Plasma Stream Research Articles

Formation of nitrogen oxides from atmospheric electrodeless microwave plasmas in nitrogen–oxygen mixtures

Electrodeless microwave plasmas were produced in nitrogen–oxygen mixtures at atmospheric pressure to investigate the formation of nitrogen oxides (NOx) from the plasma. The oxygen content in the mixtures is varied in the range of 1%–3%, and the total flowrate is varied in the range of 25–45 slpm while the microwave power is fixed at 2 kW. The rotational and vibrational temperatures of the plasma are measured based on plasma optical emission spectroscopy, and the amount of NOx is measured using a NOx analyzer far downstream from the plasma. The temperatures at the plasma region reach ∼6700 K, and little difference is observed between the rotational and vibrational temperatures as a result of fast vibrational–translational relaxation. Moreover, these temperatures are found to be independent of the flowrate. As the flowrate decreases and the oxygen content in the mixture increases, the level of NOx is increased from 1612 ppm to 9380 ppm. For detailed investigation, plasma kinetic simulations considering trans-rotational, vibrational, and electron temperatures separately are developed and conducted for the plasma region. The level of NOx from the kinetic simulations is found to be considerably smaller than that measured. As the equilibrium mole fraction of NOx is the highest at a temperature of 3120 ± 100 K, with the variation attributable to the composition of species, significant production of NOx is expected to occur at the post-plasma region when the plasma stream is quenched by mixing with the surrounding flow.

Novel test-bed facility for PSI issues in fusion reactor conditions on the base of next generation QSPA plasma accelerator

In this report a concept of a new generation QSPA with external B-field up to 2 T has been discussed. A novel test-bed facility, which was recently constructed in Kharkov IPP NSC KIPT, has been described. It allows for a new level of plasma stream parameters and its wide variation in new QSPA-M device, as well as possible combination of steady-state and pulsed plasma loads to the materials during the exposures. First plasma is recently obtained. Careful optimization of the operational regimes of the plasma accelerator’s functional components and plasma dynamics in the magnetic system of QSPA-M device has started approaching step by step the necessary level of plasma parameters and their effective variation. The relevant results on plasma stream characterization are presented. Energy density distributions in plasma stream have been measured with calorimetry. Spectroscopy and probe technique have also been applied for plasma parameters measurements. The obtained results demonstrate the ability of QSPA-M to reproduce the ELM impacts in fusion reactor, both in terms of heat load and particle flux to the surface.

Identifying the linear phase of the relativistic Kelvin-Helmholtz instability and measuring its growth rate via radiation.

For the relativistic Kelvin-Helmholtz instability (KHI), which occurs at shear interfaces between two plasma streams, we report results on the polarized radiation over all observation directions and frequencies emitted by the plasma electrons from ab initio kinetic simulations. We find the polarization of the radiation to provide a clear signature for distinguishing the linear phase of the KHI from its other phases. During the linear phase, we predict the growth rate of the KHI radiation power to match the growth rate of the KHI to a high degree. Our predictions are based on a model of the vortex dynamics, which describes the electron motion in the vicinity of the shear interface between the two streams. Albeit the complex and turbulent dynamics happening in the shear region, we find excellent agreement between our model and large-scale particle-in-cell simulations. Our findings pave the way for identifying the KHI linear regime and for measuring its growth rate in astrophysical jets observable on earth as well as in laboratory plasmas.

Single channel atmospheric pressure transporting plasma and plasma stream demultiplexing: physical characterization and application to E. coli bacteria inactivation

In this article, we developed transporting plasma sources that operate at atmospheric pressure. The effect of electrode configuration on plasma transporting was investigated. In order to increase the transporting plasma cross-section, we converted a plasma stream into four plasma channels by a cylindrical housing. Electron excitation and rotational temperatures were estimated using optical emission spectroscopy. Furthermore, the electrical and temporal characteristics of the plasma, discharge power and charge deposition on the target were investigated. The propagation characteristics of single and multi-channel transporting plasma were compared with the same cross-sectional area. Two configurations for multi-channels were designed for this purpose. Escherichia coli bacteria were exposed to the single and multi-channel transporting discharge for different time durations. After exposure, the results indicated that the inactivation zones were significantly increased by a multi-channel transporting plasma. Finally, E. coli inactivation by those plasma apparatuses was compared with that of several standard antimicrobial test discs such as Gentamicin, Tetracycline, Amoxicillin and Cefixime.

