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Besides a typical high‐density plasma source, electrical explosion of conductors is also indispensable in switches, nanomaterial synthesis, shock‐wave sources, etc. In this paper, an experimental study regarding plasma dynamics of electrical wire explosions (μs‐timescale) is presented, with spatiotemporal resolved diagnostics. Pure Cu/Ni wire and Cu‐Ni alloy wire were used and compared. The alloy wire usually has a higher resistivity, resulting in a higher initial energy deposition (heating) rate. Abel inverse transformation indicated that the plasma radiation focussed on the outer region of the discharge channel for the alloy wire. In addition, the metallic vapour determined by the material properties had a considerable influence on the plasma process and resulting nanomaterials. In particular, both transverse and axial‐layered structures were observed in alloy wire vapour. In addition, for the first time, the expanding arc‐like plasma of explosion products was understood and examined from aspects of material properties and energy relaxation. The later stage of wire explosion resembled the state of regular metal vapour arcs under 1 MPa pressure. Finally, the core factor for the fast energy deposition stage of wire explosion was ascertained. Correlations between pre‐exposition circuit parameters and post‐explosion dynamic effects were found, which is significant for practical applications.

Breakdown characteristics in dielectric-confined microcavity discharge of plate-to-plate electrodes under DC voltage are investigated in this paper. Experimental and particle-in-cell/Monte Carlo code simulated results show that the breakdown characteristic curve (the relation between the breakdown voltage V br and the product pd of gas pressure p and electrode gap d or the V br–pd curve) with a microcavity effect will deviate from the traditional Paschen curve, and seed electron adsorption by the dielectric wall is considered as the deviation mechanism. A smaller microcavity height will enhance this deviation. Based on the extent of deviation, there exist two critical microcavity heights, h cr1 and h cr2, for the breakdown characteristic curve. When the cavity height h is larger than h cr1, the V br–pd curve conforms to Paschen’s law due to the minor adsorbed electrons. When h < h cr1, the V br values in the V br–pd curve begin to increase overall, compared to those in the Paschen curve. Specifically, when h cr2 < h < h cr1, the V br–1/h curve exhibits a positive linear relation; when h < h cr2, V br increases sharply with 1/h as a nonlinear relationship due to the massive adsorbed electrons. Additionally, the type of dielectric material used to construct the microcavity also has a significant impact on V br, which is related to the different electron adsorbility η of various dielectric walls. For deeper insight, a ‘microcavity effect’ analysis model was developed to discuss the modified V br–pd curve and provide the explanation for the critical values of microcavity heights and the influence of the dielectric material. Significant adsorption of charged particles (especially the seed electrons) by the dielectric wall will reduce the electron multiplication and further improve the breakdown voltage when the cavity height h is comparable to the product ηλ e (the dielectric electron adsorbility and electron mean free path). On this basis, the modified breakdown criterion considering the microcavity effect was derived. The analytical expressions of the two critical height values h cr1 and h cr2 (h cr1 = 100ηλ e, h cr2 = 10ηλ e) and the linear relation of V br–1/h curve in h cr2 < h< h cr1 are presented quantitatively.

Helium plasma jets generated by micro-hollow cathode discharge (MHCD) with the square-wave power source of different polarities are investigated in this work. The effects of positive and negative polarity pulses on the MHCD and plasma jet were compared, and the time-resolved optical emission spectra of excited species ( N 2 + and O) were studied. The results confirm that the electric field is a key factor for the propagation of the jet during the rising edge of the positive current pulse, while the gas expansion is mainly important for the jet propagation during the current stable phase. The time-resolved spectra show that the generation of specie O in the jet-driven by the electric field is more efficient.

In the pipeline transportation process for crude oil, the most important and popular maintenance method for perforated and ruptured oil pipelines is the replacement of the damaged pipeline segment. However, this method has several disadvantages, including a complex process, large time consumption, and excessively high costs. The present study reported the preparation of a strong cross-linking hydrogel that served as a temporary blocking material during the long-distance oil pipeline partial replacement process. The prepared product was characterized by infrared spectroscopy, X-ray diffraction analysis, and scanning electron microscopy to analyze the microscopic reactions and structures. Orthogonal experiments for shear stress were performed to determine the optimal synthesis condition. The relevant experiments indicated that the proposed product can effectively isolate oil and oil gas, and a 4.5 m long hydrogel can resist the force of a 0.57 MPa overpressure. The blocked pipeline turned to a dredged state on changing the pipeline pressure. The flame resistance experiment showed that the hydrogel exhibited excellent flame resistance and could therefore ensure the safety of the hot work. On the basis of this hydrogel material, a new method for replacing the partially damaged oil pipeline was proposed.

