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Johansson, Fredrik. "Rosetta Langmuir probe performance." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-213146.
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Several Langmuir probe voltage sweeps by a model of the ESA spacecraft Rosetta was simulated in a plasma with solar wind parameters using the ESA open source software SPIS 5. The simulations were carried out to in- vestigate the features of the spacecraft’s environment in the solar wind and the effect of photoemission from the spacecraft surface on the measurements made by the Langmuir probes on board Rosetta. We report a best fit to an existing probe sweep result in the solar wind near the Earth at 1 AU from 9 Nov 2009 for a 4 million particle simulation in SPIS of an 8 V positively charged spacecraft with the following parameters: Tph = 2 eV, Te = 12 eV, Ti = 5 eV, ne = 5 cm−3. We also report that the spacecraft is shielding the Langmuir probes on Rosetta from plasma electrons, and particularly low energy electrons. In one instance, this blocking is shown to lead to an over- estimation of solar wind electron temperature by 12% and underestimate the plasma density by 24% by the Langmuir Probe for a +10 V charged spacecraft in ne= 5 cm−3, Te = 12 eV solar wind. Two models used in lit- erature on photoemission, one for isotropical emission from a plane and the other for radial emission from a point, was used and compared. We report a clear preference to the approximation of a Maxwellian energy distribution of photoelectrons emitted radially from a point source model with our sim- ulation result on the Langmuir Probe aboard Rosetta. We also report the solar aspect angle dependence on the plasma potential and plasma density result, which are in overall agreement with Rosetta measurements from the second Earth fly-by.
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Joyce, AÌine Mary. "A versatile Langmuir probe system." Thesis, University of Ulster, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268571.
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Johansson, Fredrik. "Numerical simulation of Rosetta Langmuir Probe." Thesis, Uppsala universitet, Rymd- och plasmafysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-206890.
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By modelling and simulating the ESA spacecraft Rosetta in a plasma with solar wind parameters, and simultaneously simulating a particle detection experiment of Langmuir probe voltage sweep type using the ESA open source software SPIS Science, we investigate the features of Rosetta’s envi- ronment in the solar wind and the e↵ect of photoemission from the space- craft on the measurements made by the Langmuir Probe instrument on board Rosetta. For a 10 V positively charged spacecraft and Maxwellian distributed photoelectron emission with photoelectron temperature, Tf = 2 eV in a plasma of typical 1 AU solar wind parameters: ne = 5 ⇥ 106 m3, vSW = 4 ⇥ 105 m/s, Te = 12 eV, Tion = 5 eV, we detect a floating potential of 6.4 (± 0.2) V at Langmuir probe 1. Two models used in literature on photoemission was used and compared and we report a clear preference to the Maxwellian energy distribution of photoelectrons from a point source model with our simulation result.
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Barjatya, Aroh. "Langmuir Probe Measurements In The Ionosphere." DigitalCommons@USU, 2007. https://digitalcommons.usu.edu/etd/274.
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Electric probes have been the primary instruments for the in situ investigation of plasma parameters in the Earth’s ionosphere. This dissertation is a compendium of three papers, each dealing with a separate spacecraft that carried one or more instruments based on the electric probe technique.
The first paper presents data from the Sudden Atom Layer sounding rocket that carried an RF Impedance Probe, a DC fixed-bias Langmuir Probe (DCP), and an Electric Field Probe. The combined dataset indicates a case of payload surface charging, the causes of which are investigated within the paper. A generic circuit model is developed to analyze payload charging and behavior of Langmuir-type instruments. Our analysis indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth’s mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environments.
The second paper presents data from the Floating Potential Measurement Unit (FPMU) that is deployed on the International Space Station. The FPMU instrument suite consists of three different Langmuir-type probes and a Plasma Impedance Probe (PIP). We first give a brief overview of the instrumentation, and then describe the algorithm used to reduce Langmuir probe I-V curves to plasma parameters. It is shown that the derived temperatures agree well with International Reference Ionosphere (IRI) model, while the derived density matches better with the USU-Global Assimilation of Ionospheric Measurement model. The third paper presents the dataset from the EQUIS II sounding rocket campaign. The rocket payloads carried a PIP, a DCP, and an internally heated Sweeping Langmuir Probe. The ratio of the payload surface area to the cumulative area of the instrument and its guard was about 250. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not very accurate. We further show that the ion saturation region analysis of the I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the PIP, and the derived temperatures agree reasonably well with the IRI model.
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Sinclair, Brian Collins. "Langmuir probe diagnostics of the VASIMR engine /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FSinclair.pdf.
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Mefo, Jane Ebelechukwu. "Langmuir probe characterisation of ion source plasmas." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/843557/.
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The precise conditions under which ions are generated in the ion source can have a major impact on how well the source performs, and how much of the extracted beam current can be transported. Because of the commercial focus on the repeatability and reliability of the overall ion implantation process, this vital aspect of the machine has received little scientific attention. hi order to address this issue, detailed studies of both the source and beam plasmas have been initiated. The research described in this thesis, was concerned with the former, and the characterisation of boron trifluoride (BF3) and argon plasmas created in a commercial indirectly heated cathode high current ion source, is described. Boron is still the main p-type dopant in the ion implantation industry but little information is available to date on the basic plasma parameters and the way in which they depend on the source operating conditions. Of major interest in the BF3 plasma is the cracking efficiency (gas and surface-phase phenomena may also be important), since the desired ion species is the singly charged atomic boron ion. Plasma parameters such as the density, electron and ion temperature, and the related plasma potential, dictate the nature of the processes occurring, and their rates. Detailed information on how the plasma parameters are affected by the source operating conditions (discharge "arc" voltage, discharge current, gas flow rate and confining magnetic field strength) was obtained from Langmuir probe measurements. In conjunction with the known performance of the source in field machines, the data have enabled the plasma parameters to be related to the overall system performance. Two electron temperatures were observed and significant spatial non-uniformities were apparent. The dependence of electron temperature on different operating conditions was found to be different, and source geometry and arc chamber material were also found to have an effect on the electron temperature.
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Sinclair, Brian C. "Langmuir probe diagnostics of the VASIMR engine." Thesis, Monterey, California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/1821.
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NASAâ s VAriable Specific Impulse Magnetoplasma Rocket Engine (VASIMR) will provide a highly efficient propulsion source that can dramatically reduce Martian transit times, provide for more abort contingencies, and protect astronauts from space radiation with its highly radiation-absorbent hydrogen fuel. The VASIMR is still in its developmental infancy and requires many years of research before its initial operational capability. Much is still unknown about the complex plasma interactions in the exhaust. A Langmuir probe was designed, constructed, and operated to determine current density radial profiles and total particle flux at various stages in the exhaust of VASIMR. The Langmuir probe results proved that the exhaustâ s radial profile is Gaussian, experimentally validated predictions of magnetic field line dragging, and verified the ionization efficiency of VASIMR.
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Suresh, Padmashri. "Surface Morphology Implications on Langmuir Probe Measurements." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/902.
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Langmuir probes are extensively employed to study the plasmas in space and laboratory environments. Successful measurements require a comprehensive modeling of both the plasma environment and the probe conditions in the form of current collection models. In this thesis, the surface morphology implications on the probe current collection are investigated. This problem is applied and solved in the context of a CubeSat regime. The first problem that is investigated is the consequence of surface structural variability on the current measurements. A new model for dealing with non-uniformity of the probe surface structure is developed in this paper. This model is applied to analyze the Langmuir probe data from a sounding rocket mission that was subjected to surface structural non-homogeneities. This model would be particularly useful for CubeSat platforms where elaborate probe design procedures are not feasible. The second problem that is investigated is the surface area implications on Langmuir probe measurements. It has been established that surface area ratio of the spacecraft to that of the probe needs to be sufficiently large to make successful plasma measurements. CubeSats would therefore pose a challenge for employing Langmuir-type instruments to study the space plasma. We inspect the feasibility of making plasma measurements using Langmuir probes subjected to CubeSat area constraints. This analysis is done for a forthcoming Utah State University (USU)/Space Dynamics Lab (SDL) CubeSat mission.
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McFarland, G. M. "Langmuir probe studies in a GEC Reference Reactor." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395373.
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Fanara, C. "A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas." Thesis, Cranfield University, 2003. http://dspace.lib.cranfield.ac.uk/handle/1826/96.
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The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.
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Anderson, Colin Andrew. "Temporal Langmuir probe measurements in low frequency RF plasmas." Thesis, University of Ulster, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359715.
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Chiaretta, Marco. "Numerical modelling of Langmuir probe measurements for the Swarm spacecraft." Thesis, Uppsala universitet, Rymd- och plasmafysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-148633.
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This work studies the current collected by the spherical Langmuir probes to be mounted on the ESA Swarm satellites in order to quantify deviations from idealized cases caused by non-ideal probe geometry. The finite-element particle-in-cell code SPIS is used to model the current collection of a realistic probe, including the support structures, for two ionospheric plasma conditions with and without drift velocity. SPIS simulations are verified by comparing simulations of an ideal sphere at rest to previous numerical results by Laframboise parametrized to sufficient accuracy. It is found that for probe potentials much above the equivalent electron temperature, the deviations from ideal geometry decrease the current by up to 25 % compared to the ideal sphere case and thus must be corrected if data from this part of the probe curve has to be used for plasma density derivations. In comparison to the non-drifting case, including a plasma ram flow increases the current for probe potentials around and below the equivalent ion energy, as the contribution of the ions to the shielding is reduced by their high flow energy.
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Singh, Shailendra Vikram. "Investigation of ICP RF discharges by means of a Langmuir probe." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974828998.
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Hånberg, Christian. "Analytic modelling of Rosetta Langmuir probe measurements based on SPIS simulations." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-149816.
