High Degree Of Ionization Research Articles

Plasma diagnostic by emission spectroscopy during vacuum arc remelting

The plasma produced during vacuum arc remelting of a Zircaloy4 electrode has been investigated by optical emission spectroscopy. Spatial variations of plasma emission along the arc axis has been measured with a specific apparatus consisting of nine aligned optic fibres. The plasma consists of zirconium atoms, of singly and doubly charged zirconium ions and of chromium atoms. The non-observation of emissions of tin and iron particles, which are, with chromium, the three main alloy components of Zircaloy4, suggests that the concentrations of these two species in the plasma are negligibly small. Distribution temperatures of atomic and ionic species of the order of 1 eV and high ionization degree of the plasma (greater than 70%) have been determined. The similar decay of the line intensities of the various species with increasing axial distance from the cathode surface indicates that the plasma composition remains approximately unchanged within the interelectrode region. Synthesis of the spectroscopic results has shown that the emission of vapour into the plasma cannot be accounted for by a mechanism of metal volatilization from the cathodic and anodic liquid surfaces only. It also involves emission mechanisms occurring in the cathode spot region, like the expulsion of metal droplets which volatilize or the ejection of particles.

Cleaning of erosion plasma generated by a high-current non-self-maintained arc discharge from microdroplets

This paper presents the results of experiments on cleaning from microdroplets and neutral particles of the chromium plasma flux generated by the simultaneous action of electron beam and cathode spot of a non-self-maintained arc discharge onto the material under evaporation (AIS method: atom–ion sputtering). The AIS-method combines the undoubted merits of both of these: the high evaporation rate of the electron beam method and the high ionization degree inherent in the arc discharge, which is controlled within wide limits. The separator was a curvilinear single-layer solenoid. The value of the magnetic field that was usable for plasma beam focusing was several times less that in analogous devices being used for the separation of the plasma in cathodic arc systems. It is caused by low ion energy (∼6 eV) in this discharge type. The maximum current of chromium single-charged ions at the separator exit was ∼3 A, which corresponded to ∼50% of the maximum input current. The obtained data were the basis for designing the separation device for industry installation AIS-3. The data analysis shows that further development of separating systems using the AIS method will allow us to create powerful and effective ion sources for deposition of metallic, metalloidic and diamond-like coatings.

An approach to the ejection mechanisms of Li atoms from pulsed excimer laser ablation of a LiNbO3 target

A nonequilibrium kinetic model is used for predicting the time evolution of the Li atom concentrations (ground and excited states) in the plasma produced by excimer laser ablation of a LiNbO3 target. The model predicts a very high ionization degree (∼0.97) that agrees well with the one obtained experimentally (∼1). These results together with the prediction of high (and close to local thermodynamic equilibrium) population densities of the electronically excited Li upper energy levels provide an indirect support for an electronic rather than thermal ablation mechanism of Li atoms.

Formation of hybrid polyanion/metal cation/anionic surfactant films via interface complexation and Langmuir–Blodgett technique

Abstract We demonstrate that highly-ordered supramolecular polyanion/polyvalent metal cation/anionic amphiphile complex ultrathin multilayer superlattice films with separating acidic amphiphile bilayers by highly rare-earth-doped hydrophilic polymeric interlayers can be fabricated using Langmuir–Blodgett technique along with interface ligand exchange and coordination reactions. The properties of stearic acid (SA) Langmuir monolayer on the aqueous subphase containing Gd acetate and polysterene sulfonate (PSS)-Na were studied and PSS-Gd-SA multilayer films were deposited successfully onto the solid substrates by conventional vertical dipping method. Built-up films were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction and atomic force microscopy (AFM). FTIR spectroscopy analysis of multilayer films showed high degree of amphiphile and polyanion acidic groups ionization under complexation with rare-earth cations. AFM study of surface morphology of the built-up films revealed unique structure of PSS-Gd-SA film different from polymeric Gd-PSS polymeric complex film and gadolinium stearate Langmuir–Blodgett film. The data obtained give evidence for the formation of high-quality superlattice structures PSS-Gd-SA hybrid films with stearate bilayers separated by Gd-PSS complex interlayers of ∼0.5 nm thickness.