The behavior dynamics of a droplet phase in vacuum arc discharge plasma in chemically active gas nitrogen

The charge distribution of microparticles produced at the cathode surface in the vacuum arc discharge under conditions when the reactive gas nitrogen is present in the discharge gap was studied with an electrostatic analyzer. Small fragments of titanium nitride that form on the surface are heated to electrons thermionic emission temperature in the plasma while they drift to the substrate which causes a positive charge, while the large fragments are cold, that is why they are negatively charged. The titanium microdroplets are mainly positively charged, and they keep this charge for a long period and causes difficulties of filtration in plasma streams.

Behavior of divertor and first wall armour materials at plasma heat fluxes relevant to ITER ELMs and disruptions

The paper presents the main results of numerous experiments carried out over the past 10 years at QSPA-T and QSPA-Be plasma guns in support of ITER. Special targets made of pure W, W-1%La2O3 and two types of Be (TGP-56FW and S65-C) were tested under the series of repeated plasma stream and photonic flux impact. Maximum heat load on the target surface was up to 2.5MJ/m2 in the case of plasma testing and was equal to 0.5MJ/m2 in the case of photonic flux testing. Pulse waveform was rectangular with tpulse= 0.5ms. It was found that the main erosion mechanisms of W and Be under plasma stream impact are the melt layer movement, the ejection of droplets and the cracks formation. As a result of repeated photonic fluxes a regular, “corrugated” structure are eventually formed on the Be target surface. Study of erosion products of W formed under plasma stream impact on the W target has shown that the D/W atomic ratio in the deposited W films during pulsed events may be the same or even higher than that for stationary processes.

Backward propagating branch of surface waves in a semi-bounded streaming plasma system

The influence of wake and magnetic field on the surface ion-cyclotron wave is kinetically investigated in a semi-bounded streaming dusty magnetoplasma in the presence of the ion wake-field. The analytic expressions of the frequency and the group velocity are derived by the plasma dielectric function with the spectral reflection condition. The result shows that the ion wake-field enhances the wave frequency and the group velocity of the surface ion-cyclotron wave in a semi-bounded dusty plasma. It is found that the frequency and the group velocity of the surface electrostatic-ion-cyclotron wave increase with an increase of the strength of the magnetic field. It is interesting to find out that the group velocity without the ion flow has the backward propagation mode in a semi-bounded dusty plasma. The variations due to the frequency and the group velocity of the surface ion-cyclotron wave are also discussed.

Formation of Heliospheric Arcs of Slow Solar Wind

Abstract A major challenge in solar and heliospheric physics is understanding the origin and nature of the so-called slow solar wind. The Sun’s atmosphere is divided into magnetically open regions, known as coronal holes, where the plasma streams out freely and fills the solar system, and closed regions, where the plasma is confined to coronal loops. The boundary between these regions extends outward as the heliospheric current sheet (HCS). Measurements of plasma composition strongly imply that much of the slow wind consists of plasma from the closed corona that escapes onto open field lines, presumably by field-line opening or by interchange reconnection. Both of these processes are expected to release closed-field plasma into the solar wind within and immediately adjacent to the HCS. Mysteriously, however, slow wind with closed-field plasma composition is often observed in situ far from the HCS. We use high-resolution, three-dimensional, magnetohydrodynamic simulations to calculate the dynamics of a coronal hole with a geometry that includes a narrow corridor flanked by closed field and is driven by supergranule-like flows at the coronal-hole boundary. These dynamics produce giant arcs of closed-field plasma that originate at the open-closed boundary in the corona, but extend far from the HCS and span tens of degrees in latitude and longitude at Earth. We conclude that such structures can account for the long-puzzling slow-wind observations.

Formuvannya oblasti kompresiyi v plazmovomu pototsi MPK za riznykh pochatkovykh umov

The analysis of fundamental properties of the compression zone in the self-compressed plasma streams generated by a magnetoplasma compressor (MPC) is carried out. The main attention is attended to the research of the dependences of basic plasma parameters in a compressed plasma stream depending on the initial conditions. It has been shown experimentally that the reduction of the initial concentration of a working gas leads to an increase of the plasma density in the compression zone. The detailed studies of the spatial distributions of currents in the plasma flows are fulfilled for different initial concentrations of a substance in the accelerating channel of MPC. Under the experiment conditions, it is found that a decrease of the initial concentration of a working gas leads to the displacement of the currents from the compression zone.

