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Letteratura scientifica selezionata sul tema "Interaction plasma/cathode"

Autore: Grafiati

Pubblicato: 3 maggio 2025

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Articoli di riviste sul tema "Interaction plasma/cathode"

Devia Narvaez, D. F., L. F. Alvarez, S. Ramirez Ramirez e And E. Restrepo-Parra. "Numerical analysis of the cathodic material influence on the arc plasma jet". Revista Mexicana de Física 65, n. 3 (7 maggio 2019): 291. http://dx.doi.org/10.31349/revmexfis.65.291.

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The cathodic arc discharge is a deposition technique widely used to synthesize hard coatings and thin films. The structure of the plasma generated by the electrical discharge and its interaction with neutral particles was studied using numerical simulations. Typical plasma parameters were characterized considering their spatial and temporal dependence, as well as several cathode materials that are commonly used in these systems. For the evolution of the ion density, it was observed the formation of Knudsen layer, and also a dependence of pressure gradients in the global behavior. With respect to the kinetic energy, it was found a deceleration of ions, which is represented by a shock front produced in the plasma−neutrals interaction. On the other hand, the energy releasing was generated due to the heat transference between electrons and ions. The plasma potential follows a behavior, which is similar to that of the ion density, and it is caused by the dynamics of charged particles which is directly affected by the concentration of neutrals and ions. In general, the physical quantities are directly affected by electrical and thermal conductivity of the cathode material. Our results can be applied to understand the plasma phenomena produced in a cathodic arc discharge

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Emelyanov, O., A. Plotnikov e E. Feklistov. "Positive corona streamer interaction with metalized dielectric: Possible mechanism of cathode destruction". Physics of Plasmas 29, n. 6 (giugno 2022): 064501. http://dx.doi.org/10.1063/5.0093203.

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This paper examines the effect of pulsed positive point-to-plane corona discharge in millimeter air gaps on the surface of a metalized dielectric. A footprint method was applied to reveal the streamer–surface interaction with Al and Zn thin films (20–50 nm) as a sensitive indicator. A thin metal film-dielectric substrate system was destructed at relatively low typical average currents of 20–50 μA during exposure times of 2–200 s. Destruction occurred in local zones with a size of several μm2 per one discharge pulse, which is substantially lower than the conventional streamer size of several tens of micrometers. An offered model of electro-thermal heating of the cathode layer shows that the dielectric surface temperature can achieve 1000 K and more during the single current pulse of submicrosecond duration. The indicated mechanism is possibly responsible for the effects of the discharge plasma interaction with low heat conductivity cathodes, including biological objects. Intensive heating of the cathode layer should be considered when modeling the streamer–cathode interaction.

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Yamamoto, Kentaro, Manabu Tanaka, Tashiro Shinichi, Kazuhiro Nakata, Keiichi Suzuki e Kei Yamazaki. "Numerical Modeling of Welding Arc with Complex System between Arc Plasma and Molten Electrode". Materials Science Forum 580-582 (giugno 2008): 311–14. http://dx.doi.org/10.4028/www.scientific.net/msf.580-582.311.

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It is important to consider the interaction between arc plasma and electrodes because melting of electrodes strongly affects arc plasma. Therefore, a GMA model will be developed, based on the unified model of TIG arc. As a first step, a TIG arc model with a calculation for molten cathode shape has been proposed. This model is calculated in two cases; molten W cathode and Calculation result of W cathode. In the case of W cathode, cathode shape change was found to affect the arc plasma property strongly. Calculated results of radial temperature distributions on electrode surface and arc pressure distributions at the anode surface are very similar to the experimental results.

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Trivedi, K., S. Tanguay, M. Matties e R. Sacks. "Magnetically Tailored Arc and Glow Discharge Plasmas for Atomic Spectroscopy". Applied Spectroscopy 41, n. 5 (luglio 1987): 833–43. http://dx.doi.org/10.1366/0003702874448382.

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Three magnetic field-plasma configurations are used to study the interaction of external magnetic fields with analytically useful plasma devices. First, a magnetic field oscillating at 60 Hz and normal to the electric field in a 12-A direct current arc plasma is used to obtain an Ē×B̄ drift motion of the arc current channel. This causes a periodic vertical displacement of the channel. Second, a cw magnetic field is used to alter the structure and radiative properties of a demountable glow discharge lamp that uses a center-post cathode. The magnetic field axis is parallel to the cathode axis, and the lamp is operated in a pseudo-magnetron mode. Third, a damped, oscillatory magnetic field produced by discharging a capacitor through a coil is used to alter the radiative characteristics of several commercial hollow cathode lamps. The magnetic field is parallel to the cathode axis, and again the lamps operate in a pseudo-magnetron mode. In all three systems, the presence of the magnetic field drastically alters the radiative properties of the plasmas.

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Li, Limin, Chao Liu, Xuming Zhang, Guosong Wu, Ming Zhang, Ricky K. Y. Fu e Paul K. Chu. "Plasma-target surface interaction during non-equilibrium plasma irradiation at atmospheric pressure: Generation of dusty plasma". Laser and Particle Beams 32, n. 1 (5 novembre 2013): 69–78. http://dx.doi.org/10.1017/s0263034613000888.

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AbstractThe remaining challenges, developing the relativistic electron beam sources, stimulate the investigations of cathode materials. Carbon-fiber-aluminum composite is the most appropriate cathode materials to construct the robust relativistic electron beam sources. Carbon-fiber-aluminum composite is treated by a non-equilibrium atmospheric plasma torch with a copper electrode based on high-voltage gas discharge. The axial and radial distributions of the plasma torch temperature are measured to determine the optimal treatment temperature and location. Copper-oxide particles with diameters of less than 1 µm are deposited onto the surface of the carbon-fibers and a layer of copper-oxide covers the entire surface as the treatment time is increased. Raman spectroscopy suggests that although the locations of the D and G band are similar, the areas of the D and G bands increase after the plasma treatment due to the reduced graphite crystalline size in the carbon-fibers. Analysis of the copper electrode surface discloses materials ablation arising from the discharge which releases copper from the source. Our results reveal that the atmospheric plasma torch generated by high-voltage discharge is promising in the surface modification of the carbon-fiber-reinforced aluminum composite. Further, the plasma produced by atmospheric plasma torch is dusty plasma, due to the participation of liberated copper particles. The plasma torch was analyzed by fluid dynamics, in terms of plasma density, plasma expansion velocity, and internal pressure, and it was found that the plasma produced by atmospheric torch is supersonic flow.