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The Rosetta spacecraft is on route to rendezvous with the comet 67P/ Churyomov-Gerasimenko. One of the instruments onboard is the Langmuir probe instrument (LAP) developed by the Swedish Institute of Space Physics. The LAP includes two spherical probes used to measure a number of properties of the surrounding plasma. One measured property is the plasma density for which the spacecraft potential is a good proxy. By the determining the potential between spacecraft and Langmuir probe, the spacecraft potential can be measured. But such measurements are sometimes disturbed by the potential from the spacecraft itself, the influence from photoemitted electrons and the solar wind wake behind Rosetta. In order to correct for the errors caused by spacecraft-plasma interaction in the solar wind a model depending on the spacecraft (and Langmuir probe) orientation is developed. The data is obtained from three-dimensional simulations of Rosetta, with varying plasma parameters, using the software SPIS (Spacecraft Plasma Interaction System). Least squares fitting with a set of basis functions then provide the input for a parametric modelling. The developed model makes it possible to estimate the influence of each of the disturbing effects. The developed model gives good fits to data obtained in SPIS simulations. The two angular dependent factors, modelling perturbation on potential measurements caused by photoelectrons and wake effects, show errors below the 100 mV level in all cases. The model describing the influence from spacecraft potential is slightly less accurate, with errors at or below the 400 mV level in all relevant cases.
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Monk, Raymond David. "Langmuir probe measurements in the divertor plasma of the JET tokamak." Thesis, Royal Holloway, University of London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336515.
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This thesis describes the design and application of a new array of Langmuir probes to measure the plasma parameters in the divertor region of the Joint European Torus (JET) tokamak. A novel probe tip design was developed to withstand the high heat fluxes in the divertor region following thermal analysis and beam tests to identify the most suitable material. The probes operate in the "very strong magnetic field" regime with a large projected area (4mm2) and incidence angle to the magnetic field (> 10°) to avoid the sheath expansion effects associated with flush mounted divertor probes. The probes may be remotely configured as single, triple or floating probes. The combination of triple probe measurements and strike point sweeping has provided unique high resolution profiles of plasma parameters across the divertor target. Emphasis is placed upon the evaluation of probe interpretation assumptions and comparison with non-disturbing diagnostics to assess the reliability of the measurements. The distortion of the probe current-voltage characteristics is strongest for high recycling and detached divertor conditions. Single probe analysis methods overestimate the electron temperature while the virtual asymmetric double probe assumption matches well the functional form of the current-voltage characteristics and is more consistent with independent measurements and numerical modelling than single probe interpretation. However, the effects of plasma resistivity remain difficult to evaluate quantitatively. Analysis of the divertor plasma parameters over a wide range of conditions is presented. The behavior of the ion fluxes and parallel gradients during high recycling and detached discharges is studied and compared with predictions from simple analytical models of detachment. Numerical models are used to study the impurity production from the divertor target plate. A new technique of evaluating the plasma parameters both between and during Edge Localized Modes (ELMs) using the triple probes is applied to study the influence of active pumping on the divertor parameters.
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Eckman, Robert Francis. "Langmuir Probe Measurements in the Plume of a Pulsed Plasma Thruster." Digital WPI, 1999. https://digitalcommons.wpi.edu/etd-theses/1051.
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"As new, smaller satellites are built, the need for improved on-board propulsion systems has grown. The pulsed plasma thruster has received attention due to its low power requirements, its simple propellant management, and the success of initial flight tests. Successful integration of PPTs on spacecraft requires the comprehensive evaluation of possible plume-spacecraft interactions. The PPT plume consists of neutrals and ions from the decomposition of the Teflon propellant, material from electrode erosion, as well as electromagnetic fields and optical emissions. To investigate the PPT plume, an on-going program is underway at WPI that combines experimental and computational investigations. Experimental investigation of the PPT plume is challenging due to the unsteady, pulsed as well as the partially ionized character of the plume. In this thesis, a triple Langmuir probe apparatus was designed and used to obtain electron temperature and density measurements in the plume of a PPT. This experimental investigation provides further characterization of the plume, much needed validation data for computational models, and is useful in thruster optimization studies. The pulsed plasma thruster used in this study is a rectangular geometry laboratory model built at NASA Lewis Research Center for component lifetime tests and plume studies. It is almost identical in size and performance to the LES 8/9 thruster, ablating 26.6 ug of Teflon, producing an impulse bit of 256 uN-s and a specific impulse of 986 s at 20 J. All experiments were carried out at NASA LeRC Electric Propulsion Laboratory. The experimental setup included triple Langmuir probes mounted on a moveable probe stand, to collect data over a wide range of locations and operating conditions. Triple probes have the ability to instantaneously measure electron temperature and density, and have the benefit of being relatively simple to use, compared to other methods used to measure these same properties. The implementation of this measuring technique is discussed in detail, to aid future work that utilizes these devices. Electron temperature and density was measured from up to 45 degrees from the centerline on planes parallel and perpendicular to the thruster electrodes, for thruster energy levels of 5, 20 and 40 J. Radial distances extend from 6 to 20 cm downstream from the Teflon surface. These locations cover the core of the PPT plume, over a range of energy levels that corresponds to proposed mission operating conditions. Data analysis shows the spatial and temporal variation of the plume. Maximum electron density near the exit of the thruster is 1.6 x 1020, 1.6 x 1021, and 1.8 x 1021 m-3 for the 5, 20 and 40 J discharges, respectively. At 20 cm downstream from the Teflon surface, densities are 1 x 1019, 1.5 x 1020 and 4.2 x 1020 for the 5, 20 and 40 J discharges, respectively. The average electron temperature at maximum density was found to vary between 3.75 and 4.0 eV for the above density measurements at the thruster exit, and 20 cm from the Teflon surface the temperatures are 0.5, 2.5, and 3 eV for the 5, 20 and 40 J discharges. Plume properties show a great degree of angular variation in the perpendicular plane and very little in the parallel plane, most likely due to the rectangular geometry of the PPT electrodes. Simultaneous electron temperature and density traces for a single thruster discharge show that the hottest electrons populate the leading edge of the plume. Analysis between pulses shows a 50% variation in density and a 25% variation in electron temperature. Error analysis estimates that maximum uncertainty in the temperature measurements to be approximately +/- 0.75 eV due to noise smoothing, and the maximum uncertainty in electron density to be +/- 60%, due to assumptions related to the triple probe theory. In addition, analysis of previously observed slow and fast ion components in the PPT plume was performed. The analysis shows that there is approximately a 3 us difference in creation time between the fast and slow ions, and that this correlates almost exactly with the half period of the oscillations in the thruster discharge current."
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Byrne, Lawrence Thomas. "Langmuir probe measurements in the plume of a pulsed plasma thruster." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-1219102-173938.
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Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: PPT; pulsed plasma thruster; Langmuir probe; plasma diagnostics; electric propulsion; electron temperature; electron density. Includes bibliographical references (p. 97-102).
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Gramin, Ava. "Analysis of Calibration and Surface Contamination on the Rosetta Langmuir Probe Instrument." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-317492.
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Johlander, Andreas. "Photoemission on the Rosetta spacecraft." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-188153.
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Rosetta is a European spacecraft that will rendevouz with andfollow the comet 67P/Churyumov-Gerasimenko from 2014 to 2015. Among other instruments are two Langmuir probes that measure certain plasma parameters. This study aims to describe the photoemssionon Rosetta and in particular on the Langmuir probes. More than 7800 bias voltage sweeps were analyzed and parameters such as photosaturationcurrent, spacecraft potential, photoelectron temperature and offset current were calculated from these sweeps. It is found that the photoemission is stronger on Probe 1 than Probe 2. The photosaturation currents for dierent mission phases align rather well when normalized to distance to the Sun and the solar activity, when correcting for the offset currents found on the probes the alignment became even better. The typical electron density in the photoelectron cloud is 25 cm^-3 at 1 AU and the electron temperature varies from 1 - 2 eV.
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Shebanits, Oleg. "Pre-biotic molecules and dynamics in the ionosphere of Titan : a space weather station perspective." Licentiate thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-248118.
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Saturn’s largest moon Titan (2575 km radius) is the second largest in the Solar system. Titan is the only known moon with a fully developed nitrogen-rich atmosphere with ionosphere extending to ~2000 km altitude, hosting complex organic chemistry. One of the main scientific interests of Titan’s atmosphere and ionosphere is the striking similarity to current theories of those of Earth ~3.5 billion years ago. The Cassini spacecraft has been in orbit around Saturn since 2004 and carries a wide range of instruments for investigating Titan’s ionosphere, among them the Langmuir probe, a “space weather station”, manufactured and operated by the Swedish Institute of Space Physics, Uppsala. This thesis reviews the first half of the PhD project on the production of pre-biotic molecules in the atmosphere of Titan and early Earth, focusing on the ion densities and dynamics in Titan’s ionosphere derived from the in-situ measurements by the Cassini Langmuir probe. One of the main results is the detection of significant, up to ~2300 cm-3, charge densities of heavy (up to ~13000 amu) negative ions in Titan’s ionosphere below 1400 km altitude. On the nightside of the ionosphere at altitudes below 1200 km, the heavy negative ion charge densities are comparable to the positive ion densities and are in fact the main negative charge carrier, making this region of the ionosphere exhibit properties of dusty plasma. The overall trend is the exponential increasing of the negative ion charge densities towards lower altitudes. Another important result is the detection of ion drifts that between 880-1100 km altitudes in Titan’s ionosphere translate to neutral winds of 0.5-5.5 km/s. Ion drifts define three regions by altitude, the top layer (above ~1600 km altitude) where the ions are frozen into the background magnetic field, the dynamo region (1100 – 1600 km altitudes) where the ions are drifting in partly opposing directions due to ion-neutral collisions in the presence of the magnetic and electric fields and the bottom layer (below 1100 km altitude) of the ionosphere, where the ions are coupled to neutrals by collisions.
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Sawyer, Samuel Thomas. "Experimental Studies of Spacecraft Plasma Interactions: Facility Characterization and Initial Measurements." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/33714.