Set of Measures for Improving the Quality of Powders Based on Titanium for Additive Technology

The change in morphology of polygonal powder in a low-temperature plasma generated in an arc discharge is an effective means for resolving the problem of preparing titanium alloy powder of spherical shape used in additive technology. A method is studied for preparing spherical powder of titanium and its alloys by spheroidization in streams of a polygonal powder thermal plasma, prepared by hydrogenation-dehydrogenation. A production scheme is proposed for preparing spherical titanium alloy powder for additive technology, including remelting of certified waste, ingot hydrogenation, crushing, screening its fractions, dehydrogenation, and gas centrifugal classification with final plasma treatment. A technology is developed for preparing spherical titanium alloy powder used in additive technology, with a reduced dissolved gas content. Methods are considered for improving the quality of spheroidized titanium powder including: minimization of the amount of particles with size less than 10 μm in the original polygonal powder, a change in composition of the plasma-forming gas, and prevention of contact with air by powder before and after spheroidization.

Vasoactivity of the Vasculature Directly Supplying the Rat Sciatic Nerve

ObjectivesThe purpose of this study was to determine the vasoactivity of the vasculature directly supplying the sciatic nerve in response to phenylephrine (PE) and acetylcholine (ACh) using plasma fluorescence and intravital microscopy.MethodsPE (10−4M, n=6) and ACh (10−4M, n=9) were applied to an exposed sciatic nerve in an anesthetized Sprague Dawley rat model (PE: 321.6±11.7g, ACh: 307.56±41.57g). A fluorescent dye, FITC (0.3 ml at 5%), was infused via a jugular catheter to fluoresce the plasma stream, while intravital microscopy was used to visualize the plasma stream through the vessels running directly over the sciatic nerve. Each vasoactive agent was topically applied over the sciatic nerve for 6 minutes. Measurements were taken at baseline (immediately prior to drug application), 2 minutes, 4 minutes and 6 minutes after the start of drug application, and finally at 4 minutes after PE or ACh application was stopped (recovery). Maximal diameter was achieved via application of 10−4M of Sodium Nitroprusside (SNP). Data are expressed as mean ± standard error.ResultsFollowing PE and ACh application, mean arterial pressure (baseline PE: 105.6±11.1mmHg; PE: 102.0±9.9mmHg, baseline ACh: 100.8±4.1mmHg, ACh: 100.2±4.6mmHg) was not affected. PE application resulted in a decreased diameter of the plasma stream (maximal change in diameter: −5.8±1.9um), while ACh application did not result in changes in diameter (maximal change in diameter: 1.5±0.7um). Maximal diameter in response to SNP was not significantly different from the baseline diameter (Baseline: 19.36±6.62um, SNP: 19.80±7.01um)ConclusionPE application resulted in a vasoconstriction of the vessels directly supplying the sciatic nerve, while application of ACh or SNP failed to produce significantly vasodilation. Overall, the vessels supplying the sciatic nerve appeared to be maximally dilated at baseline, which may explain the lack of dilation in response to ACh or SNP.Support or Funding InformationThis study was supported by Brescia University College Research Grant.

Characteristics of cold atmospheric plasma source based on low-current pulsed discharge with coaxial electrodes

This work investigates the characteristics of the gas discharge system used to create an atmospheric pressure plasma flow. The plasma jet design with a cylindrical graphite cathode and an anode rod located on the axis of the system allows to realize regularly reproducible spark breakdowns mode with a frequency ∼ 5 kHz and a duration ∼ 40 μs. The device generates a cold atmospheric plasma flame with 1 cm in diameter in the flow of various plasma forming gases including nitrogen and air at about 100 mA average discharge current. In the described construction the cathode spots of individual spark channels randomly move along the inner surface of the graphite electrode creating the secondary plasma stream time-average distributed throughout the whole exit aperture area after the decay of numerous filamentary discharge channels. The results of the spectral diagnostics of plasma in the discharge gap and in the stream coming out of the source are presented. Despite the low temperature of atoms and molecules in plasma stream the cathode spots operation with temperature of ∼ 4000 °C at a graphite electrode inside a discharge system enables to saturate the plasma by CN-radicals and atomic carbon in the case of using nitrogen as the working gas.

Do cosmic rays heat the early intergalactic medium?