The electric double layer in argon helicon plasma by using floating electrostatic probe and local optical emission spectroscopy under different external magnetic field was investigated. Results show that electrons generated in the plasma source can be magnetized by the magnetic field and transported by the gradient of diverging magnetic field in the diffusion chamber, giving rise to the hollowed distribution of electron temperature. The electron temperature on axis has a sudden decrease, leading to the sudden decrease of plasma density as well as the plasma potential, forming a double layer structure. The position of double layer moves along with the position of diverging magnetic field, and the potential drop increases along with the strength of magnetic field. The structure of the external magnetic field plays the decisive factor for the double layer in helicon plasma.

Beam plasma directly forms the thrust of single-stage helicon plasma thrusters and its properties are the input parameters of the two-stage helicon thruster. Therefore, the spatial distribution of the beam plasma is vital for both single-stage and two-stage helicon thrusters. Using an optical emission spectroscope with a radial resolution of 5 mm, the spatial distribution of the beam plasma parameters and its variation with different input radio frequency (RF) powers (100–1000 W) and diameters of the discharge tube (20–60 mm) was investigated. Results show that the electron density decreases with both axial and radial distances, but the electron temperature remains nearly constant. The electron density increases with increasing input RF powers because of an increase of power deposition when the electron temperature remains constant. The radial profiles of electron density are flat, and the maximum electron densities located in the center line decrease with increasing diameters of the discharge tube, which is due to the decrease in the power density.

Previous studies suggest the potential efficacy of neuroprotective effects of gaseous atmospheric-pressure plasma (APP) treatment on neuronal cells. However, it remains unclear if the neuroprotective properties of the gas plasmas benefit the ischemic stroke treatment, and how to use the plasmas in the in vivo ischemic stroke models. Rats were subjected to 90 min middle cerebral artery occlusion (MCAO) to establish the ischemic stroke model and then intermittently inhaled the plasma for 2 min at 60 min MCAO. The regional cerebral blood flow (CBF) was monitored. Animal behavior scoring, magnetic resonance imaging (MRI), 2,3,5-triphenyltetrazolium chloride (TTC) staining, and hematoxylin and eosin (HE) staining were performed to evaluate the therapeutic efficacy of the gas plasma inhalation on MCAO rats. Intermittent gas plasma inhalation by rats with experimental ischemic stroke could improve neurological function, increase regional CBF, and decrease brain infarction. Further MRI tests showed that the gas plasma inhalation could limit the ischemic lesion progression, which was beneficial to improve the outcomes of the MCAO rats. Post-stroke treatment with intermittent gas plasma inhalation could reduce the ischemic lesion progression and decrease cerebral infarction volume, which might provide a new promising strategy for ischemic stroke treatment.

Regulating the parameters of the atmospheric pressure plasma jet (APPJ) is meaningful for industrial applications. Since plasma is a typical functional fluid in the magnetic field, it is possible to control the discharge characteristics via the Lorentz force. In this study, the effects of a locally divergent magnetic field on the generation and propagation of APPJ were examined experimentally. The experiments used a coplanar dielectric barrier discharge (CDBD) device driven by a 30 kHz AC high-voltage source to generate a helium APPJ. A locally divergent magnetic field of 250 mT (maximum) was applied coupled with the electric field, and noticeable enhancement was observed. The results showed that the magnetic field changed the motion state of electrons and promoted collision ionization, leading to a 40% improvement in the APPJ length (0.6 cm) and a 23% increase in the intensity of line O (777.2 nm). In addition, the spatiotemporal evolution and flow field of APPJ were diagnosed by ICCD and schlieren technique. The combination of electric and magnetic fields may effectively optimize the APPJ in practical applications.

We report in this Letter a kind of asymmetric discharge mode in positive and negative half-cycles of dielectric barrier discharge in ambient air. This phenomenon is characterized by homogeneous and filamentary discharges occurring alternately in the two half-cycles, using two different materials of alumina ceramic and quartz as the dielectric barrier at each side. The discharge current waveforms, discharge images, optical emission spectra, and the averaged electron energy are significantly different for the asymmetric discharges. It is suggested that the seed electrons and secondary electron emission from the different dielectric materials acting as the temporary cathode are responsible for the different discharge modes.

We present here a kind of low-frequency oscillation in argon helicon discharge with a half helical antenna. This time-dependent instability shows a global quasi-periodic oscillation of plasma density and electron temperature, with a typical frequency of a few tens of Hz which increases with external magnetic field as well as radiofrequency (RF) power. The relative oscillation amplitude decreases with magnetic field and RF power, but the rising time and pulse width do not change significantly under different discharge conditions. The oscillation can only be observed in some specific conditions of low magnetic fields and low RF power when the gas flows in from one end of the discharge area and out from another end. This global instability is suggested to be attributed to the pressure instability of neutral depletion, which is the result of compound action of gas depletion by heating expansion and gas replenishment from upstream. There are two kinds of oscillations, large and small amplitude oscillations, occurring in different discharge modes. This study could be a good verification of and complement to earlier experiments. This kind of spontaneous pulse phenomenon is also helpful in realizing a pulsing plasma source without a pulsed power supply.

