Critical Plasma Parameters Research Articles

Development of efficient nonthermal atmospheric-pressure Ar-plasma jet through simultaneous spectroscopic characterization and radical quantification

The work investigates the correlation between the plasma characteristics and reactive chemical species generation in an Ar-nonthermal atmospheric pressure plasma-jet (Ar-NTAPPJ) under various operating conditions such as gas flow rate, excitation voltage, and electrode gap and demonstrates the application of such understanding in developing efficient nonthermal plasma systems. The critical plasma parameters such as electron temperature (T e) and electron density (n e) under the various operating conditions were estimated using optical emission spectroscopy coupled with the collision radiative model and Stark broadening methods. At optimal setting of 5 LPM gas flow rate, 4 kV excitation voltage, and 6 mm electrode gap resulted in maximum T e (0.6 eV), enhancing •OH production (0.056 mM) in the liquid phase and OH(A-X) emission in the gas phase, highlighting the significance of operating conditions on building energy efficient plasma systems. The enhanced performance of the optimized Ar-NTAPPJ is demonstrated by taking atrazine as a model herbicide. The degradation performance data was correlated and validated with results obtained from spectroscopic diagnostics. By adequately tuning the operating parameters, four times enhancement in energy yield (∼150 mg kWh−1) was obtained without perturbing the nonthermal plasma mode. In nonthermal mode, to best of the authors knowledge, it is the highest reported energy yield for atrazine degradation. The scalability aspect of the present plasma jet was also investigated by Intensified Charge-Coupled Device camera-based imaging technique. The study establishes the importance of adequate diagnostics in developing efficient next-generation plasma reactors.

Basement membrane product, endostatin, as a link between inflammation, coagulation and vascular permeability in COVID-19 and non-COVID-19 acute respiratory distress syndrome.

Immune cell recruitment, endothelial cell barrier disruption, and platelet activation are hallmarks of lung injuries caused by COVID-19 or other insults which can result in acute respiratory distress syndrome (ARDS). Basement membrane (BM) disruption is commonly observed in ARDS, however, the role of newly generated bioactive BM fragments is mostly unknown. Here, we investigate the role of endostatin, a fragment of the BM protein collagen XVIIIα1, on ARDS associated cellular functions such as neutrophil recruitment, endothelial cell barrier integrity, and platelet aggregation in vitro. In our study we analyzed endostatin in plasma and post-mortem lung specimens of patients with COVID-19 and non-COVID-19 ARDS. Functionally, we investigated the effect of endostatin on neutrophil activation and migration, platelet aggregation, and endothelial barrier function in vitro. Additionally, we performed correlation analysis for endostatin and other critical plasma parameters. We observed increased plasma levels of endostatin in our COVID-19 and non-COVID-19 ARDS cohort. Immunohistochemical staining of ARDS lung sections depicted BM disruption, alongside immunoreactivity for endostatin in proximity to immune cells, endothelial cells, and fibrinous clots. Functionally, endostatin enhanced the activity of neutrophils, and platelets, and the thrombin-induced microvascular barrier disruption. Finally, we showed a positive correlation of endostatin with soluble disease markers VE-Cadherin, c-reactive protein (CRP), fibrinogen, and interleukin (IL)-6 in our COVID-19 cohort. The cumulative effects of endostatin on propagating neutrophil chemotaxis, platelet aggregation, and endothelial cell barrier disruption may suggest endostatin as a link between those cellular events in ARDS pathology.

Probing local electron temperature and density inside a sheared flow stabilized Z-pinch using portable optical Thomson scattering.

We report the first optical Thomson scattering measurements inside a high electron temperature (≳1 keV) and moderate electron density (mid 1016 cm-3) plasma. This diagnostic has been built to provide critical plasma parameters, such as electron temperature and density, for Advanced Research Projects Agency-Energy-supported fusion-energy concepts. It uses an 8J laser at 532nm in 1.5ns to measure the high frequency feature of the Thomson scattering profile at 17 locations along the probe axis. It is able to measure electron density from 5 × 1017 cm-3 to several 1019 cm-3 and electron temperatures from tens of eV to several keV. Here, we describe the design, deployment, and analysis on the sheared flow stabilized Z-pinch machine at Zap Energy named FuZE. The probe beam is aimed at an axial distance of 20cm from the central electrode and is timed within the temporal envelope of neutron emission. The high temperature and moderate density plasmas generated on FuZE lie in an unconventional regime for Thomson scattering as they are between tokamaks and laser-produced plasmas. We described the analysis considerations in this regime, show that the electron density was below 5 × 1016 cm-3 at all times during these measurements, and present a sample shot where the inferred electron temperature varied from 167 ± 16eV to 700 ± 85eV over 1.6cm.