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Vannaroni, G., C. B. Cosmovici, U. Guidoni, L. Iess e L. Scandurra. "Interaction of a hollow-cathode source with an ionospheric plasma". Advances in Space Research 10, n. 7 (gennaio 1990): 147–50. http://dx.doi.org/10.1016/0273-1177(90)90289-c.

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Wroński, Z. "Plasma of the cathode zone of glow discharges and its interaction with the cathode surface". Vacuum 63, n. 4 (agosto 2001): 535–39. http://dx.doi.org/10.1016/s0042-207x(01)00235-4.

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Rakhadilov, B. K., Z. A. Satbayeva, A. E. Kusainov e E. Naimankumaruly. "Linear plasma device for the study of plasma-surface interactions". Bulletin of Shakarim University. Technical Sciences, n. 3(11) (28 settembre 2023): 82–90. http://dx.doi.org/10.53360/2788-7995-2023-3(11)-10.

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In the research and production company "PlasmaScience" (Ust-Kamenogorsk, Kazakhstan) a new laboratory linear plasma installation KAZ-PSI (Kazakstan plasma Generator for Plasma Surface Interactions) for studying the interaction of plasma with material has been developed and built. The article describes some features of the developed experimental setup for the study of surface-plasma interactions. The main elements of the linear plasma setup are an electron-beam gun with a LaB6 cathode, a plasma-beam discharge chamber, an interaction chamber, a target device, and an electromagnetic system consisting of electromagnetic coils. The KAZ-PSI facility allows generating continuous plasma of hydrogen, deuterium, helium, argon and nitrogen. The electron density of the plasma is in the range of the order of 1017 -1018 m-3 and the electron temperature is in the range of 1 to 20 eV. The incident ion energy is controlled by applying a negative bias of up to 2 kV to the target. Experiments on irradiation of tungsten with helium plasma were carried out for the first time at the KAZ-PSI facility. The paper presents the results of studies conducted to study changes in the tungsten mixture. The results have shown that after helium plasma irradiation the morphology of tungsten surface changes and relief is created on the surface due to atomisation of the surface by helium ions, as well as due to the formation of blisters.

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Jassam, H. F., e R. A. Ali. "Interaction of near-cathode plasma layers with thermionic electrodes under high pressure arc plasma". Journal of Physics: Conference Series 2322, n. 1 (1 agosto 2022): 012076. http://dx.doi.org/10.1088/1742-6596/2322/1/012076.

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Abstract Theoretical calculations and simulation data were presented to study the effect of the Xe-Dy mixture on properties of arc plasma. The effect of voltage, concentration and temperature on current flow density, power flux density and cathode temperature were studied. Different concentrations of Dysprosium (0.005, 0.01, 0.05, 0.1, and 0.5 mol) were used. The program (NCBL) was used in this work. Results showed a clear effect of concentration on plasma parameters, especially at the highest concentration, in addition to the effect of voltage. We notice that the current density increases from ≥3500k), while (3500 – 5000k) increases for all concentrations due to collisions as well as density of flowing energy For all the concentrations mentioned, we noticed that there is a clear effect of the temperature (≥ 3500k) on current density where increases and from (3500- 5000). we noticed an increase in the current density as well as the voltage especially at (25v) where the current and the energy overflow density increase due to elastic and inelastic collisions because acceleration of electrons with an increase in voltage.

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Ashurbekov, N. A., M. B. Kurbangadzhieva, K. O. Iminov, G. Sh Shakhsinov e K. M. Rabadanov. "ASYMMETRY OF THE OPTICAL TRANSMISSION SPECTRA OF A PULSED DISCHARGE WITH AN EXTENDED HOLLOW CATHODE DURING AT RESONANCE INTERACTION OF SHORT POLYCHROMATIC LASER PULSES WITH EXCITED NEON ATOMS". Journal of Applied Spectroscopy 89, n. 6 (16 novembre 2022): 815–19. http://dx.doi.org/10.47612/0514-7506-2022-89-6-815-819.

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The processes of resonant interaction of short pulses of polychromatic radiation of a dye laser with plasma of a nanosecond discharge in neon with an extended hollow cathode are experimentally studied. During the propagation of laser radiation inside the cathode cavity near the spectral absorption line of Ne I with a wavelength of 650.6 nm, the formation of asymmetric optical transmission spectra of the plasma of the dispersion type are detected, while during the propagation of laser radiation in the region between the electrodes, symmetric transmission spectra of the classical kind are formed.

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Più fonti

Tesi sul tema "Interaction plasma/cathode"

Monnoyer, Arthur. "Etude et optimisation du transfert d'énergie au sein d'une torche à plasma de forte puissance à cathode creuse". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES258.

