Search

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse modulated 13.56 MHz radiofrequency (RF) power source. This helical structure is observed in open ambient air which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse modulated RF (2 kHz modulation frequency (fp)) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters viz., duty cycle (D), gas flow rate (Q), and RF power (P) of the modulated pulse on the formation of helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species (RONS)) as these are involved in increase in air entrainment into the ionization region desired for various plasma applications., 17 pages, 12 figures

The interaction between an argon plasma jet excited using microsecond duration voltage pulses and a liquid target was examined using Thomson scattering to quantify the temporal evolution of the electron density and temperature. The electrical resistance between a liquid target and the electrical ground was varied from 1 to $$680\, \text {k}\Omega $$ 680 k Ω to mimic different conductivity liquids while the influence of the varying electrical properties on the electron dynamics within the plasma were examined. It was demonstrated that the interaction between the plasma jet and a liquid target grounded via a high resistance resulted in typical dielectric barrier discharge behaviour, with two discharge events per applied voltage pulse. Under such conditions, the electron density and temperature reached a peak of $$1\cdot 10^{15}\, \text {cm}^{-3}$$ 1 · 10 15 cm - 3 and 3.4 eV, respectively; with both rapidly decaying over several hundreds of nanoseconds. For liquid targets grounded via a low resistance, the jet behaviour transitioned to a DC-like discharge, with a single breakdown event being observed and sustained throughout the duration of each applied voltage pulse. Under such conditions, electron densities of $$2{-}3 \cdot 10^{15}\, \text {cm}^{-3}$$ 2 - 3 · 10 15 cm - 3 were detected for several microseconds. The results demonstrate that the electron dynamics in a pulsed argon plasma jet are extremely sensitive to the electrical characteristics of the target, which in the case of water, can evolve during exposure to the plasma.

In this article, the investigation has been carried out for the characterization of the proposed tapered geometry of dielectric barrier discharge (DBD)-based cold atmospheric pressure plasma jet (C-APPJ) on the basis of optical emission spectroscopy (OES) and imaging for different operating parameters, such as argon gas flow rates, applied voltages, and frequencies. The detailed characteristics for the formation of the plasma plume using argon as a working gas have been presented for a wide range of flow rates [1–3 standard liter per minute (SLM)] and frequencies (15–25 kHz). Increasing the pulse frequency, the length and the diameter of the plasma plume increase, while the length of the plasma plume increases when increasing the gas flow rate up to 2 SLM. Time-integrated images have been captured using the intensified charge couple device (ICCD) camera, which illustrates that the plasma plume comprises different emission layers of definite patterns. The propagation dynamics and formation of different emission layers of the plasma plume have also been investigated using the COMSOL Multiphysics simulation. It has been observed that the local electric field of 6 kV/cm is responsible for the propagation of the plasma bullet and the generation of the electron with an average energy of ~9 eV. OES has also been performed to understand the plasma chemistry and identify the reactive species in the C-APPJ. The discharge analysis and characteristics performed through experiment and simulation would certainly be helpful for the design and development of C-APPJ sources.

To examine the influence of radiative transitions on the performance of nonequilibrium seed-free argon plasma magnetohydrodynamic (MHD) generators, we developed MHD numerical simulation technique with a collisional-radiative (C-R) model, where neutral argon atoms with 45 discrete effective electronic excitation levels, singly ionized argon ions, and free electrons were considered under a two-temperature, low-magnetic Reynolds number MHD approximation. Furthermore, a so-called escape factor was implemented in the C-R model to consider the effects of radiation trapping by ground-state neutral atoms. Using the developed technique, we computed the performance characteristics of a nonequilibrium seed-free argon plasma MHD generator. The numerical results showed that the generator performance gets higher as the escape factor decreases, i.e., the optical thickness for radiative transitions to the ground state of neutral atoms increases. The numerical results also suggested that when the escape factor is $1.0\times 10^{-3}$ or less, the generator performance is almost the same as that for the escape factor of 0 corresponding to completely optical-thick plasma case for the radiative transitions to the ground state of neutral atoms. Furthermore, realistic escape factor values for resonance lines in the power generation channel were evaluated using a well-known estimation model. Consequently, the estimated values had the order of $10^{-4}$ . We also showed that under such relatively optically thick plasma cases, a collisional (C) model and a widely used global ionization-recombination rate model with no explicit consideration of electronically excited-state neutral atoms can reproduce the generator performance predicted by the C-R model with relatively good accuracy.

In this article, the Vlasov–Maxwell equations have been integrated by the forward semi-Lagrangian method to compute the soft X-ray (SXR) emission from a dense plasma focus device filled with pure and impure argon. The impurity has been assumed as copper of which the electrodes were made. The results have shown that, in the case of pure argon, the emission power reached up to $3.5 \times 10^{9}{\mathrm {W}}$ . However, for the impurity with a 10% volumetric fraction and with the effective charge number of 10, the emission power reduced to $4\times 10^{5}{\mathrm {W}}$ . With the further increase in the impurity amount, the emission power reduced again. However, if the impurity charge number is close to the pure gas charge number, the attenuation of the SXR emission decreases.