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The objectives of this thesis are to characterize the plasma environment of a new vacuum chamber facility at Virginia Tech and to perform initial measurements of plasma flow field for studying spacecraft-plasma interactions using this facility. An argon plasma environment was created using a hot filament cathode plasma source. Flange plates attached to the sides of the vacuum chamber were modified in order to attach various feedthroughs both now and in the future such that a probe array DAQ system could be used to expedite measurement and analysis. A Langmuir probe array was used to measure 3-D plasma flow field in the chamber. A Matlab code was developed for automatic evaluation of the Langmuir probe traces. Two sets of measurements were preformed. The first measurement characterizes the plasma produced by the hot filament cathode in the chamber. Langmuir Probes were used to characterize the plasma environment yielding the following average characteristics: Plasma Potential = 5.5486V, Electron Saturation Current = 0.003421A, Electron Temperature = 1.505eV, and the Plasma Density = 6.806*10^14 m^-3. It was found that for both the spherical and cylindrical probes used in the test facility Rs > Debye length and thus were analyzed under the thin sheath condition. The second measurement attempts to measure the 3-D plasma flow field for plasma flow over a structure composed of 4-inch biased Al box sitting on a biased Al plate. The results show signs of the the generation of the expansion pre-sheath structure at the leading edge of the plate and the box upper surface predicted by numerical models. However, the current diagnostics system does not have the spatial resolution and range as well as the data accuracy required to reach a definitive measurement of plasma presheath and plasma wake.Master of Science
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Holmberg, Madeleine. "Determination of Solar EUV Intensity and Ion Flux from Langmuir Probe Current Characteristics." Thesis, Uppsala University, Department of Physics and Astronomy, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-114460.
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This report presents a model to determine the solar Extreme UltraViolet (EUV) intensity and the ion flux in the vicinity of Saturn, by using measurements from the Langmuir probe, a plasma investigation instrument, of the Cassini satellite. The model is based on in situ measurements and does therefore provide an improved estimation of the wanted parameters compared to previously used calculations based only on the EUV flux measured near Earth. The solar EUV and ion flux were determined by analysing and processing the current measurements from the Cassini Langmuir probe in several steps. Initially the time intervals where the measured current were expected to be due only to the photoelectron current was extracted. The photoelectron current is the part of the measured probe current that is only due to electrons ejected from the probe by photons coming from the Sun. The measurements showed a periodic behaviour which was concluded to be due to the attitude of the satellite. This interfering effect was corrected for and the data was then plotted against an EUV index, estimated from a traditionally used proxy of the EUV flux near Earth; the F10.7 solar radio flux index. In agreement with the theory of the photoelectric effect a linear relationship between the EUV flux and the photoelectron current mph was expected. A least square linear fit to the extracted photoelectron current data provided the relation, for the Langmuir probe on Cassini, in the form of the equation mph=0.1842EUV+0.2405, where mph is the photoelectron current in nA and EUV is the EUV index in W/Hzm^2. The derived equation is the result of the study, showing how to estimate the solar EUV flux using the Langmuir probe current measurements. This result was used to derive the other wanted parameter, the ion flux. The derivation was done by calculating the photoelectron current mph at all time and subtracting the result from the total current. The retrieved difference gives the magnitude of the ion current for every measurement.
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Zwahlen, Jurg C. "Investigation of a Pulsed Plasma Thruster Plume Using a Quadruple Langmuir Probe Technique." Digital WPI, 2003. https://digitalcommons.wpi.edu/etd-theses/33.
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The rectangular pulsed plasma thruster (PPT) is an electromagnetic thruster that ablates Teflon propellant to produce thrust in a discharge that lasts 5-20 microseconds. In order to integrate PPTs onto spacecraft, it is necessary to investigate possible thruster plume-spacecraft interactions. The PPT plume consists of neutral and charged particles from the ablation of the Teflon fuel bar as well as electrode materials. In this thesis a novel application of quadruple Langmuir probes is implemented in the PPT plume to obtain electron temperature, electron density, and ion speed ratio measurements (ion speed divided by most probable thermal speed). The pulsed plasma thruster used is a NASA Glenn laboratory model based on the LES 8/9 series of PPTs, and is similar in design to the Earth Observing-1 satellite PPT. At the 20 J discharge energy level, the thruster ablates 26.6 mg of Teflon, creating an impulse bit of 256 mN-s with a specific impulse of 986 s. The quadruple probes were operated in the so-called current mode, eliminating the need to make voltage measurements. The current collection to the parallel to the flow electrodes is based on Laframboise's theory for probe to Debye length ratios between 5 and 100, and on the thin-sheath theory for ratios above 100. The ion current to the perpendicular probe is based on a model by Kanal and is a function of the ion speed ratio, the applied non-dimensional potential and the collection area. A formal error analysis is performed using the complete set of nonlinear current collection equations. The quadruple Langmuir probes were mounted on a computer controlled motion system that allowed movement in the radial direction, and the thruster was mounted on a motion system that allowed angular variation. Measurements were taken at 10, 15 and 20 cm form the Teflon fuel bar face, at angles up to 40 degrees off of the centerline axis at discharge energy levels of 5, 20, and 40 J. All data points are based on an average of four PPT pulses. Data analysis shows the temporal and spatial variation in the plume. Electron temperatures show two peaks during the length of the pulse, a trend most evident during the 20 J and 40 J discharge energies at 10 cm from the surface of the Teflon fuel bar. The electron temperatures after the initial high temperature peak are below 2 eV. Electron densities are highest near the thruster exit plane. At 10 cm from the Teflon surface, maximum electron densities are 1.04e20 ± 2.8e19 m-3, 9.8e20 ± 2.3e20 m-3, and 1.38e21 ± 4.05e20 m-3 for the 5 J, 20 J and 40 J discharge energy, respectively. The electrons densities decrease to 2.8x1019 ± 8.9e18 m-3, 1.2e20 ± 4.2e19 m-3, and 4.5e20 ± 1.2e20 m-3 at 20 cm for the 5 J, 20 J, and 40 J cases, respectively. Electron temperature and density decrease with increasing angle away from the centerline, and with increasing downstream distance. The plume is more symmetric in the parallel plane than in the perpendicular plane. Ion speed ratios are lowest near the thruster exit, increase with increasing downstream distance, but do not show any consistent angular variation. Peak speed ratios at a radial distance of 10 cm are 5.9±3.6, 5.3±0.39, and 4.8±0.41 for the 5 J, 20 J and 40 J discharge energies, respectively. The ratios increase to 6.05±5.9, 7.5±1.6, and 6.09±0.72 at a radial distance of 20 cm. Estimates of ion velocities show peak values between 36 km/s to 40 km/s, 26 km/s to 30 km/s, and 26 km/s to 36 km/s for the % J, 20 J, and 40 J discharge energies, respectively.
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Zwahlen, Jurg C. "Investigation or a pulsed plasma thruster plume using a quadruple Langmuir probe technique." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0108103-143841.
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Asselin, Daniel Joseph. "Characterization of the Near-Plume Region of a Low-Current Hollow Cathode." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/438.
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Electric propulsion for spacecraft has become increasingly commonplace in recent decades as designers take advantage of the significant propellant savings it can provide over traditional chemical propulsion. As electric propulsion systems are designed for very low thrust, the operational time required over the course of an entire mission is often quite long. The two most common types of electric thrusters both use hollow cathodes as electron emitters in the process of ionizing the propellant gas. These cathodes are one of the main life-limiting components of both ion and Hall thrusters designed to operate for tens of thousands of hours. Failure often occurs as a result of erosion by sputtering from high-energy ions generated in the plasma. The mechanism that is responsible for creating these high-energy ions is not well understood, and significant efforts have gone into characterizing the plasma produced by hollow cathodes. This work uses both a Langmuir probe and an emissive probe to characterize the variation of the plasma potential and density, the electron temperature, and the electron energy distribution function in the near plume region of a hollow cathode. The cathode used in this experiment is typical of one used in a 200-W class Hall thruster. Measurements were made to determine the variation of these parameters with radial position from the cathode orifice. Changes associated with varying the propellant and flow rate were also investigated. Results obtained from the cathode while running on both argon and xenon are shown. Two different methods for calculating the plasma density and electron temperature were used and are compared. The density and temperature were not strongly affected by reductions in the propellant flow rate. The electron energy distribution functions showed distinct shifts toward higher energies when the cathode was operated at lower flow rates. The plasma potential also displayed an abrupt change in magnitude near the cathode centerline. Significant increases in the magnitude of plasma potential oscillations at lower propellant flow rates were observed. Ions formed at the highest instantaneous plasma potentials may be responsible for the life-limiting erosion that is observed during long-duration operation of hollow cathodes.
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Callaway, Martin James. "Thin films of flexible chain molecules." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307080.
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Shebanits, Oleg. "Determination of Ion Number Density from Langmuir Probe Measurements in the Ionosphere of Titan." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132567.
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Saturn’s largest moon, Titan, presents a very interesting subject for study because of its atmosphere’s complex organic chemistry. Processes taking place there might shed some light on the origins of organic compounds on Earth in its early days. The international spacecraft Cassini-Huygens was launched to Saturn in 1997 for a detailed study of the gas giant and its moons, specifically Titan. The Swedish Institute of Space Physics in Uppsala has manufactured the Langmuir probe instrument for the Cassini spacecraft now orbiting Saturn, and is responsible for its operation and data analysis. This project concerns the analysis of Titan’s ionosphere measurements from this instrument, from all “deep” flybys of the moon (<1400km altitude) in the period October 2004 - April 2010. Using the Langmuir Probe analysis tools, the ion flux is derived by compensating for the atmospheric EUV extinction (that varies with the photoelectron current from the probe). The photoelectron current emitted from the probe also gives an artifact in the data that for this project needs to be deducted before analysis. This factor has already been modeled, while the extinction of Titan’s atmosphere has only been taken into account on event basis (not systematically). The EUV corrected ion flux data is then used to derive the ion number density in Titan’s atmosphere, by setting up an average ion mass altitude distribution (using the Ion Neutral Mass Spectrometer results for comparison) and deriving the spacecraft speed along the Cassini spacecraft trajectory through Titan’s ionosphere. The ion number density results proved to correlate very well with the theoretical ionospheric profiles on the day side of Titan (see graphical representation in the Results section). On the night side, a perturbation of the ion flux data was discovered by comparison with Ion Neutral Mass Spectrometer data, supporting earlier measurements of negative ions reported by Coates et al 2009. The project was carried out at the Swedish Institute of Space Physics (Institutet för Rymdfysik, IRF) in Uppsala.Saturnus största måne Titan är ett väldigt intressant forskningsobjekt på grund av dess atmosfärs komplexa organiska kemi. Processer som pågår i Titans täta atmosfär kan hjälpa oss att förstå ursprunget till organiska föreningar på Jorden i dess unga ålder. Den internationella rymdsonden Cassini-Huygens blev uppskjuten mot Saturnus 1997, för att i detalj undersöka gasjätten och dess månar, speciellt Titan. Institutet för Rymdfysik (IRF) i Uppsala är ansvariga för operation och dataanalys av Langmuirsonden ombord Cassini som ligger i omloppsbanan kring Saturnus sedan 2004. Detta projekt omfattar analys av Langmuirsondens mätningar av Titans jonosfär från alla ”djupa” förbiflygningar av månen under perioden oktober 2004 – april 2010. Med hjälp av analysverktygen för Langmuirsonden, tas jonflödet fram efter kompensation för den atmosfäriska EUV extinktionen som ger upphov till fotoelektronströmmen från sonden. Fotoelektronströmmen som utsänds från proben ger en artefakt i data och måste (för detta projekt) korrigeras före analysen. Denna faktor är redan bestämd, men extinktionen av Titans atmosfär har endast korrigerats för i enstaka fall. Det korrigerade datat används för att få fram jondensiteten i Titans atmosfär genom att en genomsnittlig jonmass/höjd fördelning antas (jämförs med resultat från INMS-instrumentet) och kombineras med den beräknade hastighet som Cassini håller i banan genom jonosfären. Projektet utfördes vid Institutet för Rymdfysik, Uppsala.
