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For atmospheric argon RF dielectric barrier discharges, a self-consistent one-dimensional fluid model based on the drift-diffusive approximations of the particles is established to investigate the role of the neutral gas temperature on the discharge process and the plasma characteristics. A finite difference method is used to solve numerically the model, and the numerical results are obtained for the cases that the neutral gas temperature varies from 300 to 600 K. It shows that an increase in the neutral gas temperature causes a decrease in the ionization rate peak and a decrease in the plasma density, but the electric field and the electron temperature do not change very much. Moreover, the discharge mode transition from α mode to α-γ mode occurs because the growing ion flux induces more secondary electron flux, even if the ions entering the sheaths decrease. In addition, the ground state ionization and the ground state excitation are the main collisions in the argon discharges. When metastable atoms are focused on, the three-body quenching is also an important collision progress. [ABSTRACT FROM AUTHOR]

Radiative divertor is an effective method for the divertor heat flux control, but excessive core impurity radiation can deteriorate the confinement in tokamaks. In recent EAST experiments, the compatibility of divertor detachment and impurity control with good core confinement (H98,y2 ∼1) has been achieved simultaneously by combining an upstream deuterium (D2) puff and divertor argon (Ar) seeding. Both experimental and SOLPS-ITER modeling reveal that additional D2 puff can further mitigate the target heat load and facilitate the detachment. The SOLPS-ITER results also show that the D2 puff makes a limited contribution to the Ar line radiation but a significant contribution to the neutral radiation in the SOL and divertor regions. The physical mechanism behind the effect of the D2 puff on the Ar retention is also revealed by the modeling. The increase in the Ar velocity is the major reason for the improved Ar retention in the partial detachment state. The increase in vAr is mainly caused by the strengthening of frictional drag of D+, which is because the additional D2 puff increases the pressure gradient force (FPG) and the electric field force (FE) on D+. Further analysis reveals that in the deep detachment state, some other negative effects play a dominant role in determining the Ar retention, such as the shift of the region of the Ar+ ionization source, the decrease in the strength of the Ar+ ionization source, and the net force on the Ar ions near the target. [ABSTRACT FROM AUTHOR]

Numerical simulations of the interchange plasma turbulence in the presence of medium-Z impurities (N2, Ne, and Ar) seeding have been performed using BOUT++. These simulation results are used to study the impurity transport mechanism in the edge and scrape-off layer (SOL) regions. An analytical relation for the impurity ion density with the vorticity, sources and sinks, and mass to charge ratio has also been derived. Simulation shows that Ar+ moves more strongly inward compared to N+ and Ne+ that has been verified from the analytical relation. The most abundant species move in both the inward and outward directions, but on average, they mainly move outward. These behaviors have been confirmed using cross-correlation techniques. The inward transport or negative flux of the impurity ions is found directly associated with the monopolar density holes in the presence of the electron temperature gradient, whereas the outward transport is associated with the plasma blobs. The inward impurity transport has been analyzed using hole fraction analysis. The percentages of Ar+, Ne+, and N+ ions of their total impurity densities transported inward mainly through the avalanche events of the turbulent plasma are presented. [ABSTRACT FROM AUTHOR]

The results of the investigation of the breakdown characteristics of the planar "open" discharge and open discharge with the generation of counter-propagating electron beams under excitation by pulses with nanosecond rise fronts are presented. The amplitude parameters of current and voltage and temporal characteristics of breakdown in helium, neon, and argon were measured. It is demonstrated that the breakdown in the open discharge is characterized by considerably larger electric field strengths at the same development delays as in the avalanche discharge. A similarity criterion based on the photoemission mechanism of electron generation, according to which the discharge development delay is inversely proportional to the squared working gas pressure, is obtained. [ABSTRACT FROM AUTHOR]

Arc plasmas have promising applications in many fields, and exploring their properties is of interest. This research paper presents detailed pressure-based finite volume simulations of an argon arc. Simulations of the free-burning argon arc show good agreement with experiment. We observe an interesting phenomenon that an argon arc concentrates intensively in a high-frequency alternating longitudinal magnetic field. This is different from existing constricting mechanisms, as here the arc is pinched through continuous dynamic transitions between shrinking and expansion. The underlying mechanism is that via working together with an arc's motion inertia, the applied high-frequency alternating magnetic field is able to effectively play a "plasma trap" role, which leads the arc plasma to be confined to a narrower space. This finding may provide a new approach to constrict arc plasmas. [ABSTRACT FROM AUTHOR]