In this work, we investigated the discharge characteristics and heating mechanisms of argon helicon plasma in different wave coupled modes with and without blue core. Spatially resolved spectroscopy and emission intensity of argon atom and ion lines were measured via local optical emission spectroscopy, and electron density was measured experimentally by an RF-compensated Langmuir probe. The relation between the emission intensity and the electron density was obtained and the wavenumbers of helicon and ‘Trivelpiece-Gould’ (TG) waves were calculated by solving the dispersion relation in wave modes. The results show that at least two distinct wave coupled modes appear in argon helicon plasma at increasing RF power, i.e. blue core (or BC) mode with a significant bright core of blue lights and a normal wave (NW) mode without blue core. The emission intensity of atom line 750.5 nm (I ArI750.5nm) is related to the electron density and tends to be saturated in wave coupled modes due to the neutral depletion, while the intensity of ion line 480.6 nm (I ArII480.6nm) is a function of the electron density and temperature, and increases dramatically as the RF power is increased. Theoretical analysis shows that TG waves are strongly damped at the plasma edge in NW and/or BC modes, while helicon waves are the dominant mechanism of power deposition or central heating of electrons in both modes. The formation of BC column mainly depends on the enhanced central electron heating by helicon waves rather than TG waves since the excitation of TG waves would be suppressed in this special anti-resonance region.

Nitrogen (N2) helicon plasma is produced with radio frequency (RF) right-helical antenna at low pressures. Several wave modes and their transitions of N2 helicon discharge are observed experimentally. Blue Core phenomenon is achieved at high magnetic fields and high RF powers, with strong local blue light emissions of N II lines and high electron temperature inside the core area. Based on actinometric ratio and pressure balance model, species kinetics of N2 helicon plasma are analyzed. It is shown that about 79% of N2 molecules are dissociated and about 49% of the neutrals are ionized inside the Blue core in high magnetic field of 850 G and RF power of 2200 W. Nearly 99% of N2 molecules inside the core area are depleted considering the neutral density before and after discharge, from 7.3 × 1013 cm−3 to 6.5 × 1011 cm−3. Serious neutral depletion of N2 and N neutrals and high electron temperature are suggested to be the dominant causes for significant enhancement of central N II emissions (blue lights). Meanwhile, evolution of reaction processes indicates that N ionization and N+ excitation become dominant in BC mode. Besides, external magnetic field is an important factor to control the discharge mode transitions as well as the radial distributions of plasmas. From the calculated results of dispersion relation, the cavity mode resonance, rather than antenna coupling resonance, of helicon waves plays a dominant role on the wave mode formation and RF energy coupling between RF antenna and plasma. The mode transition results from excitation of helicon wave of higher axial eigenmode. N2 helicon plasma shows different characteristics from argon in mode transition, spectral emission and Blue Core formation. It is due to the high dissociation energy of N2 molecules (9.8 eV) and extensive dissociation and ionization processes. This results in a higher RF power as well as magnetic field for helicon wave coupled mode in N2 helicon plasma than that in Ar plasma.

In this paper we report the semi-conductor of zinc oxide (ZnO) thin film deposited by reactive high power impulse magnetron sputtering (R-HiPIMS) on glass substrates without external heating. We focus on the influence of deposition parameter, the ratio of O2/Ar exactly, on the crystalline and electrical properties of ZnO films. It is found that n-type ZnO film with a high carrier concentration can be grown through HiPIMS technique, the ratio of O2/Ar remarkably affects the ZnO crystalline and electrical properties. At O2/Ar = 14/80 sccm, the ZnO film was orientated at c-axis (002) plane. Based on the temporal resolution optical emission spectroscopy (OES), for the proposal of the correlation of film structure with plasma radicals and the reaction process in ZnO growth, the components in plasma are diagnosed. It is concluded that in a higher oxygen partial pressure, owing to the high ionization rate in HiPIMS, the oxide layer formed between pulses is removed, the growth of a new oxide layer during the pulse is hindered, hence the growth rate is increased, and the carrier concentration caused from point defects in ZnO film is high.