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Wantock, Thomas. "Thrust balance performance characterisation and internal Langmuir probe plasma diagnostics for a Halo thruster." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/845862/.
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Electric Propulsion (EP) systems can enable novel spacecraft missions requiring high total change in velocity, owing to their high specific impulse compared to chemical propulsion systems. Mature devices, such as Hall Effect Thrusters (HETs), have accumulated significant flight heritage. How- ever, established technologies do not satisfy the requirements of the rapidly growing small satellite sector, because of adverse scaling to low powers. The Halo thruster concept falls within the cat- egory of Cusped Field Thrusters (CFTs), aimed at addressing this issue. The concept concerns the use of ‘magnetic null regions’, formed through the deliberate cancellation of magnetic fields. Two such regions are produced in the thruster, a ‘null point’ at the thruster exit and an annular ‘halo’ near the anode. The work presented in this thesis has provided foundational knowledge of the performance and internal physics of the Halo thruster, using a 5 cm channel diameter, electromagnet laboratory model. Measurements of thrust, specific impulse and thrust efficiency were obtained over a wide range of operating conditions using a pendulum thrust balance in representative high vacuum, and the sensitivity of the measured performance to facility effects was assessed. Trends in plasma potential, electron temperature and plasma density internal to the discharge channel were obtained using a translating Langmuir probe, allowing the basic physics of operation of the device to be inferred. The thruster was found to exhibit comparable performance to other CFTs, with measurements shown to be robust to facility effects. Internal plasma measurements revealed behaviour similar to that of the Cylindrical Hall Thruster, with some differences due to the presence of the halo magnetic null region near the anode which might be exploited to improve performance. As a result of the research presented, design changes are suggested for future iterations. In its current embodiment, the thruster already offers advantages over heritage small satellite EP systems, and is a viable candidate for near-term industrialisation.
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Auman, Andrew Jay. "The Adaptability of Langmuir Probes to the Pico-Satellite Regime." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/165.
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The purpose of this thesis is to investigate whether it is feasible to use Langmuir probes on pico-satellites flying in low Earth orbit over mid- to low-latitude geographic regions. Following chapters on the expected ionospheric conditions and an overview of Langmuir probe theory, a chapter addressing the difficulties involved with pico-satellite Langmuir probes is presented. Also, the necessary satellite-to-probe surface area requirements in order to achieve confidence in pico-satellite Langmuir probe data, for the orbital regions of interest to this thesis, are stated.
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Lyons, Laurence Anthony. "Construction and operation of a Mirror Langmuir Probe diagnostic for the Alcator C-Mod tokamak." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40321.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 119-120).
Langmuir probe diagnostic systems presently employed on Alcator C-Mod and elsewhere generally suffer from a severe limitation: unless multiple electrode or high-frequency bias techniques are employed, these systems can not resolve the rapid changes in plasma electron temperature, floating potential and ion saturation current that are associated with plasma turbulence. Moreover, no existing system can provide real-time output of these three parameters using a single electrode. To remedy this limitation, an advanced, high-bandwidth Langmuir probe system has been constructed for Alcator C-Mod using state-of-the-art design tools and components. The system produces a fast-switched, three-state probe bias waveform and employs a new method for outputting plasma conditions in real-time, a 'Mirror Langmuir Probe' (MLP), which utilizes high-bandwidth bipolar transistors to electrically simulate a Langmuir probe's response. Detailed information on the design, construction and performance of this new diagnostic is described in this thesis, representing the first proof-of-principle demonstration of the MLP technique. The MLP system was found to meet all the performance goals set forth at the beginning of the project: real-time output of electron temperature, floating potential and ion saturation current, ability to track changes in plasma parameters within a ~1 [mu]s timescale, while utilizing only a single Langmuir electrode. The system was tested using an 'electronic Langmuir probe' and also using an actual Langmuir probe in Alcator C-Mod. In both cases, the system accurately locked onto changing plasma conditions (< ~5% error in outputted parameters), with the exception of some severe transient events found in C-Mod plasmas (ELMs), which challenged the system's accuracy.
(cont.) Further refinements to the system have been identified to handle such cases. The MLP clearly demonstrated superior performance to existing Langmuir probe systems on Alcator C-Mod and should enable researchers to study edge plasma turbulence in much greater detail in the future.
by Laurence Anthony Lyons.
S.M.
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Partridge, James Michael. "Development and Implementation of diagnostics for unsteady small-scale plasma plumes." Worcester, Mass. : Worcester Polytechnic Institute, 2009. http://www.wpi.edu/Pubs/ETD/Available/etd-011409-150444/.
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Dissertation (Ph.D.)--Worcester Polytechnic Institute.Keywords: TLP; RPA; retarding potential analyzer; triple Langmuir Probe; plume; probe; diagnostic; thruster; Plasma. Includes bibliographical references (leaves 183-190).
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Zechar, Nathan E. "Experimental Investigation of a Parametric Excitation of Whistler Waves." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1495802386539665.
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Usoltceva, Mariia. "Advancements in Langmuir probe diagnostic for measurements in RF sheath and in modelling of the ICRF slow wave." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0061.
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Injecter de la puissance au plasma avec les ondes au voisinage de la fréquence cyclotron ionique (ICRF) est une technique prometteuse pour chauffer les plasmas de tokamak aux températures de fusion requises. Pour le rendement élevé, l'antenne ICRF doit être placée à proximité du plasma, mais ils accroissent les interactions plasma-paroi néfastes. Les ions accélérés par le champ électrique dans la gaine radiofréquence (RF) se sont avérés être à l'origine de ces interactions. La conception de l'antenne ICRF pourrait être optimisée pour réduire les effets observés. Ces études peuvent être réalisées sur une simple expérience dédiée. Aline (A Linear Experiment) est une machine linéaire avec un plasma cylindrique à basse température que s'appuie sur la caractérisation du plasma avec la sonde de Langmuir. Le champ magnétique modifie complètement le transport de particules dans le plasma. Par conséquent, les méthodes classiques d'analyse de sondes ne sont plus applicables. Cela est particulièrement vrai pour une sonde de Langmuir cylindrique de petit diamètre parallèle au champ magnétique ou avec un petit angle avec celui-ci. Les théories développées pour le traitement des données de la sonde de Langmuir pour le plasma magnétisé sont présentés. Les résultats sont comparés aux densités obtenues par interférométrie. Les techniques d'analyse des données présentées sont non seulement importantes pour l'application sur Aline, mais aussi pour d’autre machines à plasma magnétisé. IShTAR (Ion cyclotron Sheath Test Arrangement) fournit des conditions plus proches de celles du tokamak que celles d'Aline car possédant une antenne ICRF imitant celles d'un tokamak. L'objectif est d'étudier la propagation des ondes ICRF dans la configuration IShTAR. Les diagnostics de sonde ont été utilisés pour quantifier les paramètres plasma et les champs des ondes ICRF pertinents. Des simulations numériques de l'onde lente ICRF ont été réalisées à COMSOL. Le plasma a été mis en œuvre en tant que matériau avec des propriétés physiques ajustées manuellement. Les structures de champ obtenues pour l'onde lente diffèrent significativement de celles de l'onde rapide (autre solution de la relation de dispersion), et présentent une forte dépendance du profil de densité sur le bord du plasma. Les résultats de cette thèse contribuent aux études de la physique de la gaine RF sur des dispositifs linéaires dédiés, ainsi que de la physique des ondes ICRF sur le bord du plasma du tokamak en généralCoupling power to the plasma with ion cyclotron range of frequencies (ICRF) waves is a promising method for heating tokamak plasmas to fusion relevant temperatures. For high efficiency, the ICRF antenna must be placed close to the plasma, but they enhance destructive plasma-wall interactions. Plasma ions accelerated by the electric field in the radio-frequency (RF) sheath have been found to be the main cause of these interactions. The ICRF antenna design could be optimized to reduce the observed effects. The physics of these effects can be studied on a simple specially designed experiment. Aline (A LINear Experiment) is a linear low-temperature plasma device. The machine is focused on plasma characterization with the Langmuir probe diagnostic. The presence of magnetic field changes completely the particle transport in plasma, therefore conventional methods of data analysis are not applicable. Especially it is true for a small cylindrical Langmuir probe parallel to the magnetic field or at a small angle to it. In this thesis theories are presented which were developed for Langmuir probe data processing for magnetized plasma. The first results are also presented, as well as a comparison to line-averaged densities by interferometry. Presented data analysis techniques are not only important for application on Aline but can be used on any machine with magnetized plasma. IShTAR (Ion cyclotron Sheath Test Arrangement) is closer to tokamak conditions than Aline because it has an ICRF antenna which mimics tokamak antennas. In the framework of this thesis the objective is to study comprehensively the ICRF wave propagation in IShTAR configuration. Probe diagnostics were employed to quantify the relevant plasma parameters and the relevant ICRF wave fields. Numerical simulations of the ICRF slow wave were done in COMSOL. Plasma was implemented as a material with manually assigned physical properties. Field structures obtained for the slow wave differ significantly from the other mode, fast wave, and exhibit strong dependence on the density profile on the plasma edge. The results of this thesis work contribute to the studies of the RF sheath physics on dedicated linear devices, as well as the physics of ICRF waves on the tokamak plasma edge in general. In ICRF simulations for tokamak devices the slow wave propagation on the edge is avoided. Results of this thesis can be used to improve the complex tokamak ICRF simulations
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Grenfell, Gustavo Guedes. "Estudo de efeitos da polarização eletrostática periférica no Tokamak TCABR." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-03062016-110840/.