Climatology of Deep O+ Dropouts in the Night‐Time F‐Region in Solar Minimum Measured by a Langmuir Probe Onboard the International Space Station

AbstractThe Floating Potential Measurement Unit onboard the International Space Station includes a Wide sweeping Langmuir Probe that has been operating in the F‐region of the ionosphere at ∼400 km since 2006. While traditional Langmuir probe estimates include critical plasma parameters like electron density and temperature, we have also extracted the O+ percentage from the total ion constituents. This O+ composition data set from the recent minimum in the Solar Cycle 24 reveals orbits with dropouts in O+ to below 80% of the total background ion density at International Space Station orbital altitudes. The observed O+ percentages during these dropouts are much lower than the values predicted by the International Reference Ionosphere 2016 (IRI2016) empirical model. In this paper, we present the climatology of these O+ dropouts with their dependency on season, local time and geographical location. The results show that the lowered O+ percentages are more significant in the winter hemispheres and are routinely observed for orbits in the pre‐sunrise periods. The patterns in O+ dropouts can be explained in part from the lowering of the O+/H+ transition height during solar minimum along with patterns in neutral wind variation.

NUCLEAR DATA V&V ANALYSIS FOR FUSION APPLICATIONS: INTEGRAL BENCHMARKS AND DECAY DATA

A reliable estimation of the operational parameters is one of the primary concerns in the design of magnetic fusion devices such as ITER and DEMO. Methods of diagnostics and control over the critical plasma parameters determining its stability and efficiency rely on the high-energy neutron field monitoring. Extreme operational environment, such as high-energy neutron flux, electromagnetic radiation, and high temperatures might reduce the performance of the detector systems. Therefore, research and development activities in detector prototyping are carried out to address this problem. To predict the performance of the detector materials, simulations using the latest releases of the nuclear data libraries as input for the inventory codes are carried out. This paper describes the latest validation and verification (V&V) benchmark exercise for FISPACT-II & TENDL-2017 based on the fusion decay heat measurements performed at the Japanese FNS facility for the materials in the diagnostic components for the radiation measurements. The breakdown of decay-heat contributions from individual radionuclides have been employed to interpret the simulated results, benchmark the data against the experimental measurements, and revise the neutron-induced reactions cross-section and decay data for the associated radionuclides for the upcoming release of the TENDL-2019 nuclear data library.

Spatiotemporally resolved optical emission spectroscopy and harmonic generation in Cu plasmas

Laser-induced ablation plasmas of Cu generated by nanosecond 1064 nm pulses have been examined as media for third harmonic generation of a nanosecond driving pulse. A narrow window of ablation fluences where third harmonic generation is optimized has been identified in a region around twice the ablation threshold. A detailed analysis of the features of the Cu plasma across this critical fluence window, through spatially and temporally resolved optical emission spectroscopy, has been used to assess critical plasma parameters such as temperature, electron density, and abundance of Cu species in different ionization stages. This description has been correlated with the conditions for optimum low-order harmonic generation in the Cu plasma.

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Fast estimation of ion temperature from EAST charge exchange recombination spectroscopy using neural network

Ion temperature, as one of the most critical plasma parameters, can be diagnosed by charge exchange recombination spectroscopy (CXRS). Iterative least-squares fitting is conventionally used to analyze CXRS spectra to identify the active charge exchange component, which is the result of local interaction between impurity ions with a neutral beam. Due to the limit of the time consumption of the conventional approach (∼100 ms per frame), the Experimental Advanced Superconducting Tokamak CXRS data is now analyzed in-between shots. To explore the feasibility of real-time measurement, neural networks are introduced to perform fast estimation of ion temperature. Based on the same four-layer neural network architecture, two neural networks are trained for two central chords according to the ion temperature data acquired from the conventional method. Using the TensorFlow framework, the training procedures are performed by an error back-propagation algorithm with the regularization via the weight decay method. Good agreement in the deduced ion temperature is shown for the neural networks and the conventional approach, while the data processing time is reduced by 3 orders of magnitude (∼0.1 ms per frame) by using the neural networks.