Investigation of carbon nitride films at various arc currents deposited by vacuum cathodic arc method

Considerable interest was devoted to carbon nitride alloys since Liu and Cohen [1] predicted the existence of a metastable covalent carbon nitrogen compound (βC3N4) having interesting properties. Vacuum cathodic arc deposition method is a promising technique, of which the arc plasma is characterized by a high degree of ionization and consists of a streaming plasma with ions in the energy range 10–100 eV which is enough to cause ionization and combine with reactive gas such as nitrogen and form compound films [2, 3]. Up to now, there are several groups which have prepared and investigated the carbon nitride films by this technique [4–7]. However most of them studied the carbon nitride films only by adjustment of supply of nitrogen in the deposition atmosphere [4, 5, 7]. In this work, we make a research of the variation of N content and microstructure of carbon nitride films with various arc currents. The experimental setup is shown schematically in Fig. 1. The distance between target and substrate is 300 mm. N2 and Ar are fed into the chamber during the deposition. The rotatable shielding plate was not rotated aside to start the deposition until the arc current and pressure became stable in order to prevent the deposition of nonideal films at the initial stage. The flow of Ar and N2 was fixed to 8.33 × 10−7 and 4.17 × 10−6 m3 s−1 respectively. The arc current was kept at 20, 30, 40, 50, 60 and 70 A respectively. All the deposition process is sustained for 15 s because of the rapid deposition ratio. The Si (100) substrate was biased at 0 V to study the growth of CNx films. The substrate temperature was less than 100 ◦C during the deposition. X-ray photoelectron spectroscopy (XPS) was used to analyze the film composition; a PHI ESCA 5700 instrument, with an Mg Kα (1253.6 eV) X-ray source operating at a pressure of 1.33 × 10−7 Pa, was used. To avoid damaging the films, they were not subjected to an Ar+ bombardment for sputter cleaning before the analysis. The composition of the films was calculated from the ratio of net intensity of N1s and C1s peaks, corrected by the instrumental sensitivity factors. Raman spectroscopy (SEPX1403) was also used to analyze the small dimensional carbon network in the films. Fig. 2 presents the N content in the carbon nitride films as a function of arc current. It could be observed that upon increasing the arc current from 20 A to 40 A, the N concentrations of these samples were constantly

Integral Field Spectroscopy of Seyfert Galaxies

The present work is based on a spectroscopically selected sample of Seyfert galaxies and consists of the observation, reduction, and analysis of three-dimensional data, obtained through the MPFS, the integral field spectrograph designed and developed by the scientists of the Special Astrophysical Observatory (Russia) for the 6 m telescope. Our aim is focused on a study of the circumnuclear and extranuclear environment of our sample of Seyfert galaxies, within the more general frame of finding clues to the “unified model,” such as the existence of the ionization cones, by applying a modern technique that has proved to be very powerful and advantageous in the case of extended sources. In chapter 1 an overview of active galactic nuclei (AGNs) and the unified model is presented and in particular a description of the main characteristics, similarities, and differences of the Seyfert galaxies. Chapter 2 contains a description of the radiation processes in AGNs, the mechanisms at the origin of the formation of the emission lines, and the diagnostic line ratios that allow one to discriminate between photoionization by thermal and nonthermal sources. Chapter 3 is an introduction to the method of two-dimensional spectroscopy and describes the properties of our observed data, the necessary starting point for developing a reduction procedure. In particular, we can appreciate the advantages and disadvantages in using a simple lenslet array or a more complex combination of a lenslet array and a bundle of optical fibers to decompose the image of a source into several elements. The following chapters present the results obtained through the analysis of the reduced data of three Seyfert galaxies: Mrk 917, NGC 4388, and IRAS 04502 0317. Mrk 917 shows a thick luminous bar, evident both in the images and in the distorted pattern of the velocity field of the gas. The nucleus of the galaxy has a typical spectrum of a Seyfert 2, with index of the power-law continuum . a p 1.5 The excitation map [O iii] l5007/Ha does not show any indication of possible ionization cones. Moreover, the emissionline spectrum of a region close to the active nucleus, classified as AGN-like but showing a high star formation rate, is probably produced by the combined effects of a local starburst and of not absorbed nonthermal radiation from the nucleus. In NGC 4388 we have observed part of one of the two ionization cones known in this galaxy, the so-called southwest cone. The regions inside the cone show spectra of an AGNlike nature. The FWHM of the lines is ∼500 km s , typical of the narrow-line region of the Seyfert galaxies, even if a broad Ha component (FWHM ∼2000 km s ) can be seen, suggesting the idea of scattered photons from the broad-line region. A high degree of ionization, almost constant even at large distances from the active nucleus, cannot be explained only by nuclear photons but is also probably due to the interaction between the known radio jet, aligned with the cone, and the gas within the cone. In IRAS 04502 0317 we have revealed a previously unknown one-sided ionization cone. In spite of its narrow emission lines (FWHM ∼ 300 km s ) more common in a LINER, the nuclear spectrum is typical of a Seyfert galaxy and is modeled by a nonthermal continuum with . A bright a p 1.2 region very close to the nucleus and partially crossed by the ionization cone is present in both the images and the spectra. Some evidence, such as tidal tails (or faint spiral arms), two non-coplanar dust lanes, an offset of the kinematical center with respect to the nucleus, and a negligible circumnuclear star formation, suggests that this bright region could be a secondary nucleus resulting from a minor merger between a gas-poor galaxy and a nucleated companion.