The uniform gas discharge has long been pursued for realizing or improving some practical applications but is difficult to achieve due to the fact that nonuniform discharges are much easier to be generated in most cases. Usually, achieving uniform gas discharge requires sophisticated devices, and the operation is complicated and time-consuming. In this paper, we introduce simple and flexible multimethods for realizing uniform discharge from patterned structures under dielectric-barrier discharge (DBD) systems by varying experimental controlling parameters, and these methods can be employed in combination. The effects of driving frequency, voltage, duty ratio, and magnetic/electric field on glow DBD structure are investigated. It is found that a uniform glow DBD is obtained when frequency, voltage, and duty ratio are either very high or very low and also by the introduction of strong magnetic/electric field. The underlying physics of these methods is consistent as the elimination of a focusing effect of space electrons. It is concluded that the key of achieving uniform discharge is to uniformize the distribution of space charges.

We present here a new design of ion blower based on bipolar corona discharge of needle-dielectric-needle configuration. With the help of the dielectric plate, the new ion blower can endure higher voltage before spark than the traditional bipolar corona discharge, with the similar discharge characteristics and current-voltage curve. The high operating voltage provides a much greater ionic wind velocity compared with the traditional needle-to-needle corona. The neutral ionic wind can reach as far as 0.45m with a velocity of 0.2m/s. This feature is very helpful for eliminating mechanical rotating components in the design of ion blowers, so that the size of ion blower can be greatly compressed and the noise significantly reduced, which is more suitable for electrostatic elimination in small areas and some specific scenarios. The design of self-balancing regulation unit can effectively monitor the charged characteristics of mixed ion wind and make corresponding adjustments to ensure the neutrality of positive and negative discharge. This new ion blower has an excellent performance, including an offset voltage of ±5V, a short discharge time of 5s or less at distance of 20cm.

Helicon plasma density may show a non-monotonic dependence on the magnetic field at low strength, so-called “low-field peak (LFP).” We presented the multiple LFPs and the formation mechanism in argon helicon plasmas in this paper. Propagating conditions of helicon (H) and Trivelpiece–Gould (TG) waves in collisional plasmas were calculated based on the dispersion relation. It is demonstrated that there are two mechanisms during mode transition responsible for LFP, i.e., resonance of H- and TG-waves and anti-resonance of TG-wave. Especially, H-TG resonance of the highest axial mode in the helicon plasma results in a density jump rather than a density peak due to the mode transition from non-wave to co-H/TG-wave mode. Higher plasma density in lower magnetic fields is helpful for achievement of multiple LFPs in argon helicon plasmas.

In this study, a bayonet dispensing mental slim tube-ring structure based on dielectric barrier discharge (DBD) was adopted to generate micro-plasma jet at atmospheric pressure. The micro-plasma jet has a diameter of 500 μm and can propagate into the open air. The electrical and optical diagnoses revealed that this device is of good repeatability and controllability, which is essential for precision plasma medicine applications. A detailed analysis on the touchability of the jet suggests that this device is safe enough to operate. It will be applied in our further research on the neuroprotective effects of plasma treatment.

Argon helicon plasma is typically associated with a blue core, namely a radially localized central area of strong ion light emission. An experimental study was carried out to study the morphology and radiation characteristics of blue core in argon helicon plasma discharge. Experiments were carried out with two technics including Local Optical Emission Spectroscopy (LOES) and time-integrated images with digital camera. In particular, the helicon mode, characterized by the intense blue core plasma, can be achieved by adjusting the input parameters such as RF power, magnetic field, and operating pressure. Analysis of a prominent characteristic line (ArII 481.0 nm) of blue core indicates that the intensity of ion line increases linearly with the RF power, magnetic field, or operating pressure in certain intervals (when 1000 W 0 < 500 Gauss or 0.1 Pa< p< 1.0 Pa). Apart from this, blue core width increases with the power while decreases with an increase in magnetic field or operating pressure. In order to further understand the formation of the blue core, parameter regarding electron temperature is adopted to reveal that the increase of the intensity of ion line depends strongly on the increase of electron temperature.

Formation and propagation of surface plasmons (SPs) of microwaves (MWs) along a dense non-uniform plasma column were investigated by employing the finite-difference time-domain method and evidenced by experiment of argon helicon plasma. The effects of plasma density, incident frequency, and radius of plasma column on the SP features were discussed. Results showed that when the MW frequency and the density distribution of plasma column satisfy suitable conditions, SPs can be excited on the surface of a uniform plasma column when the frequency is 2–5 times of the MW, while inside a nonuniform plasma column when the plasma frequency is only a little higher (about 5%–20%) than the MW. The SP wavelength depends on the plasma density for a given incident MW frequency. The forward scatter MW field will be enhanced significantly when SP appears along the nonuniform plasma column.

