ICCD Camera Research Articles

Effects of Tube Diameter and Gas Flow Rate on the Discharge Dynamics Characteristics and Reactive Species of Nanosecond Pulsed Discharge Plasma in Contact With Water

ABSTRACTThe use of millimeter quartz tubes to generate non‐thermal plasma in contact with liquid is widely applied in medicine, such as the effective disinfection of catheter tubes and tooth cavities. Here, the effects of tube diameter and gas flow rate on discharge dynamics and reactive species characteristics of nanosecond pulse needle‐water discharge are studied using an ICCD camera and optical emission spectra. The discharge diffusion is increased significantly by an appropriate combination of tube diameter and gas flow rate. Besides, the discharge intensity, emission spectra intensities of reactive species, gas temperature, and electron density increase with the increase of quartz tube diameter and gas flow rate, which contributes to enhance the production of OH and H2O2 species in aqueous samples.

2D Raman imaging for vibrational and rotational temperature mapping in H2

We showcase a Raman scattering diagnostic for 2D imaging of the rotational and vibrational temperatures of H2. Applications include environments with vibrational-rotational non-equilibrium such as H2-containing supersonic jets and plasma reactors. We image segments of the laser scattering spectrum, containing one or more Raman features, using an ICCD camera that is equipped with one of several bandpass filters. Knowing their transmission spectrum allows the construction of calibration curves that relate the relative intensities of the multi-spectral image to the rotational and vibrational temperatures. Additionally, the absolute intensity indicates the density of H2. We illustrate the capability to independently measure rotational (300–3000 K, ±150 K) and vibrational temperatures (1000–3000 K, ±50 K). The technique is demonstrated on two different H2 microwave plasmas and validated against conventional fitting of 0D and 1D Raman spectra.

Influence of Voltage Rising Time on the Characteristics of a Pulsed Discharge in Air in Contact with Water: Experimental and 2D Fluid Simulation Study

In the context of plasma–liquid interactions, the phase of discharge ignition is of great importance as it may influence the properties of the produced plasma. Herein, we investigated the influence of voltage rising time (τrise) on discharge ignition in air as well as on discharge propagation on the surface of water. Experimentally, τrise was adjusted to 0.1, 0.4, 0.6, and 0.8 kV/ns using a nanosecond high-voltage pulser, and discharges were characterized using voltage/current probes and an ICCD camera. Faster ignition, higher breakdown voltage, and greater discharge current (peak value) were observed at higher τrise. ICCD images revealed that higher τrise also promoted the formation of more filaments, with increased radial propagation over the water surface. To further understand these discharges, a previously developed 2D fluid model was used to simulate discharge ignition and propagation under various τrise conditions. The simulation provided the spatiotemporal evolution of the E-field, electron density, and surface charge density. The trend of the simulated position of the ionization front is similar to that observed experimentally. Furthermore, rapid vertical propagation (<1 ns) of the discharge towards the liquid surface was observed. As τrise increased, the velocity of discharge propagation towards the liquid increased. Higher τrise values also led to more charges in the ionization front propagating at the water surface. The discharge ceased to propagate when the charge number in the ionization front reached 0.5 × 108 charges, irrespective of the τrise value.

Discharge and mass transfer characteristics of atmospheric pressure gas-solid two-phase gliding arc

In this work, a gas-solid two-phase gliding arc discharge (GS-GAD) reactor was built. Gliding arc was formed in the gap between the blade electrodes, and solid powder was deposited on the sieve plate positioned beneath the blade electrodes. A range of experimental parameters, including the inter-electrode spacing, gas flow rate, applied voltage, and the type of the powder, were systematically varied to elucidate the influence of solid powder matter on the dynamics of gliding arc discharge (GAD). The discharge images were captured by ICCD and digital camera to investigate the mass transfer characteristics of GS-GAD, and the electrical parameters, such as the effective values of voltage, current, and discharge power were record to reveal the discharge characteristics of GS-GAD. The results demonstrate that powder undergoes spontaneous movement towards the upper region of the gliding arc due to the influence of electric field force. Increasing the discharge voltage, decreasing relative dielectric constant of the powder and reducing the electrode-to-sieve-plate distance all contribute to a greater involvement of powder in the GAD process, subsequently resulting in an enhanced powder concentration within the GAD region. Additionally, powder located beneath the gliding arc experiences downward resistance caused by the opposing gas flow and arc. Excessive gas flow rate notably hampers the powder concentration within the discharge region, and the velocity of powder motion in the upper part of the GAD region is reduced. Under the condition of electrode-to-sieve-plate distance of 30 mm, gas flow rate of 1.5 L/min, and peak-to-peak voltage of 31 kV, the best combination of arc gliding and powder spark discharge phenomena can be achieved with the addition of Al2O3 powder.

