Dissertationen zum Thema „Plasma nozzle“

A means of space propulsion using the channeling of plasma by a divergent magnetic field, referred to as a magnetic nozzle has been explored by a number of research groups. This research develops the capability to apply the high order accurate Runge-Kutta discontinuous Galerkin numerical method to the simulation of magnetic nozzles. The resistive magnetohydrodynamic model of plasma behavior is developed for these simulations. To facilitate this work, several modeling capabilities are developed, including the implementation of appropriate inflow and far-field boundary conditions, the application of a technique for correcting errors that develop in the divergence of the magnetic field, and a split formulation for the magnetic field between the applied and the perturbed component. This model is then applied to perform a scaling study of the performance of magnetic nozzles over a range of Bk and Rm. In addition, the effect of the choice of simulation domain size is investigated. Finally, recommendations for future work are made.
Master of Science

In this thesis, theoretical studies are conducted to see whether plasma will detach from the magnetic field lines of the VASIMR thruster, and if so, at which location detachment takes place. A magnetic field similar to the field of the VASIMR VF-24 engine [1] is used and ions of different speed and massare sent from various radial positions in the exhaust. Calculation with different values of the anomalous resistivity parameter ωτ is conducted and the sensitivity to this parameter is studied. The validity of the method is studied by comparing results to previous work by Carl Wesslén [2]. From the results it is concluded that using heavy ions sent at high speeds will achieve detachment and high thrust efficiency, even when assuming relatively high values of ωτ. Ejecting ions at a slower pace or using lighter ions will make the engine less efficient, requiring low ωτ which is difficult to achieve. For some combinations of mass and speed, detachment is not possible at all. Ions with heavy mass are recommended to use as propellant for this type of thruster.

With an increased demand in Cube Satellite (CubeSat) development for low cost science and exploration missions, a push for the development of micro-propulsion technology has emerged, which seeks to increase CubeSat capabilities for novel mission concepts. One type of micro-propulsion system currently under development, known as Pocket Rocket, is an electrothermal plasma micro-thruster. Pocket Rocket uses a capacitively coupled plasma, generated by radio-frequency, in order to provide neutral gas heating via ion-neutral collisions within a gas discharge tube. When compared to a cold-gas thruster of similar size, this gas heating mechanism allows Pocket Rocket to increase the exit thermal velocity of its gaseous propellant for increased thrust. Previous experimental work has only investigated use of the gas discharge tube's orifice for propellant expansion into vacuum. This thesis aims to answer if Pocket Rocket may see an increase in thrust with the addition of a micro-nozzle, placed at the end of the gas discharge tube. With the addition of a conical ε = 10, α = 30° micro-nozzle, performance increases of up to 6% during plasma operation, and 25% during cold gas operation, have been observed. Propellant heating has also been observed to increase by up to 60 K within the gas discharge tube.