Electrostatic discharge (ESD) event usually destroys the electrical properties of dielectric films, resulting in product failure. In this work, the breakdown characteristic of machine mode (MM) ESD on three different nano size films of head gimble assemble are obtained experimentally. The breakdown voltage and thickness parameters show a positive proportional relationship, but they are generally very low and have large discrete characteristics (∼30%). The maximum and minimum breakdown voltages of the tested samples are 1.08 V and 0.46 V, which are far lower than the requirement of the current standard (25 V). In addition, the judgment criterion of product damage is given, and the relationship between discharge voltage polarity, initial resistance and breakdown voltage is studied. Finally, the theoretical analysis of the breakdown characteristic law has been given.

In this study, a coplanar dielectric barrier discharge (CDBD) device driven by a 30 kHz AC high voltage source was adopted to generate a helium atmospheric pressure plasma jet (APPJ). The influence of a NdFeB magnetic ring on the behavior of APPJ has been experimentally investigated. Electrical and optical diagnostic methods were used to characterize the APPJ properties with and without the magnet. The results revealed that the configuration with a magnetic ring could change the state of DBD and enhance the propagation of the plasma jet under some circumstances. It can be anticipated that the combination of electric and magnetic fields may be an effective way to optimize the APPJ in practical applications.

Plasma has shown excellent potential prospects in sterilization applications nowadays. In this paper, we firstly design a novel sterilizer based on bipolar corona discharge of needle-dielectric-needle configuration. With the help of the dielectric plate, the new sterilizer can effectively avoid spark or arc discharge and eventually converge into a neutral ionic wind. The electrical and optical characteristics of bipolar corona discharge were studied in detail, and the ionic wind velocity with different electrode spacings was measured. The results revealed that the average current had a quadratic relationship with the overvoltage following Townsend relation, and the ionic wind velocity was positively correlated with the overvoltage. Furthermore, we simply estimated the sterilization effect of bipolar corona discharge. It was found that the sterilization efficiency increases with the increase of exposure time, and decreases with the rise of distance from the grounded electrode to the petri dish. In particular, the bipolar corona has a satisfactory sterilization efficiency which can reach 100% at 6 minutes.

This paper studied the influence of water parameters on the behaviour of an electrical wire explosion. In the experiments, a Cu wire of four sizes was exploded in water medium with different conductivity, hydrostatic pressure, and temperature. Under three typical discharge types, the electrical characteristics, shock wave, and optical emission phenomena were obtained and analysed. It has been found that the ambient medium changed the wire explosion process via adjusting the energy deposition or suppressing the later cavity expansion. Furthermore, wire explosion and its accompanied phenomena could be regulated based on the shunt effect. Finally, the mechanisms of the influence of water medium on a water gap breakdown and wire explosion were compared, and possible applications discussed.

We present in this paper the comparison of an electric double layer (DL) in argon helicon plasma and magnetized direct current (DC) discharge plasma. DL in high-density argon helicon plasma of 13.56 MHz RF discharge was investigated experimentally by a floating electrostatic probe and local optical emission spectroscopy (LOES). The DL characteristics at different operating parameters, including RF power (300–1500 W), tube diameter (8–60 mm), and external magnetic field (0–300 G), were measured. For comparison, DL in magnetized plasma channel of a DC discharge under different conditions was also measured experimentally. The results show that in both cases, DL appears in a divergent magnetic field where the magnetic field gradient is the largest and when the plasma density is sufficiently high. DL strength (or potential drop of DL) increases with the magnetic field in two different structures. It is suggested that the electric DL should be a common phenomenon in dense plasma under a gradient external magnetic field. DL in magnetized plasmas can be controlled properly by magnetic field structure and discharge mode (hence the plasma density).

This work deals with an experimental study of a Cu planar wire array (PWA) in air and water under the stored energy 300–1200 J. A single Cu wire is adopted as a controlled trial. Four configurations of PWA and a wire with the same mass (cross-section area) but the different specific surface areas (15–223 cm2 g−1) are exploded. The transient process is analyzed using high-speed photography in combination with the results of optical emission and discharge. Discharge characteristics revealed that PWA always has a higher electric power peak, early but higher voltage peak, as well as faster vaporization and ionization process than the single-wire case. Two to three times stronger optical emission could be obtained when replacing the single-wire with PWA, indicating a higher energy-density state is reached. Phenomenologically, in both air and water, single-wire load tends to develop a transverse stratified structure, while PWA is dominated by the uneven energy deposition among wires. Finally, the synchronism and uniformity of the PWA explosion are discussed.

In this paper, two types of stationary striations appearing in an argon helicon plasma source are presented. The formation and features of the striations were investigated experimentally under different conditions, including RF power, gas pressure, and external magnetic field. The results show that the striation spacing decreases as the gas pressure increases but does not change significantly along with the magnetic field and the RF power. It is suggested that these striations are strongly related to the non-local effect of electron kinetics in the plasma channel with a weak electric field. The different pressures in downstream and antenna regions will lead to different types of striations in an argon helicon plasma source.