Imaging of low Z masked with high Z (Pb, U) materials using 14 MeV neutron

An experimental study has been performed using 14 MeV neutrons for imaging of low Z material (particularly composed of C, H, O elements) masked with thick layers of dense and high Z materials. The experimental setup consists of a D-T neutron generator, a metallic collimator and an imaging system. The imaging system is designed with a polypropylene zinc sulphide scintillator screen integrated with a lens coupled 16-bit ICCD camera. Imaging capability of the system was investigated using iron test samples with holes and line pair features. The minimum hole size of 2 mm could be imaged at a contrast of 36% and a line of 2 mm width visible at a contrast of 24% indicating the system's resolution of ∼ mm. Low Z samples such as water (H2O) and polyethylene (C2H2) n placed behind thick layers of Pb (40 mm) and Uranium (35 mm), were imaged successfully. These images reveal the system's ability towards low Z material imaging in the presence of heavier metals. Good contrast images acquired at a lower neutron yield of ∼ 5 × 108 n/sec of D-T neutron generator has provided a possibility to realise fast neutron imaging having moderate resolution (∼ mm) with a smaller footprint and an economical system design for field applications.

Atmospheric pressure uniform dielectric barrier discharge (DBD) in a wide air gap initiated from a narrow starting point

Generating a uniform non-equilibrium plasma in atmospheric pressure air has always been a challenge. It is believed that the maximum spacing for generating a uniform non-equilibrium plasma in atmospheric pressure air, whether using AC or nanosecond pulse drive, is 4 mm. Discharges are always non-uniform when the spacing is greater than 4 mm. In this paper, we propose a new type of dielectric barrier discharge structure to address this challenge. The left end of the structure rapidly increases the discharge spacing from 0.5 mm to 6 mm, while the right side of the main discharge gap maintains a uniform spacing of 6 mm. Nanosecond pulse voltage is used to drive the plasma, an ICCD camera is used to capture the image of the plasma during a discharge pulse cycle, which indicates that a uniform plasma within the 6 mm spacing of the main discharge gap is generated. Upon further reducing the ICCD camera’s exposure time to 20 ns, it is revealed that the uniform plasma is formed due to the rapid propagation of the plasma from left to right at a speed of order of 105 m s−1. Due to the small transverse component of the external electric field, this rapid propagation behavior cannot be due to the external electric field. Therefore, this paper further proposes the hypothesis of electric dipole formation leading to this fast propagation. The hypothesis suggests that the charge separation on the surface of the anode forms an electric dipole, which generates a local discharge at its right end. This local discharge further triggers the discharge in the main gap, and the main gap discharge, in turn, forms a dipole due to charge separation again, by repeating this cycle, the plasma propagates rapidly to the right. Further analysis demonstrates that this dipole can indeed produce a strong electric field of up to 41 kV cm−1 at its right end, which is sufficient to induce a local discharge. Moreover, under such a strong electric field, the electron migration rate can indeed reach 105 m s−1. These findings support the plausibility of this hypothesis.