Population densities of excited states of argon atoms in a high power impulse magnetron sputtering (HiPIMS) discharge are examined using a global discharge model and a collisional-radiative model. Here, the ionization region model (IRM) and the Orsay Boltzmann equation for electrons coupled with ionization and excited states kinetics (OBELIX) model are combined to obtain the population densities of the excited levels of the argon atom in a HiPIMS discharge. The IRM is a global plasma chemistry model based on particle and energy conservation of HiPIMS discharges. OBELIX is a collisional-radiative model where the electron energy distribution is calculated self-consistently from an isotropic Boltzmann equation. The collisional model constitutes 65 individual and effective excited levels of the argon atom. We demonstrate that the reduced population density of high-lying excited argon states scales with (p *) − 6 , where p * is the effective quantum number, indicating the presence of a multistep ladder-like excitation scheme, also called an excitation saturation. The reason for this is the dominance of electron impact processes in the population and de-population of high-lying argon states in combination with a negligible electron–ion recombination. [ABSTRACT FROM AUTHOR]

Control of the hysteresis phenomenon in a high-pressure (250 mTorr) argon inductively coupled plasma was experimentally investigated by applying a DC magnetic field. Electron energy probability functions (EEPFs) were measured with and without DC magnetic fields to obtain electron densities. Without the magnetic field, a hysteresis loop is clearly observed during the E and H mode transitions, but surprisingly, when 20 G of DC magnetic field is applied, the hysteresis loop gets smaller, and it vanishes completely when the applied DC magnetic field is increased to over 40 G. Measured EEPFs show that there is a significant evolution of the EEPFs by DC magnetic field. The EEPF without magnetic field is a Druyvesteyn distribution, but evolves to a Maxwellian-like distribution under a strong DC magnetic field condition. This evolution of the EEPF causes significant reduction in the collisional energy loss εc in E-mode. The evolution of EEPFs is explained by a decrease in Ohmic power absorption of low-energy electrons and an increase in electron–electron collisions, and the vanishing of the hysteresis is explained by the suppression of nonlinear changes in EEPF and nonlinear changes in collisional energy loss. [ABSTRACT FROM AUTHOR]

A parametric study of the characteristics of coaxial dielectric barrier discharge sustained in atmospheric pressure argon is carried out. The numerical model is based on the drift-diffusion theory of gas discharges. The integral characteristics of the discharge, such as the root mean square of the discharge current, the period average dissipated power, and the efficiency of the power deposition, are explored in the parameter space spanned by the voltage amplitude and frequency of the applied AC field, the barrier dielectric constant, and the gas gap width. [ABSTRACT FROM AUTHOR]

A considerable difference in the breakdown potential of a uniform pressure gas (specifically argon) under an asymmetric non-uniform electric field is observed depending on the polarity of the field. The degree of variation in the breakdown potential between the two polarities can be explained if one assumes a strong variation of the ion-induced secondary electron emission coefficient with the magnitude of the reduced electric field at the cathode. The magnitude of the breakdown potential can be predicted by evaluating the breakdown criterion along multiple field lines if one includes a numerical factor to account for diffusion of electrons out of the preferred breakdown channel. [ABSTRACT FROM AUTHOR]

In this paper, a methodology is presented to compute the plasma properties (e.g.,, density and temperature) accounting for the dynamics of the excited states. The proposed strategy applies to both zero-dimensional (0D) models and multidimensional fluid and hybrid codes handling low-pressure (<50 mTorr) plasma discharges filled with argon, neon, krypton, and xenon gases. The paper focuses on two main aspects: (i) a lumping methodology is proposed to reduce the number of reactions and species considered in order to keep at bay the computational cost without a major loss of accuracy; (ii) the influence that different datasets of cross sections have on the results has been assessed. First, the lumping methodology has been implemented in a 0D model accounting for singly charged ions, neutrals, along with 1s and 2p excited states (Paschen notation). Metastable and resonant are treated as two separate species within the 1s energy level (1 s M and 1 s R , respectively). The results have been benchmarked against those obtained treating each energy level of the excited states as an individual species. Differences lower than 1% have been obtained. Second, the results of the 0D model have been compared against measurements of electron density and temperature performed on an inductively coupled plasma. Numerical predictions and experiments present a disagreement up to 20%–30%, which is comparable to the uncertainty band of the measurements. Finally, the lumping strategy has been implemented in a 2D fluid code to assess its computational affordability, and the results have been compared against the experiments as well. A variance up to 30% in electron density and temperature is registered adopting different datasets of cross sections. [ABSTRACT FROM AUTHOR]