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Ces travaux, menés en collaboration avec la société Europlasma, sont consacrés à l'étude et à la prédiction de quelques phénomènes au sein des torches à plasma thermique de forte puissance (300 kW à 1 MW) à cathode creuse. Outre la géométrie particulière de la cathode, cette technologie de torche est composée d'une chambre d'injection en vortex du gaz plasmagène et d'une bobine créant un champ magnétique extérieur permettant de déplacer le pied d'arc cathodique par force de Laplace, afin de réduire l'érosion de cette électrode. Dans un premier temps, nous mettons en place un modèle fluide à l'équilibre thermodynamique local permettant la description de la dynamique de l'arc au sein de la torche. Ce modèle prenant en compte la turbulence par un modèle de type k-epsilon Realizable, permet de prédire le positionnement axial du pied d'arc cathodique et sa vitesse de rotation. Afin de nous affranchir de la description des phénomènes de claquage ayant lieu au sein de l'anode, un modèle d'anode poreuse est utilisé. Cette approche permet une première caractérisation du jet de plasma en sortie de torche. Les approches de la littérature consistant à tronquer la géométrie en entrée d'anode pour caractériser les phénomènes dans l'électrode amont sont comparées avec notre modèle utilisant la géométrie complète. Un bon accord est obtenu en termes de la trajectoire du pied d'arc cathodique ce qui justifie ces approches. Une étude paramétrique est alors menée sur la géométrie tronquée. En particulier, l'influence du gaz plasmagène et de diverses configurations magnétiques de la bobine de champ sur la trajectoire du pied d'arc cathodique sont étudiées. L'usure des électrodes, et notamment de la cathode, est un problème majeur lors de l'utilisation de ce type de torche. Ainsi, en parallèle de l'étude de la dynamique de l'arc, nous avons cherché à caractériser les phénomènes conduisant à cette usure. Dans un premier temps, le champ de température au sein du matériau est caractérisé grâce à un modèle analytique. Cette étude nécessite de connaître les caractéristiques du dépôt de puissance sur la surface cathodique par le pied d'arc (puissance totale et rayon de la tâche d'accrochage). Ces caractéristiques sont obtenues à l'aide de diverses mesures expérimentales de la littérature. Le champ de température calculé dépend aussi de la vitesse de rotation du pied d'arc (qui peut être déterminée avec le modèle fluide) et du refroidissement mis en place. Ce calcul prédit que la température maximale atteinte dans le matériau ne dépasse pas la température de fusion, en contradiction avec l'existence expérimentale de l'usure. Ce résultat provient d'une description insuffisante de la zone d'interaction arc-cathode qui doit prendre en compte la présence de micro-spots cathodiques. Une part importante de ces travaux est donc dédiée à l'étude théorique de cette interaction, prenant en compte les déviations à l'état d'équilibre thermodynamique local, la physique de la gaine cathodique et la vaporisation du matériau. En nous basant sur les travaux de M.S. Benilov, nous proposons un modèle de spot cathodique sur une cathode non-réfractaire. Cette étude permet de lever la contradiction précédente et donne de bons ordres de grandeur du taux d'usure observé expérimentalement
This work, carried out in collaboration with the company Europlasma, is devoted to the study and prediction of some phenomena within high-power well-type cathode thermal plasma torches (300 kW to 1 MW). In addition to the particular geometry of the cathode, this torch technology is composed of a vortex injection chamber for the plasma gas and a coil creating an external magnetic field making it possible to move the cathode arc foot by Laplace force, in order to reduce the erosion of this electrode. First, we set up a fluid model with local thermodynamic equilibrium allowing the description of the dynamics of the arc within the torch. This model, taking into account turbulence using a k-epsilon Realizable type model, makes it possible to predict the axial positioning of the cathode arc base and its rotation speed. In order to free ourselves from the description of the breakdown phenomena taking place within the anode, a porous anode model is used. This approach allows a first characterization of the plasma jet at the torch exit. Literature approaches consisting of truncating the geometry at the anode inlet to characterize the phenomena in the upstream electrode are compared with our model using the complete geometry. A good agreement is obtained in terms of the trajectory of the cathode arc foot which justifies these approaches. A parametric study is then carried out on the truncated geometry. In particular, the influence of plasma gas and various magnetic configurations of the field coil on the trajectory of the cathode arc foot are studied. Erosion of the electrodes, and particularly the cathode, is a major issue when using this type of torch. Thus, in parallel with the study of the dynamics of the arc, we sought to characterize the phenomena leading to this erosion. First, the temperature field within the material is characterized using an analytical model. This study requires knowing the characteristics of the power deposition on the cathode surface by the arc foot (total power and radius of the arc foot). These characteristics are obtained using various experimental measurements from the literature. The calculated temperature field also depends on the rotation speed of the arc foot (which may be determined using the fluid model) and the electrode cooling. This calculation predicts that the maximum temperature reached in the material does not exceed the melting temperature, in contradiction with the experimental existence of erosion. This result comes from an insufficient description of the arc-cathode interaction zone which must take into account the presence of cathode micro-spots. A significant part of this work is therefore dedicated to the theoretical study of this interaction, taking into account deviations from the state of local thermodynamic equilibrium, the physics of the cathode sheath and the vaporization of the material. Based on the work of M.S. Benilov, we propose a model of a cathode spot on a non-refractory cathode. As a result, the previous contradiction disappears and the orders of magnitude of the calculated erosion rates are in good agreement with the experiment

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Cayla, François. "Modélisation de l'interaction entre un arc électrique et une cathode". Toulouse 3, 2008. http://www.theses.fr/2008TOU30033.

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Ce travail est relatif à l'étude et à la mise en place d'un modèle décrivant l'interaction entre un plasma thermique d'argon à la pression atmosphérique et une cathode en tungstène. Après une étude bibliographique sur les différents modèles décrivant la zone d'interaction, la théorie proposée par Benilov a été retenue comme base de nos développements. Dans une seconde partie, le modèle d'interaction arc/cathode est amélioré notamment par la prise en compte de l'émission secondaire. Le modèle est ensuite confronté et validé par des résultats expérimentaux issus de la littérature. Notre objectif était de coupler ce modèle d'interaction à une modélisation plus globale représentant aussi bien le passage du courant dans la cathode, la zone d'interaction (gaine et pré-gaine) que la colonne du plasma. Nous exposons les différents paramètres d'entrée possibles et justifions le choix de la densité de courant. Dans une dernière partie, le modèle d'interaction développé est couplé à un modèle bidimensionnel (2D) de plasma thermique en écoulement. Le passage du courant entre la cathode et le plasma est assuré grâce à une estimation de la conductivité électrique à deux températures dans la pré-gaine. L'influence de paramètres physiques (valeurs du coefficient d'émission secondaire, du travail de sortie,. . . ) et géométriques sur les grandeurs caractéristiques de la décharge (tension cathodique, champ de température dans le plasma,. . . ) dans une configuration d'arc libre avec une cathode cylindrique a pu être étudiée
This work deals on the study and the development of a model describing the interaction between argon thermal plasma and a tungsten cathode. A bibliographical study of the different models describing the interaction region is performed leading to the theory proposed by Benilov as base of our developments. In a second part, the arc/cathode interaction model has been realized taking into account secondary emission phenomenon. Then the model has been compared and validated by experimental results found in the literature. The final aim of this study was to couple the developed interaction model to a more global modeling describing the electrical conduction in the cathode bulk, the interaction region (sheath and pre-sheath) and the plasma column. We expose the rule of different possibilities for the input parameters and we justify the choice of the current density as main entry. In a last part, the interaction model has been coupled to a two dimensional coordinate system model of thermal plasma flow. The current continuity between cathode and plasma has been assumed using an estimation of the two temperature electrical conductivity in the pre-sheath. The influence of physical parameters (values of the secondary emission coefficient, work function. . . ) and geometrical ones on the characteristics of the discharge (cathode drop voltage, plasma temperature field. . . ) in a free burning arc configuration using cylindrical cathode has been realized showing the good ability and behavior of the model to a global thermal plasma description

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Le, Ludec Jean-Pierre. "Instrumentation et traitement du signal pour la caractérisation thermique et mécanique d'un four de tirage Czochralski sous champ magnétique : application à la croissance de GaAs". Grenoble 1, 1989. http://www.theses.fr/1989GRE10141.