Les propulseurs plasmas sont le sujet d’un intérêt grandissant pour équiper de petits satellites. Des miniaturisations de technologies matures ont été proposées ainsi que des concepts innovants, tels le propulseur à résonance cyclotron électronique muni d’une tuyère magnétique (ECRT). Ce propulseur pourrait réaliser une rupture technologique car il est sans grilles, sans neutraliseur et n’a besoin que d’un seul générateur. Le présent travail consiste à développer un ECRT accompagné du dispositif expérimental nécessaire, capable de démontrer avec précision une grande efficacité durant un fonctionnement prolongé en régime permanent. Les précédentes études sur l’ECRT étaient limitées par un manque de précision sur des mesures clés, en raison du dispositif et des technologies nécessaires à l’étude de ce propulseur. La procédure et le dispositif expérimentaux sont donc largement améliorés pour augmenter la précision des mesures. Toutefois, des spécificités dues à la tuyère magnétique compliquent l’interprétation des mesures de densité de courant d’ion. Notre analyse s’appuie donc principalement sur des mesures de poussées obtenues avec une balance. Par ailleurs, nous montrons que les performances du propulseur augmentent significativement quand on diminue la pression dans le caisson de test jusqu’à 10-7 mbar Xénon. En outre, d’éventuels effets de caisson sont explorés en testant le propulseur à l’ONERA (Palaiseau, France) et à JLU (Giessen, Allemagne). En prenant en considération ces difficultés expérimentales, nous étudions l’efficacité du propulseur en fonction de la géométrie de l’injection de gaz neutre, de la topologie du champ magnétique, et des conditions aux limites de la tuyère magnétique. De plus, nous abordons la question de l’érosion du propulseur, de deux manières : premièrement par une modification des matériaux et deuxièmement par une modification de la structure de couplage (coaxiale, ou guide d’onde circulaire). Le couplage de type guide d’onde produit des ions à des énergies trop faibles pour les exigences de la propulsion spatiale ; en revanche, une structure de couplage coaxiale usinée en graphite semble diminuer substantiellement l’érosion sans compromettre l’efficacité. Ces résultats permettent de concevoir et de tester un propulseur ~ 30 W et un propulseur ~ 200 W dont les performances sont répétables dans le temps. L’efficacité et la durée de vie sont considérablement augmentées : une première campagne de test indique une efficacité allant jusqu’à ~ 50% et une durée de vie estimée de un à quelques milliers d’heures. Pour éclairer les résultats expérimentaux, nous proposons une nouvelle démarche de modélisation, fondée sur l’étude des trajectoires des électrons et sur une approche du chauffage électronique au moyen d’une équation de Fokker-Planck. Cette démarche débouche sur le calcul de la fonction de distribution en énergie des électrons dans le propulseur ; celle-ci détermine le courant d’ions extrait et l’énergie des ions
Plasma thrusters are the subject of growing interest as a means for small satellite propulsion. Miniaturizations of mature technologies as well as innovative concepts have been proposed such as the electron-cyclotron resonance thruster with magnetic nozzle (ECRT). This thruster appears as a potentially disruptive technology because it is gridless, neutralizerless, and only requires one power supply. This work consists in the development of an ECRT with magnetic nozzle and its accompanying experimental test bench, able to accurately demonstrate high thruster efficiency during prolonged steady state operation. Previous studies on the ECRT were limited by a significant lack of accuracy on key measurements, due to the specific setup and technology needed for this thruster. The experimental procedure and the setup are thus heavily upgraded to improve the accuracy of experimental data. However, peculiarities of the magnetic nozzle complicate the interpretation of the ion current density measurements, thus our analysis of performance is mainly based on thrust balance measurements. Besides, thruster performance is shown to significantly increase when decreasing vacuum tank pressure down to 10-7 mbar Xenon, and facility effects are investigated by testing the thruster both at ONERA (France) and at JLU (Germany). Well aware of these experimental difficulties, we study the efficiency of the thruster as a function of neutral gas injection, magnetic field topology, and boundary conditions of the magnetic nozzle. In addition, we address erosion issues in two ways: first by a change of materials, and second by a change of coupling structure (coaxial, or circular waveguide). Waveguide coupling yields insufficient ion energies for space propulsion requirements but manufacturing the coaxial coupling structure with graphite appears to substantially mitigate erosion. These results enable to design and test a ~ 30 W and a ~ 200 W thruster consistently yielding state-of-the-art efficiencies as compared to other thruster types while having sufficient estimated lifetime. In order to shed light on the experimental outcomes, a new modelling approach is developed based on the study of electron trajectories and a Fokker-Planck heating model calculating the formation of the electron energy distribution function in the thruster