Upon inclusion of collisions, the speed-limited particle-in-cell (SLPIC) simulation method successfully computed the Paschen curve for argon. The 1D3V simulations modeled an electron cascade across an argon-filled capacitor, including electron-neutral ionization, electron-neutral elastic collisions, electron-neutral excitation, and ion-induced secondary electron emission. In electrical breakdown, the timescale difference between ion and electron motion makes traditional PIC methods computationally slow. To decrease this timescale difference and speed up computation, we used SLPIC, a time-domain algorithm that limits the speed of the fastest electrons in the simulation. The SLPIC algorithm facilitates a straightforward, fully kinetic treatment of dynamics and collisions. SLPIC was as accurate as PIC, but ran up to 200 times faster. SLPIC accurately computed the Paschen curve for argon over three orders of magnitude in pressure. [ABSTRACT FROM AUTHOR]

A nanosecond pulsed atmospheric pressure dielectric barrier glow discharge in helium with 1% of argon was studied. The effects of the electric field, frequency, and gas mixture ratio on the temporal behavior of the plasma discharge were captured with an ICCD camera. Special interest was given to the timing and scale of the secondary or return stroke. It was found that the external electric field can control the occurrence of the return stroke in a dielectric barrier discharge. If the electric field is high enough, the return stroke occurs earlier than previously observed in other works. Increasing frequency leads to faster discharge initiation times for both the primary and secondary discharges. Increasing the argon ratio of the mixture leads to an increased intensity of the primary discharge, a decrease in the intensity of the secondary discharge, and a delay in the timing of the primary discharge. [ABSTRACT FROM AUTHOR]

An atmospheric argon discharge plasma was induced by a high-power microwave beam using a 28 GHz gyrotron and investigated at pressures of 40 kPa–100 kPa and Gaussian peak intensities of 0.115 GW/m2 (0.204 MV/cm) and 0.168 GW/m2 (0.246 MV/cm). According to high-speed imaging results, the propagation velocity of the discharge front increased with the backpressure to maintain a range of 600 m/s–1000 m/s. The propagation velocity was 25 times larger in argon than in air. Applying the collisional-radiative (CR) model to the spectroscopic results showed that the electron density increases with the pressure from 5.0 × 10 21 m − 3 at 40 kPa to 5. 0 × 10 22 m − 3 at 100 kPa and lies on the critical density curve. The electron temperature decreases as the background pressure increases from 2 eV to 0.5 eV, and the gas temperature was 300–400 K. According to CR analysis, the population densities of 3dn and 2sn excitation levels in the fast velocity condition are much lower than that in any other conditions. The results revealed that the energy transfer from electrons to ionized particles is more remarkable in the high background pressure and the fast velocity condition. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma (ICP) argon discharge with additional RF bias on the electrode is studied numerically and compared with experimental data. The role of ion inertia is shown by comparing the two numerical approaches: drift-diffusion approximation and a separate equation for ion momentum in the model. Two different discharge geometries are studied: simple cylindrical geometry and two chambers geometry with a downstream plasma. The difference in the calculated plasma density is shown for lower pressure values. Two approaches give similar results at a pressure of 100 mTorr. The downstream ICP discharge with an additional 12 MHz bias was calculated for the range of voltage amplitude from 20 to 215 V. The ion energy distribution function at the RF-biased electrode is calculated by the kinetic model. The results are compared with experimentally measured plasma density and ion energy spectra in the two-chamber discharge geometry. A good agreement was obtained between the calculated and experimental data. [ABSTRACT FROM AUTHOR]

A 1D radial diffusion model is developed to study the observed rapid expulsion of argon from the runaway electron plateau in the DIII-D tokamak following secondary massive low-Z ( D 2 or He) gas injection. The expulsion of argon is found to be caused by further cooling of the background plasma due to the added neutrals, accompanied by recombination of argon ions and the greatly increased outward radial transport rate of argon (now dominantly in neutral form) out of the runaway electron beam. After argon expulsion, power loss out of the runaway electron plateau is found to be dominated by neutral transport to the wall (rather than by radiation); this result resolves the power balance discrepancy highlighted in previous work on argon expulsion out of the runaway electron plateau. [ABSTRACT FROM AUTHOR]