Anatomy of modified Korteweg–de Vries equation for studying the modulated envelope structures in non-Maxwellian dusty plasmas: Freak waves and dark soliton collisions

In this work, we study, in a systematic way, dust-acoustic modulated envelope structures such as rogue waves (unstable waves) and dark soliton (stable waves) collisions in a complex plasma with nonthermal ions and Boltzmann electrons. In the present plasma system, we can have both negative and positive potential structures associated with the nonlinear dust-acoustic structures. Therefore, we derived the modified Korteweg–de Vries (mKdV) equation, by using the reductive perturbation technique, to describe the nonlinear structures at critical plasma parameters. For studying the properties of the modulated envelope structures, the mKdV equation transformed to a nonlinear Schrödinger equation. Depending on the modulational instability analysis, the stability and instability regions for the propagating nonlinear modulated waves have been determined precisely. After that, the properties of the dust-acoustic rogue waves are examined within the instability regions. Moreover, the effects of physical parameters, such as the ion-to-electron temperature ratio and the ion nonthermal parameter on the profile of dust-acoustic rogue waves are examined. Furthermore, our investigations extended to study the head-on collisions of two-dark solitons in the stability regions. Using the extended Poincaré–Lighthill–Kuo perturbation method, the dark solitons in the present plasma system develop according to two quasi-Korteweg–de Vries equations. After that, the phase shifts induced by the face-to-face collisions between two-dark solitons are obtained analytically. Also, the effects of the above physical parameters on the phase shifts are reported. The results may have relevance in space and laboratory dusty plasmas.

The Application of Advanced Pulsed Plasma in Fin Etch Loading Improvement

With the background of general integrated circuit (IC) feature size shrinking designers to get high performance transistors, Self-Alignment-Double-Patterning (SADP) FinFETetch was widely used in 14/16 nm technologies node and beyond. Rigorous process loading control (CD, profile, depth) in reactive ion etch (RIE) becomes more critical and challenging to ensure precise patterning and to avoid performance degradation among different features.[1]However, it’s quite hard to tackle such notorious loading for its inherent high Te induced ionization in traditional continuous wave (CW) plasmas.Thus, significant improvements in controlling plasma properties in a dry etching reactor are essential to satisfy such stringent requirement. Pulsed plasmas have demonstrated several advantages compared to CW plasmas. By varying the pulse frequency and the duty cycle, pulsed plasma provide additional “control knobs” in controlling critical plasma parameters, such as ion and electron densities, electron temperature, flux and energy of the ions and radicals incident on surface. These critical factors affecting overall on-wafer performance during plasma etching processes at both within wafer and within die levels, etching and deposition, vertical and lateral etch rate, profile control, feature sidewall passivation and plasma damage.[2]In view of characters of pulsed plasma noted above, it appears to be a promising approach to improve RIE-lag loading in SADP fin etch. In this paper, we systematically investigated the influence of both bias pulsed plasma and synchronous pulsed plasma to fin CD, profile (sidewall angle) and depth loading performance among dense and semi-isolated lines. It was found that proper duty cycle and frequency of pulsed power could drastically impact the loading performance. Based on the above learning, we finally delivered the overall solution by introducing synchronous pulsed plasma etch in mandrel and shallow trench isolation (STI) to address the rigorous loading control between dense and isolated patterns. [1] Y. Wang, et al, CSTIC, “Process Loading Reduction on SADP FinFET Etch”, 2015 [2] S. Banna, et al, JVST A, “Pulsed High-density Plasmas for Advanced Dry Etching Process”, 2012

Dust-acoustic solitary waves and double layers with two temperature ions in a nonextensive dusty plasma

Small amplitude dust-acoustic solitary waves in an unmagnetized dusty plasma consisting of electrons and two temperature ions obeying the q-nonextensive distribution are investigated. Employing reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived. From the solitonic solutions of KdV equation, the influence of nonextensivity of electrons as well as ions and dust concentration on the amplitude and width of dust-acoustic solitary waves has been studied. It is observed that both positive and negative potential dust acoustic solitary waves occur in this case. The modified KdV (mKdV) equation is derived in order to examine the solitonic solutions for the critical plasma parameters for which KdV theory fails. The parametric regimes for the existence of mKdV solitons and double layers (DLs) have also been determined. Positive potential double layers are found to occur in the present study.