In 2012, plasma figuring was proven to be an alternative solution for the fabrication of large scale ultra-precise optical surfaces. Indeed, plasma figuring was successfully demonstrated on a metre class glass surface. The process was exceptionally rapid but residual errors were observed. This thesis addresses this issue by proposing an enhanced tool that provides a highly collimated plasma jet. The enhanced tool is characterized by a targeted material removal footprint in the range 1 to 5 mm FWHM. The energy beam is provided by an Inductively Coupled Plasma (ICP) torch equipped with a De-Laval nozzle. This thesis focuses on characterization and optimisation of the bespoke plasma torch and its plasma jet. Two research investigations were carried out using both numerical and experimental approaches. A novel CFD model was created to analyse and understand the behaviour of high temperature gas in the De-Laval nozzle. The numerical approach, that was based on appropriate profiles of temperature and velocity applied to the nozzle inlet, led to a significant reduction of computational resources. This model enabled to investigate the aerodynamic phenomena observed from the nozzle inlet up to the processed surface. Design rules and the effect of changing nozzle parameters were identified. Sensitivity analysis highlighted that the throat diameter is the most critical parameter. A challenging power dissipation analysis of the plasma torch was carried out. Temperature and flow rate in key components of the torch were measured. Experimental results enabled to calculate the power dissipation values for RF power up to 800 W and for the entire series of designed nozzles. This work enabled to scientifically understand the power dissipation mechanism in the bespoke ICP torches. In addition, by comparing the intensity of the power dissipation values, one nozzle was clearly identified as being more capable to provide a highly efficient plasma jet.

In order to enable comparison of Helicon ion thruster performance across different vacuum test facilities, an understanding of the effect of operating pressure on plasma plume properties is required. Plasma property measurements are compared for thruster operation at two separate vacuum facility operating pressures to determine the effect of neutral ingestion on Helicon ion thruster operation. The ion energy distribution function (IEDF), electron temperature, ion number density, and plasma potential are measured along the thruster main axis for a replica of the Madison Helicon eXperiment. Plasma property values recorded at the ‘high-pressure condition’ (3.0×10^(-4) Torr corrected for argon) are compared to values recorded at the ‘low-pressure condition’ (1.2×10^(-5) Torr corrected for argon) for thruster operation at 100 - 500 watts radio frequency forward power, 340 – 700 gauss source region magnetic field strength, and 1.3 - 60 sccm argon volumetric flow rate (0.039-1.782 mg/s). Differences in plasma behavior at the ‘high-pressure condition’ result from two primary neutral-plume interactions: collisions between accelerated beam ions and ingested neutrals leading to a reduction of ion energy and neutral ionization downstream of the thruster exit due to electron-neutral collisions. Electron temperature at higher operating pressures is lowered due to an electron cooling effect resulting from repeated collisions with neutral atoms. Results suggest that Helicon ion thruster plasma properties are greatly influenced when subjected to neutral ingestion.

Ce travail de thèse porte sur le propulseur électrique de type ECR (résonance cyclotron électronique) développé à l’ONERA. Ce propulseur quasi-neutre, qui utilise une tuyère magnétique pour accélérer le plasma, produit une poussée d’environ 1 mN pour des puissances inférieures à 50 W. Dans cette thèse, on se propose de développer et d’optimiser les diagnostics de mesure des performances du propulseur ECR, d’identifier les paramètres expérimentaux pouvant influencer les performances et d’améliorer la compréhension des phénomènes physiques ayant lieu dans le propulseur. Ces objectifs ont pour finalité l’amélioration des performances. Pour répondre à ces objectifs, plusieurs prototypes à aimant permanent ont été développés, et une balance permettant de mesurer directement la poussée a été modifiée pour caractériser le propulseur. Différentes études paramétriques ont été conduites, qui ont montré que les performances dépendaient directement du rapport entre le débit de xénon et la puissance micro-onde injectée. Il a également été observé que la longueur du conducteur externe de la source plasma et la pression ambiante ont une influence significative sur le niveau de performance. Après optimisation de la géométrie, un rendement total supérieur à 12 % a été obtenu. Des mesures séparées de la poussée thermique et magnétique ont permis de montrer que la composante magnétique était la contribution principale de la poussée dans tous les cas testés. Un code PIC 1D-3V a été utilisé pour simuler le comportement du propulseur, et a permis de reproduire le chauffage des électrons par résonance et l’accélération des espèces chargées dans la tuyère. L’ensemble des travaux ont mis en avant le rôle des composantes parallèle et perpendiculaire de la pression électronique
Electric propulsion is an alternative technology to the chemical propulsion that enables reducing propellant consumption for satellites. ONERA is developing an electric ECR thruster with a thrust around 1 mN and an electric power less than 50 W. The thruster creates a plasma by electron cyclotron resonance and accelerates it through a magnetic nozzle. In this thesis work, an optimization of the measurement diagnostics is done. The work also aims at identifying the important parameters for the performances of the thruster and at improving the understanding of underlying physics, in order to increase the thruster efficiency. Several prototypes have been developed and a thrust stand that can directly measure the thrust has been modified. Some parametric studies have been led and have shown that the thruster performance strongly depends on xenon mass-flow rate to microwave power ratio. It has also shown that the external conductor of the plasma source and the ambient pressure have a significant influence on the performances. Following a geometric optimization, a maximum total efficiency of more than 12% has been obtained. Separate measurements of the magnetic and thermal thrust have shown that the magnetic thrust is the main component of the total thrust. A 1D-3V PIC code has been used to simulate the behavior of the thruster. The analysis of the results has shown that the ECR heating and particle acceleration in the magnetic nozzle could be properly computed. The role of the parallel and perpendicular component of electron pressure has been evidenced by this work