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Une approche systematique de l'evolution des caracteristiques courant-tension et pression-tension, completee par une etude par spectroscopie d'emission et par la mesure de la densite electronique, nous a conduits a une interpretation fine de la decharge en cathode creuse de titane sous plasma d'argon. Une tension minimale de decharge fonction d'une pression optimale et d'un courant optimal de decharge, est mise en evidence, ces deux derniers parametres evoluant de facon proportionnelle. Nous montrons que l'efficacite maximale d'excitation et d'ionisation des electrons se produit a des pressions inversement proportionnelles aux classes d'energie electronique considerees. Nous mettons egalement en evidence une modification des caracteristiques de la decharge etroitement liee aux phases cristallographiques alpha et beta du titane. Ce phenomene semble etre associe a une variation du travail de sortie du titane a la transition de phase

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Pagaud, Francis. "Control and stability of magnetised plasma columns : plasma-cathode interactions and helicon plasma operation". Electronic Thesis or Diss., Lyon, École normale supérieure, 2024. http://www.theses.fr/2024ENSL0016.

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Le transport, les ondes et les instabilités sont des problématiques courantes des plasmas magnétisés, à l’origine de problèmes fondamentaux et de limites opératoires pour les plasmas de fusion, les accélérateurs de particules à plasma ou la propulsion plasma. Le contrôle des propriétés du plasma est souhaitable mais complexe. Ce doctorat vise à utiliser une cathode émissive comme nouveau paramètre de contrôle et à comprendre la stabilité du plasma hélicon. Le dispositif expérimental est une enceinte à vide cylindrique de 80 cm de long et 20 cm de diamètre, connecté à un tube source en verre de 11 cm de diamètre. L’argon est injecté en continu à 0,13 Pa et ionisé par une antenne radio-fréquence inductive de 1 kW enroulée autour du tube source. Un champ magnétique de 170 G à 340 G garantit une faible magnétisation. Une cathode chaude injecte un fort courant thermionique à l’autre extrémité de la colonne de plasma. Les mesures optiques de température de la cathode ont révélé un profil fortement inhomogène dû aux interactions plasma-cathode, et fut reproduit numériquement avec succès par un modèle thermique détaillé. Le régime opératoire prédit est en excellent accord avec les expériences. L’influence expérimentale de l’injection d’électrons sur les propriétés plasmas, et plus particulièrement le potentiel plasma, a été couplée à une approche analytique basée sur un modèle de plasma magnétisé. Un accord qualitatif entre les prédictions théoriques et le contrôle effectif du potentiel plasma a été trouvé. La perspective de l’utilisation d’une cathode émissive comme nouveau paramètre de contrôle ouvre la possibilité d’un réglage fin de la dynamique globale du plasma, ainsi que la mitigation du transport et des instabilités au sein du plasma. Des améliorations sont discutées en vue d’une prédiction quantitative accrue. Enfin, une source de plasma hélicon haute densité a été implémentée afin d’atteindre des taux d’ionisation importants et un couplage antenne-plasma optimal. Ce nouveau système a été caractérisé à l’aide de sondes et d’imagerie rapide. Des signatures typiques des plasmas hélicons ont été retrouvées telles que des transitions de mode E-H-W, une rupture de symétrie liée au champ magnétique et la propagation d’ondes whistler m = +1. En outre, des oscillations basse-fréquence telles que des oscillations H-W et W-W, et des instabilités coexistantes de Rayleigh-Taylor et Kelvin-Helmholtz ont été identifiées. Une forte instabilité multi-échelles à 1080 G a été également brièvement explorée. L’identification des mécanismes d’instabilité via le calcul des taux de croissance, la décomposition 2D-FT et POD ont permis de comprendre les mécanismes physiques à l’oeuvre
Radial transport, azimuthal waves and instabilities are common features in magnetised plasmas, causing major challenges for plasma propulsion, plasma wakefield particle acceleration or fusion devices. Plasma properties control is desirable yet complex. This PhD thesis follows two goals, one being the use of an emissive cathode as a new parameter control and the other being the fundamental understanding of the helicon plasma operational stability. Firstly, the role of the injection of electrons inside a magnetised plasma column has been studied experimentally and numerically. The experimental set-up is a 80 cm long and 20 cm diameter vacuum vessel connected to a 11 cm wide glass tube. The argon gas at a base pressure of 0.13 Pa is ionised by a 3-turns inductive radio-frequency antenna supplied at 1 kW. Magnetic field ranging from 170 G to 340 G, ensures a weak magnetisation of the plasma. A large tungsten hot cathode was placed at the end of the plasma column to inject an important thermionic current. Electrical and optical measurements of the cathode temperature revealed a highly inhomogeneous cathode temperature profile due to plasma–cathode interactions. A detailed thermal modelling solved numerically accurately reproduces the heterogeneous rise in temperature witnessed experimentally. The operating regime was predicted in excellent agreement with experimental results.The fine understanding of the emissive cathode behaviour in presence of a surrounding magnetised plasma permitted to explore its influence on the plasma properties, and especially the plasma potential. An analytical approach based on a two-fluids plasma model and anisotropic electrical conductivities, predicting plasma potential control and plasma rotation regulation as a function of thermionic emission, has been applied and compared to a wide experimental dataset of plasma properties. The works presented confront the role of cross-field ion transport to experimental radial plasma potential scans with a semi-quantitative agreement, highlighting a new major application of emissive cathodes.Finally, a state-of-the-art helicon plasma source has been implemented to produce higher ionization rates. This new system required a complete characterisation of plasma properties through electrostatic probes and high-speed camera imaging. It reproduced well-known helicon plasma features such as E-H-W mode transitions, bistability and hysteresis, chirality emerging from the external magnetic field direction and the propagation of m = +1 whistler waves. Besides, it displayed complex behaviours such as H-W and W-W oscillations, or coexisting low-frequency Kelvin-Helmholtz and Rayleigh-Taylor instabilities. A strong multiscale core instability at 1080 G was also briefly investigated. Wave-mode identification based on theoretical growth rates, 2DFT modal decomposition and POD has been conducted, unravelling the physical mechanisms at stake

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Kaufmann, Helena Teresa da Costa. "Advanced modeling of plasma-cathode interaction in vaccum and unipolar arcs". Doctoral thesis, 2019. http://hdl.handle.net/10400.13/2302.

