in the diffuse artificial skyglow of cities.

Parameters of the Plasma of a Large-Scale High-Voltage Discharge in Air at Reduced Pressures

The Sprite device allows one to ignite an ~1-m-long pulsed high-voltage discharge detached from the metal chamber walls in both a uniform gas and a gas with a large-scale pressure gradient. A microwave interferometer, a magnetic probe, and optical photography are used to diagnose the discharge plasma. It is established that, at pressures of 0.05−1 Torr, the transverse profile of the diffuse discharge glow is close to the current profile. The plasma density in the diffuse discharge reaches 1012 cm–3. The results of interferometric measurements of the plasma density agree well with the values obtained from measurements of the current density in the approximation of a steady-state electron drift. The results obtained are necessary for laboratory modeling of high-altitude discharges in the Earth’s atmosphere.

A New Species of Photuris Dejean (Coleoptera: Lampyridae) from a Mississippi Cypress Swamp, with Notes on its Behavior

Photuris walldoxeyi Faust, new species, is described as a member of the Photuris versicolor species-group. It can be distinguished by its complex, unique flash-train + glow (FT+G) male courtship flash pattern, one of the most easily recognizable displays in North America. The primary FT+G male courtship pattern consists of a flash-train of 4–9 bright, quick, rhythmic pulses given every 0.4 seconds followed by a prolonged diffuse glow (ca. 1 second) of medium intensity at 17° C while the male hovers flashing near the tips of the branches of bald cypress and swamp vegetation growing in water. The primary FT+G is often followed immediately by a 2-pulsed secondary FT+G that effectively increases the male's visibility. Photuris walldoxeyi has thus far been confirmed in cypress and tupelo-cypress swamps of Mississippi, west Tennessee, and Indiana. During its month-long flight from May to mid-June, peak numbers are present ca. 900–1200 modified growing degree days.

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow**Project supported by the National Natural Science Foundation of China (Grant Nos. 11472306, 51407197, and 51507187).

In this paper, aerodynamic actuation characteristics of radio-frequency (RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable. Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency (MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.

Dermoscopy is a new diagnostic tool in diagnosis of common hypopigmented macular disease: A descriptive study.

One of the most frequent complaints in dermatology clinics is the eruption of hypopigmented patchy skin lesions. The aim of the study was to investigate the utility of dermoscopy in common hypopigmented macular diseases. Patients with the followings diseases were examined by dermoscopy: vitiligo, pityriasis alba, nevus depigmentosus, achromic pityriasis versicolor, idiopathic guttate hypomelanosis, and extragenital guttate lichen sclerosus.This study showed that these hypopigmented macular diseases might display specific dermoscopic features. In vitiligo, the mean dermoscopic features were the presence of a diffuse white glow with perifollicular pigment, perilesional hyperpigmentation, leukotrichia and the pigmentary network. In idiopathic guttate hypomelanosis, the characteristic features were the presence of multiple, shiny, scaly macules with welland ill-defined edges borders that coalesced into polycyclic macules. For nevus depigmentosus, the mean features were hypopigmented patches with irregular border with a faint reticular network. For pityriasis alba, the fairly ill-demarcated hypopigmented macules with fine scales were the mean feature. In lichen sclerosus, there were white structureless areas, perilesional erythematous halo, follicular plugging and white chrysalis like structures. Dermoscopy of achromic pityriasis versicolor showed a fairly demarcated white area with fine scales localized in the skin creases.

A stable and diffusive atmospheric pressure glow discharge in ambient air obtained by applying an axial magnetic field between pin-to-plate electrodes

In recent years, a lot of research focuses on atmospheric pressure glow discharge, but how to obtain a stable and uniform large-volume glow discharge at atmospheric pressure is still a difficult technological problem, especially in large ambient air gap. In this paper, with an external axial magnetic field applied in the pin-to-plate electrode gap, a stable and diffusive atmospheric pressure glow discharge in ambient air is obtained. Influences of different factors such as the output-voltage amplitude of the power supply, the intensity of the magnetic field, the resonant frequency of power supply, and different inter-electrode gap sizes are studied. The results show that a more diffusive and bigger-volume glow discharge can be obtained by increasing the amplitude of the output voltage of the power supply, the intensity of the external magnetic field, or the resonant frequency in the longer-distance pin-to-plate gap.

A diffusive atmospheric pressure glow discharge obtained by applying an external transverse magnetic field

The atmospheric pressure glow discharge has a good industrial application prospect, but it is difficult to obtain a stable and diffusive atmospheric pressure glow discharge, especially in the large ambient air gap. In this paper, with a transverse magnetic field applied in the pin-to-ring electrode gap, a stable and diffusive atmospheric pressure glow discharge in ambient air was obtained. The influence of different factors such as the output-voltage amplitude of the power supply, the intensity of the external magnetic field, and the different sizes of ring-cathode were studied from the discharge voltage and current waveforms and the discharge morphology. The results show that a more diffusive and bigger-volume glow discharge can be obtained by increasing the amplitude of the output voltage or the intensity of the external magnetic field, and the more uniform and effective glow discharge can be obtained when choosing the smaller pin-to-ring inter-electrode gap.