Blue core (BC) is a special spectral phenomenon in argon helicon plasma, with intense blue lights from ion emission around the radial center of discharge tube. In this paper, the characteristics of BC in argon (Ar) helicon plasma were investigated experimentally from aspects of discharge mode transitions, plasma spatial distributions, and spectral features. It is found that the BC generally appears at strong magnetic field (480 G or above in this work) with high plasma density in wave mode, accompanied by exponentially rising of ion line intensity. The electron density and temperature, the neutral density and temperature, and the line emission intensity show a radial profile with a central peak in BC mode. The steep gradient of ion line intensity (corresponding to the ion density) defines a clear boundary of the core. Further, a pressure balance model was developed to investigate the influence of neutral depletion on BC formation. The neutral density is depleted significantly from 7.24 × 10 13 to 0.38 × 1013 cm−3 at magnetic field of 600 G in BC mode, while to 3.13 × 1013 cm−3 at magnetic field of 250 G in normal wave (NW) mode. The ionization rate in BC reaches as high as 70% compared with 9.6% of that in NW mode. The ionization rate and the ion line intensity show similar radial profiles, indicating the BC phenomenon is closely related to the distribution of peaked ion density and hollowed neutral density. Fundamentally, the central electron heating and strong magnetic field contribute to the centrally local high ionization rate and strong neutral heating. The severe neutral depletion with prominent central heating is considered to be the immediate cause of appearance of blue core.

In this paper, an ion source based on wire-to-plate corona is developed for Ion Mobility Spectrometer (IMS). The characteristics of the corona discharge and the ion current detected on Faraday plate are investigated under different electrode spacing and voltage. The effect of voltage polarity is also studied. The features of this new designed ion source are compared with that of point-to-plate corona. The results show that the present IMS prototype machine can provide a much larger value of ion current connected by Faraday plate than the point-to-plate corona and/or the traditional 63Ni source. The corona configuration can also act as a good electromagnetic shielding to defense the electromagnetic emission from the corona discharge.

The influence of gas flow, current level, and different shapes of anode on the oscillation amplitude and the characteristics of the hollow cathode discharge were investigated. The average plasma potential, temporal measurements of plasma potential, ion density, the electron temperature, as well as waveforms of plasma potential for test conditions were measured. At the same time, the time-resolved images of the plasma plume were also recorded. The results show that the potential oscillations appear at high discharge current or low flow rate. The potential oscillation boundaries, the position of maximum amplitude of plasma potential, and the position where the highest ion density was observed, were found. Both of the positions are affected by different shapes of anode configurations. This high amplitude of potential oscillations is ionization-like instabilities. The xenon ions ionized in space was analyzed for the fast potential rise and spatial dissipation of the space xenon ions was the reason for the gradual potential delay.

We investigated the potential oscillations near a hollow cathode for ring-type anode configuration and planar disc anode configuration using diagnostic tools. The waveform of potential oscillations, amplitude of plasma potential and ion density were measured. The plasma potential oscillations show rapid rising but slow decrease. The results show that ionization in a ring-type anode is more effective than that in a planar disc anode and the amplitude of plasma potential in a ring-type anode is much larger than that in a planar disc anode at the same operating conditions. The highest amplitude of plasma potential that occurred corresponds to the area where the highest ion density appeared for both anode configurations, which shows that xenon ions in space play an important role for this kind of plasma potential.

Plasma is an ionized gas. It is typically formed at high temperature. As a result of both the development of low-temperature plasma sources and a better understanding of complex plasma phenomena over the last decade, “plasma medicine” has become a booming interdisciplinary research topic of growing importance that explores enormous opportunities at the interface of chemistry, plasma physics, and biomedical sciences with engineering. This review presents the latest development in plasma medicine in the area of the central nervous system and aims to introduce cutting-edge plasma medicine to clinical and translational medical researchers and practitioners.

This paper presents the experimental and numerical results about the influence of nitrogen (N2) and oxygen (O2) admixture on the development of a helium (He) atmospheric-pressure plasma jet (APPJ) in a long dielectric tube. The results revealed that the jet length and the propagation velocity are strongly affected by introducing N2 or O2 into the He flow. Specifically, it was observed that a higher N2/O2 admixture led to the decrease in the density of both energetic and relative low-energy electrons outside the grounded electrode, which corresponds to the shortening of the jet length. In the He/O2 mixture, the electrons are easily captured by O2/O in the region of the plasma bulk. In the He/N2 mixture, the jet propagation characteristics will change since N2 has many low-level excitation states that consumed a large number of energetic electrons. The simulation shows that the magnitude of the axial electric field in the jet head depends strongly on the amount of N2 and/or O2 in the gas flow. In both cases, the peak electric field is on the order of 5 kV/cm, which is significantly higher than that in pure helium of 3 kV/cm even if the admixture is low (less than 4% N2 or 2% O2 in this work). Positive charges of higher density in the jet head are needed to induce a stronger electric field for the jet propagating in N2(x%)/He and O2(x%)/He mixtures compared with that in pure He.