The experiments demonstrated a strong dependence of the spatial structures of exploding aluminum wires on ambient pressures. Depending on whether having a current pause, electrical explosion of wires processes was classified into two types and analyzed by stage division. Through shadow, schlieren, and interference images, the spatial structures of exploding wires in two breakdown modes (internal and shunting) were observed. It was indicated that the basic difference is the relative positions of the wire core and the plasma channel. The breakdown mode makes a transition from the shunting mode to the internal mode with increasing pressures. Radial positions of the wire core boundary and the shockwave front were determined by comparing shadowgraphs and multi-frame photographs at different moments. The results demonstrated a gradual separation of the wire core and the shockwave, as well as their parabolic expansion trajectories. Furthermore, the average expansion velocity of wire cores decreases from ∼1.41 km/s to ∼0.78 km/s with the pressure varying from 50 kPa to 400 kPa. [ABSTRACT FROM AUTHOR]

A two-dimensional model is employed to investigate the evolution of radial discharge columns (or filamentary channels) and the potential mechanism in an atmospheric argon dielectric barrier discharge (DBD). As the applied voltage amplitude increases, the number of discharge columns first increases and then deceases, and finally, the discharge evolves into the diffuse mode. With a lower voltage amplitude range, the more uniform distribution of surface charge density makes the original discharge column move outwards, providing a wider inner space to increase the filament number. A similar filamentation process is also observed in atmospheric helium. However, when the voltage amplitude is further increased, considering the lower ionization threshold of argon, even the relatively small amount of residual electrons diffusing from filaments to adjacent regions can serve as seed electrons to activate the former inhibition positions, which makes the filament number further increase. Moreover, influenced by the stronger radial electric field between the central column and its neighborhoods, more electrons located at the column near the middle position will drift toward the center. As a result, once charged particles move over the inhibition region with voltage amplitude rising further, the two discrete discharge columns will merge, causing the decrease in the filament number. Finally, it is revealed in our simulations that when the voltage amplitude exceeds one certain level, seed electrons of the preionization stage get harder to gather and all discharge columns vanish. These results may help to provide a new perspective on the evolution of radial filamentary channels in an atmospheric argon DBD. [ABSTRACT FROM AUTHOR]

The results of experimental investigations of heavy noble gas breakdown thresholds in a focused beam of powerful subterahertz radiation are presented. The gas discharge, maintained by the powerful radiation of the terahertz frequency band, is a new specific object of gas discharge physics. This paper presents the experiments with pulsed gyrotrons capable of generating a power of 250 kW at a frequency of 250 GHz. The gyrotron wave beam was focused by means of quasioptical mirrors into the spot with a diameter less than 3 mm that provided intensity into the focal spot up to 3.5 MW/cm2. The achieved electrical field intensity was enough for gas breakdown into the range of pressure values of 1–1500 Torr for heavy noble gases (argon and krypton). The boundary values of field intensity for discharge existence were measured. Experimental data were compared to the analytical model of Raizer and Vyskrebentsev for monatomic gases. [ABSTRACT FROM AUTHOR]

In spite of its high cost, xenon gas is known as both the most efficient and commonly used propellant for plasma thrusters in space technologies. Argon, a gas by far less costly, is widely used in other technologies, but a much lower efficiency of ionization, as obtained for example in closed electron drift thrusters, prevents its use in R&D programs and development of space thrusters. This paper shows that a drastic increase in argon ionization can be obtained in a low power thruster when only a few percent of xenon are added in the argon flow. Besides the increase in the ion beam current in the plume generated by the thruster, a net increase in the ion kinetic energy is observed. These two features are of interest in terms of thrust efficiency. These results, obtained for a small size closed electron drift thruster, could be even more spectacular for higher power devices, suggesting further investigations for space propulsion and/or ion source applications. [ABSTRACT FROM AUTHOR]

Thermal modes of the argon inductively coupled plasma stream (13.56 MHz) were investigated with the respect to macroscopic parameters. The pressure in the vacuum chamber was varied from 10 to 80 Pa and the RF generator power from 500 to 2500 W. Thus, the radial temperature distribution in the stream was studied at different distances from the plasma torch. It was established that the temperature of the plasma-forming gas can reach 800 °C at the center of the stream and smoothly decreases to the periphery. Specific heat capacity and the heating rate of a two-phase, SiO2 based, glass-ceramic material were investigated in the plasma stream with different plasma parameters. [ABSTRACT FROM AUTHOR]