In electrostatic tandem charged particle accelerators, gas stripping targets are used to convert negative ions into positive ones. Partial ionization of the gas by ions leads to the formation of an undesirable beam of stripping gas ions in the accelerating channels. In this work, the current of a beam of argon ions produced in a tandem accelerator with vacuum insulation was measured by mass spectroscopy. It is shown that the current of argon ions is 2000 times smaller than the current of the proton beam. The reliability of the measurements is provided by visualization of an argon ion beam on the surface of a lithium target and is also confirmed by an experiment with increased gas injection and an estimate of the possible contribution of the proton beam. It is shown that such a small value of the argon ion current does not pose a danger either as a source of additional heating of a lithium target, or as an additional load of a high-voltage power supply, and therefore does not require the previously proposed means for its suppression.

A high-efficiency microwave atmospheric pressure plasma jet (APPJ) has been developed in previous work. Long and stable plasma filament is excited directly in the open air with 2.45-GHz microwave power and double-channel argon flow by a double-coaxial structure. Unlike those plasma jets that strongly rely on a high flow rate to shape the plasma jet, this method produces a stable filamentous plasma jet at a low flow rate whose length and diameter are in a linear relationship with absorbed microwave power. This study aims to investigate the fundamental parameters of this special plasma filament under different power levels and gas flow rates by optical emission spectroscopy (OES), including the electron temperature and the spectrum. The electron temperature is determined to be 0.71–0.81 eV. It decreases slightly as the power increases, which is different from other high-voltage or radio frequency excited plasma jets under high power. The electron temperature does not change significantly with the change of microwave power and argon flow rate, more manifested as a change in the length, which indicates that this special plasma filament is related to the complex interaction of the microwave field and plasma. This study provides basic parameters for further investigation of this kind of plasma jet for theoretical and numerical simulation.

The purpose of this article is to study the influence of different powers, pressures, frequencies, and gases on the electron density distribution in special structures. A simulation model is established, and the electronic density in a special capacitance coupled plasma (CCP) device is calculated over the power range of 0–10 kW, pressure range of 0–50 Pa, and frequency range of 13.56–300 MHz. The results show that the power is a logarithmic function of the electron density in helium and argon plasmas, and the peak value for the electron density occurs in the diffusion region. At a certain power, collisions between particles increase with increasing pressure, which leads to an increase in electron density. However, the high electron density region in the helium plasma is concentrated near the electrode, while the high density region in the argon plasma moves from the center of the device to the electrode with increasing gas pressure. At the same time, the increase in the power frequency increases the ionization rate, and energy is transferred to the electrons, which increases the electron density. However, the rate of increase in the electron density decreases with increasing power frequency at the same voltage and pressure. With increasing power frequency, the 2-D electron density distribution in the argon and helium plasmas is found to vary in a similar way to that found for increasing pressure.

The laser intensity dependence of the recoil energies from the Coulomb explosion of small argon clusters has been investigated by resolving the contributions of the individual charge states to the ion recoil energy spectra. Between $10^{14}$ and $10^{15}$ W/cm$^2$ the high-energy tail of the ion energy spectra changes its shape and develops into the well-known knee feature, which results from the cluster size distribution, laser focal averaging, and ionization saturation. Resolving the contributions of the different charge states to the recoil energies, the experimental data reveal that the basic assumption of an exploding homogeneously charged sphere cannot be maintained in general. In fact, the energy spectra of the high-$q$ show distinct gaps in the yields at low kinetic energies, which hints at more complex radial ion charge distributions developing during the laser pulse impact., Comment: 15 pages, 5 figures

Emission spectra of argon behind the front of a strong shock wave are studied in the range of shock-wave velocities of 4.6–8.3 km/s and pressures before the wave front of 0.25–5.00 Torr. Time-integrated sweeps of radiation in a wide spectral range from the ultraviolet to infrared (190–1100 nm) and time dependences of the argon radiation intensity at wavelengths of 420, 532.8, and 740 nm are obtained. Three characteristic stages of the temporal evolution of the emission lines are defined. The dependences of the duration and intensity of the emission lines on the initial gas pressure and shock-wave velocity are established. Data are obtained on the background radiation intensity and can be used to separate the intensities of certain argon-atom lines from the total radiation.

We present the first space-borne observation of optical emissions of both neutral and ionized argon atoms resulting from a radio-frequency glow discharge (RF-GD) from a sounding rocket payload. The Observations of Electric-field Distributions in the Ionospheric Plasma — a Unique Strategy-C (OEDIPUS-C) payload was designed to separate into two sub-payloads on its up-leg. This separation permitted a number of two-point measurements, including those on radio wave propagation from the active dipole antennas on the upper sub-payload to the synchronized receiving dipoles on the lower sub-payload. A white-light video camera on the lower sub-payload recorded strong luminosity around the active dipoles during the first 15 s after sub-payload separation, when argon gas jets were providing propulsion to separate the two sub-payloads. Parts of the ejected argon appeared as a glowing volume where the large radio-frequency (RF) fields from the two active dipoles excited the optical emission, as the sub-payload separation increased from 2 to 55 m. The shape and intensity of the luminosity were well repeated as a function of the swept frequency (0.025–8.000 MHz), but their frequency dependences were distinctly different from those of sounder-accelerated electrons measured onboard, and deduced to result from the nonlinearity of the glow discharge. The observation is to our knowledge the first of its kind, and is interpreted in terms of a RF-GD energized by the strong near electric fields of the transmitting dipoles.