This diploma thesis was focused on the possibility of using a plasma nozzle to accelerate the wound healing process. The benefits of using low-temperature plasma in medicine or biomedical applications are known from many studies, and low-temperature plasma is already used to sterilize medical devices, materials or surgical instruments. Some studies also report a high potential of usinh plasma nozzle in the treatment of skin wounds. In the experimental part of this work, an in vitro wound healing test was performed using two different low-temperature plasma sources. Source No. 1 was a surface wave microwave discharge and source No. 2 was a torch microwave discharge. An in vitro scratch healing test was performed on a monolayer of HaCaT keratinocytes and testing was performed using various parameters. The influence of the plasma treatment time was monitored, as well as the influence of the plasma discharge power and also the influence of the argon working gas flow. Especially when using a torch microwave discharge, faster wound healing was recorded at most of the parameters used compared to the control. Thus, it can be said that this source appears to be potentially suitable for faster wound healing. Furthermore, in the work using the MTT cytotoxicity test, the viability of skin cells after their plasmination was also monitored using the same conditions as in the in vitro wound healing test. When performed in the standard MTT assay, none of the settings or sources used showed any cytotoxic effects on keratinocytes. LDH cytotoxicity tests were also performed concurrently to verify the accuracy of the MTT assays. The results of both tests agreed and the use of low-temperature plasma in skin treatment can be considered as safe. Overall, the results show that the plasma nozzle can find use in medicine in the healing of skin wounds and chronic defects as a potentially fast, inexpensive and effective method.