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Efeitos da polarização eletrostática de eletrodos na periferia de tokamaks têm sido investigados em pequenos tokamaks e mesmo em alguns tokamaks de grande porte. Em geral as experiências são realizadas em condições em que bifurcação do campo elétrico radial é obtida, processo este identificado como modo H de polarização. No Tokamak TCABR, as experiências indicam que o confinamento aumenta para tensões aplicadas até +300 volts, atingindo um máximo de duas vezes o tempo de confinamento do modo L, mas sem bifurcação. Indícios de bifurcação foram notados com +400 V de polarização, mas a descarga termina devido à excitação da atividade MHD, ainda sob investigação. No presente trabalho, a pesquisa é aprofundada com a utilização de uma sonda de Langmuir com 18 pinos dispostos em duas fileiras sob a forma de um ancinho (rake probe) o que permite a medição da temperatura, densidade e flutuação de potencial ao longo do raio menor na periferia do Tokamak. A resolução temporal desse sistema é de cerca de 0,5 ms, para a temperatura, e 5 microssegundos para densidade e potencial flutuante do plasma. Outra sonda eletrostática com 5-pinos na mesma posição radial, mas em diferentes posições poloidal e toroidal foi usada para medições de turbulência e transporte de partículas. Os efeitos da polarização foram investigados e indicam que os níveis de turbulência e transporte começam a diminuir entre +150 e +200 V e para +300 V chegam a atingir uma quase supressão. Nesse mesmo intervalo de tensão a densidade começa a aumentar e para +300 V chega a ser um fator de aproximadamente 2. Quanto ao perfil de temperatura a variação é pouco significativa, mas as incertezas das medidas são maiores. Esses dados são compatíveis com a criação de uma barreira de transporte na região entre o eletrodo em r = 17 cm e o limitador em a = 18 cm. Além disso, o campo elétrico radial mostra forte cisalhamento nessa região. Tomando o início da subida do potencial flutuante como origem de uma escala de tempo, o atraso temporal do início da subida da densidade de elétrons e o atraso do início do decréscimo do transporte de partículas foram medidos. Os resultados são 50 microssegundos para a densidade de elétrons e 60 microssegundos para o transporte de partículas. A questão dos limiares de potência é discutida no texto. Os dados desta experiência indicam que o campo elétrico radial desempenha o papel principal para a melhoria do confinamento.Electrode biasing effects in the periphery of tokamaks have been investigated in small tokamaks and in a few large tokamaks. Usually the experiments are performed in conditions were bifurcation of the radial electric field is achieved, identified as biased H mode. In the tokamak TCABR, the biasing experiments indicate that the confinement increases for applied voltages up to +300 Volts, reaching a maximum of twice the confinement time of the L mode, but without bifurcation. Indications of bifurcation were detected with +400 V biasing, but the discharge terminates due to excitation of MHD activity, still under investigation. In the present work, the research is improved with the use of a rake shaped 18-pins Langmuir probe, allowing the measurement of electron temperature, density and potential fluctuations along the minor radius near the edge of the tokamak with time resolution of about 0.5 ms, for the temperature and 5 microseconds for density and floating potential. Another electrostatic probe with 5-pins all in the same radial position, but in different poloidal and toroidal position was used for turbulence and particle transport measurements. The effects of biasing indicate that the levels of turbulence and transport begin to decrease between +150 and +200 V and for +300 V reaches an almost suppression. In that same voltage interval the density, begin to increase and for 300 V reach a factor of about 2. The temperature profile does not change significantly but the uncertainty of the measurements is larger. These data are compatible with the creation of a barrier between the position of the electrode at r = 17 cm and the limiter of the tokamak at a = 18 cm. In addition, the radial electric field data show strong shear in this region. Taking the start of the increasing of the fluctuation potential as the origin of a time scale, the temporal delay of the start of the edge electron density increase and transport decrease were measured. The results are 50 microseconds for the electron density and 60 microseconds for the particle transport. The power threshold for the confinement improvement is discussed in the text. The data obtained in this experiment confirm that the shear of the electric field has the stronger role for the confinement improvement with biasing in TCABR tokamak.
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Kubic, Martin. "Étude expérimentale d'interactions entre antennes HF et plasma périphérique d'un Tokamak." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0220/document.
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Les antennes en opération dans la gamme de fréquence cyclotron ionique représentent un moyen utile pour chauffer du plasma dans les tokamaks et autres plasmas de fusion. Ces systèmes de chauffage sont amenés à jouer un rôle important dans le projet ITER. Conjointement avec le chauffage souhaité, les interactions parasites avec le bord du plasma et de la limite des matériaux apparaissent. Plusieurs de ces effets délétères sont causés par la formation de la radio-fréquence des gaines. L'objectif de cette thèse est d'étudier, principalement de façon expérimentale, les modifications du plasma de bord «scrape-off layer» causées par les effets non-linéaires des gaines RF. Cela se fait en utilisant les sondes électrostatiques (de Langmuir, Retarded Field Analyser, tunnel) pour différentes configurations du plasma et des antennes: avec des études paramétriques en fonction du déséquilibre entre les émetteurs de l'antenne, de la puissance injectée et de la densité SOL. De plus, l'influence des gaines RF sur les mesures du potentiel de la gaine avec le RFA sont analysées. Cette étude s'effectue à l'aide d'un code 1D basé sur le modèle cinétique «particle-in-cell». Ces simulations ont montré que la RFA est capable de mesurer de manière fiable le potentiel gaine, toutefois cela reste limité pour les fréquences de plasma ionique wpi proche de la fréquence injectée wrf. Par contre, pour des conditions réelles du SOL (wpi>wrf), quand RFA est magnétiquement connectée à la structure de l'antenne RF, il est fortement sous-estimé. Enfin, les mesures de RFA dans Tore Supra indiquent que les potentiels RF se propagent au moins jusqu'à de 12m de l'antenne le long de lignes de champ magnétiquesAntennas operating in the ion cyclotron range of frequency (ICRF) provide a useful tool for plasma heating in many tokamaks and are foreseen to play an important role in ITER. However, in addition to the desired heating in the core plasma, spurious interactions with the plasma edge and material boundary are known to occur. Many of these deleterious effects are caused by the formation of radio-frequency (RF) sheaths. The aim of this thesis is to study, mainly experimentally, scrape-off layer (SOL) modifications caused by RF sheaths effects by means of Langmuir probes that are magnetically connected to a powered ICRH antenna. Effects of the two types of Faraday screens' operation on RF-induced SOL modifications are studied for different plasma and antenna configurations - scans of strap power ratio imbalance, injected power and SOL density. In addition to experimental work, the influence of RF sheaths on retarding field analyzer (RFA) measurements of sheath potential is investigated with one-dimensional particle-in-cell code. One-dimensional particle-in-cell simulations show that the RFA is able to measure reliably the sheath potential only for ion plasma frequencies wpi similar to RF cyclotron frequency wrf, while for the real SOL conditions (wpi > wrf), when the RFA is magnetically connected to RF region, it is strongly underestimated. An alternative method to investigate RF sheaths effects is proposed by using broadening of the ion distribution function as an evidence of the RF electric fields in the sheath. RFA measurements in Tore Supra indicate that RF potentials do indeed propagate from the antenna 12m along magnetic field lines
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Taillefer, Zachary R. "Characterization of the Near Plume Region of Hexaboride and Barium Oxide Hollow Cathodes operating on Xenon and Iodine." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-dissertations/44.
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The use of electric propulsion for spacecraft primary propulsion, attitude control and station-keeping is ever-increasing as the technology matures and is qualified for flight. In addition, alternative propellants are under investigation, which have the potential to offer systems-level benefits that can enable particular classes of missions. Condensable propellants, particularly iodine, have the potential to significantly reduce the propellant storage system volume and mass. Some of the most widely used electric thrusters are electrostatic thrusters, which require a thermionic hollow cathode electron source to ionize the propellant for the main discharge and for beam neutralization. Failure of the hollow cathode, which often needs to operate for thousands of hours, is one of the main life-limiting factors of an electrostatic propulsion system. Common failure modes for hollow cathodes include poisoning or evaporation of the thermionic emitter material and erosion of electrodes due to sputtering. The mechanism responsible for the high energy ion production resulting in sputtering is not well understood, nor is the compatibility of traditional thermionic hollow cathodes with alternative propellants such as iodine. This work uses both an emissive probe and Langmuir probe to characterize the near-plume of several hollow cathodes operating on both xenon and iodine by measuring the plasma potential, plasma density, electron temperature and electron energy distribution function (EEDF). Using the EEDF the reaction rate coefficients for relevant collisional processes are calculated. A low current (< 5 A discharge current) hollow cathode with two different hexaboride emitters, lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6), was operated on xenon propellant. The plasma potential, plasma density, electron temperature, EEDF and reaction rate coefficients were measured for both hexaboride emitter materials at a single cathode orifice diameter. The time-resolved plasma potential measurements showed low frequency oscillations (<100 kHz) of the plasma potential at low cathode flow rates (<4 SCCM) and spot mode operation between approximately 5 SCCM and 7 SCCM. The CeB6 and LaB6 emitters behave similarly in terms of discharge power (keeper and anode voltage) and plasma potential, based on results from a cathode with a 0.020�-diameter. Both emitters show almost identical operating conditions corresponding to the spot mode regime, reaction rates, as well as mean and RMS plasma potentials for the 0.020� orifice diameter at a flow rate of 6 SCCM and the same discharge current. The near-keeper region plasma was also characterized for several cathode orifice diameters using the CeB6 emitter over a range of propellant flow rates. The spot-plume mode transition appears to occur at lower flow rates as orifice size is increased, but has a minimum flow rate for stable operation. For two orifice diameters, the EEDF was measured in the near-plume region and reaction rate coefficients calculated for several electron- driven collisional processes. For the cathode with the larger orifice diameter (0.040�), the EEDFs show higher electron temperatures and drift velocities. The data for these cathodes also show lower reaction rate coefficients for specific electron transitions and ionization. To investigate the compatibility of a traditional thermionic emitter with iodine propellant, a low-power barium oxide (BaO) cathode was operated on xenon and iodine propellants. This required the construction and demonstration of a low flow rate iodine feed system. The cathode operating conditions are reported for both propellants. The emitter surface was inspected using a scanning electron microscope after various exposures to xenon and iodine propellants. The results of the inspection of the emitter surface are presented. Another low current (< 5 A), BaO hollow cathode was operated on xenon and iodine propellants. Its discharge current and voltage, and plume properties are reported for xenon and iodine with the cathode at similar operating conditions for each. The overall performance of the BaO cathode on iodine was comparable to xenon. The cathode operating on iodine required slightly higher power for ignition and discharge maintenance compared to xenon, as evident by the higher keeper and anode potentials. Plasma properties in the near- plume region were measured using an emissive probe and single Langmuir probe. For both propellants, the plasma density, electron energy distribution function (EEDF), electron temperature, select reaction rate coefficients and time-resolved plasma potentials are reported. For both propellants the cathode operated the same keeper (0.25 A) and discharge current (3.1 A), but the keeper and anode potentials were higher with iodine; 27 V and 51 V for xenon, and 30 V and 65 V for iodine, respectively. For xenon, the mean electron energy and electron temperature were 7.5 eV and 0.7 eV, with bulk drift energy of 6.6 eV. For iodine, the mean electron energy and electron temperature were 6.3 eV and 1.3 eV, with a bulk drift energy of 4.2 eV. A literature review of relevant collisional processes and associated cross sections for an iodine plasma is also presented.