Autoionization phenomena in dense photoionized plasmas

Elementary electron–ion collisional and spontaneous radiative transitions involving autoionizing resonances play important roles in atomic ionization, recombination, and radiative-emission processes in high-temperature astrophysical and laboratory plasmas. When electron–ion collisions are dominant, the ionization structure is usually determined by the steady-state (or dynamical) balance between electron-impact ionization (including autoionization following inner-shell-electron excitation) and radiative recombination combined with dielectronic recombination. The atomic radiative-emission spectrum tends to be dominated by the electron-impact excitation of ordinary spectral lines together with dielectronic satellite lines. In photoionized plasmas, a much higher degree of ionization can be established at a lower electron temperature, particularly as a result of multiple ionization due to Auger transitions following K inner-shell-electron photo-ionization. Radiative and dielectronic recombination can occur predominantly via transitions that are usually not considered to be important, and the unified quantum-mechanical description of the combined electron–ion photo-recombination process may be necessary. The satellite-line emission produced by the radiative decay of multiple-vacancy states can be more prominent, relative to the characteristic-line emission from the decay of single-vacancy states. We have developed a multiple-vacancy-state model for single and multiple ionization, together with characteristic-line and satellite-line emission, resulting from the cascade decay (by spontaneous radiative and Auger transitions) of an arbitrary initial inner-shell-electron vacancy distribution. The initial vacancy distribution may be created by electron or photon impact. We have also developed a unified description of the combined electron–ion photo-recombination process, taking into account the quantum-mechanical interference between radiative and dielectronic recombination. Results of calculations for Fe ions are discussed, which are expected to be valid at low densities. Implications for the detailed kinetics and spectral modeling of dense photoionized plasmas are discussed.

Development of a Blumlein generator dedicated to a fast capillary discharge XUV source

After the feasibility of discharge pumped X-ray lasers was shown by J.J. Rocca et al., different experimental set-up have been proposed as fast capillary discharge drivers. At GREMI we develop a high voltage pulsed generator in order to drive a Z-pinch capillary discharge which is capable to create a plasma highly emissive in the XUV region. The generator is based on a Blumlein-like pulse forming line (PFL). Two transmission lines in parallel discharge through a polyacetal capillary which is 53.5 mm long and 3.5 mm in diameter. The discharge can be triggered by a low inductive surface switch, Rates of current rise time up to 1.4.10 12 A.s -1 have been achieved. Electrical as well as time integrated spectroscopic investigations have been carried out. High degrees of ionization were obtained even at rather low stored energy (E=20 J). Argon ion lines have been identified up to Ar XII.