The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Objetivou-se avaliar a quantidade e qualidade da deposição da calda de pulverização em duas cultivares de amendoim (Aracahis hypogaea L.) e na planta daninha Brachiaria plantaginea (Link) Hitch., presente na linha e entrelinhas de semeadura da cultura, além da deposição no solo, em aplicações de pós-emergência. O estudo foi realizado a campo com duas cultivares de amendoim (‘IAC Tatu-ST’ e ‘Runner IAC 886’), sendo as aplicações dos tratamentos realizadas nos estádios vegetativo (V1) e reprodutivo (R2). Foi utilizado como marcador o corante Azul Brilhante FDC -1 na concentração de 500 ppm. Os tratamentos foram constituídos por sete pontas de pulverização: XR 110015 VS (150 L ha-1), XR 11002 VS (200 L ha-1), TX-VK 6 (150L ha-1), TX-VK 8 (200 L ha-1), AI 110015 VS (150 L ha-1), AI11002 VS (200 L ha-1) e TJ60 11002 VS (150 e 200 L ha-1). Utilizou-se o delineamento em blocos ao acaso, com 4 repetições. Os dados dos resultados quantitativos de deposição foram analisados nos seguintes esquemas em fatorial: para os depósitos em plantas de amendoim foi utilizado o esquema 8 x 2 (8 situações de pulverização x 2 estádio de desenvolvimento da cultura); para as plantas daninhas presentes na linha e na entrelinha da cultura do amendoim, o esquema foi 8 x 2 [8 situações de pulverização x 2 posições (linha e entrelinha)]; para as estimativas de deposição no solo, o esquema foi 8 x 2 [8 situações de pulverização x 2 posições (linha e entrelinha)]. Foram amostradas 25 plantas por repetição em cada parcela, tanto para as plantas de amendoim quanto para as plantas daninhas presentes na linha e na entrelinha da cultura. Após a aplicação, as plantas foram imediatamente coletadas, e em seguida foram lavadas em 100 mL de água destilada para posterior quantificação do marcador em espectrofotômetro. Para as análises qualitativas, cada planta selecionada...
The objective of this study was to evaluate the quantity and quality of the spray deposition in two peanut cultivars (Aracahis hypogaea L.) and weed Brachiaria plantaginea (Link) Hitch., current in the crop row and spacing row, beyond the deposition in soil, in applications of post-emergency. The study was conducted in the field with two peanut cultivars (‘IAC Tatu-ST’ e ‘Runner IAC 886’), and the applications of treatments performed in the vegetative stage (V1) and reproductive (R2). It was used the Brilliant Blue FDC – 1 as tracer in water solution, at 500 ppm. The treatments consisted of seven spray nozzle XR 110015 VS (150 L ha-1), XR 11002 VS (200 L ha-1), TX-VK 6 (150L ha-1), TX-VK 8 (200 L ha-1), AI 110015 VS (150 L ha-1), AI11002 VS (200 L ha-1) e TJ60 11002 VS (150 e 200 L ha1). It was used a randomized blocks design, with four replications. Being that, the results of the quantitative data of deposition had been analyzed in following factorial schemes: for the deposits in peanut plants was used 8 x 2 factorial scheme (8 situations spray x stage of development of culture), for the Brachiaria plantaginea plants was used 8 x 2 factorial scheme [8 situations spray x 2 positions (row and spacing row)]; for the soil deposition estimates, the factorial scheme was 8 x 2 [8 situations spray x 2 positions (row and spacing row)]. Were sampled 25 plants for replication in each plot, as much for the peanut plants as current weeds in crop row and spacing row. After application, the plants were immediately collected, and after they had been washed in 100 mL of distilled water for tracer remover. The tracer quantification was made in spectrophotometer. For the quantitative analysis, each random selected plant inside of boom application stripe bar was considered a replication, representing a total of 100 replications. The obtained data had been adjusted a regression curve for Gompertz... (Complete abstract click electronic access below)

The numerical simulation and modeling of plasma detachment from a magnetic nozzle is presented. The detachment problem is of key importance to the plasma-based propulsion concepts that employ a guiding magnetic field to control plasma flow and motivated by the needs of the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) project. The detachment of the plasma exhaust is required to produce directed thrust. In the present scenario plasma can stretch the magnetic field lines to infinity, similar to the solar wind. In order to extend the magnetic nozzle model beyond the limitations of analytic theory, a numerical code is developed to simulate steady-state kinetic plasma flows and to evaluate nozzle efficiency. The direct solution of a steady-state problem, as opposed to an initial value problem, eliminates the need to deal with transient phenomena that are of secondary importance for continuously operated plasma thrusters. The new simulation code is verified against the analytic results and then used to model the plasma behaviour for the conditions of the Detachment Demonstration Experiment (DDEX) at the NASA Marshall Propulsion Research Center, Huntsville, Alabama.
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The results of an experimental study of an electrodeless electric propulsion device using electron cyclotron resonance (ECR) heating for plasma production are presented. The effects of pressure, propellant flow rate, and microwave input power on the plasma properties were examined. In addition, the effect of a magnetic nozzle on a plasma beam were examined experimentally and computationally. A laboratory ECR thruster was operated with argon propellant in a vacuum tank at pressures in the 10(-5) torr range using a 2.115 GHz microwave beam at power levels up to several kilowatts. Several movable plasma diagnostics were used to measure the spatial variation of various plasma properties in the plume of the thruster. At low pressures, ion flux profiles showed an unexpected annular plasma plume with a depressed ion flux along the thruster axis. The ion energy measurements indicate that the ion kinetic energy is invariant with input microwave power. However, increases in pressure cause the plasma to lose kinetic energy due to friction with the background neutrals in the vacuum tank. Propulsion parameters were calculated from the ion flux and energy data. The results are greatly affected by additional ion flux due to entrainment of the background gas. The plasma potential and electron temperature both decreased with increasing pressure in the tank but were invariant with changes in microwave power. Microwave power reflected from and transmitted through the ECR region was measured and the results indicate that inefficient absorption may contribute significantly to energy losses in the laboratory device. Plasma detachment from the magnetic nozzle was identified as a critical issue for ECR and other applied-field thrusters. A collisionless model was used to calculate the trajectories of plasma rings in a magnetic nozzle. The code predicted that the plasma will detach under certain conditions and that the acceleration due to the force on the dipole moments of the electrons is inconsequential to the plasma trajectories. The radii of 90° deflection were calculated for several plasma initial conditions, and it was shown that the nozzle configuration can be manipulated to reduce beam divergence and increase the useful radius of the thruster. An attempt was made to experimentally examine detachment using an ion thruster in an applied magnetic nozzle. The magnetic field could then be varied independent of the ion energy. The grids of the thruster were masked to extract a thin ring of plasma coaxial with the magnetic nozzle, and the ion flux density profile was measured to determine the effect of the magnetic field on the trajectory of the annular plasma. A radial electric field was established in presence of the magnet nozzle that caused the annulus to spread and decrease in radius making detachment unobservable. It is believed that the magnetic field inhibited neutralization of the ion beam causing the electric field to develop.