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Behlman, Nicholas James. "Electron Energy Distribution Measurements in the Plume Region of a Low Current Hollow Cathode." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/72.
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A hollow cathode is an electron source used in a number of different electric thrusters for space propulsion. One important component of the device that helps initiate and sustain the discharge is called the keeper electrode. Cathode keeper erosion is one of the main limiting factors in the lifetime of electric thrusters. Sputtering due to high-energy ion bombardment is believed to be responsible for keeper erosion. Existing models of the cathode plume, including the OrCa2D code developed at Jet Propulsion Laboratory, do not predict these high-energy ions and experimental measurement of the electron energy distribution function (EEDF) could provide useful information for the development of a high fidelity model of the plume region. Understanding of the mechanism by which these high-energy ions are produced could lead to improvements in the design of hollow cathodes. The primary focus of this work is to determine the EEDF in the cathode plume. A single Langmuir probe is used to measure the current-voltage (I-V) characteristic of the plasma plume from a low current hollow cathode in the region downstream of the keeper orifice. The EEDF is obtained using the Druyvesteyn procedure (based on interpretation of the second derivative of the I-V curve), and parameters such as electron temperature, plasma density and plasma potential are also obtained. The dependence of the EEDF and other parameters on the radial position in the plume is examined. Results show that the EEDF deviates from the Maxwellian distribution, and is more accurately described by the Druyvesteyn distribution directly downstream of the cathode. Off-axis measurements of the EEDF indicate the presence of fast electrons, most likely due to the anode geometry. The cathode used in these tests is representative of the cathode used in a 200W class Hall thruster. Data is presented for a hollow cathode operating on argon gas for two cases with different discharge currents.
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Zang, Linge. "Study on Edge Fluctuation of Supersonic Molecular-Beam Fueled Plasmas Using Langmuir probes and Fast Cameras in Heliotron J." Kyoto University, 2014. http://hdl.handle.net/2433/188823.
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Odelstad, Elias. "Rosetta spacecraft potential and activity evolution of comet 67P." Licentiate thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-294395.
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The plasma environment of an active comet provides a unique setting for plasma physics research. The complex interaction of newly created cometary ions with the flowing plasma of the solar wind gives rise to a plethora of plasma physics phenomena, that can be studied over a large range of activity levels as the distance to the sun, and hence the influx of solar energy, varies. In this thesis, we have used measurements of the spacecraft potential by the Rosetta Langmuir probe instrument (LAP) to study the evolution of activity of comet 67P/Churyumov-Gerasimenko as it approached the sun from 3.6 AU in August 2014 to 2.1 AU in March 2015. The measurements are validated by cross-calibration to a fully independent measurement by an electrostatic analyzer, the Ion Composition Analyzer (ICA), also on board Rosetta. The spacecraft was found to be predominantly negatively charged during the time covered by our investigation, driven so by a rather high electron temperature of ~5 eV resulting from the low collision rate between electrons and the tenuous neutral gas. The spacecraft potential exhibited a clear covariation with the neutral density as measured by the ROSINA Comet Pressure Sensor (COPS) on board Rosetta. As the spacecraft potential depends on plasma density and electron temperature, this shows that the neutral gas and the plasma are closely coupled. The neutral density and negative spacecraft potential were higher in the northern hemisphere, which experienced summer conditions during the investigated period due to the nucleus spin axis being tilted toward the sun. In this hemisphere, we found a clear variation of spacecraft potential with comet longitude, exactly as seen for the neutral gas, with coincident peaks in neutral density and spacecraft potential magnitude roughly every 6 h, when sunlit parts of the neck region of the bi- lobed nucleus were in view of the spacecraft. The plasma density was estimated to have increased during the investigated time period by a factor of 8-12 in the northern hemisphere and possibly as much as a factor of 20-44 in the southern hemisphere, due to the combined effects of seasonal changes and decreasing heliocentric distance. The spacecraft potential measurements obtained by LAP generally exhibited good correlation with the estimates from ICA, confirming the accuracy of both of these instruments for measurements of the spacecraft potential.
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Ronchi, Gilson 1985. "Estudos de descargas de plasma contínuas." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278560.
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Orientador: Munemasa MachidaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-19T18:26:47Z (GMT). No. of bitstreams: 1 Ronchi_Gilson_M.pdf: 6202845 bytes, checksum: e9580b7846e57a9eb526cdf45b808564 (MD5) Previous issue date: 2012
Resumo: O conhecimento das condições para ruptura de gases e a formação de plasma são questões importantes, não apenas de interesse fundamental, mas também para muitas aplicações, tais como em deposição de filmes finos de óxido ou polímeros, limpeza de superfície de materiais ou implantação iônica, por exemplo. A ruptura de gases descrita pela lei de Paschen com a teoria de Townsend, na qual a tensão de ruptura é uma função do produto da pressão p do gás pela distância d entre os eletrodos, proporciona uma adequada descrição em certas condições, em gases sob baixa pressão, quando a distância entre os eletrodos é muito menor que o raio R dos mesmos. A medida que a razão desses valores aumenta, as curvas de Paschen são deslocadas para regiões de tensão de ruptura mais elevadas, bem como para valores pd mais elevados. Investigamos aqui, os motivos e as consequências desse fenômeno, bem como uma proposta de lei de escalas capaz de determinar a tensão de ruptura em condições distintas de descargas. Tal lei de escalas obtida empiricamente faz uso, além da pressão e distância dos eletrodos, da razão R/d, que surge naturalmente ao se considerar o processo de difusão na descarga. Discutimos ainda sobre as principais técnicas de diagnósticos aplicáveis ao plasma, para obtenção, por exemplo, das temperaturas e densidades eletrônicas/iônicas. Em particular, revisamos as técnicas de espectroscopia e sonda de Langmuir, que são técnicas importantes amplamente utilizadas
Abstract: The understanding of the gas breakdown mechanism and plasma formation are important issues not only of fundamental interests, but also for many applications such as oxide thin films or polymers deposition, surface cleaning and ion implantation, for example. The breakdown described by Paschen¿s law with Townsend¿s theory, where the breakdown voltage is a function of the product of the gas pressure p and the gap distance d, provides a very accurate description under certain conditions as in low pressure gases when the distance between the electrodes is much smaller than its radius R. As the ratio d/R increases, the Paschen curves are shifted to regions of higher breakdown voltage, as well as higher pd values. In this work we investigate the reasons and consequences of this phenomenon, as well as a scaling law capable of determining the breakdown voltage of discharges in different conditions. This scalling law, obtained empirically, uses the gas pressure, the electrodes gap distance and the ratio R/d, which arises naturally when one consider the diffusion process in the discharge. We also discuss the main diagnostic techniques applicable to plasma to obtain, for example, temperature and electronic/ionic density. In particular, we review the techniques of spectroscopy and Langmuir probe, which are important techniques widely used
Mestrado
Física
Mestre em Física
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Scharlemann, Carsten A. "Investigation of thrust mechanisms in a water fed pulsed plasma thruster." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1070354149.
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Welzel, Thomas. "Time-resolved characterisation of pulsed magnetron discharges for the deposition of thin films with plasma diagnostic methods." Doctoral thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-81968.