Experiments involving exploding aluminum wires immersed in argon gas and driven by a pulsed current source (in the microsecond time scale) were carried out in this work. Apart from electrical measurements, a multi-frame optical camera was used to observe the spatial and temporal distributions of the plasmas produced by the explosion. A time-integrated spectrometer and a photo-electric multiplier were used to analyze the light emitted from exploding aluminum wires. Electrical explosion of wires has been classified into three types according to current and voltage waveforms. By using photographic evidence and spectrum-based measurements, characteristics of the spatial and temporal distributions of the exploding wires associated with different experimental parameters were obtained and analyzed. Furthermore, the expansion trajectories of the exploding Al wires with different specific energy depositions are presented. It was found that more deposited energy leads to faster expansion velocities of the exploding products. [ABSTRACT FROM AUTHOR]

We develop two cascade arc plasma sources for application to plasma windows for virtual vacuum interfaces. For windowless vacuum–atmosphere separation, a compact arc discharge source having a channel diameter of 3 mm is fabricated, and an atmospheric Ar thermal plasma is generated. For an alternative differential pumping system, separating low- and high-pressure vacuum chambers, a larger arc device with an 8-mm diameter is also constructed, producing a high-density He plasma. The performances of the two cascade arcs as plasma windows are investigated. The 3-mm arc discharge generates a steep pressure gradient of Ar 100 kPa–100 Pa through the discharge channel, while the 8-mm discharge apparatus isolates the high-pressure side at 7 kPa from the lower pressure of 54 Pa. Emission spectroscopy of visible and vacuum UV radiation reveals the characteristics of the Ar and He plasmas. Spectral analysis yields a plasma temperature of around 1 eV in both discharges. Stark broadenings of the H-β and Ar I lines give an electron density of 6.5 × 1016 cm−3 for Ar 60 A with a gas flow rate of 1.0 l/min and 4.7 × 1013 cm−3 under a He 100-A and 0.45-l/min condition. [ABSTRACT FROM AUTHOR]

Effective transformation of moisture into hydrogen in argon containing 100% relative humidity employing dielectric barrier discharge cold plasma is reported. The coaxial reactor with a common outer Pyrex tube having an inner diameter of 14 mm accompanied by a central electrode combination is employed for H2 generation through water splitting. Three different central electrodes such as Pyrex (double dielectric surfaces), copper (Cu), and stainless steel (SS) [single dielectric (SD) surface] are used separately, investigating the H2 production efficiency with the variation of gas residence time (GRT), electric field, working frequency, electrode surface, and discharge gas-gap (GG). Optimal electric fields 3.5, 1.7, and 1.3 kV mm−1 at 14.5 kHz are required for the highest H2 production at 45 s GRT for Pyrex, SS, and Cu reactors, respectively. The utmost H2 productions 2500 and 4500 ppmv are observed with 100 mm long, 4 mm GG and 290 mm long, 2 mm GG Cu SD reactors, respectively. [ABSTRACT FROM AUTHOR]

By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (Te) and number density of argon metastable atoms [n(Arm)] were determined in argon-ethyl lactate dielectric barrier discharges. The influence of a square pulse power supply on Te, n(Arm), and discharge current is evaluated and correlated with the chemistry and the topography of plasma-deposited coatings. Pulsed discharges were found to have shorter (100 ns) but stronger (1 A) current peaks and higher electron temperatures (0.7 eV) than when using a 35 kHz sinusoidal power supply (2 μs, 30 mA, 0.3 eV). The n(Arm) values seemed to be rather stable around 1011 cm−3 with a sinus power supply. In contrast, with a pulse power supply with long time off (i.e., time without discharge) between each pulse, a progressive increase in n(Arm) from 1011 cm−3 up to 1012–1013 cm−3 was observed. When the time off was reduced, this increase was measured in sync with the current peak. The chemical composition of the coatings was not significantly affected by using a pulse signal, whereas the topography was strongly influenced and led to powder formations when reducing the time off. [ABSTRACT FROM AUTHOR]

Hall-effect thrusters (HETs) operated with xenon are one of the most commonly used electric propulsion technologies for a wide range of space missions, including drag compensation in low Earth orbit, station-keeping, and orbital insertion, as access to space becomes more affordable. Although anomalous electron transport, the electron drift instability (EDI), and secondary electron emission (SEE) have been studied experimentally and numerically in xenon-based HETs, the impact of alternative propellants is still poorly characterized. In this work, a two-dimensional particle-in-cell/Monte Carlo collision code is used to model the (r – θ) plane of a HET operated separately with four different noble gases: xenon, krypton, argon, and helium. Models for electron induced secondary electron emission (SEE) and dielectric walls are implemented in order to investigate the coupling between the propellant choice and the radial thruster walls. For all conditions and propellants studied, an EDI and enhanced electron cross-field transport are observed. The frequency of the instability, as well as the electron mobility, is compared with analytical expressions from a recently developed kinetic theory. Confirming this theory, it is shown that while the frequency of the EDI depends on the propellant mass, the electron mobility appears to be almost independent of the propellant choice. [ABSTRACT FROM AUTHOR]