This article presents a systematic investigation on the behavior of electrons in the bullet in the Ar/H2O plasma jet in increasing the applied voltage and water vapor concentration based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte Carlo method. The scattering angle of the electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The following results are obtained. The evolution characteristic of the angle spectrum of electrons in the bullet in increasing the applied voltage is the same as that in increasing water vapor concentration, namely, the electrons scattered toward the target get increasingly less. When increasing the applied voltage, the OH density, the electron density, and the average electron energy $E_{\mathrm {ave}}$ increase. However, the increase in water vapor concentration leads to an evidently increasing OH density and a decrease in both the electron density and $E_{\mathrm {ave}}$ . In the range of electron scattering angles below 90° in the bullet, the percentage of electrons with energy above 3.27 eV (the threshold of inducing dissociative electron attachment to water molecule) increases with increasing applied voltage but presents a slight decrease in increasing water vapor concentration. The majority of electrons to most probably interact with the target are of energies higher than 3.27 eV. Finally, a notable effect of H2O admixture is that it gives rise to the decrease in not only $E_{\mathrm {ave}}$ but also the electron density in the bullet, especially the latter decreases evidently.

The characteristics of the electron beams emitted from the hydrogen ( $H$ ), nitrogen ( $N$ ), neon (Ne), and argon plasma pinches have been numerically investigated and compared by solving the Vlasov–Maxwell system with the forward semi-Lagrangian approach. Several outcomes have been obtained. For examples, it was found that, in the case of 1-mbar H, the electron current density reached a value of about $1.431\times 10^{9} \,\,\text {A}\cdot \text {m}^{-2}$ due to turbulence, while it reached ${2.554} \times {10}^{7} \,\,\text {A}\cdot \text {m}^{-2}$ due to other phenomena. For 2-mbar $N$ , the calculated voltage drops across the $m = 0$ regions ranged from about 817 kV to 4 MV. Among these gases, Ne had the biggest upstream emission current of about 9.7 kA, while $N$ emitted the least electron beam current of about 4.1 kA. Computations showed that the total charge delivered by each gas beam was of order 0.1 mC. The method of modeling, presented in this article, can be efficiently used to study the dynamics of a plasma pinch. Since the estimated electron beam currents for various gases are in good agreement with the measured ones, the proposed method can be used for designing the plasma focus devices for the electron beam source purpose.

This work is dedicated to a method for preionization of a laser medium (that is the most popular ones-CO2- and CO-lasers) using X-ray radiation created by a nanosecond sliding discharge (NSD). An experimental study has been carried out on the influence of the initial pressure and the composition of the gaseous medium on the intensity of X-ray bremsstrahlung. In order to estimate this intensity, a special sensor is used; it can measure free electron density that, in our, case is created during photoionization by X-ray radiation from an NSD. It is shown that in case an X-ray emitter is filled with argon, the photoelectron density in the vicinity of a cathode is about 15 times higher than in case the X-ray emitter is filled with helium. Moreover, when the gas volume of the X-ray emitter is filled with argon, the energy spectrum of the “runaway” electrons shifts to the region of lower values of their energy.

In this paper, the incorporation of auxiliary grids/electrodes into the design of the sputtering method is scrutinized by studying the impact of factors such as grid size, grid position, grid bias voltage, electrode sheath design, substrate bias voltage, reactive gas partial pressure, and magnetic trap configuration on the discharge condition and thin-film growth. In this regard, utilizing the updated Berg model for reactive sputtering, the authors obtained a formulation for the reactive grid-assisted sputtering. By the newly-developed formulation, the sputtering rate and the reactive gas partial pressure were simulated as a function of the reactive gas flow rate for various grid-to-target distances, argon partial pressures (0.67, 1.6, and 3.6 Pa), and discharge current densities (0.01, 0.015, and 0.02 A/cm2). According to the computation results, with a grid being utilized, the width of the hysteresis loops can be modified in a broader range by changing either the grid-to-target distance, the argon partial pressure, or the discharge current, resulting in better control over the deposition process. Moreover, the novel configuration of anode-spot-assisted sputtering was proposed to significantly ionize sputtered/neutral atoms near the substrate and to simultaneously deposit sputtered species and products produced as the direct result of introducing dust into the dense plasma. Finally, diverse configurations of the grid-assisted co-sputtering method were introduced for two prime purposes: deposition of composite films in any desired ratios of constituents without significantly changing the other co-sputtering parameters, and favorable alternation of a hysteresis loop for one of the guns at shared gas flow rates.

Typical ionization waves (IWs) are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets (APPJs) with argon flow, combining both the measurement of the axial electric field (Ez) and the temporal resolved optical imaging. The movement of the luminous APPJ head is recognized as the development of the IW front, accompanied with the propagation of the peak electric field. Especially, the radial distribution of Ez transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front. As for the temporal Ez trend, there is a mode transition from the single‐peak feature under a low peak voltage to the double‐peak feature under a higher peak voltage, indicating the existence of both primary and secondary IWs. The effect of target conditions on the IWs in APPJs is also explored. With a metal target, no residual electric field is observed before imposing the high‐voltage pulses. However, with a dielectric target, the residual surface charges generate a background electric field in the opposite direction to that during IW propagation. In the free APPJ (with no target), on the voltage falling edge, a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propagation on the voltage rising edge.