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Este trabalho Ø dedicado modelaªo da interacªo plasma-cÆtodo em descargas de arco em vÆcuo e em descargas de arco unipolares. Pela primeira vez foi desenvolvido um modelo numØrico detalhado de manchas catdicas solitÆrias em descargas de arco em vÆcuo. O modelo leva em conta todos os mecanismosrelevantesdosfenmenosfsicosdemanchascatdicas: obombardeamento dasuperfciedocÆtodoporiıesprovenientesdeumplasma prØ-existente; avaporizaªo do material do cÆtodo na mancha, a ionizaªo deste material vaporizado e a interacªo do plasma produzido com o cÆtodo; desenvolvimento do efeito de Joule no interior do cÆtodo; fusªo do material do cÆtodo e movimento do metal fundido sob o efeito da pressªo exercida pelo plasma e da fora de Lorentz; a deformaªo da superfcie fundida do cÆtodo; a formaªo de crateras e jactos de metal fundido; a ejecªo de gotas. Os resultados da modelaªo permitem identicar as diferentes fases da vida de uma mancha solitÆria. A emissªo de electrıes da superfcie do cÆtodo e o transporte de calor por convecªo sªo os mecanismos dominantes de arrefecimento na mancha catdica, limitando deste modo a temperatura mÆxima possvel no cÆtodo. A formaªo de crateras na superfcie do cÆtodo ocorre sem explosıes, seguida da formaªo de um jacto de metal fundido e da ejecªo de uma gota. Os resultados da modelaªo sªo concordantes com estimativas efectuadas para diferentes mecanismos de erosªo do cÆtodo, com base nos dados experimentais relativos erosªo em cÆtodos de cobre de descargas de arco em vÆcuo. A fase inicial de uma descarga de arco unipolar em condiıes relevantes para a fusªo nuclear em reactores tokamak foi investigada no mbito do modelo detalhado de manchas catdicas solitÆrias em descargas de arco em vÆcuo. Mais concretamente, a interacªo de um uxo intenso de energia com uma placa de tungstØnio imersa num plasma de hØlio e a correspondente transferŒncia de corrente foi estudada em condiıes baseadas em experiŒncias laboratoriais. Uma vez que o arco Ø de natureza unipolar, a transferŒncia de corrente fora da mancha Ø tida em consideraªo no modelo utilizado e a variaªo da diferena de potencial entre o plasma e a placa Ø avaliada a partir da condiªo de corrente total nula transferida para a placa a cada instante. Os resultados da modelaªo revelam a formaªo de uma cratera, mas sem a formaªo de um jacto de metal fundido ou a ejecªo de uma gota. A modelaªo Ø realizada para diferentes condiıes e demonstra-se que Ø necessÆrio ter em consideraªo a limitaªo da corrente terminica de electrıes pela banha de carga de espao.
This work is dedicated to modeling of the plasma-cathode interaction in vacuum and in unipolar arcs. A detailed numerical model of individual cathode spots in vaccum arcs has been developed for the rst time. The model takes into account all the relevant mechanisms of the physics of cathode spots: the bombardment of the cathode surface by ions coming from a pre-existing plasma cloud; vaporization of the cathode material in the spot, its ionization, and the interaction of the produced plasma with the cathode; Joule heat generation in the cathode body; melting of the cathode and motion of the molten metal under the e⁄ect of the plasma pressure and the Lorentz force; the change in shape of the molten cathode surface; the formation of craters and liquid-metal jets; the detachment of droplets. The simulation results allow the identication of the di⁄erent phases of life of an individual spot. Electron emission cooling and convective heat transfer are dominant mechanisms of cooling in the spot, limiting the maximum temperature of the cathode. Craters are formed on the surface without explosions, followed by the the formation of a liquid-metal jet and the ejection of a droplet. The modeling results conform to estimates of di⁄erent mechanisms of cathode erosion derived from the experimental data on the net and ion erosion of copper cathodes in vacuum arcs. The initial stage of unipolar arcing in fusion-relevant conditions was investigated in the framework of the detailed model of cathode spots in vacuum arcs. In particular, the interaction of an intense heat ux with and current transfer to a tungsten metal plate immersed in a helium background plasma is studied in conditions based on experiments. Since the arc is unipolar, the model is supplemented with an account of current transfer outside the arc attachment and the potential di⁄erence between the plasma and the plate is evaluated from the condition of the net current transferred to the plate being zero at each moment. The simulation results reveal the formation of a crater, but no jet formation or droplet detachment. Simulations are performed for di⁄erent sets of conditions, and it is found that in order for the developed model to be applicable to real experimental situations, space-charge limited thermionic electron emission must be considered.

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Almeida, Pedro Jorge Gomes Camacho de. "Investigation of modes of current transfer to cathodes of glow and arc discharges". Doctoral thesis, 2011. http://hdl.handle.net/10400.13/1471.

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This work is dedicated to modelling of di⁄erent modes of current transfer to cathodes of glow discharges and to experimental investigation of formation of transient spots on thermionic arc cathodes. Multiple steady-state solutions in the theory of DC glow discharge have been found for the rst time. The modelling was performed in the framework of the basic model of glow discharges and also in the framework of a more detailed model. The basic model comprises equations of conservation of a single ion species and the electrons, transport equations for the ions and the electrons written in the local approximation, and the Poisson equation. The detailed model takes into account atomic and molecular ions, atomic excited states, excimers, and non-locality of electron transport and kinetic coe¢ cients. These multiple solutions describe modes with a normal spot as well as modes with patterns of several spots similar to those observed in experiments with microdischarges in xenon. It is shown that modes with more than one spot can, in principle, occur not only in xenon but also in other plasma-producing gases. Formation of transient spots on thermionic cathodes was studied in experiments with COST529 standard HID lamps. There is a generally good agreement between experiment and results of numerical modelling. A possibility of prevention of appearance of transient spots by means of a brief reduction of the arc current shortly after the initial current increase is proposed and justied. It is shown that the main mechanism of blackening of burners of HID lamps that accompanies appearance of transient cathode spots is evaporation of the cathode material and not sputtering.
Este trabalho Ø dedicado modelaªo de diferentes modos de transferŒncia de corrente aos cÆtodos de descargas luminescentes e investigaªo experimental da formaªo de manchas transitrias em cÆtodos terminicos de descargas de arco. Mœltiplas soluıes estacionÆrias existentes na teoria da descarga luminescente foram calculadas numericamente pela primeira vez. A modelaªo foi realizada no mbito do modelo bÆsico da descarga luminescente e no mbito de um modelo detalhado. O modelo bÆsico contØm equaıes de conservaªo de uma espØcie inica e dos electrıes, equaıes de transporte dos iıes e electrıes escritas na aproximaªo local e a equaªo de Poisson. O modelo detalhado leva em conta iıes atmicos e moleculares, estados excitados dos Ætomos, dmeros excitados e nªo-localidade dos coecientes de transporte e cinØticos dos electrıes. As mœltiplas soluıes descrevem modos com uma mancha normal e modos com padrıes de vÆrias manchas semelhantes aos observados nas experiŒncias com micro-descargas em xØnon. Demonstra-se que modos com mais que uma mancha podem, em princpio, ocorrer em descargas noutros gases que nªo o xØnon. A formaªo de manchas transitrias em cÆtodos terminicos foi estudada em experiŒncias com lmpadas HID padrªo, COST-529. Existe uma concordncia genØricamente boa entre os resultados experimentais e da modelaªo numØrica. Uma possibilidade de prevenªo do aparecimento de manchas transitrias atravØs da breve reduªo da corrente da descarga logo aps um salto na corrente Ø proposta e justicada. Demonstra-se que o principal mecanismo de escurecimento das lmpadas HID que acompanha a formaªo de manchas catdicas Ø a evaporaªo do material do cÆtodo.