Analytical estimates of electron quasi‐linear diffusion by fast magnetosonic waves

Quantifying the loss of relativistic electrons from the Earth's radiation belts requires to estimate the effects of many kinds of observed waves, ranging from ULF to VLF. Analytical estimates of electron quasi‐linear diffusion coefficients for whistler‐mode chorus and hiss waves of arbitrary obliquity have been recently derived, allowing useful analytical approximations for lifetimes. We examine here the influence of much lower frequency and highly oblique, fast magnetosonic waves (also called ELF equatorial noise) by means of both approximate analytical formulations of the corresponding diffusion coefficients and full numerical simulations. Further analytical developments allow us to identify the most critical wave and plasma parameters necessary for a strong impact of fast magnetosonic waves on electron lifetimes and acceleration in the simultaneous presence of chorus, hiss, or lightning‐generated waves, both inside and outside the plasmasphere. In this respect, a relatively small frequency over ion gyrofrequency ratio appears more favorable, and other propitious circumstances are characterized. This study should be useful for a comprehensive appraisal of the potential effect of fast magnetosonic waves throughout the magnetosphere.

Pulsed high-density plasmas for advanced dry etching processes

Plasma etching processes at the 22 nm technology node and below will have to satisfy multiple stringent scaling requirements of microelectronics fabrication. To satisfy these requirements simultaneously, significant improvements in controlling key plasma parameters are essential. Pulsed plasmas exhibit considerable potential to meet the majority of the scaling challenges, while leveraging the broad expertise developed over the years in conventional continuous wave plasma processing. Comprehending the underlying physics and etching mechanisms in pulsed plasma operation is, however, a complex undertaking; hence the full potential of this strategy has not yet been realized. In this review paper, we first address the general potential of pulsed plasmas for plasma etching processes followed by the dynamics of pulsed plasmas in conventional high-density plasma reactors. The authors reviewed more than 30 years of academic research on pulsed plasmas for microelectronics processing, primarily for silicon and conductor etch applications, highlighting the potential benefits to date and challenges in extending the technology for mass-production. Schemes such as source pulsing, bias pulsing, synchronous pulsing, and others in conventional high-density plasma reactors used in the semiconductor industry have demonstrated greater flexibility in controlling critical plasma parameters such as ion and radical densities, ion energies, and electron temperature. Specifically, plasma pulsing allows for independent control of ion flux and neutral radicals flux to the wafer, which is key to eliminating several feature profile distortions at the nanometer scale. However, such flexibility might also introduce some difficulty in developing new etching processes based on pulsed plasmas. Therefore, the main characteristics of continuous wave plasmas and different pulsing schemes are compared to provide guidelines for implementing different schemes in advanced plasma etching processes based on results from a particularly challenging etch process in an industrial reactor.

Higher-order nonlinear electron-acoustic solitary excitations in partially degenerate quantum electron-ion plasmas

Propagation of dressed solitary excitations are studied in a partially degenerate quantum plasma in the framework of quantum-hydrodynamics model using multiple scales technique. The evolution equation together with a linear inhomogeneous differential equation is solved using Kodama–Taniuti renormalizing technique. It is shown that the type of solitary excitations (bright or dark) is defined by two critical plasma parameter values.

Universal characteristics of ion-acoustic wave dynamics in magnetized plasmas with emphasis on Tsallis distribution

Using the extended Poincaré-Lighthill-Kuo (PLK) reductive perturbation method, which incorporates the phase-shift variations, it is shown that common features on propagation and head-on collisions of ion-acoustic waves exist for a magnetized plasmas of different inertial-less particle distributions. For instance it is remarked that, the soliton amplitude is always independent of magnetic field strength while strictly depends on its angle regarding the propagation direction. Both types of solitons (compressive or rarefactive) are shown to exist which are defined through the critical angle γ=π/2 or other critical values depending on plasma fractional parameters. These critical plasma parameter values also define the sign of head-on collision phase shift. Furthermore, it is proved that for a given set of plasma parameters there is always a relative angle of propagation regarding to that of the magnetic-field for which the soliton width is maximum. Current findings apply to a wide range of magnetized plasmas including those containing background dust ingredients or two-temperature inertial-less particles and may be used to study laboratory or astrophysical magnetoplasmas.