Atmospheric gas discharge is very likely to constrict into filaments and diffuse plasma formation is inefficient in most cases. Developing cost-efficient atmospheric diffuse plasma devices represents a significant challenge for high performance in biomedical decontamination and material processing. Here, we propose an alternative roadmap to produce a diffuse argon plasma jet by expanding and quenching the existing filamentary discharge at the initial or middle stage of streamer development. Possible mechanisms are summarized. With the gas flow velocity comparable to the ion drift one, enhancing ambipolar diffusion near the edge of the positive-streamer channel promotes the radial diffusion of newly-produced electrons, realizing the radial expansion of channel. Weakening electric field in front of the streamer head through head expansion and field offset, prevents the further development of streamer, leading to a positive-pseudo-streamer discharge. Reducing electric field in front of the negative-streamer head through ion compensation, impedes the initial growth of streamer, resulting in a negative pulseless glow discharge. The positive-pseudo-streamer and negative pulseless glow discharges function together to form the diffuse plasma jet. Streamer coupling theory is traditionally used to engineer the generation of diffuse plasmas in the regime preceding filamentary discharge, but this method remains inefficient. Here, an alternative route to cost-efficient diffuse plasma generation is proposed, involving the expansion and quenching of existing filamentary discharge.

The 6-D Vlasov–Maxwell equations in the cylindrical coordinates have been solved to calculate the electron beam emission from mixtures of argon and neon. The forward semi-Lagrangian approach was used for solutions. The simulation of the electron velocity field has shown that at the early stage of the pinch evolution of a 4-mbar 90% Ar–10% Ne mixture, the sausage instabilities began to develop from the top parts of the pinch due to bigger $B_{\theta }$ with respect to $B_{z}$ . In the turbulence regions, the electrons could accelerate up to speeds of $905 \times 10^{5}$ and $2387.5 \times 10^{5} \,\,{\text {m}}/{\text {s}}$ at 90.9 and 181.82 ns, respectively. It has been observed that in the high turbulence region, $E_{z}=-2.04\times {10}^{7}\,\,{\text {V}}/{\text {m}}$ , while in the weak turbulence region, $E_{z}=-1.46\times {10}^{7}\,\,\text {V}/{\text {m}}$ . Increasing the neon percentage in the mixture changed the turbulence regions and the upstream and downstream emissions.

The effects of the atomic number of the fill gas on hard x-ray and ion beam emission from a 2.2 kJ plasma focus were studied. Hydrogen, Nitrogen and Argon gases were used in the experiment. The ano...

The recently constructed cryogenic cylindrical ion trap velocity map imaging spectrometer (CIT-VMI) has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic species. The prepared ions are cooled down in a home-made cryogenic cylindrical ion trap and then extracted for photodissociation experiments. With the newly designed electric fields for extraction and acceleration, the ion beam can be accelerated to more than 4500 eV, which is necessary for velocity imaging of the neutral photofragments by using the position-sensitive imaging detector. The setup has been tested by the 355 nm photodissociation dynamics of the argon dimer cation (Ar \begin{document}$_2$\end{document} \begin{document}$^+$\end{document} ). From the recorded experimental images of both neutral Ar and ionic Ar \begin{document}$^+$\end{document} fragments, we interpret velocity resolutions of \begin{document}$\Delta v/v$\end{document} \begin{document}$\approx$\end{document} 4.6% for neutral fragments, and \begin{document}$\Delta v/v$\end{document} \begin{document}$\approx$\end{document} 1.5% for ionic fragments, respectively.

We report on results of investigation into the structure of a plasma jet generated by a coaxial plasma accelerator with conical insert in the discharge formation region. Using high-speed optoelectronic camera, we detected an inhomogeneous structure of glowing fractions of argon and deuterium jets. It was found that the jet radiation intensity oscillates with a characteristic frequency of 0.3–0.9 MHz. The argon plasma jet consisted of fragments diverging from the axis; plasma recombined 20 μs after the beginning of the discharge. The deuterium plasma jet resembled flakes. Its radiation intensity decreased significantly by 8 μs. The characteristic frequencies of radiation nonuniformities on the jet axis were about 0.09 cm–1 for argon and 0.3 cm–1 for deuterium. Analysis of the behavior of the discharge in the plasma accelerator revealed that a diffuse discharge was initiated at the base of the conical insert. After 0.5 μs, the discharge emerged at the outer boundary of the insert, was contracted, and occurred between central and external electrodes. The emergence of the discharge from the accelerator was observed 3 μs later and was accompanied with a glow of the end face of the central electrode. In the measurements of temperature of the lateral surface of external electrode using an infrared camera, it was found that heating is localized near the edge of conical insert and at the outlet of the accelerator. Results of investigations can be used for gas ionization, material irradiation, and simulation of interaction of plasma flows with the magnetic field in the outer space in laboratory conditions.

CO2 gas is being considered as one of the potential plasma forming gases in plasma arc material processes due to its thermophysical properties, cost, and easy availability. The understanding of the thermal behavior of CO2 plasma arc is essential for an effective utilization of it. However, the studies on CO2 arc characteristics are scanty. In this study, a 2-D axisymmetric model is built for the simulation of CO2 and Ar arcs with and without evaporation of anode. The thermal characteristics of CO2 arc are compared with those of Ar arc at different arc currents and anode materials. CO2 arc possesses higher temperature compared to Ar arc and the arc current strongly influences the temperature of CO2 arc. The anode flux in CO2 arc is higher compared to that of Ar arc and the effects of arc current and nature of the anode material on the same are stronger in CO2 arc. The arc heating efficiency in CO2 is higher than that in Ar and it reduces with increasing arc current.