Full textAbstract:
Research on the characterisation and understanding of pulsed magnetron discharges used for the deposition of thin, especially dielectric, films has been carried out between 2003 and 2008 at Chemnitz University of Technology. This thesis is a collection and summary of the original research during this period. In the main part of the thesis, work published in peer-reviewed scientific papers is summarised and yet unpublished results are given in more detail. Different aspects highlighted in the publications are described in a general context of the characterisation of the pulsed discharges for the principal understanding. The cross-linking of the published results is addressed and where necessary extensions to the publications are given. The main part is organised in three sections. In the first one, basics of pulsed magnetron discharges, their application, and important questions are summarised. The second section describes general results and physics of the discharges that have been obtained during the research work. It also emphasises the successful development or modifications of experimental techniques for the time-resolved characterisation. The third section addresses the possibilities to modify and control the process by external parameters that are typically accessible during the application or required by it. An appendix to the thesis comprises selected published research work which is made available as reprints of the original publications. Other publications which are not included as reprints are referenced to in the main partUntersuchungen zur Charakterisierung und zum Verständnis gepulster Magnetronentladungen, die zur Abscheidung von dünnen Schichten, besonders von dielektrischen Schichten, verwendet werden, wurden in den Jahren 2003 bis 2008 an der Technischen Universität Chemnitz durchgeführt. Diese Arbeit ist eine Sammlung und Zusammenfassung von neuen Forschungsergebnissen, die in diesem Zeitraum gewonnen wurden. Im Hauptteil der Habilitationsschrift werden die Arbeiten, die in referierten wissenschaftlichen Zeitschriften erschienen sind, zusammengefasst und noch unveröffentlichte Ergebnisse ausführlicher beschrieben. Verschiedene Aspekte, die in den Veröffentlichungen herausgestrichen wurden, werden in einem allgemeinen Zusammenhang der Charakterisierung gepulster Entladungen für ein prinzipielles Verständnis dargestellt. Querverbindungen zwischen den veröffentlichten Ergebnissen werden herausgearbeitet und wo nötig werden Erweiterungen der Originalveröffentlichungen vorgenommen. Der Hauptteil der Habilitationsschrift ist in drei Abschnitte unterteilt. Im ersten Teil werden Grundzüge gepulster Entladungen, ihre Anwendung und wesentliche Fragestellungen zusammengefasst. Der zweite Abschnitt beschreibt allgemeine Ergebnisse und die Physik der Entladungen, die während der Forschungsarbeit herausgearbeitet wurden. Er stellt auch die erfolgreiche Neuentwicklung oder Modifikation von Messtechniken zur zeitaufgelösten Charakterisierung heraus. Der dritte Abschnitt befasst sich mit den Möglichkeiten, den Beschichtungsprozess durch externe Parameter, die typischerweise während der Prozessanwendung zugänglich oder auch erforderlich sind, zu modifizieren und zu steuern. Der Anhang der Schrift beinhaltet ausgewählte Originalveröffentlichungen, die in Form von Reprints zugänglich gemacht werden. Andere Veröffentlichungen, die nicht im Anhang enthalten sind, werden im Hauptteil zitiert
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Welzel, Thomas. "Time-resolved characterisation of pulsed magnetron discharges for the deposition of thin films with plasma diagnostic methods." Doctoral thesis, Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000922.
Full textAbstract:
Research on the characterisation and understanding of pulsed magnetron discharges used for the deposition of thin, especially dielectric, films has been carried out between 2003 and 2008 at Chemnitz University of Technology. This thesis is a collection and summary of the original research during this period. In the main part of the thesis, work published in peer-reviewed scientific papers is summarised and yet unpublished results are given in more detail. Different aspects highlighted in the publications are described in a general context of the characterisation of the pulsed discharges for the principal understanding. The cross-linking of the published results is addressed and where necessary extensions to the publications are given. The main part is organised in three sections. In the first one, basics of pulsed magnetron discharges, their application, and important questions are summarised. The second section describes general results and physics of the discharges that have been obtained during the research work. It also emphasises the successful development or modifications of experimental techniques for the time-resolved characterisation. The third section addresses the possibilities to modify and control the process by external parameters that are typically accessible during the application or required by it. An appendix to the thesis comprises selected published research work which is made available as reprints of the original publications. Other publications which are not included as reprints are referenced to in the main partUntersuchungen zur Charakterisierung und zum Verständnis gepulster Magnetronentladungen, die zur Abscheidung von dünnen Schichten, besonders von dielektrischen Schichten, verwendet werden, wurden in den Jahren 2003 bis 2008 an der Technischen Universität Chemnitz durchgeführt. Diese Arbeit ist eine Sammlung und Zusammenfassung von neuen Forschungsergebnissen, die in diesem Zeitraum gewonnen wurden. Im Hauptteil der Habilitationsschrift werden die Arbeiten, die in referierten wissenschaftlichen Zeitschriften erschienen sind, zusammengefasst und noch unveröffentlichte Ergebnisse ausführlicher beschrieben. Verschiedene Aspekte, die in den Veröffentlichungen herausgestrichen wurden, werden in einem allgemeinen Zusammenhang der Charakterisierung gepulster Entladungen für ein prinzipielles Verständnis dargestellt. Querverbindungen zwischen den veröffentlichten Ergebnissen werden herausgearbeitet und wo nötig werden Erweiterungen der Originalveröffentlichungen vorgenommen. Der Hauptteil der Habilitationsschrift ist in drei Abschnitte unterteilt. Im ersten Teil werden Grundzüge gepulster Entladungen, ihre Anwendung und wesentliche Fragestellungen zusammengefasst. Der zweite Abschnitt beschreibt allgemeine Ergebnisse und die Physik der Entladungen, die während der Forschungsarbeit herausgearbeitet wurden. Er stellt auch die erfolgreiche Neuentwicklung oder Modifikation von Messtechniken zur zeitaufgelösten Charakterisierung heraus. Der dritte Abschnitt befasst sich mit den Möglichkeiten, den Beschichtungsprozess durch externe Parameter, die typischerweise während der Prozessanwendung zugänglich oder auch erforderlich sind, zu modifizieren und zu steuern. Der Anhang der Schrift beinhaltet ausgewählte Originalveröffentlichungen, die in Form von Reprints zugänglich gemacht werden. Andere Veröffentlichungen, die nicht im Anhang enthalten sind, werden im Hauptteil zitiert
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Colin, Clothilde. "Turbulent transport modeling in the edge plasma of tokamaks : verification, validation, simulation and synthetic diagnostics." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4350/document.
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La possibilité de produire de l'énergie en utilisant la fusion par confinement magnétique est un défi scientifique et technologique. La perspective d'ITER transmet des signaux forts afin d'intensifier les efforts de modélisation pour les plasmas de fusion. Le succès de la fusion est conditionnée par la qualité du confinement du plasma dans le cœur du réacteur et par le contrôle des flux de particules et de chaleur qui arrivent sur la paroi. Les deux phénomènes sont liés au transport turbulent. L'étude de ces phénomènes est d'autant plus compliquée que la géométrie magnétique est complexe. Cela nécessite une amélioration de notre capacité à développer des outils numériques capables de reproduire les propriétés du transport turbulent fiables.Cette thèse présente le modèle fluide du code TOKAM3X pour simuler plasma de bord turbulent. Une attention particulière a été portée sur la vérification et la validation de ce code, ce qui est une étape nécessaire avant d'utiliser un code comme un outil prédictif. Ensuite, de nouvelles études sur les propriétés physiques de la turbulence bord du plasma sont examinées. En particulier, les asymétries poloïdales induites par la turbulence et observées expérimentalement côté faible champ sont étudiées en détail. Un grand soin est dédié à la reproduction du scénario MISTRAL, qui consiste à changer la configuration magnétique et à en observer l'impact sur les flux parallèles dans le plan poloïdal. Les simulations reproduisent les mesures expérimentales et fournissent de nouvelles informations sur l'effet du point de contact plasma-paroi sur les caractéristiques de la turbulence, qui ne sont pas accessibles dans les expériencesThe possibility to produce power by using magnetically confined fusion is a scientific and technological challenge. The perspective of ITER conveys strong signals to intensify modeling effort on magnetized fusion plasmas. The success of the fusion operation is conditioned by the quality of plasma confinement in the core of the reactor and by the control of plasma exhaust on the wall. Both phenomena are related to turbulent cross-field transport that is at the heart of the notion of magnetic confinement studies, particle and heat losses. The study of edge phenomena is therefore complicated by a particularly complex magnetic geometry.This calls for an improvement of our capacity to develop numerical tools able to reproduce turbulent transport properties reliable to predict particle and energy fluxes on the plasma facing components. This thesis introduces the TOKAM3X fluid model to simulate edge plasma turbulence. A special focus is made on the code Verification and the Validation. It is a necessary step before using a code as a predictive tool. Then new insights on physical properties of the edge plasma turbulence are explored. In particular, the poloidal asymmetries induced by turbulence and observed experimentally in the Low-Field-Side of the devices are investigated in details. Great care is dedicated to the reproduction of the MISTRAL base case which consists in changing the magnetic configuration and observing the impact on parallel flows in the poloidal plane. The simulations recover experimental measurements and provide new insights on the effect of the plasma-wall contact position location on the turbulent features, which were not accessible in experiments
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Akbar, Demiral Salih. "The Non-uniform Argon Dc Glow Discharge System Parameters Measured With Fast Three Couples Of Double Probe." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607109/index.pdf.
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The non-uniform dc glow discharge plasma system is studied by using isolated computer controlled three couples of double probe system (TCDP) in argon gas, simultaneously. TCDP system has been developed to use for magnetized, unmagnetized, and for low oscillating plasma systems by using low pass filter with optically isolated circuitry to minimize the measurement errors with higher resolution and accuracy. Difference in the shapes and diameters of the discharge tube from region to region leads to change in the positive column
glow discharge properties. This is because the positive column
inhomogeneities, rising from the increase in the electron densities at the small tube radius region than the large one. Therefore, the axial electric field and the electron temperature have been diverted from their normal behavior in the positive column. However, at the large radius regions, the axial electric field seams to stay approximately constant at higher discharge currents.
On the other hand, In this work the radial dependence of the
electron temperature, density, floating potential, and the
normalized probe radius (ξ
=rp&
#955
D) has been investigated. Since, the probe radius is smaller than Debye length, the orbital motion limited (OML) theory has been used. As a result, the electron temperature (at the center) decreased and density increased with decreasing tube radius, and they have maximum values at the first probe (near the cathode). The electron density ne was observed to decrease and electron temperature Te to increase with increasing the discharge current. The floating potential has less negative value with decreasing tube radius except at the higher currents. Finally, it has been found that the &
#958
is proportional with electron density, but it remains constant depending on the value of Te and ne.
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Milligan, David J. "The baffle aperture region of an ion thruster." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342779.
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Bause, Marlon Luis. "Plasma density characteristics of magnetic holes near the Kronian magnetosphere boundary surfaces." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414766.