A large-scale cold plasma jet: generation mechanism and application effect

Atmospheric pressure cold plasma jets (APCPJs) typically exhibit a slender, conical structure, which imposes limitations on their application for surface modification due to the restricted treatment area. In this paper, we introduce a novel plasma jet morphology known as the large-scale cold plasma jet (LSCPJ), characterized by the presence of both a central conical plasma jet and a peripheral trumpet-like diffuse plasma jet. The experimental investigations have identified the factors influencing the conical and the trumpet-like diffuse plasma jet, and theoretical simulations have shed light on the role of the flow field and the electric field in shaping the formation of the LSCPJ. It is proved that, under conditions of elevated helium concentration, the distributions of impurity gas particles and the electric field jointly determine the plasma jet’s morphology. High-speed ICCD camera images confirm the dynamic behavior of plasma bullets in LSCPJ, which is consistent with the theoretical analysis. Finally, it is demonstrated that when applied to the surface treatment of silicone rubber, LSCPJ can achieve a treatment area over 28 times larger than that of APCPJ under equivalent conditions. This paper uncovers the crucial role of impurity gases and electric fields in shaping plasma jet morphology and opens up the possibility of efficiently diversifying plasma jet generation effects through external electromagnetic fields. These insights hold the promise of reducing the generation cost of plasma jets and expanding their applications across various industrial sectors.

CH4/NH3 Flame Structure and Extinction Limit under Flame-Flame Interactions.

Ammonia is considered to play an important role in replacing traditional fossil fuels in future energy systems. In the experimental study, CH4/NH3 flame was lit by applying a double-nozzle burner to gain insight into the structure, and the laminar diffusion flame structure, CH*/OH* intensity maximum, and flame size were analyzed by an ICCD camera. In addition, the extinction limit (lower limit) of the CH4/NH3 flame under different conditions was also studied. The results showed that with the increase of burner pitch, the two diffusion flames showed four states of merged flames, merging flames, inclining separated flames, and independent flames in turn. In the process of flame separation, the continuous pitch between merging flames was short. At this point, higher syngas flow could help increase the continuous pitch to keep merging form. The paper investigated the flame structure and found that the flame size would decrease when the NH3 content in the fuel was high. The flame stability also decreased with an increase of the NH3 content in the fuel. These findings provided experimental proof and a theoretical basis for future studies on the stability of CH4/NH3 co-firing.

Formation of Extended Tubular Plasma in Argon at Low Pressure and in a Weak Longitudinal Magnetic Field

The results of experimental studies on the formation and subsequent evolution of extended (l = 300 mm) and thin-walled (Δr ≈ 10 mm) tubular (2r ≈ 110 mm) plasma in a weak longitudinal magnetic field (B = 175 G) without the use of a thermionic cathode are presented. The cylindrical chamber in which the tubular plasma was formed was pumped with high purity argon (99.998%) at an average velocity of about 1 m/s at a pressure of P = 10–3–10–2 Torr. Two methods of creating seed electrons initiating the development of ionization avalanches were used. The difference inherent to these methods has been established in the dynamics of breakdown, completing in the formation of a tubular discharge. In the first of them, a pulsed discharge preceding the high voltage supply of the main discharge created gas preionization in a small area around the sectioned cathodes. In the second method, seed electrons were created in the entire working area of the discharge chamber by an RF discharge with a frequency of 85 kHz and duration of about 1 s. High-speed shooting with a 4-frame ICCD camera allowed us to establish the dynamics of tubular discharge formation at all its stages. Measurements of the longitudinal and radial discharge current were carried out. The results we obtained showed the possibility of spatial isolation of an extended tubular plasma from the close located metal wall of the discharge chamber by using a weak longitudinal magnetic field.

Trumpet-shaped diffuse plasma jet in a semi-confined environment

Abstract This paper reports a unique trumpet-shaped diffuse plasma jet (TDPJ) with a caliber exceeding 30 mm in a semi-confined environment, which is larger than the diameter of existing atmospheric pressure plasma jets (APPJs) in an open environment. The morphology of the TDPJ is attributed to the influence of the electric field on the development characteristics of ionization waves in the ambient environment. High-speed ICCD camera images show that the plasma bullets in the TDPJ have a completely different propagation trajectory compared to the APPJ. Different shapes of diffuse plasma jets can also be formed by adjusting the doping gas, which is due to the Penning ionization and consistent with the impact of the electric field. This research reveals the long-neglected effect of the electric field on ionization waves and provides a way to manipulate the morphology of plasma jets efficiently. The generation mechanism of the TDPJ can provide preliminary guidance for the effective medical treatment of plasma jets in semi-confined environments, such as human internal organs.

