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Plasma diagnostics by probes with complex geometries
Palacký, Jakub ; Hrach, Rudolf (advisor) ; Roučka, Štěpán (referee)
In investigating the behaviour of the plasma, it is important to know its parameters. For this purpose, there are many diagnostic methods, one of which is a probe diagnostic. It is a local method in which there is contact of the plasma with embedded material. This work deals with this diagnostic method. It gives a comprehensive overview of the currently used probes in low-temperature and especially in high-temperature plasmas. It focuses on the development and use of the latest advances in the field of computational physics for creating two-dimensional model of low-temperature plasma with immersed solid. The task is prepare particle model of low-temperature plasma with immersed metal electrode, then run simulation of measurement and to interpret measured data.
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Analýza sondové charakteristiky s využitím neuronových sítí
Rafaj, Filip ; Roučka, Štěpán (advisor) ; Kocán, Pavel (referee)
Langmuir probes are used on our faculty to measure current-voltage characteristics of low-temperature weakly ionized plasma. From these measurements an electron temperature and an electron number density are obtained. Classical method of doing that is based on the linear least squares fitting. In this thesis we use neural networks as an alternative method of determining the plasma parameters. We train a feedforward neural network with a help of a stochastic gradient descent and a backpropagation algorithms together with a training data based on an analytical model the characteristic. We study network's accuracy, robustness and computational resources demands, all compared with the classical methods. Powered by TCPDF (www.tcpdf.org)
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Ion imaging method in molecular beam photodissociation experiments
Košťál, Pavel ; Fárník, Michal (advisor) ; Roučka, Štěpán (referee)
During my master thesis I became familiar with ion imaging and velocity map imaging (VMI) techniques in experiments with molecular beam. My major contribution was writing a computer program for data acquisition and pre-analysis. The program features initial filtering of the data, improving significantly signal to noise ratio. Non-trivial effort was required to make the program compatible with three different CCD cameras implemented on different experiments in the laboratory. I have also simulated ion trajectories in VMI and wrote a program code to imulate VMI image distortions due to imperfections in apparatus geometry. These programs will be useful in aligning and tuning the apparatus. Finally, I wrote a program for data manipulation and conversion to formats compatible with various data analysis programs available in the laboratory. All the above programs I have tested by measurements of 243 nm photodissociation of HBr molecules.
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Production of cold ions
Tran, Thuy Dung ; Plašil, Radek (advisor) ; Roučka, Štěpán (referee)
1 Abstract: For understanding of the evolution of chemical composition in cold interstellar gas clouds, it is necessary to study the ion-molecule reactions at temperatures from 10 K to 300 K at low pressures. The Ion Trap equipment, which is available in the laboratory of the Department of Surface and Plasma Science, allows this type of experiment. The main element of the Ion Trap is a 22-pole radiofrequency trap that examined reactions take place. For capturing ions in the trap, they need to be well focused in space, time and energy. To meet these conditions, it is necessary to find a suitable parameters of the source, which is used in the laboratory. The aim of this bachelor thesis is the design of optimized ion source and then using the program in LabVIEW to optimize the ion source N+ .
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Laboratory astrochemistry and applications of computer simulations
Roučka, Štěpán
This work is focused on laboratory studies of ion chemistry at conditions relevant for astrophysics. The three main outcomes of the thesis are: (1) The experimental study of the reaction rate coefficient of the associative detachment reaction H- + H → H2 + e- ; measurement of the thermal rate coefficient at the temperatures in the range 10-135 K is described. (2) The design of a novel apparatus for detecting the electrons produced in the RF trap and measuring their energy; numerical simulations and preliminary experimental results are presented. (3) The development of a model of the electron cooling in the afterglow plasma and the application of the model in the analysis of the H3 + recombination measurements.
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Laboratory astrochemistry and applications of computer simulations
Roučka, Štěpán ; Hrach, Rudolf (advisor) ; Bonaventura, Zdeněk (referee) ; Novák, Stanislav (referee)
This work is focused on laboratory studies of ion chemistry at conditions relevant for astrophysics. The three main outcomes of the thesis are: (1) The experimental study of the reaction rate coefficient of the associative detachment reaction H- + H -> H2 + e-; measurement of the thermal rate coefficient at the temperatures in the range 10-135 K is described. (2) The design of a novel apparatus for detecting the electrons produced in the RF trap and measuring their energy; numerical simulations and preliminary experimental results are presented. (3) The development of a model of the electron cooling in the afterglow plasma and the application of the model in the analysis of the H3+ recombination measurements.
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Study of plasma-solid interaction at medium pressures
Roučka, Štěpán ; Hrach, Rudolf (advisor) ; Novotný, Dušan (referee)
The thesis is aimed at particle simulation of plasma at medium pressures. Main results concern modelling of collisions in particle-in-cell algorithm. Dierent methods of modelling of collisions are discussed and their accuracy and eciency are investigated. Furthermore a new modication of particle-in-cell algorithm for modelling at medium pressures was proposed. Numerical benchmarks in the nal chapter show advantages of the new algorithm.
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