The electronegativity of the A r − C O 2 gas mixture was investigated, and the total relative negative oxygen ion density O2− + O− in the bulk of a dc discharge has been determined employing Langmuir probe assisted laser photo-detachment. The relative electron density and absolute temperature were obtained for the mixture at discharge powers between 200 and 3000 mW and pressures between 0.2 and 0.6 mbar, employing the collisional radiative model for several Ar gas mixtures. The absolute metastable number density for 1s3 and 1s5 levels was measured, and both showed an increasing trend as a function of pressure and power. The absolute number density of the 1s5 level was found to be higher than that of the 1s3 level. Electronegativity was found to decrease as a function of power and as a function of the increasing Ar percentage in the gas mixture. [ABSTRACT FROM AUTHOR]

A diffuse argon plume at atmospheric pressure is generated downstream of a longitudinal slit jet equipped with a dielectric barrier discharge in a quadri-electrode configuration. Results indicate that both the plume length and the spectral line intensities increase with the increase in the peak voltage. With fast photography it is found that there is a clear difference for discharges with different polarities. The positive discharge is composed of nonuniform branching filaments; however, it is fairly uniform for the negative discharge. Due to the charge overflow of the intra-electrode discharge, the streamer mechanism is involved in the plume discharge. In fact, the positive discharge and the negative one correspond to a cathode-directed streamer and an anode-directed streamer, respectively. The formation mechanisms of the branching filaments and the diffuse background are discussed at last. [ABSTRACT FROM AUTHOR]

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas. [ABSTRACT FROM AUTHOR]

The tandem hollow cathode discharge, formulated by arranging two discharges in series, is an important method used to increase the irradiance of a hollow cathode discharge. In this paper, based on a two-dimensional fluid model we studied a five-layer tandem hollow cathode discharge, with three hollow electrodes stacked together and separated by the insulators to obtain the configuration of anode/insulator/cathode/insulator/anode from the top to the bottom. In the model, the thickness of both electrodes and insulators is set at 1 cm and the diameter of the hollow cavity is 2 cm. The pressure effect on the discharge properties is investigated with gas pressure ranges from 100 Pa to 5 kPa. The gap voltage first decreases, reaching a minimum sustaining voltage at 1 kPa, and then increases. Based on the two-dimensional electron density distributions, the discharges parameters (including the electron density, ion density, electric potential, and electric field) of one integrated hollow cathode discharge at 1 kPa and two relatively independent discharges at 100 Pa and 4 kPa are presented, respectively. The results indicate that the paralleled hollow cathode discharges can be manipulated into one integrated discharge with a higher plasma density by the monotonous control of gas pressure. [ABSTRACT FROM AUTHOR]

A needle-plate geometry is used to generate two barrier-discharge filaments composed of volume discharge and surface discharge in atmospheric pressure argon, interactions of which are investigated for the first time on the nanosecond timescale using an intensified charge-coupled device. The results indicate that the onset of volume discharges for the two filaments have a periodical discharge sequence, which implies interactions of the two filaments. Moreover, strong interactions of the two filaments are controlled through surface discharges, one of which is induced by that of the other filament during the positive discharge. Different from repulsive streamers, counter-propagating streamers are attractive between the two filaments. [ABSTRACT FROM AUTHOR]

Studies of a blast wave produced from carbon rods and plastic spheres in an argon background gas have been conducted using the Vulcan laser at the Rutherford Appleton Laboratory. A laser of 1500 J was focused onto these targets, and rear-side observations of an emission front were recorded using a fast-framing camera. The emission front is asymmetrical in shape and tends to a more symmetrical shape as it progresses due to the production of a second shock wave later in time, which pushes out the front of the blast wave. Plastic spheres produce faster blast waves, and the breakthrough of the second shock is visible before the shock stalls. The results are presented to demonstrate this trend, and similar evolution dynamics of experimental and simulation data from the FLASH radiation-hydrodynamics code are observed. [ABSTRACT FROM AUTHOR]

In this study, the processes of back diffusion in Ar subjected to crossed fields are analyzed by using the Monte Carlo simulation method in the E/N range of 50 to 500 Td (1 Td=1×10-17V cm2) for 0