Depth profile CF LIBS analysis of the wall deposited layer in the COMPASS tokamak after LiSn testing campaign

Plasma-facing materials in tokamak nuclear reactors are subject to intense heat and radiation. The design of liquid metal (LM) divertor walls has several advantages over the solid counterparts. It is important to understand the migration and re-deposition of LMs such as lithium (Li), lead (Pb) or even tin (Sn). This work presents CF LIBS depth profile analysis of the deposited layer on Ni–Cr based screws situated at different places in the COMPASS tokamak vessel during the Capillary Porous System (CPS) LM (LiSn) divertor testing campaign. The experiment was carried out at low Ar pressure (100 mbar) using ns Nd:YAG laser operating at 532 nm. The spectra were recorded using echelle spectrometer (M5000, Andor Tech.) equipped with an iCCD camera (iStar DH743, Andor Tech.). The quantification was based on observed C I, B I, Li I and (weak) Sn I lines, in addition to trace elements (Ca, Na, K) and main matrix elements (Cr, Ni, Fe). The evaluation of electron temperature and density was based on Cr I-II, Ni-II and Fe I-II lines. The LM based content is estimated to be Li (0.3-0.81 at.%) and Sn (0.1-0.23 at.%) with Li/Sn at.% ratio ranging from 3 to 3.5 (wt.% ratio of 0.17-0.20). In practise, the limit of detection of Sn by CF LIBS for this type of Cr-Ni-Fe based matrix is observed to be ∼0.1 at.%.

Single-Grating Monolithic Spatial Heterodyne Raman Spectrometer: An Investigation on the Effects of Detector Selection.

Spatial heterodyne Raman spectrometers (SHRSs) are modified forms of Michelson interferometers, except the mirrors in a Michelson interferometer are replaced with stationary diffraction gratings. This design removes the need for an entrance slit, as is the case in a dispersive spectrometer, and removes the need to scan the spectrum by using a moving mirror in a modern Michelson interferometer. In previous studies, various SHRS variants, such as free-standing two-grating SHRS, single-grating SHRS (1g-SHRS), monolithic SHRS (mSHRS), and single-grating mSHRS (1g-mSHRS), have been evaluated. However, the present study exclusively focuses on the 1g-mSHRS configuration. The 1g-mSHRS and 1g-SHRS increase the spectral range at fixed grating line density while trading off spectral resolution and resolving power. The mSHRS benefits from increased rigidity, lack of moving parts, and reduced footprint. In this study, we investigate how the choice of detector impacts the performance of the 1g-mSHRS system, with a specific focus on evaluating the performance of three types of cameras: charged-coupled device (CCD), intensified CCD (ICCD), and complementary metal-oxide-semiconductor (CMOS) cameras. These systems were evaluated using geological, organic, and inorganic samples using a 532 nm continuous wave laser for the CMOS and CCD cameras, and a 532 nm neodymium-doped yttrium aluminum garnet pulsed laser for the ICCD camera. The footprint of the 1g-mSHRS was 3.5 × 3.5 × 2.5 cm3 with a mass of 272 g or 80 g, depending on whether the monolith housing is included or not. We found that increasing the number of pixels utilized along the x-axis of the camera increases fringe visibility (FV) and optimizes the resolution (by capturing the entirety of the grating and magnifying the fringes). The number of pixels utilized in the y-axis, chip size, and dimensions, affect the signal-to-noise ratio of the systems. Additionally, we discuss the effect of pixel pitch on the recovery of Fizeau fringes, including the relationship between the Nyquist frequency, aliasing, and FV.

High-Speed Flow Visualization by a Nanosecond Volume Discharge during Shock Wave Diffraction on an Obstacle

We study the spatial structure of nonstationary inhomogeneous supersonic airflows as shock wave diffraction on an obstacle occurs in a shock tube of a rectangular cross section. The Mach numbers of shock waves were 2.7–4.4 at initial air pressures of 10–30 Torr. The supersonic flow in the discharge chamber was visualized by high-speed shadowgraphy and by the registration of radiation of combined volume discharge by photo camera and by ICCD camera. In experiments, a combined volume discharge with a current duration of ~ 500 ns was initiated 40–150 μs after the initial shock wave have passed an obstacle. It has been established that the radiation of the volume phase of discharge lasts 400–700 ns, and the displacement of the flow during this time does not exceed 0.6 mm. A correlation is established between the spatial distribution of discharge radiation and the low-density local areas determined as a result of two-dimensional Navier-Stokes based numerical simulation of the flow. As visualized by the glow of the discharge, the shape of the shock wave front is in good agreement with the results of shadowgraphy at different stages of diffraction and with the numerical simulation results.