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Capece, Angela Maria. "Plasma-Surface Interactions in Hollow Cathode Discharges for Electric Propulsion". Thesis, 2012. https://thesis.library.caltech.edu/7108/4/Capece_Thesis_ChapterBib.pdf.

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Electric thrusters generate high exhaust velocities and can achieve specific impulses in excess of 1000 s. The low thrust generation and high specific impulse make electric propulsion ideal for interplanetary missions, spacecraft station keeping, and orbit raising maneuvers. Consequently, these devices have been used on a variety of space missions including Deep Space 1, Dawn, and hundreds of commercial spacecraft in Earth orbit. In order to provide the required total impulses, thruster burn time can often exceed 10,000 hours, making thruster lifetime essential.

One of the main life-limiting components on ion engines is the hollow cathode, which serves as the electron source for ionization of the xenon propellant gas. Reactive contaminants such as oxygen can modify the cathode surface morphology and degrade the electron emission properties. Hollow cathodes that operate with reactive impurities in the propellant will experience higher operating temperatures, which increase evaporation of the emission materials and reduce cathode life. A deeper understanding of the mechanisms initiating cathode failure will improve thruster operation, increase lifetime, and ultimately reduce cost.

A significant amount of work has been done previously to understand the effects of oxygen poisoning on vacuum cathodes; however, the xenon plasma adds complexity, and its role during cathode poisoning is not completely understood. The work presented here represents the first attempt at understanding how oxygen impurities in the xenon discharge plasma alter the emitter surface and affect operation of a 4:1:1 BaO-CaO-Al₂O₃ hollow cathode.

A combination of experimentation and modeling was used to investigate how oxygen impurities in the discharge plasma alter the emitter surface and reduce the electron emission capability. The experimental effort involved operating a 4:1:1 hollow cathode at various conditions with oxygen impurities in the xenon flow. Since direct measurements of the emitter surface state cannot be obtained because of the cathode geometry and high particles fluxes, measurements of the emitter temperature using a two-color pyrometer were used to determine the oxygen surface coverage and characterize the rate processes that occur during poisoning.

A model describing the material transport in the plasma discharge was developed and is used to predict the barium and oxygen fluxes to the emitter surface during cathode operation by solving the species continuity and momentum equations. The dominant ionization process for molecular oxygen in the plasma gas is resonant charge exchange with xenon ions. Barium is effectively recycled in the plasma; however, BaO and O₂ are not. The model shows that the oxygen flux to the surface is not diffusion limited.

Experimental results indicate that the oxygen poisoning rate is slow and that the oxygen poisoning coverage on the emitter surface is less than 3%. A time-dependent model of the reaction kinetics of oxygen and barium at the tungsten surface was developed using the experimental results.

The experiments and kinetics model indicate that the dominant processes at the emitter surface are dissociative adsorption of O₂, sputtering of the O₂ precursor, and desorption of O. Ion sputtering of the weakly bound O₂ precursor state limits the poisoning rate and yields low oxygen coverage. Removal of chemisorbed atomic oxygen is dominated by thermal processes. Based on the low oxygen coverage and long poisoning transients, plasma cathodes appear to be able to withstand higher oxygen concentrations than vacuum cathodes.

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Guerrero, Vela Pedro Pablo. "Plasma Surface Interactions in LaB₆ Hollow Cathodes with Internal Xe Gas Discharge". Thesis, 2019. https://thesis.library.caltech.edu/11673/39/Guerrero_Pablo_2019.pdf.

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The ultimate goals of space vehicles are to move faster, further, and more reliably in the space environment. Electric propulsion (EP) has proven to be a necessary technology in the exploration of our solar system ever since its working principle was empirically tested in space in 1964. Thanks to the high exhaust velocities of ionized propellant gases, EP enables efficient utilization of the limited supply of propellant aboard spacecrafts. This technology has opened the possibility of long distance autonomous space missions.

EP devices require electron sources to ionize the propellant gas and to neutralize charges that are leaving the spacecraft. In modern EP thrusters, this is achieved by the use of hollow cathodes -- complex devices that employ low work function materials to emit electrons. Hollow cathodes using polycrystalline LaB₆ inserts are attractive candidates for long duration EP based space missions. However, the physics behind LaB₆ hollow cathode operation has not been studied in detail, which limits the possibility of their optimization. This work presents an integrated experimental and computational approach to investigate LaB₆ hollow cathode thermal behaviour and the interplay between LaB₆ insert surface chemistry and xenon plasma.