The electron temperature and the density of argon arc plasma plume injected into water were observed through optical emission spectroscopic measurement. Argon arc plasma jets were generated with a DC arc current of 40–200 A by a non‐transferred arc discharge plasma torch under atmospheric pressure, and ejected through a nozzle on the anode into water or gas‐phase argon. The electron temperature of the plasma plume was determined by the Boltzmann plot with line intensity measurement of atomic argon lines, while the electron density is examined with the Stark broadening measurement of Hα line. It was found that the electron temperature increased from approximately 6500–8000 K, and the electron density also increased up to the order of 10^{16}cm^{−3}, as the discharge current increased for the underwater argon arc plasma plume, both of which were observed at 20 mm in the downward direction from the plasma generator nozzle. In addition, the electron temperature of the underwater plasma plume was slightly lower than that of the gas‐phase argon plasma plume, while the electron density of the underwater plasma was slightly higher than that of the gas‐phase plume. Longitudinal variation of the electron temperature and density of the underwater plasma plume was also observed, and the lowering rate was found to depend on the arc discharge current.

The results of modeling a nanosecond discharge in a uniform electric field in argon at atmospheric pressure based on two kinetic models are compared: with one and with six excited states, respectively. The analysis of the development of ionization waves in a centimeter gap in a two-dimensional axisymmetric geometry is performed. It is shown that the obtained result is influenced by the choice of the transport cross-section of electron scattering on the argon atom. The electric field strengths, charged particle concentrations, and velocities of cathode- and anode-directed ionization waves at different time points are compared.

In this work, the rotational temperatures of the atmospheric pressure AC-excited argon gas-liquid-phase discharge estimated by employing disparate spectroscopic methods on the rotational structure of molecular OH (A–X), NO- $\gamma $ (A–X), and N2 (C–B) bands-spectra emanating from the gas-phase discharge region were compared with those obtained from the liquid-phase region to analyze their variations based on the metastable species and rotational quantum numbers. The electrical characteristics and images of the discharge were also examined to analyze the discharge nature. Realization of the estimated values for rotational temperatures, as an estimation of the gas temperature, depend on thermalization of the accounted excited rotational population levels. Excitations to higher rotational quantum numbers ( ${N}'$ ) inhibited thermalization of the rotational distributions, and the rotational temperatures were found to increase proportionally with excitations to higher ${N}'$ numbers. The phenomenon of rotational excitation to higher ${N}'$ numbers was particularly prominent for the wet discharge region, and thus, substantially higher rotational temperatures were obtained. The excitation to higher ${N}'$ numbers is related to the basic production processes largely those involving $\textrm {Ar}_{\textrm {meta}}^{\ast } $ and N2 (A) metastable states that populate predominantly the levels with large ${N}'$ numbers (e.g., ${N}'=8$ and ${N}'=25$ , respectively for OH and NO), and thus, their contemplated rotational population is not indicative of the kinetic gas temperature. With respect to spectral diagnostics techniques, the Boltzmann plot constructed by adopting a unique single fitting model (compared to the conventional double fitting models approach used for liquid discharges) only calculating the rotational population of the $Q_{1}$ branch of OH (A–X) for lower ${N}'$ numbers ( ${N}'\le 4$ ) affords the opportunity to estimate the gas temperature in wet plasma discharge.

We report thermometry and new Raman linewidth data using a novel method for time-domain rotational coherent anti-Stokes Raman spectroscopy (RCARS) on single-shot basis. The coherences are generated by two fs pulses and probed by a ns pulse. The resulting signal is detected using a combined spectrograph/streak camera setup with high spectral and temporal resolution. Rotational CARS spectrograms of nitrogen (N2), ethylene (C2H4), ethane (C2H6), and argon (Ar) are demonstrated at ambient condition. Self-broadened N2–N2 S-branch Raman linewidths were measured on single-shot basis and show excellent agreement with literature values. Furthermore, Raman linewidths of N2 S-branch perturbed by C2H4 and C2H6 were measured for the first time. The time-resolved approach was also utilized to separate complex spectra from a mixture of species through their difference in coherence lifetimes. Since the Raman coherences decay much faster for both ethane and ethylene than for nitrogen, pure nitrogen spectra could be obtained by analyzing only the temporal tail of the signal. Moreover, a model for time-resolved RCARS of N2 was developed, which employs the single-shot measured Raman linewidths to calculate the corresponding spectro-temporally resolved spectrograms at different temperatures. The model was used to evaluate the temperature from single-shot data of an N2/C2H6 mixture, showing very high accuracy. The demonstrated method constitutes an essential improvement for single-shot thermometry as it does not require pre-knowledge about collider species concentrations and their impact on linewidths.

The effect of a shock wave on the temperature of plasma electrons of the positive discharge column in argon is simulated. A one-dimensional hydrodynamic model of a gas discharge plasma along with a formula for the relationship between the relative electron temperature and the reduced electric field strength has been used. The distribution of the electron temperature in the shock wave has been obtained and the effect of the shock wave intensity has been estimated. The simulation results were compared with the experimental data.