Breakdown development in a nanosecond pulsed dielectric barrier discharge in humid air in plane-to-plane geometry

We used the ns electric field induced second harmonic (EFISH) generation diagnostic to measure the electric field evolution in a 200 ns pulse, dielectric barrier, plane-to-plane discharge in humid air, on the time scale shorter than the laser pulse duration. Plasma imaging by an ICCD camera detected a uniform evolution of the discharge emission during the breakdown. Spectroscopic measurements tracked the N2 second positive and first negative systems to infer the reduced electric field (E/N) evolution. EFISH measurements showed the electric field persistent during the entire HV pulse, with the residual field between pulses and the field inversion at the start and end of the HV pulse. The experimental data are consistent with the simulations, with the electron attachment and negative ion kinetics incorporated. The modeling predictions indicate that the rapid electron density decay due to attachment and recombination is the dominant factor sustaining the electric field in the plasma after breakdown. Spectroscopic E/N determination showed the time evolution at variance with the EFISH measurements, which may be due to the electron attachment and non-locality of the EEDF. Possible explanations are discussed.

The Development of the Streamer Discharge to Flashover Along the Dielectric Surfaces

The development of the streamer to flashover along the dielectric surfaces was studied in-depth. Three photomultipliers were applied to measure the development of streamer discharge to flashover. An ICCD camera was used to take photos of paths and micromorphology of streamer discharge. A digital camera was used to acquire paths of flashover discharge. The researchers found that the criterion of breaking the short gap is whether the secondary streamer crossing the gap can be generated. The micromorphology of streamer discharge along the different dielectric surfaces has significant differences. Furthermore, the streamer discharge is similar to the subsequent flashover with the influence of the applied electric field and the propagation path. It would be more accurate to say the ‘Stability’ fields for flashover propagation increase with that for streamer propagation along the different materials. The propagation path of the subsequent flashover is the same as that of the secondary streamer before the flashover.

Influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma

In the present work, we have studied the influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma (NELPP) for two different metals, copper and aluminum. The targets were ablated using a Q-switched Nd:YAG laser operating at its primary wavelength of 1064 nm. The plasma imaging was recorded using the fast-gated ICCD camera. Although spectroscopic investigation of signal enhancement of emission line intensities in presence of nanoparticles (NPs), nanoparticle enhanced LIBS (NELIBS), has been performed extensively, expansion dynamics for NELIBS is not yet studied. We have carried out a detailed investigation of the plume propagation of NELPP for different pulse energies and ambient pressures. Temporal evolution of the distance of propagation of the plume front at different laser fluences and pressures shows a good agreement with the existing theoretical models. By comparing different plume propagation parameters, such as diameter, aspect ratio and expansion velocity, we have shown that the NELPP plume shows similar behavior as of LPP and its evolution can be explained with the existing models. Hence NPs, though influence the ablation process, do not alter the overall plume dynamics during the course of plasma evolution as observed for the two metals.

Thin Luminous Tracks of Particles Released from Electrodes with A Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

Features of the nanosecond discharge development in a non-uniform electric field are studied experimentally. High spatial resolution imaging showed that thin luminous tracks of great length with a cross-section of a few microns are observed against the background of discharge glow in air and argon. It has been established that the detected tracks are adjacent to brightly luminous white spots on the electrodes or in the vicinity of these spots, and are associated with the flight of small particles. It is shown that the tracks have various shapes and change from pulse to pulse. The particle tracks may look like curvy or straight lines. In some photos, they can change their direction of movement to the opposite. It was found that the particle’s track abruptly breaks and a bright flash is visible at the break point. The color of the tracks differs from that of the spark leaders, while the bands of the second positive nitrogen system dominate in the plasma emission spectra during the existence of a diffuse discharge. Areas of blue light are visible near the electrodes as well. The development of glow and thin luminous tracks in the gap during its breakdown is revealed using an ICCD camera. Physical reasons for the observed phenomena are discussed.