碩士
逢甲大學
材料與製造工程所
96
In this paper, we investigate the application of the high accurate plasma cutting machine with water quantity controlled nozzle to cut the SUS304 stainless steel plates, and do the characteristic analysis. The cutting accuracy of the work-pieces is highly affected by the variation of the machine parameters and the sizes of the nozzle. To improve the quality of work-pieces and to promote the advantage of competency, we adopt the L18 orthogonal array of Taguchi methods for test and experience, and to do parameter optimization. Based on the L18 orthogonal array, we adopt 8 control factors, each has 3 levels, and focus on 5 cutting qualities. We also adopt the objective of the smaller the better (STB) for doing parameter optimization. The experimental results show that the following set of parameter combination: the working voltage 187V, the working current 200 mA, the nozzal diameter 1.9 mm, the Air pressure 100 , the distance between the nozzel and the work piece 10 mm, the rate of water discharge 60 lph, the weld track wide 4.0 mm, and the cutting speed 950 mm/min will get the optimal result.

Magnetic nozzles, like Laval nozzles, are observed in several natural systems and have application in areas such as electric propulsion and plasma processing. Plasma flowing through these nozzles is inherently tied to the field lines and must separate for momentum redirection or particle transport to occur. Plasma detachment and associated mechanisms from a magnetic nozzle are investigated. Experimental results are presented from the plume of the VASIMR® VX-200 device flowing along an axisymmetric magnetic nozzle and operated at two ion energies to explore momentum dependent detachment. The argon plume expanded into a 150m3 vacuum chamber where the background pressure was low enough that charge-exchange mean-free-paths were longer than experiment scale lengths. This magnetic nozzle system is demonstrated to hydrodynamically scale up to astrophysical plasmas, particularly the solar chromosphere, implying general relevance to all systems. Plasma parameters were mapped over a large spatial range using measurements from multiple plasma diagnostics. The data show that the plume does not follow the magnetic field lines. A mapped integration of the ion flux shows the plume may be divided into three regions where 1) the plume briefly follows the magnetic flux, 2) diverges quadratically before 3) expanding with linear trajectories. Transitioning from region 1→2, the ion flux departs from the magnetic flux suggesting ion detachment. An instability forms in region 2 driving an oscillating electric field that causes ions to expand before enhancing electron cross-field transport through anomalous resistivity. Transitioning from region 2→3 the electric field dissipates, the trajectories linearize, and the plume effectively detaches. A delineation of sub-to-super Alfvénic flow aligns well with the inflection points of the linearization without a change in magnetic topology. The detachment process is best described as a two part process: First, ions detach by a breakdown of the magnetic moment when the quantity |v/fcLB| becomes of order unity. Second, the turbulent electric field enhances electron transport up to a factor of 4±1 above collisional diffusion; electron cross-field velocities approximate that of the ions and depart on more centralized field lines. Electrons are believed to detach by breakdown of magnetic moment further downstream in the weaker magnetic field.