Our investigation of the thermal behaviour of LaB₆ cathodes led to the unexpected discovery of a thermal transient when a new insert is first used. Specifically, we observed that the cathode temperature decreases by approximately 300 degrees over 50 hours before reaching steady state. This finding suggests a beneficial dynamic evolution of the cathode's chemical state when it interacts with its own plasma. This evolution is intrinsic to cathode operation and can only be precisely understood when the multiphysic nature of the cathode is self-consistently simulated. Thus, we built a numerical platform capable of combining the plasma, thermal and chemical behavior of a discharging hollow cathode. Simulations incorporating different neutralization models, inelastic ion-surface interaction and heterogeneous chemical evolution led to two major conclusions. First, simulations predicted a significant reduction of the LaB₆ work function (0.42~eV) compared to previously reported baseline values, which is of paramount importance for EP thruster efficiency and operational lifetimes. Second, simulations suggested that the interaction between xenon low energy ions (< 50 eV) and the LaB₆ surface occurs following a two step neutralization mechanism. The predicted work function reduction was experimentally confirmed by photoemission spectroscopy. Furthermore, using a combination of crystallographic analysis, scanning electron microscopy and profilometry, we demonstrated that work function reduction is caused by the creation of a crystallographic texture at the LaB₆ surface upon interaction with Xe plasma. In addition, we postulated the existence of a work function enhancing mechanism of secondary importance, which can be explained by forced cationic termination of plasma exposed crystals.

Our results revealed the unexpected phenomenon of work function reduction upon plasma exposure of LaB₆. These findings suggest that LaB₆ hollow cathodes may outperform current technologies and become the component of choice in EP thrusters for future space missions.

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Bieniek, Matthew Simon. "Modelling self-organization on electrodes of DC glow discharges". Doctoral thesis, 2018. http://hdl.handle.net/10400.13/2114.

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O trabalho apresentado nesta dissertaªo refere-se modelaªo de padrıes de autoorganizaªo de densidade de corrente em elØtrodos de descargas DC luminescentes. Padrıes de manchas andicas foram modelados de forma auto-consistente pela primeira vez e os fenmenos nas manchas foram investigados. As soluıes que descrevem as manchas foram encontradas num intervalo de correntes com mœltiplas soluıes. Foi descoberta uma inversªo da densidade de corrente local do nodo no centro de cada uma das manchas, isto Ø, mini-cÆtodos sªo formados dentro das manchas; poder-se-ia dizer, as manchas do nodo funcionam como uma descarga luminescente unipolar. As soluıes nªo se enquadram no padrªo convencional de auto-organizaªo em sistemas dissipativos nªo-lineares biestÆveis; por exemplo, as transiıes de um modo para outro nªo se realizam atravØs de bifurcaıes. Padrıes auto-organizados de manchas catdicas em descargas luminescentes foram modelados na camada de plasma junto ao cÆtodo, numa geometria igual utilizada na maioria das experiŒncias descritas na literatura. O efeito da geometria da cmara de descarga nas manchas foi investigado. Os padrıes de manchas modelados sªo idŒnticos aos observados nas experiŒncias e similares aos calculados na conguraªo de elØtrodos planos em paralelo. Uma tentativa foi feita para modelar quantitativamente a descarga DC luminescente com manchas catdicas. Uma descriªo detalhada desta modelaªo, a mais precisa deste fenmeno atØ data, Ø apresentada. Em geral, os padrıes calculados sªo semelhantes aos observados nas experiŒncias, mas as CVC sªo qualitativamente diferentes. CenÆrios de transiıes entre modos com diferentes padrıes de manchas em elØtrodos de descargas DC luminescentes e em cÆtodos de descargas de arco sªo investigados. No caso de transiıes entre padrıes em cÆtodos de descargas DC luminescentes, foram encontradas as transiıes observadas nas experiŒncias que podem estar diretamente relacionados a bifurcaıes de soluıes estacionÆrias, e as bifurcaıes correspondentes foram modeladas. Os padrıes encontrados na modelaªo numØrica estªo em conformidade com os observados no decurso das transiıes nas experiŒncias. No caso dos cÆtodos de descargas de arco, mostra-se que qualquer transiªo entre diferentes modos de transferŒncia de corrente estÆ relacionada a uma bifurcaªo de soluıes estacionÆrias.
In this work self-organized patterns of current density on electrodes of dc glow discharges were modelled. Patterns of anodic spots were modelled self-consistently for the rst time and their physics was investigated. The solutions describing the spots were found to exist in a region of current with multiple solutions. A reversal of the local anode current density in the middle of each of the spots was discovered, i.e. mini-cathodes are formed inside the spots or, as one could say, the anode spots operate as a unipolar glow discharge. The solutions do not t into the conventional pattern of self-organization in bistable nonlinear dissipative systems e.g. the modes are not joined by bifurcations. Self-organized patterns of cathodic spots in glow discharges were computed in the cathode boundary layer geometry, which is the one employed in most of the experiments reported in the literature. The e⁄ect that the geometry of the vessel has on the spots was investigated. The computed spot patterns are the same as the ones observed in the experiment and similar to the ones computed in the parallel plane electrode conguration. An unsuccessful attempt was made to quantitatively model DC glow discharge with cathodic spots, an account of this, the most accurate modelling of the phenomenon yet performed, is given. In general, the computed patterns are observed in the experiment but the CVC are qualitatively di⁄erent. Scenarios of transitions between modes with di⁄erent patterns of spots on electrodes of dc glow discharges and cathodes of arc discharges are investigated. In the case of transitions between patterns on dc glow cathodes, those transitions reported in the experiments that may be directly related to bifurcations of steady-state solutions are found and the corresponding bifurcations are computed. Patterns found in the numerical modelling conform to those observed in the course of the transitions in the experiment. In the case of cathodes of arc discharges, it is shown that any transition between di⁄erent modes of current transfer is related to a bifurcation of steady-state solutions.

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Libri sul tema "Interaction plasma/cathode"

J, Heberlein, e United States. National Aeronautics and Space Administration., a cura di. Arc-cathode interaction study: Final report for NASA contract NASA/NAG3-1332. Minneapolis, MN: High TemperatureLab, Dept. of Mechanical Engineering, University of Minnesota, 1992.

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Center, Lewis Research, a cura di. Investigation of beam-plasma interactions: Final report. Huntsville, Ala: University of Alabama in Huntsville, 1987.

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Center, Lewis Research, a cura di. Investigation of beam-plasma interactions: Final report. Huntsville, Ala: University of Alabama in Huntsville, 1987.

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Center, Lewis Research, a cura di. Investigation of beam-plasma interactions: Final report. Huntsville, Ala: University of Alabama in Huntsville, 1987.

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Estes, Robert D. Investigation of plasma contactors for use with orbiting wires [microform]: Semiannual report #2 for the period 1 July 1986 through 31 December 1986. Houston, Tex: National Aeronautics and Space Administration, Lyndon B. Johnson Space Center, 1987.

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Investigation of beam-plasma interactions: Final report. Huntsville, Ala: University of Alabama in Huntsville, 1987.