Cluster mechanism of the energy accumulation in a ball electric discharge

1. OBSERVATIONAL RESULTSExperiments on a man-made initiation of a ball-lightning discharge attract attention in the context ofemploying this phenomenon in technological applica-tions [1]. There are well-known hypotheses that treatthis form of discharge as matter with a condensedexcited phase (E. Manykin, M. Ozhovan), as a systempossessing magnetic self-organization (B. Kadomtsev),as a result of the electromagnetic-field capture into aplasma waveguide (V. Kunin, V. Pleshivtsev, L. Furov),as a consequence of electromagnetic-wave interfer-ence, etc. There are also rather exotic hypotheses likeV. Korshunov’s model, which invokes Dirac magneticmonopoles for the explanation of plasma-ball “pump-ing” or the “polymer” model (V. Bychkov et al. ). Thesehypotheses were reviewed in [2], as well as in mono-graphs [3, 4]. Undeniably, any of the scenarios pro-posed corresponds to usual atmospheric conditions andis unavoidably accompanied by physicochemical pro-cesses in gas, ionization being the most importantamong them. Ionization necessarily causes ion hydra-tion at sufficiently low temperatures.The lack of a generally recognized ball-lightningtheory is an essential gap in the general gas-dischargetheory. The key problem is the energy-accumulationmechanism. Estimates of the energy released in the dis-charge for its lifetime show that the mechanism cannotbe reduced to simple gas heating. At high temperatures,a plasma ball would be of a low density, would beentrained vertically upwards by the Archimedean buoy-ancy force, and would disintegrate in the presence ofturbulent flows caused by its own motion. As observa-tions reveal, the plasma bunch (plasmoid) has a densityof the same, or slightly higher, order of magnitude asthat of ambient air and the stable spherical shape is aconsequence of the positive surface tension at the plas-moid boundary. An excess specific weight of a ball,even in the moderate-heating state, testifies to an ele-vated average molecular weight of its material. This isindirect evidence of intense clustering. A short but pow-erful electric-field pulse is undoubtedly required forball-lightning initiation. Such conditions occur in a lin-ear electric discharge of lightning.The relatively rare occurrence of ball lightning inthe course of a thunderstorm suggests that the coinci-dence of several conditions is necessary for ball-dis-charge formation. As a consequence of the requirementof a high degree of ionization in combination with amoderate gas temperature, spontaneous ball-lightningformation is a relatively rare phenomenon. The mostfavorable prerequisites for ball-discharge initiation are,apparently, realized at the periphery of a powerful lin-ear discharge. A shock acoustic wave is capable ofcausing fast adiabatic gas expansion and its local cool-ing. The optimum geometry of a linear-discharge cur-rent-conducting channel might be responsible for thelocal interference amplification of an electromagneticwave. Apparently, a combination of antinodes for astanding electromagnetic wave and a standing shockacoustic wave composes an origin in which the genera-tion of a ball plasma bunch is most likely to beexpected.Independent measurements of the hydrated-ion con-tent in the atmosphere indicate that the concentration ofcharged clusters is moderate and does not exceed10

The next step in the development of a negative ion beam plasma neutralizer for ITER NBI

Deuterium atom beam injectors developed for ITER plasma heating and current drive are based on negative ion acceleration and further neutralization with a gas target. The maximal efficiency of the gas stripping process is 60%. The replacement of the gas neutralizer by a plasma one must increase the neutral yield to 80%. An overview of experimental studies of microwave discharges in a multicusp magnetic system chosen as the base device for plasma neutralizer (PN) realization and design development of PNs for ITER neutral beam injectors (NBIs) is presented. The experimental results achieved with the PN model PNX-U are discussed. Plasma confinement, gas flows and ionization degree were investigated. High density plasmas with ne ∼1018 m-3 with low electron and ion temperatures ( ≈ 5-6 eV) and a high ionization degree (not less than 40%) at its centre have been generated in operation with argon.

X-ray transmission through a plasma window

Traditional solid window materials used for x-ray synchrotron beamlines may introduce undesirably high attenuation, or are subject to failure under high heat loads. A plasma window can in principle obviate these problems over a wide range of energies. Experiments were performed at the Brookhaven National Laboratory National Synchrotron Light Source on beamline X6A to study the transmission characteristics of a plasma window using argon as the arc gas. Measurements were made around the Ar K edge and far from resonance. The “white-line” absorption at the K edge was actually suppressed during arc operation as compared to room temperature gas at the same pressure. This is attributed to the high degree of ionization in the plasma. The relative strength of the white line to the edge jump does not seem to be a strong function of arc current at the argon K edge. Away from resonance (∼3 times the edge energy) x-ray attenuation was negligible.

