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Low temperature plasma and nanoparticles: effects of gas flow and surfaces
Ali-Ogly, Suren ; Kousal, Jaroslav (advisor) ; Blažek, Josef (referee) ; Kudrna, Pavel (referee)
Title: Low temperature plasma and nanoparticles: effects of gas flow and surfaces Author: Ing. Suren A. Ali-Ogly, B.Eng Department / Institute: Department of Macromolecular Physics / Charles University Supervisor of the doctoral thesis: Mgr. Jaroslav Kousal, PhD, Department of Macromolecular Physics / Charles University Abstract: This PhD thesis investigates the role of carrier gas flow in the magnetron-based gas aggregation cluster source and its impact on nanoparticle transportation. The research encompasses both theoretical and experimental aspects of low-temperature plasma interaction with surfaces and material engineering applications. Numerical models and computational fluid dynamics simulations are employed to understand the underlying physics of nanoparticles motion in gas aggregation cluster sources. The study demonstrates that carrier gas flow, particularly its velocity and inlet configuration, significantly influences the nanoparticles trap region and their residence time in the plasma. Brownian diffusion is identified as a critical factor affecting the spatial behaviour of NPs, contributing to both their escape and loss in gas aggregation cluster sources. The deposition of thin films using magnetron sputtering of PLA, a promising polymer material, is shown to facilitate nanoparticle adhesion....
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2D & 3D computer modelling of low-temperature plasma sheaths with a particular focus on their mutual interaction
Hromádka, Jakub ; Hrachová, Věra (advisor) ; Novotný, Dušan (referee) ; Kudrna, Pavel (referee)
The presented thesis deals with the study of the sheath layer which is formed during the interaction of a low-temperature plasma with a solid object using computer modelling techniques. The theoretical part of the thesis summarizes knowledge about the physics of the sheath layer of electropositive and electronegative plasma and presents the theory of measuring plasma parameters using a Langmuir probe, including a discussion of the effect of collisions of charged particles with neutrals on the probe measurements. Further, theoretical descriptions of the plasma are presented which are the basis of the computer models created in the framework of the thesis: a particle model based on the Particle-in-Cell method and a fluid model of the drift-diffusion approximation of the plasma. The developed particle model works in 3D space, uses the null-collision Monte Carlo method to account for the effects of collisions of charged particles with neutrals and implements the Intel Math Kernel Library functions to solve the Poisson's equation. The fluid model is implemented using FeniCS software. At first, the developed models are used for the calculation of the sheath layer and the current-voltage characteristics of free-standing Langmuir probes of several types: a 1D model of an infinitely large planar probe, a 2D model of...
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Computer study of probe diagnostics in high-temperature plasma
Lachnitt, Jan ; Hrach, Rudolf (advisor) ; Kudrna, Pavel (referee)
Title: Computational study of probe diagnostics in high-temperature plasma Author: Jan Lachnitt Department: Department of Surface and Plasma Science Supervisor: prof. RNDr. Rudolf Hrach, DrSc., Department of Surface and Plasma Science Abstract: This work is concerned to the particle computer modelling of the interaction of plasma, especially edge plasma, with immersed solids, especially probes. First, the speed and accuracy of several algorithms of the electrostatic force calculation were compared. One of the algorithms has been newly proposed. Then, a two-dimensional model of the interaction of collision-less plasma with a probe was created. This model has been applied to experimental data from CASTOR tokamak. The crucial point of this work is the creation of a fully three-dimensional particle model. This model has been tested for accuracy and speed and has been parallelized for higher efficiency. Keywords: plasma, probe diagnostics, computational physics, particle modelling
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Design and implementation of the plasma control system for the COMPASS tokamak
Janky, Filip ; Horáček, Jan (advisor) ; Kudrna, Pavel (referee) ; Svoboda, Vojtěch (referee)
Design and implementation of the plasma control system Mgr. Filip Janky The COMPASS tokamak was recommissioned in 2007 and it needed new digital controllers for its experimental research. This thesis presents the design and imple- mentation of control of main plasma parameters such as plasma current, plasma position, plasma shape and electron density. Improved plasma current control with resetting set points suppresses overshooting and thus increases the length of the flat top phase. A method for estimating the plasma position, gain tuning for the controller and decreasing latencies and delays to obtain robust position control are presented. Lower delays improve plasma stability and decrease the frequency of disruptions. The plasma shape controller is a feedforward controller with a method to suppress oscillations which are coming from mutual inductance between power supplies controlling plasma horizontal position, plasma shape and plasma current, which all use the same coil. Averaged electron density is corrected in real-time according to the interferometer line of sight and a non-linearity of measurement. Controllers and their improvements described here, played a major role in achiev- ing H-mode scenario and fulfilling the experimental program. Keywords: tokamak, plasma current control, plasma position...
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Magnetic field Supported Discharge Based Plasma Sources
Havlíček, Josef ; Kudrna, Pavel (advisor) ; Tichý, Milan (referee)
Main aim of this work was measurement of a floating potential fluctuations in the cylindrical magnetron in classical configuration in neon. Two Langmuir probes were used for measurement of wave vector. The following values were measured: pressure p in range 1-7 Pa, magnetic induction B in range 10-40 mT, discharge current I in range 5-100 mA, discharge voltage U and floating potential Uf. Fluctuations were described by dependencies of power spectral density on frequency S(f) and by histograms S(k,f), where k is wave vector. Several discharge modes were observed in the magnetron. These are characterized by different values of discharge voltage, electric field in positive column, magnitude of the floating potential etc. The discharge conditions, where peaks were observed in spectra, were determined. Only one peak with frequency in range 4-16 kHz was mostly observed. Most of these peaks had zero wave vector in histogram S(k,f), i.e. the floating potential synchronously oscillated in the whole discharge area. For some discharge conditions histograms with non-zero wave vector for noise background were observed.
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The Process of the Transition to Democracy in Czechoslovakia in the Period of November - December 1989
Kudrna, Pavel ; Štefek, Martin (advisor) ; Koubek, Jiří (referee)
This bachelor thesis analyses the transition of Czechoslovakia towards democracy with emphasis on the first period of the transition: November and December 1989. The paper introduces different transitological approaches and applies them to the Czechoslovakia case. Traditional approaches, for instance Rustow, Mainwaring, Karlová and Schmitter, Przeworski, and others, are used to reflect upon the transition phases and typology. The thesis furthermore takes into consideration major historiographical works on the final phase or fall of non-democratic regimes and establishing a new system. The analysis also emphasises the actors of the transition. Powered by TCPDF (www.tcpdf.org)
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