Propagation and oblique collision of electron-acoustic solitons in two-electron-populated quantum plasmas

Oblique interaction of small- but finite-amplitude KdV-type electron-acoustic solitary excitations is examined in an unmagnetized two-electron-populated degenerate quantum electron–ion plasma in the framework of quantum hydrodynamics model using the extended Poincaré–Lighthill–Kuo (PLK) perturbation method. Critical plasma parameter is found to distinguish the types of solitons and their interaction phase-shifts. It is shown that, depending on the critical quantum diffraction parameter H cr, both compressive and rarefactive solitary excitations may exist in this plasma and their collision phase-shifts can be either positive or negative for the whole range of collision angles 0 < θ < π.

Stability conditions of argon and helium gas mixtures in an atmospheric pressure plasma jet

Non-equilibrium plasmas can be generated by atmospheric pressure glow discharges, amongst others by atmospheric pressure plasma jets (APPJ), which feature a capacitive radio-frequency discharge between bare metallic electrodes. We investigated the stability conditions for discharges in an APPJ operated with helium–argon mixtures. Uniform α-discharges can be sustained in mixtures ranging from pure helium to pure argon. The ignition voltage increases drastically with argon content. There is also an upper limit for the existence of the α-mode, where α-sheath breakdown occurs. Critical plasma parameters for the α-mode were determined by equivalent circuit models and discussed in respect to dependences on the different models. A critical electron density of 2.4×10 11 cm −3 was obtained for pure helium. It increases steadily with argon content and reaches a value of 1.2×10 12 cm −3 for pure argon. Sheath thicknesses for α-sheath breakdown were calculated in the range of 0.17–0.29 mm for helium–argon mixtures.

Effects of Cathode Configuration on Hall Thruster Cluster Plume Properties

Abstract : Clusters of Hall thrusters are being considered for use on a variety of missions requiring electric propulsion systems capable of operating at power levels in excess of the current state of the art. One of the key factors to be considered in determining the optimum cluster architecture is the configuration of the electron-emitting cathode(s). This work presents experimentally determined plume properties and discharge current characteristics obtained with multiple thrusters coupled to a single cathode. Spatially resolved plasma density, electron temperature, and plasma potential data are presented during both single thruster and cluster operation. Measurements taken in this configuration are compared to previously published data obtained with each thruster coupled to its own independent cathode. Significant differences between the two configurations are noted and explained. Additionally, critical plasma parameters in the cluster plume are shown to be strongly influenced by the location of the hollow cathode.

Plasma shape control for the JET tokamak: an optimal output regulation approach

The eXtreme Shape Controller, designed and implemented on the JET tokamak, was described. The controller regulates the plasma shape as specified in terms of plasma-wall distances and maintains this plasma shape in the presence of significant variations of critical plasma parameters, namely the poloidal beta, the internal inductance, and the plasma current. The design procedure is based on the SVD of the plant output matrix. This procedure accounts for specifications on the accuracy of the controller variables as well as the maximum allowable control effort. The new controller has been fully commissioned on the JET tokamak, is in regular operation, and is delivering the expected performance.

Electron mobility in mixtures of optically excited sodium vapor, molecular nitrogen and heavy inert gases

A study is made of the processes of formation of a nonequilibrium electron energy distribution in mixtures of sodium, molecular nitrogen, and heavy inert gases. It is shown that in these mixtures, a local maximum on the electron energy distribution, can form in the energy range corresponding to the Raumsauer minimum in the elastic cross section for inert gases. The question is discussed of whether the electron mobility can become negative during the resonant optical excitation of the 3S-3P transition in sodium. The electron distribution function is calculated parametrically to determine the critical plasma parameters for which negative electron mobility can be observed in experiments, specifically, the composition of the mixture, the concentration of resonantly excited sodium atoms, the temperature corresponding to the distribution of vibrationally excited molecules, the degree of ionization and the electric field strength.