We present triple-differential cross section results for the positron and electron induced single ionization of the Ar (3p) and Ar (3s) atoms at incident energy 1 keV. The triple-differential cross sections (TDCSs) have been calculated in the modified distorted wave formalism using the second Born approximation. The TDCSs have been calculated in coplanar asymmetric geometry for different kinematical conditions. The second Born term has been found to be significant in obtaining the TDCS for electron as well as positron impact at smaller values of momentum transfer and it produces better agreement with the recent available measurements for Ar (3p). With the increase of momentum transfer, the dominance of binary emission of electrons has been found to increase for the positron impact ionization of Ar (3s).

In the subthreshold microwave discharge (the wavelength of 4 mm) in argon at the pressure of 750 Torr at intensities of the wave beam from 3 to 7.8 kW/cm2, the velocity of the ionization front, measured from the phase change of the reflected wave, increases approximately as the intensity on the wave beam axis in the power of 3/2 from 0.5 × 105 to 2.9 × 105 cm/s. This velocity of the discharge front in argon is 20–30 times higher than the velocity of the discharge front in air at the same intensities in the microwave beam. The glow structure of the discharge at intensities higher than 3 kW/cm2 is similar to the glow structure in molecular gases. An even finer structure of the discharge is observed at glow intensities on the wave beam axis below 3 kW/cm2. The gas temperature in the discharge at radiation intensity of 6 kW/cm2 is 6 kK. It is concluded that the volume of high-temperature regions in the discharge is 0.01 of the volume of the discharge region. The problem of the mechanism of the argon ionization and the possibility of the development of ionization-overheating instability in a non-self-sustained microwave discharge in the UV halo of the discharge front are discussed.

In this paper, the effect of feeding gas type on the dynamics of channel spark pulsed electron deposition system is investigated. Electrical, magnetic, and optical characterisations of the system were measured for different feeding gases, oxygen (O2), nitrogen (N2), and argon (Ar). The discharge current for each gas type was measured with maximum value of 1189 A for O2 at -13 kV applied voltage. The discharge current and voltage waveforms were simulated by LRC circuit theory. Effect of gas pressure on the maximum discharge current and total inductance was also investigated. The beam current investigated by faraday cup and reached maximum electron beam current of 136 A for O2 gas. Two magnetic pickup coils were employed for the measurements of beam kinetic dynamics and the measured beam speed was around 0.4× 106 m/sec. Electron beam plasma density was calculated from faraday cup and magnetic coils signals and found to be 1.96×1020 m-3. Optical emission spectra were also measured to identify reactive species and its role in electron beam interaction with graphite target for thin film deposition application. The ability of using the system for thin film deposition is demonstrated by depositing amorphous hydrogenated carbon (a-C:H) films over silicon substrates.

Particle-induced gamma-ray emission spectroscopy is a quantitative, sensitive technique that measures light element abundance in materials using external reference standards with known beam energy and intensity. When the ion beam is used ex vacuo, gamma-ray spectroscopy on targets in air greatly increases sample throughput. However, for most targets the accuracy of these measurements is limited by the uncertainty of the collected charge. An indirect beam current measurement technique has been developed using an ion beam reaction on atmospheric argon, the only atmospheric component with sufficient abundance (~1%) that produces abundant gamma rays with low-energy proton beams. The 40Ar(p,nγ)40K reaction has been studied here, and the characteristic 770 keV gamma ray is observed to serve as a reliable monitor for proton flux. This method allows a real-time calibration of beam intensity on target to measured upstream currents for ion beam analysis at beam energies above 3.5 MeV.

During the approximation of kinetic energy transfer in collision cascades, a numerical estimate of the sputtering coefficient of the copper anode of a magnetron is considered. It has been shown that when a 1–10 keV ion beam is injected into a magnetron, the sputtering coefficient of the copper anode of the magnetron is three to six atoms per incident ion, which makes it possible to introduce and control impurities, in particular copper, under conditions of synthesis of superhard TiN–Cu coatings by reactive magnetron sputtering and directed action on the nanocrystalline structure of the coatings with high accuracy and in small fractional ratios (units of at %).

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.

Plasma was generated in the focal region of a multikilowatt, 4.7-GHz continuous-wave (CW) microwave beam far removed from the walls of the vacuum chamber, minimizing the nonideal effects associated with plasma–wall and beam–wall interactions. Experiments were conducted with gas mixtures of argon, nitrogen, and oxygen at gas pressures ranging from 100 to 200 mtorr. Three types of discharges were observed during these experiments: unstable, quasi-stable, and stable discharges. It was determined that the stability of the discharges could be controlled through adjustments of the gas composition, gas pressure, and power of the microwave beam. This article reports on the operational conditions in which stable discharges were achieved and the general behavior of these discharges as the control parameters were varied.

This article presents a comparative investigation on behaviors of electrons in the Ar and He plasma jets by means of the numerical simulation based on a typical needle-plate discharge configuration with positive applied pulsed voltage and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. Emphasis is placed on the electrons in the bullet in the jets. In Ar, the bullet velocity is low and the electron density in the bullet is high, compared to He. In He, the energy spectrum of electrons (ESEs) in the bullet is of a low peak and a wide distribution, and the corresponding average electron energy is evidently high, contrary to Ar. The reason for this evident difference is mainly due to their different excitation energies and ionization energies as well as their different cross sections. In Ar and He, two electron densities $N_{e}$ and $N_{\mathrm {ext}}$ in the bullet have been calculated. The former is the electron density in the bullet and the latter refers to a density of electrons in the bullet with energy above the lowest excitation threshold inducing the dissociative electron attachment (DEA) to water molecules. Consequently, not only $N_{e}$ but also $N_{\mathrm {ext}}$ in Ar is higher than in He, meaning more generation of reactive species in aqueous solution via DEA mechanism. The ESEs in the bullet in Ar are more sensitive to the applied voltage amplitude than in He, thus in Ar, the increase in the applied voltage amplitude induces more evident increase in the average electron energy in the bullet than in He.