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Localized structures of the magnetic field strength depression are often observed in the interplanetarymedium, and they are called ‘magnetic holes’ after the original work of Turner et al. 1977. A numberof observations of similar features have been reported, while the mechanisms of their origin have notfully understood yet. The scale size of their structures varies from several to a few thousand of the protongyro radii, and their characteristic orientations of the magnetic field also vary, and therefore differenttypes of the magnetic holes have been suggested. To date, the magnetic holes are classified into Mirrormode and magnetic decreases (Tsurutani et al. 2011). Despite a large number of papers that report theobservational characteristics of the magnetic holes, many identify the feature using only the magneticfield data. This is due to the scale size of the structure at a large speed of the solar wind medium, thespatial resolution of the plasma instruments is often insufficient while the magnetic field instrument canusually obtain the data in high enough time resolution.The Cassini spacecraft orbited Saturn for almost 17 years and obtained a large amount of data in/near theKronian magnetosphere, where the series of the magnetic depletions have been also observed (Smith et al.1980). The Langmuir Probe (LP) onboard Cassini measures the spacecraft potential and, in turn, measuresthe electron density in in-situ in the outer magnetosphere and solar wind region. This measurement hasbeen done using the LP sweep mode which samples the current-voltage curve of the probe every 10 minin the outer magnetosphere. The LP has also been operated in the continuous mode that measures theprobe current at a fixed bias potential every 16 s allowing to calculate the electron density in a smallerscale that is required for the studies magnetic holes. However, there is no general calibration so far inorder to conduct a statistical study in the outer magnetosphere region. The goal of this project is toinvestigate the possibility to use the LP data for the magnetic hole study, calibrate the LP continuousmode to derive the plasma density near the magnetospheric of Saturn, and investigate the scale size of theplasma density structure in the magnetic holes, i. e. plasma β, the field strength and density.The calibration of the continuous data was done by finding a relation between the current at 11 V, whichis a typical bias voltage of continuous mode, and the spacecraft potential obtained by the LP the sweepmode data. Is is expected that the current at 11V is linearly proportional to the floating potential andtherefore can be used to derive the electron density with the potential and density relationship presentedby Morooka et al. 2009. I found that the spacecraft attitude against the sun has a strong effect on therelation, and derived 11V current-floating potential relationship depending on the different spacecraftattitude.Using the LP continuous data calibration above, I investigated the electron density characteristics aroundthe magnetic hold structure, and confirmed that they are generally in anticorrelation relationship. I estim-ated also the plasma β assuming a constant temperature of 100 eV and investigated their characteristicsfor the different types of magnetic holes (linear and rotational holes) both in the magnetosheath and theholes in the solar wind for the year 2011. For the Cassini dataset during 2011, various different shapeand sizes of magnetic hole events have been found. Most (80%) of the MHs appeared within a groupedstructure, while the rest (20%) are found as isolated type holes in the magnetosheath. Among the isolatedMHs, about 30% had "Gaussian shape" and about 40% had a substructure. The scale size for the electrondensity for the isolated holes were on average 50 s in the solar wind, and 75 s (the rotational holes) and120 s (the linear holes) in the magnetosheath. Therefore, I confirmed that the LP can obtain enough datapoints to resolve the magnetic holes structure in the magnetosheath. The Cassini LP data resolution isalso capable to resolve some of the magnetic hole structure in the solar wind.In summary, I confirmed that the Cassini LP continuous data calibrated in this study is capable toinvestigate the different types of magnetic hole structures. Using this calibrated electron data statisticallyfor the large number of Cassini orbit would helpful to further identify the MHs structures in the solar wind and the magnetosheath that can be a key to understand the generation mechanisms of the magneticholes.Lokaliserade strukturer med låg magnetfältstyrkan ses ofta i interplanetära mediet och de kallas ’mag-netiska hål’ (MH) (Turner et al. 1977). Trots et antal observationer av sådana strukturer har observeratsär deras generationsmekanism ännu förstådd. Storleken av strukturerna varierar från ett fåtal till någratusen protongyroradier och även deras kännetecknande inriktningar i magnetfältet varierar. På grund avdetta har olika typer av MH förslagits. Idag klassificerar man MH som ’mirror mode’ och magnetiskaminskningar (Tsurutani et al. 2011). Många studier har undersökt de magnetiska hålens egenskaper,men tyvärr oftast baserats endast på magnetfältsdata. Detta kan bero på strukturernas storlek vid en storsolvindshastighet, där plasmainstrumenten oftast inte har tillräckligt hög tidsupplösning för mätningar,medan magnetfältsinstrumenten kan oftast tillhandahålla data i hög tidsupplösning.Cassini-rymdfarkosten kretsade runt Saturnus i nästan 17 år och erhöll stora mängder data i och näraSaturnus magnetosfär. Langmuir-sonden (LP) ombord Cassini mäter rymdfarkostens potential ochdärmed mäter den elektrontätheten i rymden. Instrumentet fungerar som en slags väderstation för rym-dplasma och möjliggör mätningen av fundamentala plasmaparametrar såsom elektrontäthet, jontäthet,elektrontemperatur och jonmassa i en tät plasmaområdet av nära Saturnus. I den yttre magnetosfären därden plasmatätheten är låg, kan LP mäta rymdfarkosts potential och plasmatätheten. Mätningen, så kallade’sweep mode’ kan skaffades var 10:e minuter. LP:en mäter också i ’kontinuerlig mode’ som möjligenkan mäta plasmatätheten i mer frekventa men den behöver allmän kalibrering. I detta projekt undersökerjag möjligheten att använda LP kontinuerlig data för att studera MH, skapa kalibraring funktion för’kontinuerlig mode’ för att uppskatta plasmatätheten i Saturnus magnetosfär, och även att undersökastorleken och karaktär av plasmatäthetenstrukturen i MH.Jag undersökte först relationen mellan LP ström vid 11V och rymdfarkostens potential i sweep mode data.De härledda funktionerna användes vidare för att uppskatta densiteten med användning av relationenmellan rymdfarkostens potential och elektrontätheten (Morooka et al. 2009). Jag upptäckte också attden kontinuerlig mode funktionen är olika beroende på LP sensors läge i förhållande till solen ochrymdfarkosten. Hur Cassini är inriktad har en stor effekt på relationen och därför beskriva jag fyra olikarelationer för olika inriktningsregioner. Med den kontinuerlig mode funktionen jag härlett, undersöktejag struktur av magnetiska hålen som har listats av Tomas Karlsson på KTH. År 2011 innehåller MH medmycket olika former och storlekar. Den mest (80%) MH identifierades som grupp och resten (20%) varsom isolerade MH i magnetosheath. Av dessa isolerande hål har ca. 30% en Gauss-form och nästan 40%av MH verkar ha en understruktur. Genom att jämföra magfältdatan med elektrontätheten bekräftadejag den allmänna antikorrelationen mellan magnetfältstyrkan och elektrontätheten i MH-strukturerna.Dessutom hittar jag en ökning av elektron β som beräknas med en temperatur av 100 eV för linjära ochroterade MH i den magnetosheath samt MH i solvinden under 2011. Storleken av de isolerade magnetiskahålen är i genomsnitt 50 s i solvinden, 75 s (roterade magnetiska hål) och 120 s (linjära magnetiska hålen)i magnetosheath:en. Därför kan Cassini LP ha tillräcklig många datapoäng för att upplösa struktur avMH i magnetosheath. I solvinden kan LP upplösa en del av relativt stora MH.Sammanfattningsvis kan LP:s kontinuerlig kalibreringen från detta projekt användas för att analyserade olika strukturerna och storlekar av MH. Med denna kalibrerade plasmatäthet data är det möjligt attidentifiera olika MH karaktär i statistiskt för det stora antalet Cassini data. Det skulle vara en stor hjälpför att förstå genereringsmekanismerna av de magnetiska hålen.
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Dagtekin, Ebru. "Measurement Of Nonuniform Magnetized Argon Plasma Discharge Parameters." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607934/index.pdf.
Full textAbstract:
Effects of a magnetic field on the double-probe technique are studied experimentally by means of symmetric floating computer controlled fast double probes in low and intermediate pressure plasmas. In addition, the effects of the magnetic field on the electron temperature, electron density, and electric field have been investigated. As it is expected, when there is no magnetic field, properties of the discharge plasma are best described by Langmuir theory. Whereas, when there&rsquos a magnetic field of sufficient strength Schottky&rsquo
s theory of ambipolar diffusion applies.
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Alami, Jones. "Plasma Characterization & Thin Film Growth and Analysis in Highly Ionized Magnetron Sputtering." Doctoral thesis, Linköping : Dept. of Physics and Measurement Technology, Univ, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-4147.
Full text
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Ågren, Karin. "On the Formation and Structure of the Ionosphere of Titan." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-172148.
Full textAbstract:
We present results on the ionospheric structure around Titan observed during numerous deep (<1000 km) flybys by the Cassini spacecraft. Our results are based on measurements by the radio and plasma wave science instrument, in particular the Langmuir probe. In addition, data from the magnetometer and electron spectrometer have contributed. The ionosphere of Titan is created when the atmosphere of the moon becomes ionised. There are several mechanisms that contribute to this, the most important of which are considered to be photoionisation by EUV from the Sun with associated photoelectron ionisation, and particle impact ionisation by electrons and ions from Saturn’s corotating magnetosphere. We investigate the influence of the solar zenith angle on the electron number density at the ionospheric peak. The results show on average four times more plasma on the dayside compared to the nightside, with typical densities of 2500 – 3500 cm-3 and 400 – 1000 cm-3, respectively. In a complementary study, we make a case study of a nightside flyby and show that the altitude structure of the deep ionosphere is reproducible by a simple electron impact ionisation model. Taken together, this leads to the conclusion that solar photons are the main ionisation source of the dayside ionosphere. However, magnetospheric particle precipitation also contributes and can explain the electron densities seen on the nightside. As Titan does not exhibit any large intrinsic magnetic field, the fact that it is embedded in the magnetosphere of Saturn means that the Kronian field drapes around the moon and gives rise to an induced magnetosphere. We show that there are currents of the order of 10 – 100 nA m-2 flowing in the ionosphere of the moon. Associated with the currents are perpendicular electric fields ranging from 0.5 to 3 µV m-1. Finally, we investigate measurements obtained during T70, the deepest Titan flyby performed to date. We show that there is a substantial amount of negative ions present below an altitude of 900 km. This confirms previous result by the electron spectrometer, showing negative ions at higher altitudes in Titan’s ionosphere.