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Investigation of plasma contactors for use with orbiting wires: Final report for the period 1 January 1986 through 30 June 1987. Cambridge, Mass: Smithsonian Institution Astrophysical Observatory, 1987.

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Capitoli di libri sul tema "Interaction plasma/cathode"

Beilis, Isak. "Application of Cathode Spot Theory to Laser Metal Interaction and Laser Plasma Generation". In Plasma and Spot Phenomena in Electrical Arcs, 1027–66. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44747-2_24.

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Oettinger, P. E., e I. Bursuc. "Emission Characteristics and Surface Phenomena of Laser Heated Thermionic Cathodes". In Laser Interaction and Related Plasma Phenomena, 307–14. Boston, MA: Springer US, 1986. http://dx.doi.org/10.1007/978-1-4615-7335-7_24.

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"Modelling interaction of metal halide plasmas with a thermionic cathode". In Light Sources 2004 Proceedings of the 10th International Symposium on the Science and Technology of Light Sources, 565–66. CRC Press, 2004. http://dx.doi.org/10.1201/9781482269178-207.

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Atti di convegni sul tema "Interaction plasma/cathode"

Ma, C., J. Li, Z. Duan, F. He e J. Ouyang. "Study on the interaction of pulsed micro-hollow cathode discharge plasma jet with target". In 2024 IEEE International Conference on Plasma Science (ICOPS), 1. IEEE, 2024. http://dx.doi.org/10.1109/icops58192.2024.10626486.

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Hartmann, W., O. Almen, H. Bauer, K. Frank, A. Linsenmeyer e J. Christiansen. "Plasma-cathode interaction in superdense glow discharges". In 1990 Plasma Science IEEE Conference Record - Abstracts. IEEE, 1990. http://dx.doi.org/10.1109/plasma.1990.110511.

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Ho, A. Y., e S. P. Kuo. "Interaction dynamics of hollow cathode discharge plasmas". In 1990 Plasma Science IEEE Conference Record - Abstracts. IEEE, 1990. http://dx.doi.org/10.1109/plasma.1990.110772.

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Kaufmann, Helena T. C., Werner Hartmann, Mario D. Cunha, Norbert Wenzel e Mikhail S. Benilov. "Advanced Modeling of Plasma-Cathode Interaction in Vacuum and Low-Pressure Arcs". In 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV). IEEE, 2018. http://dx.doi.org/10.1109/deiv.2018.8537038.

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Shmelev, Dmitry L., Gennady A. Mesyats e Sergey A. Barengolts. "Kinetic model of the ignition of cathode explosive emission center by plasma surface interaction". In 2012 IEEE 39th International Conference on Plasma Sciences (ICOPS). IEEE, 2012. http://dx.doi.org/10.1109/plasma.2012.6383284.

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Abdel-Rahman, Ahmed F., e Tamer M. Abuelfadl. "Particle wave interaction using cavity modal expansion with an application on simulation of virtual cathode oscillator". In 2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) held with 2014 IEEE International Conference on High-Power Particle Beams (BEAMS). IEEE, 2014. http://dx.doi.org/10.1109/plasma.2014.7012686.

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Rossignol, J., P. Teste, E. Bourillot, B. de Fonseca e J. Jouhannaud. "Experimental approach of the interaction between a sub-microscopic cathode tip and the plasma". In 2007 8th International Conference on Electric Fuses and their Applications. IEEE, 2007. http://dx.doi.org/10.1109/icefa.2007.4419978.

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Mauer, G., R. Vaßen, D. Stöver, S. Kirner, J. L. Marqués, S. Zimmermann, G. Forster e J. Schein. "Improving Powder Injection in Plasma Spraying by Optical Diagnostics of the Plasma and Particle Characterization". In ITSC2010, a cura di B. R. Marple, A. Agarwal, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima e G. Montavon. DVS Media GmbH, 2010. http://dx.doi.org/10.31399/asm.cp.itsc2010p0510.

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Abstract Powder injection parameters like gas flow, injection angle and injector position strongly influence the particle beam and thus coating properties. The interaction of the injection conditions on particle properties based on DPV-2000 measurements using the single-cathode F4 torch is presented. Furthermore, the investigation of the plasma plume by emission computer tomography is described when operating the three-cathode TriplexPro torch. By this imaging technology, the three-dimensional shape of the radiating plasma jet is reproduced based on images achieved from three CCD cameras rotating around the plume axis It is shown how the formation of the plasma jet changes with plasma parameters and how this knowledge can be used to optimize particle injection.

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Benilov, M. S. "Modern theory of plasma-cathode interaction in high-pressure arc discharges and perspectives of its application to cathode spots in vacuum arcs". In 2008 XXIII International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV 2008). IEEE, 2008. http://dx.doi.org/10.1109/deiv.2008.4676788.

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Zimmermann, S., A. Atzberger, M. Szulc e J. Zierhut. "Pulsed Current and Pulsed Powder Operation of the One-Cathode-One-Anode-Plasma-Generator (OCOAPG)". In ITSC2017, a cura di A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen e C. A. Widener. DVS Media GmbH, 2017. http://dx.doi.org/10.31399/asm.cp.itsc2017p1150.

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Abstract In most plasma spraying SMEs a One-Cathode-One-Anode-Plasma-Generator (OCOAPG) is used due to its cost-effectiveness. To achieve high deposition rates, the highest possible fraction of the injected powder has to be melted and accelerated towards the substrate. Adequate to the amount and size of the particles, a sufficiently long and reproducible residence time in plasma is therefore needed. This can be achieved by a long plasma jet with little or no temporal variation in length and temperature. In OCOAPG an arc is operated between a cathode and a central tubular anode, which causes different instabilities in the effluent plasma jet. Due to the instable interaction between the plasma jet and the carrier gas jet continuously incorporating the powder, fluctuations occur resulting in reduced coating quality. Coating systems with a higher amount of electrodes (and hence using several arcs) show higher stability and therefore can provide higher coating quality. However, due to their complexity and cost intensity, the investment hurdle for SMEs usually turns out to be too high. Recently, research steps to improve the plasma spraying process with OCOAPG have been undertaken by using a controllable current source to create a uniform particle gas jet interaction. As the movement of the anodic arc attachment point can be actively controlled by current pulses, the plasma jet can be lengthened and shortened at periodic intervals. Furthermore, by pulsing the particle delivery synchronously to the power modulation an improved particle penetration and consistent residence times can be achieved. First diagnostic results, including coatings, are presented and discussed within the paper.

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