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Simulations of dynamics of ultra-cold quantum plasma
Rendek, Andrej ; Hejduk, Michal (advisor) ; Roučka, Štěpán (referee)
Title: Simulations of dynamics of ultra-cold quantum plasma Author: Andrej Rendek Department: Department of Surface and Plasma Science Supervisor: Mgr. Michal Hejduk, Ph.D., Department of Surface and Plasma Science Abstract: We investigate the confinement of charged particles in an oscillating electromagnetic field, intending to trap electrons and calcium ions simultaneously. The theoretical part of this thesis focuses on the derivation of exact and effective potentials in a single frequency quadrupole trap. We show a general treatment of stability in such a field. Passing attained knowledge onto two-frequency trapping, which is much more suitable for confining two species with widely different charge-to-mass ratios. We follow up by studying the stability of electrons, employing computer simulations in the ideal two- frequency Paul trap. Our ambition is to identify a stable configuration minimizing electrons' temperature. We create multiple ion Coulomb crystals and examine the effect of their presence on electrons' stability. These efforts support the development of an experiment with the ambition to create and study quantum plasma. The composition of this experiment is outlined here as well. Keywords: Ion trapping, Coulomb crystal, Two frequency Paul trap
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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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Study of Positive Column in Glow Discharge under Medium Pressures Using Computational Experiment
Laca, Marek ; Hrachová, Věra (advisor) ; Novák, Stanislav (referee) ; Roučka, Štěpán (referee)
The positive column of the oxygen and argon-oxygen direct current glow discharge was investigated using a fluid plasma model at pressures around hundreds of pascals and discharge currents from ten to forty miliampers. The model describes the infinitely long positive column in cylindrical discharge tube. It is based on the continuity equation for particle concentration with the collisional right hand side. The model utilises the drift-diffusion approximation of particle flux and the mean-electron-energy approximation for the description of the electron interaction. The radial profile of particle concentration and interaction with the glass wall of the discharge tube is taken into account. The model predicts the electric field and the particle concentration in the positive column. The simulation results were compared with the measured intensity of electric field strength in the oxygen and argon-oxygen mixture. The impact of discharge conditions, like the pressure and gas composition, on the properties of the positive column was investigated. The model confirmed that the strength of longitudinal electric field at medium pressures is about 40 V/cm in oxygen, molecular gas, and it is about 3 V/cm in argon, noble gas.
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Study of probe diagnostics of tokamak edge plasma via computer simulation
Podolník, Aleš ; Pánek, Radomír (advisor) ; Cavalier, Jordan (referee) ; Roučka, Štěpán (referee)
The aim of the thesis is to examine plasma-wall interaction using computer modeling. Tokamak- relevant plasma conditions are simulated using the particle-in-cell model family SPICE working in three or two dimensions. SPICE model was upgraded with a parallel Poisson equation solver and a heat equation solver module. Plasma simulation aimed at synthetic Langmuir probe measurements were performed. First set considered a flush-mounted probe and the effect of variable magnetic field angle was studied with aim to compare existing probe data evaluation techniques and assess their operational space, in which the plasma parameters estimation via fit to the current-voltage characteristic is accurate. Second simulation set studied a protruding probe pin. Effective collecting area of such probe was investigated with intentions of density measurement collection. This area was found to be influenced by a combination of two factors. First, the density dampening inside the magnetic pre-sheath of the probe head, and the second, the extension of the area caused by Larmor rotation. A comparison with experimental results obtained at COMPASS tokamak was was performed, confirming these results. Keywords Langmuir probe, simulation, particle-in-cell, tokamak, Poisson equation, COMPASS 1
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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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Study of electron - molecular ion recombination in low temperature plasma using Cavity Ring-Down Spectroscopy
Kassayová, Miroslava ; Dohnal, Petr (advisor) ; Roučka, Štěpán (referee)
The interactions of electrons with ions and ions with neutrals are among the most important processes in the chemical evolution of molecules, allowing us to gain a deeper understanding of chemical processes in low-temperature environments in space such as interstellar gas clouds and to obtain feedback for quantum-mechanical calculations. Vari- ous plasma parameters such as kinetic and rotational temperature of ions, their concen- tration, etc. can vary by several orders of magnitude and different diagnostic techniques are used to determine them. Diagnostics such as SA-CRDS and Cryo-CRDS were used in this work. The subject of the study were two molecular ions: N2H+ and N+ 2 from the temperature range of 80-350 K, where we examined their recombination and absorption rate coefficients utilizing the absorption line involving the most populated states. 1
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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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Study of Positive Column in Glow Discharge under Medium Pressures Using Computational Experiment
Laca, Marek ; Hrachová, Věra (advisor) ; Novák, Stanislav (referee) ; Roučka, Štěpán (referee)
The positive column of the oxygen and argon-oxygen direct current glow discharge was investigated using a fluid plasma model at pressures around hundreds of pascals and discharge currents from ten to forty miliampers. The model describes the infinitely long positive column in cylindrical discharge tube. It is based on the continuity equation for particle concentration with the collisional right hand side. The model utilises the drift-diffusion approximation of particle flux and the mean-electron-energy approximation for the description of the electron interaction. The radial profile of particle concentration and interaction with the glass wall of the discharge tube is taken into account. The model predicts the electric field and the particle concentration in the positive column. The simulation results were compared with the measured intensity of electric field strength in the oxygen and argon-oxygen mixture. The impact of discharge conditions, like the pressure and gas composition, on the properties of the positive column was investigated. The model confirmed that the strength of longitudinal electric field at medium pressures is about 40 V/cm in oxygen, molecular gas, and it is about 3 V/cm in argon, noble gas.
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