A universal analytical model is proposed for calculating coefficients γ of broadening of absorption lines of the H2S molecule by inert gas atoms A (helium, neon, argon, krypton, and xenon). In this model, only one parameter depends on the broadening atom A; other parameters are common for all atoms. This parameter determines the ratio γ(A)/γ(A′) for the A and A′ atoms. The model parameters are determined from values of γ calculated for the fundamental bands ν1, ν2, and ν3 of the H2S molecule, as well as from known experimental values of γ. Values of γ calculated using the model are compared with available experimental data. For some lines from the ν1 and ν3 bands, there is a significant discrepancy between the experiment and calculation.

Electrons are generated abundantly in the plasma jet and play an active role in the mass transfer of reactive species in the aqueous solution in plasma medicine. Such an importance requires knowledge of the behavior of electrons in the plasma jet. The objective of this work is to understand the electron behaviors in the bullet in the plasma jet, including the angle spectrum of electrons (ASEs) and the related energy spectrum, so as to have an insight into those electrons which most probably interact with the target. The numerical modeling based on a needle–plate discharge configuration in conjunction with a 1-D Particle-in-Cell Monte-Carlo Collision (PIC-MCC) simulation method was used to achieve this task. The scattering angle of electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The ASE in the bullet is close to a sinusoidal distribution. As the bullet propagates, the temporal evolution of ASE indicates that relatively more electrons in the bullet are scattered into the angle range below 90°, but at any moment when the propagating bullet is close to the target, ASE in the bullet generally remains unchanged. In addition, relatively less electrons in the bullet are scattered into the angle range below 90° due to the increase of the applied voltage amplitude. For the considered voltage amplitudes below 7 kV, the number of electrons in the angle range below 90° is within 47% of electrons in the bullet and, in these electrons, the proportion of non-subionization electrons reaches about 12%. These results may be taken into consideration in investigating the mass transfer of reactive species in plasma medicine.

In this paper, the irradiation of porous silicon with Ar $${}^{+}$$ ions with the energies of 100 and 200 keV and fluences from $$10^{12}$$ cm $${}^{-2}$$ up to $$3\times 10^{13}$$ cm $${}^{-2}$$ has been performed and studied. The effect of ion irradiation at different fluences and energies of incident particles on the photoluminescence spectrum of porous silicon has been analyzed. It has been shown that ion irradiation leads to a shift of the photoluminescence maximum, which grows with increasing energy. An increase in the fluence reduces the photoluminescence intensity, but, at the same time, has no effect on the magnitude of the maximum shift. The main mechanisms of the photoluminescence in porous silicon are also discussed.

The results of experimental study and modeling of the evolution of the Si profile of comb-like nanostructures during low energy (Ei ~ 100 eV) sputtering in an Ar plasma of RF discharge are presented. Simulation is performed depending on the Si–Si sticking coefficients, taking into account the angular dependence of the output of sputtered Si atoms. The results of the numerical simulation are in good agreement with the experiment with a sticking coefficient of Si atoms equal to 0.9–1 and an angular yield function of sputtered Si atoms close to the cos0.1 (x) distribution. From the simulation data of the test structures, the dependence of the Si atomic yield coefficient on the angle of incidence of Ar+ ions is determined. The maximum of this function is at an angle of ~65° relative to the surface normal. The dependence of the sputtering coefficient of Si at Ar+ ions on the energy of ions on a flat surface in the range of 50–200 eV is experimentally determined.

A 2D two-temperature chemical non-equilibrium model has been developed to investigate the plasma characteristics inside a DC arc plasma torch of argon. In this study the chemical kinetic model is carefully examined in order to properly capture the spatial variations of plasma characteristics, especially near the electrodes and arc fringe, where large gradients of plasma parameters exist. Two different sets of chemical kinetic processes are adopted in the calculation. The first chemical kinetic model [model (a)] includes the ground-state argon atoms, excited argon 4s state, atomic ions, molecular ions, and electrons, while the second model [model (b)] only considers the ground-state argon atoms, excited argon 4s state, atomic ions, and electrons. The predicted exit temperature and arc voltage by model (a) are in better agreement with experimental measurements. A delayed anode attachment with a higher arc voltage occurs in model (a) due to the low electron density in the upstream region of arc-anode attachment. Compared with the wide arc-anode attachment zone of model (b), model (a) exhibits a more constricted anode arc root with higher current density, which leads to a higher heat flux and temperature on the anode. This phenomenon may be explained by the rapid loss of electrons outside the arc-anode attachment zone due to the dissociative recombination of argon molecular ions. Moreover, model (a) produces a longer arc column with slightly higher maximum temperature and velocity on the axis, which is caused by its larger input energy.