Electrical and thermal characterization of near-surface electrical discharge plasma actuation driven by radio frequency voltage at low pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11472306, 51407197, and 51507187).

The electrical and thermal characterization of near-surface electrical discharge plasma driven by radio frequency voltage are investigated experimentally in this paper. The influences of operating pressure, electrode distance, and duty cycle on the discharge are studied. When pressure reaches 60 Torr (1 Torr = 1.33322 × 102 Pa) the transition from diffuse glow mode to constricted mode occurs. With the operating pressure varying from 10 Torr to 60 Torr, the discharge energy calculated from the charge–voltage (Q–V) Lissajous figure decreases rapidly, while it remains unchanged between 60 Torr and 460 Torr. Under certain experimental conditions, there exists an optimized electrode distance (8 mm). As the duty cycle of applied voltage increases, the voltage–current waveforms and Q–V Lissajous figures show no distinct changes.

Thermal characterisation of dielectric barrier discharge plasma actuation driven by radio frequency voltage at low pressure

In this study, the thermal characterisation of dielectric barrier discharge plasma actuation driven by radio frequency (RF) voltage waveform at low pressure is studied. The RF discharge images and voltage–current waveforms are quite different under 3 and 40 kPa. The thermographic method has been proposed for the spatial–temporal temperature field on the actuator surface . At 3 kPa, the high-temperature region is mainly concentrated on the surface of the high-voltage electrode. Along the spanwise direction, the surface temperature gradually increases until it reaches the maximum at the edge of the electrode and then decreases. Similarly, in the chordwise direction, there also exists the maximum value on the surface of the electrode. After discharge starts, the surface temperature rises rapidly, and subsequently, the increasing slope of temperature curves gradually decreases until thermal equilibrium has been reached at about 100 s. The effects of the pressure, duty cycle, and operating power on the thermal characterisation are also investigated experimentally. At low pressure, the discharge mode is diffuse glow discharge, and the high-temperature region covers the whole electrode. As the pressure increases the surface temperature ascends non-linearly, while the surface temperature is linearly dependent on the duty cycle and operating power.

Transitions between patterned discharges and diffuse discharges in atmospheric helium under applied voltages far below the discharge inception voltage

A diffuse glow discharge was generated in atmospheric helium with a background air pressure of 40 Pa. When the applied voltage was slowly decreased to lower ones than the discharge inception voltage, the diffuse discharge showed transitions to a patterned one with a central column, then a patterned one with double circles, including one central column and seven or eight nearby columns in a circle, followed by a pattern with three circles, and finally a partial diffuse discharge under an applied voltage of about 66% of the discharge inception voltage.

Characteristics and applications of diffuse discharge of water electrode in air

Plasma water treatment technology, which aims to produce strong oxidizing reactive particles that act on the gas–liquid interface by way of discharging, is used to treat the organic pollutants that do not degrade easily in water. This paper presents a diffuse-discharge plasma water treatment method, which is realized by constructing a conical air gap through an uneven medium layer. The proposed method uses water as one electrode, and a dielectric barrier discharge electrode is constructed by using an uneven dielectric. The electric field distribution in the discharge space will be uneven, wherein the long gap electric field will have a smaller intensity, while the short one will have a larger intensity. A diffuse glow discharge is formed in the cavity. With this type of plasma water treatment equipment, a methyl orange solution with a concentration of 10 mg l−1 was treated, and the removal rate was found to reach 88.96%.

Path, place, and pace in mid-Ming Suzhou landscape painting

Path, place, and pace in mid-Ming Suzhou landscape painting

A diffusive atmospheric pressure glow discharge in a coaxial pin-to-ring gap with a transverse magnetic field

Atmospheric pressure glow discharge (APGD) has been widely used in the industrial field. The industrial applications are based on achieving stable and diffusive APGD in a relatively large space. The existing sources only achieved stable and diffusive APGD between a short inter-electrode distance within 5 millimeters. In this paper, the effect of a transverse stationary magnetic field on the diffusion of filamentary APGD was studied in a pin-to-ring coaxial gap. The APGD was driven by a high-voltage resonant power supply, and the stationary magnetic field was supplied by a permanent magnet. The stable and diffusive APGD was achieved in the circular area, which diameter was 20 millimeters. The experimental results revealed that more collision ionization occurred and the plasma was distributed diffusively in the discharge gap by applying the external transverse magnetic field. Besides, it is likely to obtain more stable and diffusive APGD in the coaxial pin-to-ring discharge gap when adjusting the input voltage, transverse magnetic flux density and resonant frequency of the power supply.

25 keV electron beam formation based on a three-electrode system of the obstructed glow discharge in H2 and D2

The results of experimental study on the formation of high-current electron beams using three-electrode system are presented. This system enables to create a diffusive obstructed glow discharge in a pulsed regime with an amplitude of applied voltage up to 25 kV. The influence of such experimental parameters as the pressure of plasma forming gas and the amplitude of applied voltage on the obstructed glow discharge duration was investigated. Both the transverse and the longitudinal structure of formed electron beam was determined.