A study of plasma parameters in a BAI 730 M triode ion plating system by means of a Langmuir probe and plasma mass and energy spectroscopy

The plasma in a physical vapor deposition (PVD) system used for the deposition of hard coatings (TiN, CrN) was studied by means of a Langmuir probe and energy resolved spectroscopy (Balzers plasma process monitor PPM 421). I– V measurements gave the plasma ( U pl) and floating ( U fl) potentials, as well as the electron temperature T e and plasma density n i . U pl deduced from I– V measurements agreed well with the peak of the positive ion energy distribution, as well as with the highest positive potential for the given operational mode. Energy spectra measured in deposition of TiN show a high degree of ionization of Ti, with Ti 2+ as the prevalent ion. T e calculated from the Maxwellian distribution for the standard deposition of TiN is rather high ( T e=6–8 eV). We believe that the oscillations of the plasma potential with the measured amplitude up to 15 V are most probably the reason. The electron energy distribution F( E) is better described by the Druyvesteyn distribution one than by a Maxwellian one.

Plasma-based low-energy ion implantation for low-temperature surface engineering

This paper summarizes the plasma-based low-energy ion implantation technique, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, developed from a combination of two techniques based on conventional plasma-based ion implantation and low-energy ion beam implantation for improvement in wear resistance and corrosion resistance for metals and alloys. An electron cyclotron resonance (ECR) microwave plasma source is used to produce the plasma with the high plasma density, electron temperature and ionization degree. The ions are accelerated from the plasma by a low pulsed negative bias of −0.4–−3 kV, which is similar to the cathode potential of conventional plasma thermo-chemical diffusion processing. The low process temperature is in the range from 150°C to 500°C, which corresponds to the upper limit of conventional ion beam implantation and to the lower limit of plasma thermo-chemical diffusion processing, respectively. Low-energy ion implantation and simultaneous indiffusion is the main mass transfer mechanism, and direct thermo-chemical diffusion absorption is an additional mass transfer mechanism for formation of the nitrided/carburized layer and thin film. It has been proved that plasma-based low-energy ion implantation technique has the potential for applications in industry for surface modification of metals and alloys.

Enhanced interfacial roughness in metallic multilayers prepared by pulsed cathodic arc deposition

The interfacial roughness of Fe/C multilayers with individual layer thicknesses from a few angstroms to a few tens of angstroms, fabricated using a pulsed cathodic arc, have been studied by cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy (AFM). Very thin perfect 100-period Fe/C multilayers were prepared with flat and smooth interfaces in the sub-nanometer range by a high degree of ionization of the pulsed plasma.

Water-Soluble Polymers. 77. Amphoteric Cyclocopolymers with Sulfobetaine Units: Phase Behavior in Aqueous Media and Solubilization of p-Cresol in Microdomains

A novel series of cyclocopolymers containing the pH-responsive hydrophobic monomer, N,N-diallyl-N-methylamine (DAMA), and the sulfobetaine monomer, 3-(N,N-diallyl-N-methylammonio)-propanesulfonate (DAMAPS), have been prepared in 0.5 M NaCl aqueous solution (pH = 4.0) using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The feed ratio of DAMA:DAMAPS was varied from 100:0 to 0:100 mol % with the total monomer concentration held constant at 2.5 M. 13 C NMR data indicate that the resulting polymers maintain the five-membered-ring structure in the cis conformation common to cyclized diallylammonium salts. Reactivity ratio studies predict that the sulfobetaine monomer is incorporated randomly along the polymer backbone. Weight-average molecular weights and second virial coefficients vary from (4.00 to 8.42) x 10 4 and (2.14 to 4.62) x 10 -4 mL mol g -2 , respectively. Solution behavior is dependent upon pH as determined by turbidimetric titration, steady-shear viscometry, and equilibrium surface tensiometry. At high degrees of ionization, the copolymers assume an extended conformation due to the charge-charge repulsions along the copolymer backbone. As the molar incorporation of the sulfobetaine increases, the copolymer assumes a more globule-like conformation due to zwitterionic interactions. With decreasing degree of ionization of the DAMA units, hydrophobic associations increasingly dominate the solution behavior. For copolymers with a low incorporation of the sulfobetaine, chain collapse leading to phase separation occurs. However, at higher incorporations, the sulfobetaine acts as a hydrophilic segment to limit hydrophobic packing and minimizes the chain collapse. Equilibrium dialysis experiments demonstrate that these pH-reversible microdomains can be used to control the sequestration of organic foulants and thus have potential application as polymeric surfactants in micellar enhanced ultrafiltration processes for water purification.