Experimental and numerical investigation of surface streamers in a nanosecond pulsed packed bed reactor

Packed bed reactor (PBR) is the commonly used configuration in plasma catalysis, and its plasma characteristics have been extensively investigated. The filled catalysts in PBR make it challenging to carry out in-situ measurements of electric fields, and limited experimental data have been obtained. We investigated the surface streamer propagation and electric field distribution in a simplified PBR through simulations and experiments. The simplified PBR in the experiments is comprised of a blade-plate electrode structure filled with an Al2O3 column (ϵr = 9) in the discharge gap. An ICCD camera and an electric field diagnosis method called EFISH (electric field induced second harmonic generation) were employed, and a two-dimensional fluid model was established for the simulation. Four discharge types in the PBR were identified based on ICCD images and simulation results, including polar discharge at the contact areas, surface streamer along the dielectric column, expansion of surface discharge along the dielectric column, and surface ionization waves along the dielectric plate. Surface streamers with opposite propagation directions were found in the model, namely the forward streamer during the pulse rising time and the reverse streamer during the pulse falling time. Notably, the reverse streamer exhibits a significantly lower velocity compared to the forward streamer. Both experimental measurements and simulation were conducted to investigate the spatiotemporal electric field near the surface of the packing material. The results of both E exp and E sim showed peaks with opposite polarities, and exhibited similar trends. In the simulation, the forward streamer head showed a higher electric field compared to the reverse streamer head. Moreover, during the rest pulse time, the surface electric field was more intense at the contact areas than in other regions. The findings of this work provide valuable insights into the discharge mechanism and electric field on the catalytic material surface within the PBR.

1D profile measurement of ion velocity distribution with glass-tube-pair type Doppler probe array

We developed a glass-tube-pair type Doppler probe array for ion velocity distribution function measurement with high spatial and time resolution. By four mirrors and four optical fibers fixed in two parallel glass tubes, the light from ions in each measurement area (3.2 × 2.5 × 1.0 cm3) between tubes is collected in three different directions, and the fibers are led to a Czerny–Turner spectrometer and finally to an ICCD camera (the exposure time of 2 μs) for Doppler spectra measurements with high time resolution. Since the Doppler spectrum profile in each viewing line represents the distribution of the ion velocity component in the line, we can reconstruct 2D velocity distribution by the measured spectra in three viewing lines with tomography techniques. We tested the accuracy of some reconstruction methods from spectra to velocity distribution in numerical simulation and chose the iterative method as the best one. By use of this new diagnostic, we successfully measured the radial profile of ion velocity distribution during magnetic reconnection of merging spherical tokamak plasmas and revealed that their ions have anisotropic velocity distributions.

From Repeatability to Self-Organization of Guided Streamers Propagating in a Jet of Cold Plasma

In this work, a jet of cold plasma is generated in a device supplied in helium and powered with a high-voltage nanopulse power supply, hence generating guided streamers. We focus on the interaction between these guided streamers and two targets placed in a series: a metal mesh target (MM) at floating potential followed by a metal plate target (MP) grounded by a 1500 Ω resistor. We demonstrate that such an experimental setup allows to shift from a physics of streamer repeatability to a physics of streamer self-organization, i.e., from the repetition of guided streamers that exhibit fixed spatiotemporal constants to the emergence of self-organized guided streamers, each of which is generated on the rising edge of a high-voltage pulse. Up to five positive guided streamers can be self-organized one after the other, all distinct in space and time. While self-organization occurs in the capillary and up to the MM target, we also demonstrate the existence of transient emissive phenomena in the inter-target region, especially a filamentary discharge whose generation is directly correlated with complexity order Ω. The mechanisms of the self-organized guided streamers are deciphered by correlating their optical and electrical properties measured by fast ICCD camera and current-voltage probes, respectively. For the sake of clarity, special attention is paid to the case where three self-organized guided streamers (α, β and γ) propagate at vα = 75.7 km·s–1, vβ = 66.5 km·s–1 and vγ = 58.2 km·s–1), before being accelerated in the vicinity of the MM target.