Cosmic rays (CRs) govern the energetics of present-day galaxies and might have also played a pivotal role during the Epoch of Reionization. In particular, energy deposition by low-energy ($E \lesssim 10$ MeV) CRs accelerated by the first supernovae, might have heated and ionized the neutral intergalactic medium (IGM) well before ($z \approx 20$) it was reionized, significantly adding to the similar effect by X-rays or dark matter annihilations. Using a simple, but physically motivated reionization model, and a thorough implementation of CR energy losses, we show that CRs contribute negligibly to IGM ionization, but heat it substantially, raising its temperature by $\Delta T=10-200$ K by $z=10$, depending on the CR injection spectrum. Whether this IGM pre-heating is uniform or clustered around the first galaxies depends on CR diffusion, in turn governed by the efficiency of self-confinement due to plasma streaming instabilities that we discuss in detail. This aspect is crucial to interpret future HI 21 cm observations which can be used to gain unique information on the strength and structure of early intergalactic magnetic fields, and the efficiency of CR acceleration by the first supernovae.

Development of a high power Helicon system for DIII-D

A mechanism for driving current off-axis in high beta tokamaks using fast electromagnetic waves, called Helicons, will be experimentally tested in the DIII-D tokamak. This method is calculated to be more efficient than current drive using electron cyclotron waves or neutral beam injection, and it may be well suited to reactor-like configurations [1,2]. A low power (100W) 476MHz “combline” antenna, consisting of 12 inductively coupled, electrostatically shielded, modular resonators [3], was recently installed in DIII-D. Initial operation showed that the plasma operating conditions were achieved under which helicon waves can be launched. Plasma operations also showed that the location of the antenna has not reduced the performance of, or introduced excessive impurities into, the discharges produced in DIII-D.The development of a high power (1MW) Helicon system is underway. This antenna consists of 30 modules mounted on the inside of the outer wall of the vacuum vessel slightly above the midplane. Carbon tiles around the antenna protect the antenna from thermal plasma streaming along field lines. A 1.2MW, 476MHz klystron system will be transferred from the Stanford Linear Accelerator to DIII-D to provide the RF input power to the antenna.A description of the design and fabrication of high power antenna and the RF feeds, the klystron and RF distribution systems, and their installation will be presented.

Comparison of quiet time vertical plasma drifts with global empirical models over the Indian sector: Some insights

The threshold vertical plasma drifts and their polarities are inferred from E-region irregularities reported earlier using different experiments conducted from India during geomagnetically quiet time. In addition, the hourly variations of magnetometer data sets are used in conjunction with an equatorial electrojet model (Anandarao, 1976) to deduce the vertical drifts around noon time (10:00–140:00 LT). These results are then compared with the vertical drifts presented by empirical models (Scherliess and Fejer, 1999; Fejer et al., 2008a) corresponding to the 60°E longitude sector. In general, the vertical drifts presented by empirical models are consistent with those inferred from snapshot measurements of E-region irregularities at different local times of the day except around sunrise hours. Further, the vertical drifts presented by Fejer et al. (2008a) model match fairly well with seasonally averaged vertical drifts deduced (within 1σ variation) using magnetometer data. A time difference is noticed between occurrence of pre-reversal enhancement in vertical drifts over India reported earlier using different techniques and Scherliess and Fejer (1999) model. Probable reason for the time difference is discussed. The occurrence characteristic of afternoon equatorial counter electrojet in June solstice during low solar epoch is consistent with the drifts obtained from empirical models. The seasonally averaged vertical drifts during nighttime reported earlier using ionosonde/HF radar experiments are not consistent with the presence of streaming plasma waves on a few occasions. Further, nocturnal vertical drifts are systematically under-estimated and probable reason for this is discussed.

Beryllium layer response to ITER-like ELM plasma pulses in QSPA-Be

Material migration in ITER is expected to move beryllium (Be) eroded from the first wall primarily to the tungsten (W) divertor region and to magnetically shadowed areas of the wall itself. This paper is concerned with experimental study of Be layer response to ELM-like plasma pulses using the new QSPA-Be plasma gun (SRC RF TRINITI). The Be layers (1→50µm thick) are deposited on special castellated Be and W targets supplied by the ITER Organization using the Thermionic Vacuum Arc technique. Transient deuterium plasma pulses with duration ∼0.5ms were selected to provide absorbed energy densities on the plasma stream axis for a 30° target inclination of 0.2 and 0.5MJm−2, the first well below and the second near the Be melting point. This latter value is close to the prescribed maximum energy density for controlled ELMs on ITER. At 0.2MJm−2 on W, all Be layer thicknesses tested retain their integrity up to the maximum pulse number, except at local defects (flakes, holes and cracks) and on tile edges. At 0.5MJm−2 on W, Be layer melting and melt layer agglomeration are the main damage processes, they happen immediately in the first plasma impact. Melt layer movement was observed only near plasma facing edges. No significant melt splashing is observed in spite of high plasma pressure (higher than expected in ITER). Be layer of 10µm thick on Be target has higher resistance to plasma irradiation than 1 and 55µm, and retain their integrity up to the maximum pulse number at 0.2MJm−2. For 1µm and 55µm thick on Be target significant Be layer losses were observed at 0.2MJm−2.