Nitrogen Incorporation into Tetrahedral Hydrogenated Amorphous Carbon

Structural changes induced by the incorporation of nitrogen into ta-C : H films have been studied by Electron Energy Loss Spectroscopy, X-Ray Photoelectron Spectroscopy, Fourier Transformed Infrared Spectroscopy and Ultraviolet-Visible Spectroscopy. ta-C:H films have been synthesised using a low pressure Electron Cyclotron Wave Resonance (ECWR) source which provides a plasma beam with a high degree of ionisation and dissociation. Nitrogen was incorporated by adding N 2 to the C 2 H 2 plasma used for the deposition of ta-C : H films. The N/C atomic ratio in the films rises rapidly until the N 2 /C 2 H 2 gas ratio reaches three, and then increases more gradually, while the deposition rate decreases steeply. Chemical sputtering of the forming films and the formation of molecular nitrogen within the films limit the maximum nitrogen content to about N/C = 0.6. For low nitrogen content the films retain their diamond-like properties, however as N/C atomic ratio increases, a polymeric-like material is formed, with > C=N- structures and terminating C=N and NH groups that decrease the connectivity of the network.

Spectroscopy of planetary nebulae with [WR] nuclei

We have started an extensive program of systematic observations of planetary nebulae excited by [WR] nuclei with the aim of understanding the evolutionary status of the central stars. Detailed analysis of the nebular and stellar properties might reveal the presence of abundance variations across the nebulae, and allows to detect possible interactions between the massive stellar wind and the nebula. Such an analysis requires spatially resolved spectra, together with a reliable procedure to derive chemical abundances. This is best achieved by constructing individual photo-ionization models that reproduce the main observed properties. Here we present the spectroscopic analysis made for different knots of PB6, NGC2452, NGC2867, NGC6905 and He2–55. All these nebulae are ionized by [WC 2–3] stars and present very high ionization degrees.

Development of a laser-produced plasma target for beam–plasma interaction researches

A laser-produced plasma target system was developed for beam–plasma interaction experiments concerning heavy-ion inertial fusion. Irradiating a small particle of lithium hydride (LiH) with a pulsed laser, transformed the particle into a plasma. The isotropy of the plasma expansion was monitored by charge collectors. The electron density distribution was measured by interferometry. For particle sizes below and irradiation energies above certain critical values, we obtained a spherically symmetric Gaussian-like density distribution and a high degree of ionization. The expected density and size of the spherical plasma as a target for ion beams are roughly ∼10 18 cm −3 and ∼1 mm, respectively.

Ionization efficiency in a geometrically pinched cascaded arc

Remote deposition allows separate optimization of the plasma production source and of the deposition process. To improve the ionization performance of the source, an argon cascaded arc plasma is studied by simulations. Improvements of the source performance in ion yield are achieved by constricting the bore of the arc channel near the entrance. Such a geometrical pinch construction leads to a higher neutral density at the arc inlet which results in increased ionization in the cascaded arc. The improved ionization performance is analysed by solving numerically the conservation laws of mass, momentum and energy in a two-dimensional hydrodynamic approximation using a pressure linked algorithm. The results are compared with those of a simplified one-dimensional formulation in order to identify the main mechanisms. The results indicate that, by constricting the bore of the arc channel, a very high ionization degree can be obtained.

Electron-impact multiple ionization of singly and multiply charged titanium ions

Using the crossed-beams technique the following absolute cross sections have been measured for the reaction : <PRE/> double ionization triple ionization quadruple ionization . Measurements for high charge states and ionization degrees, respectively, show significant contributions of inner-shell processes which partly dominate the respective cross section. The results are compared with the scaling laws of Fisher et al and the semiempirical formula published by Shevelko and Tawara, respectively.