In this paper, the helium plasma jet generated by micro-hollow cathode discharge (MHCD) was studied. The MHCD was driven by a square-wave pulsed power source, and the characteristics of discharge and plasma jet were measured experimentally. The influences of the gas flow rate on the MHCD and the plasma jet were investigated. And the propagation mechanisms of the plasma jet were analyzed. The results show that within 100–1000 sccm of the gas flow rate, the breakdown delay time of the MHCD increases with the helium flow increasing. It is considered that the gas flow affects the density of seed electrons and thus the breakdown delay time. With the helium flow rate increasing, the whole plasma jet length increases firstly and then decreases. A detailed investigation shows that during one discharge pulse, two distinguishable propagation processes of the plasma jet are observed. It is found that the jet of the first stage is formed during the rising edge of the current pulse, while the other is generated after the discharge current becomes stable. The propagation velocity of jet in the first stage is on the order of several km s−1, which is similar to that of the discharge evolution obtained by simulation. And the propagation speed of the jet in the second stage is on the order of several hundred m s−1, which is close to the velocity of gas flow. The spatial–temporal distributions of light emission show that high-energy electrons can only be observed during the jet propagation in the first stage, and low-energy electrons can be detected in both the first and second stages. The results show that the electric field plays an important role on the jet propagation in the first stage, and the jet propagation during the second stage is mainly promoted by the thermal gas expansion.

The scattering features of microwave (MW) by planar plasma layer, plasma column and plasma-column array under different parameters have been numerically studied by the finite-difference time-domain (FDTD) method. The effects of the plasma frequency and electron collision rate on MW's reflectance, transmittance and absorptance are examined. The results show that for the planar plasma layer, the electron collision plays an important role in MW absorption and the reduction of wave reflection. In the plasma column condition, strong scattering occurs in certain directions. The scattering pattern depends on the plasma frequency, electron collision rate and column radius. A collisional, non-planar shaped plasma object like the plasma-column array can reduce significantly the wave reflection comparing with the planar plasma layer.

The electrical and mechanical characteristics of the wire-to-plate surface dielectric barrier discharge and the induced ionic wind are investigated experimentally. The different temporal behaviors in positive and negative half-cycles are studied by time-resolved images. It is shown that the discharge and the light emission are generally stronger in the positive half cycle. The discharge is inhomogeneous and propagates in streamer mode; however, in the negative half-cycle, the discharge appears visually uniformly and operates in the diffuse mode. The surface discharge can produce ionic wind about several m/s above the dielectric surface. There exists an optimal width of the grounded electrode to produce a larger plasma area or active wind region. Increasing of the applied voltage or normalized dielectric constant leads to a larger wind velocity. The performance of ionic wind on flow control is visualized by employing a smoke stream.

In this work, striations in pulsed glow discharges are studied by experiments and Particle-In-Cell/Monte Carlo Collision (PIC/MCC) simulation. The spatio-temporal evolution of the potential and the electron energy during the discharge are analyzed. The processes of striation formation in pulsed glow discharges and dielectric barrier discharges (DBD) are compared. The results show that the mechanisms of striation in pulsed DC discharge and DBD are similar to each other. The evolution of electron energy distribution function before and after the striation formation indicates that the striation results from the potential well of the space charge. During a pulsed breakdown, the striations are formed one by one towards the anode in a weak field channel. This indicates that the formation of striations in a pulsed discharge depends on the flow of modulated electrons.

In this paper, the effects of electrode gap on the discharge characteristics in low-pressure argon radio frequency (RF) discharge with a hollow electrode were investigated by a two-dimensional particle-in-cell/MCC model. The results show that the time-averaged electric field, electron density, sheath potential drop, and sheath thickness change with the increasing electrode gap. It is also found that the electron density varies non-monotonically with the electrode gap increasing from 4 to 12 mm due to the different intensities of the hollow cathode effect (HCE) and electron heating at different electrode gaps. The axial sheath at the bottom of the hollow electrode is found to determine the depth of the plasma in the hole and can significantly modulate the intensities of the HCE and electron heating. With the reducing electrode gap, the hole of the hollow electrode is eventually filled with the sheath, and the bulk plasma region is compressed. The results indicate that a small electrode gap is not beneficial to obtain large area plasma with high density outside the hole. Altering the electrode gap can tailor the spatial distribution of the plasma in the RF discharge with a hollow electrode and obtain an optimal electron density.