Plasma flow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. Toward that end, in this thesis we: i) perform an extensive literature survey of magnetic nozzle physics, ii) assess the validity of magnetohydrodynamics for studying magnetic nozzle physics, and iii) illustrate the effects of the Hall term in simple flows as well as in magnetic nozzle configurations through numerical experiments with the Magneto-Gas Kinetic Method (MGKM). The crucial steps necessary for thrust generation in magnetic nozzles are energy conversion, plasma detachment, and momentum transfer. These three physical phenomena must be understood to optimize magnetic nozzle design. The operating dimensionless parameter ranges of six prominent experiments are considered and the corresponding mechanisms are discussed. An order of magnitude analysis of the governing equations reveal: i) most magnetic nozzles under consideration operate at the edge of the continuum regime rendering continuum-based description and computation valid; ii) in the context of MHD framework, the generalized Ohm’s law must be used to capture all of the relevant physics. This work also continues the development of the Magneto Gas Kinetic Method (MGKM) computational tool. Validation of the solver is performed in shock-tube and Hartmann channel flows in the Hall physics regime. Comparison with theory and available data is made whenever possible. Novel numerical experiments of magnetic nozzle plasma jets in the Hall regime are performed, confirming the theoretically predicted azimuthal rotation of the plasma jet due to Hall physics. The primary conclusion from this work is that the addition of the Hall effect generates helical structures in magnetic nozzle plasma flows. Preliminary results are encouraging for future magnetic nozzle studies and further challenges are identified.

碩士
國立成功大學
航空太空工程學系
107
This master thesis focuses on the study of the influence that different diverging nozzle angles have on the performances and reliability of a pulsed plasma thruster. This study was done in part with ODYSSEUS Space, a Taiwan based space tech start-up, in part working on the development of a 3-axis attitude control for CubeSats. This research was thus done using the power and size requirements that a thruster would have if designed for such a satellite. Pulsed plasma thrusters are some of the oldest electrical thrusters to have been designed, tested and used in the space industry. While more recent designs such as Hall effect thrusters became more popular, there seems to be a rise in interest for pulsed plasma thruster thanks to their increased simplicity, affordable price in terms of both research and development, and the fact that universities and young start-ups can easily study and improve them. The research was done during the 2018-2019 scholar year for this master thesis revolved around the design and testing of 4 different thruster configurations: an original thruster without any nozzles, and 3 configurations with 0-degrees, 20-degrees and 40-degrees nozzles to be added to the original design. The entire thruster was thought and designed to be modular, to allow for easy replacement of the nozzles, and even further improvements that might be done after this master thesis. Vanilla pulsed plasma thruster, most commonly parallel plate thrusters, most create thrust through the plasma created, while the remaining neutral particles created very little additional thrust. However, some research had started investigating the use of divergent nozzles to greatly improve the gas expansion contribution of the neutral particles, while only limiting the loss of electromagnetic thrust generated by the plasma. The aim of this study was to investigate which nozzle angle provided the best overall performance. The initial performance measurements were supposed to combine tracking the electromagnetic and electrothermal thrust for each thruster design to compare their performances. While the electromagnetic thrust could be measured, the method used to measure the electrothermal thrust showed to be flawed and provided incoherent results. The impulse bit measurement showed expected results: the narrower the nozzles, the weaker the impulse bit, with the original configuration without nozzles providing the maximum impulse bit, this was mostly attributed to friction. Reliability tests were also done, for 30 minutes to compare the lifespan of each configuration. It was shown that the original nozzles were to narrow, and after widening them, these tests showed that while the configuration without nozzles was the most reliable, adding nozzles did decrease operational lifespan, but with very little regard to the nozzle angle.