In a tokamak, the poloidal magnetic field provided by the toroidal plasma current forms an essential part of the magnetic field confining the plasma. However, instabilities of magnetohydrodynamic equilibrium can lead to an uncontrolled sudden loss of plasma current and energy, which is called a disruption. Disruptions are of significant concern to future devices due to the large amount of energy released during the rapid quenching of the plasma. One important consequence of disruption is the generation of significant current carried in multi-MeV runaway electrons that are eventually lost into plasma components. They can damage the tokamak walls and its structure if they are not controlled. Disruption control by neutral beam injection has been performed on IR-T1 to study the effect on runaway electron generated by plasma disruptions. Noble gases are used for injection, pure Hydrogen, Helium and Argon. The use of these non-reactive gases for disruption control ensures they fast removed from the vessel after the termination of a tokamak discharge. A piezo-valve is used for injection which has the precision of 1 ms. The effect of runaway electron generation control during disruption is studied using a comparison between reference disruptive discharge and a discharge into which different impurity species are injected. The data collected can then be used to optimize the performance of these energetic electrons control generated in disruption.

A steady-state kinetic model of argon–helium high-pressure radio frequency dielectric barrier discharge is developed using a simplified reaction rate package appropriate for pressures ranging from 200 to 500 torr. Electron production and loss rates are analyzed as a function of pressure and Ar–He mixture, highlighting the importance of the Ar2* dimer for higher pressures and Ar rich mixtures. As pressure increases, the primary ionization mechanism shifts between ionization of ground state Ar to dimer ionization, which affects the steady-state reduced electric field due to the electron energy required for the two dominant ionization mechanisms. The resulting reduced electric field profile controls the metastable Ar(1s5) production, which, combined with the Ar(1s5) loss rates, reveals the metastable density as a function of pressure and Ar-fraction. This simplified 0-D steady-state model shows close agreement with previous time-dependent simulations using a robust reaction rate package.

IR laser radiation of XeI atoms in the range of 1700–2050 nm is obtained for the first time upon the pumping of xenon and mixtures of it with helium and argon by a pulsed longitudinal induction discharge. The spectrum of generation consists of two lines with wavelengths of 1733 nm and 2026 nm. The half-amplitude duration of the optical radiation is 60 ± 2 ns (FWHM).

The limiting mode of the generation of low-frequency torsional whistlers is obtained for the first time. Laser plasma clouds create only weak whistlers in a weakly magnetized laboratory plasma (argon), allowing the whistler magnetic field to reach record values of ~25% of the background magnetic field.

The potential energy of the atom–atom interaction, taking into account the Pauli principle, is constructed for atomic potentials that were chosen in the Moliere approximation. It is shown that the potential energy of interaction between neon atoms and argon atoms lies above the experimental data, and that between krypton atoms and xenon atoms lies below the experimental data. It is shown that at large distances between xenon atoms the potential interaction energy satisfactorily agrees with the results of calculation by the density functional method, and at small distances between atoms the shielding function of the potential interaction energy lies below that of the Ziegler–Biersack—Littmark (ZBL) potential.

The results of experimental studies of the effect of pumping conditions on the spectral and temporal characteristics of IR Ar I laser radiation under excitation of the active medium by longitudinal pulsed inductive discharge are presented. The lasing was obtained at transitions of neutral argon atoms at wavelengths of 1213, 1240, 1270, 1694, and 1791 nm in pure argon and in its two-component mixtures with helium and neon. The optical pulse length at half maximum was (5 ± 1) ns. The radiation energy attained 0.1 mJ.

Atmospheric pressure plasmas produced by a dielectric barrier discharge in a gas atmosphere of Ar and Ar/CO2 have been numerically investigated. A 1-D plasma discharge and a chemical 0-D model have been coupled. The simulation results for the electric current are benchmarked against experimental results. Impurities seem to affect the discharge characteristics significantly. First, impurities are able to “quench” and reduce the amount of metastables, decreasing the Penning ionization. The deactivation of the Penning ionization from the model leads to a transitory state between glow and filamentary discharges, i.e., pseudoglow discharge, in the gas atmosphere of Ar/CO2. Second, the addition of electronegative impurities to the model, namely, oxygen, lead to relevant changes in the electron density and the electric current, matching the experimental current in an improved way. The reactive species O and O3 reach a maximum in their number density during the first minute of operation, undergoing a reduction of at least one order of magnitude in the following minutes. This behavior corresponds well with the observed effects of Ar/CO2 plasma on $Photobacterium~ phosphoreum$ bacteria.

The main results of a completed cycle of complex studies of a strongly coupled dusty plasma conducted in the unique, experimental Plasma Crystal-3 Plus space laboratory that operated on the International Space Station are discussed. The experiments on the physics of phenomena in the dusty plasma are analyzed. A new state of dusty plasma, the electrorheological plasma, in which there is a transition from an isotropic plasma-dusty liquid to an anisotropic state, is studied. The study of the interpenetration of particles streams of various diameters, a nonequilibrium transition, is described. Experimental studies of the liquid–crystal phase transition in a three-dimensional dusty plasma system in which it is established that the dust component is compressed and crystallized upon a decrease in the neutral gas pressure are discussed. The nearly free motion of large particles in the volume of a plasma crystal, a nonviscous, irrotational flow about a large particle by a “liquid” of small dust particles, is analyzed. An experimental study of the dynamics of the crystallization of three-dimensional plasma-dust systems at a constant argon pressure under the effect of a low-frequency, alternating electric field and without its influence under microgravity conditions is described. The formation of the crystallization front and its propagation in the three-dimensional plasma-dust system with a velocity on the order of the average interparticle distance per second were discovered.