The characteristics of electrons play a dominant role in determining the ionization and acceleration processes of plasmas. Compared with electrostatic diagnostics, the optical method is independent of the radio frequency (RF) noise, magnetic field, and electric field. In this paper, an optical emission spectroscope was used to determine the plasma emission spectra, electron excitation energy population distributions (EEEPDs), growth rates of low-energy and high-energy electrons, and their intensity jumps with input powers. The 56 emission lines with the highest signal-to-noise ratio and their corresponding electron excitation energy were used for the translation of the spectrum into EEEPD. One discrete EEEPD has two clear different regions, namely the low-energy electron excitation region (neutral lines with threshold energy of 13–15 eV) and the high-energy electron excitation region (ionic lines with threshold energy ≥19 eV). The EEEPD variations with different diameters of discharge tubes (20 mm, 40 mm, and 60 mm) and different input RF powers (200–1800 W) were investigated. By normalized intensity comparison of the ionic and neutral lines, the growth rate of the ionic population was higher than the neutral one, especially when the tube diameter was less than 40 mm and the input power was higher than 1000 W. Moreover, we found that the intensities of low-energy electrons and high-energy electrons jump at different input powers from inductively coupled (H) mode to helicon (W) mode; therefore, the determination of W mode needs to be carefully considered.

Coal dust diffusion during coal transportation and storage causes serious environmental pollution. The existing dust suppressant in previous studies was unable to achieve the expected effects owing to severe wind damage and rain erosion. Therefore, the current study synthesized and prepared an efficient and applicable dust suppressant for coal transportation and storage. Infrared spectroscopy and scanning electron microscope experiments were conducted during the synthesis to analyze the microstructure changes in the synthetic products. Moreover, viscosity was used as the evaluation index in the single-factor experiments to obtain the optimal synthesis conditions. Performance measurement results showed that the prepared dust suppressant had a strong protective effect on coal powder and could effectively resist the impact of wind damage and rain erosion. Compared with other dust suppressants, the proposed dust suppressant prepared showed more evident positive effects and longer lasting action time in the quantitative test. Moreover, the dried product could synergistically combust with coal powder, thereby possibly mitigating the tedious post-treatment process and increasing the utilization rate of resources.

In order to obtain a uniform large-area plasma jet at the atmospheric pressure, a new structure of coplanar dielectric barrier discharge (DBD) is proposed in this paper. The structure used in large-area DBD plasma jet consists of two coaxial annular dielectric tubes, and an alternating current electric field is applied by metal film electrodes outside the tubes to form dielectric barrier discharge in the air gap. Based on this configuration, a uniform annular jet is achieved, with diameter of 12 mm and thickness of 2–3 mm. The discharge characteristics of the proposed structure and the development process of plasma jet are studied. The spectra of the discharge, the electron temperature, the electron density, and the discharge waveforms are diagnosed. The results show that the physical characteristics of the large-area jet obtained in this work are basically the same as that of the traditional small-diameter DBD jet. It is considered that the physical mechanism of the large-area jet propagation is the mutual coupling propulsion process of a large number of positive corona discharges. The influence of electrode structure and air gap structure on the characteristics of the large-area DBD plasma jet is further studied by experiments, and the optimization principle of the large-area DBD plasma jet is proposed.

Large area uniform plasma sources, such as high-density magnetized inductively coupled plasma (ICP) and helicon plasma, have broad applications in industry. A comprehensive comparison of ICP and helicon plasma, excited by a single-loop antenna, is presented in this paper from the perspectives of mode transition, hysteresis behavior, and density distribution. The E-H mode transition in ICP and the E-H-W mode transition in helicon plasma are clearly observed in the experiments. Besides, the considerable variation of hysteresis behavior from inverse hysteresis to normal hysteresis by the influence of the magnetic field is explored. The bi-Maxwellian and Maxwellian electron energy distribution functions in each discharge are used to explain this phenomenon, which is essentially related to the transition from a nonlocal kinetic property to a local kinetic property of electrons. In addition, we notice that the plasma density, in the radial direction, is peaked in the center of the tube in ICP, but a complicated distribution is formed in helicon plasma. In the axial direction, the maximum plasma density is still in the center of the antenna in ICP, whereas the highest plasma density is located downstream, far away from the antenna, in helicon plasma. It is believed that the reflected electrons in the sheath and pre-sheath by the upper metallic endplate and downstream propagated helicon wave will be responsible for this plasma density profile in helicon plasma. Due to the constrained electron motion in the magnetic field, an extremely uniform density distribution will be obtained with an appropriate axial magnetic field in the wave discharge mode.