Nonlinear effects in the bounded dust-vortex flow in plasma.

The vortex structures in a cloud of electrically suspended dust in a streaming plasma constitutes a driven system with a rich nonlinear flow regime. Experimentally recovered toroidal formations of this system have motivated study of its volumetrically driven-dissipative vortex flow dynamics using two-dimensional hydrodynamics in the incompressible Navier-Stokes regime. Nonlinear equilibrium solutions are obtained for this system where a nonuniformly driven two-dimensional dust flow exhibits distinct regions of localized accelerations and strong friction caused by stationary fluids at the confining boundaries resisting the dust flow. In agreement with observations in experiments, it is demonstrated that the nonlinear effects appear in the limit of small viscosity, where the primary vortices form scaling with the most dominant spatial scales of the domain topology and develop separated virtual boundaries along their periphery. This separation is triggered beyond a critical dust viscosity that signifies a structural bifurcation. Emergence of uniform vorticity core and secondary vortices with a newer level of identical dynamics highlights the applicability of the studied dynamics to gigantic vortex flows, such as the Jovian great red spot, to microscopic biophysical intracellular activity.

The Studies of Plasma Torch Processes by Laser Beam Welding

The manufacturing of significant products with help of laser beam welding technologies requires higher stability characteristics of such technologies; this explains the necessity to run on-line testing procedures of through pro-melting process. This type of testing can be carried out by the registration of plasma streams that occur under a work piece by through pro-melting [i.e. metal undergoes an intensive laser beam thermal processing].

A “Cosmic Comb” Model of Fast Radio Bursts

Abstract Recent observations of fast radio bursts (FRBs) indicate a perplexing, inconsistent picture. We propose a unified scenario to interpret diverse FRBs observed. A regular pulsar, otherwise unnoticeable at a cosmological distance, may produce a bright FRB if its magnetosphere is suddenly “combed” by a nearby, strong plasma stream toward the anti-stream direction. If the Earth is to the night side of the stream, the combed magnetic sheath would sweep across the direction of Earth and make a detectable FRB. The stream could be an AGN flare, a GRB or supernova blastwave, a tidal disruption event, or even a stellar flare. Since it is the energy flux received by the pulsar rather than the luminosity of the stream origin that defines the properties of the FRB, this model predicts a variety of counterparts of FRBs, including a possible connection between FRB 150418 and an AGN flare, a possible connection between FRB 131104 and a weak GRB, a steady radio nebula associated with the repeating FRB 121102, and probably no bright counterparts for some FRBs.

The role of plasma slowdown in the generation of Rhea's Alfvén wings

AbstractAlfvén wings are known to form when a conducting or mass‐loading object slows down a flowing plasma in its vicinity. Alfvén wings are not expected to be generated when an inert moon such as Rhea interacts with Saturn's magnetosphere, where the plasma impacting the moon is absorbed and the magnetic flux passes unimpeded through the moon. However, in two close polar passes of Rhea, Cassini clearly observed magnetic field signatures consistent with Alfvén wings. In addition, observations from a high‐inclination flyby (Distance > 100 RRh) of Rhea on 3 June 2010 showed that the Alfvén wings continue to propagate away from Rhea even at this large distance. We have performed three‐dimensional hybrid simulations of Rhea's interaction with Saturn's magnetosphere which show that the wake refilling process generates a plasma density gradient directed in the direction of corotating plasma. The resulting plasma pressure gradient exerts a force directed toward Rhea and slows down the plasma streaming into the wake along field lines. As on the same field lines, outside of the wake, the plasma continues to move close to its full speed, this differential motion of plasma bends the magnetic flux tubes, generating Alfvén wings in the wake. The current system excited by the Alfvén wings transfers momentum to the wake plasma extracting it from plasma outside the wake. Our work demonstrates that Alfvén wings can be excited even when a moon does not possess a conducting exosphere.