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The Role of Secondary Electron Emission in Dust Grain Charging
Richterová, Ivana ; Němeček, Zdeněk (advisor) ; Stöckel, Jan (referee) ; Tomková, Eva (referee) ; Frank, Luděk (referee)
Title: The Role of Secondary Electron Emission in Dust Grain Charging Author: Ivana Richterová Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc. Abstract: This work presents a secondary emission model focused on micron and submicron dust grains. The results allowed us to predict surface potentials of grains charged by 50 eV -- 15 keV electron beams. The probability that such electrons penetrate through grains increases with their energy and decreases with a grain size and depends on a grain shape. Model predictions were experimentally verified for glass, gold, and carbon spherical grains and for lunar regolith simulants. In dusty plasmas, charge accumulated on dust grains and plasma parameters govern the ensemble dynamics. The model can be thus utilised in calculations of phenomenon in planet magnetospheres (e.g. spokes in Saturn's rings), in tokamak edge plasmas, etc. Keywords: Secondary emission, dust grains, dust charging
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Hamiltonian chaos and its application to anomalous dynamics in turbulent environment
Kurian, Matúš ; Krlín, Ladislav (advisor) ; Rohlena, Karel (referee) ; Stöckel, Jan (referee)
(Hamiltonian chaos and its application to anomalous dynamics in turbulent environment) RMP-induced ELM control has been tested on several tokamaks. It is believed that increase of electron transport across the magnetic field plays an important role. Edge plasma turbulence also affects dynamics in the edge region of tokamak. We study the simultaneous effect of plasma turbulence and RMP-induced stochastic magnetic field within the single-particle framework. We find out that the plasma turbulence is an important element of dynamics that should be taken into account in further (especially single-particle) studies.
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Sputtering of dust grains and its consequences for space processes.
Vyšinka, Marek ; Šafránková, Jana (advisor) ; Stöckel, Jan (referee) ; Wild, Jan (referee)
Title: Sputtering of dust grains and its consequences for space processes Author: Marek Vyšinka Department: Department of Surface and Plasma Science Supervisor: prof. RNDr. Jana Šafránková, DrSc., Department of Surface and Plasma Science Abstract: A great part of matter in a space has a form of dust grains, tiny pieces of rocks with the dimensions of hundreds nanometers to hundreds micrometers. In this environment dust grains undergo collisions with energetic particles (electron, ions, UV photons) that leads to their charging and modification. The presented thesis studies ion-dust interactions and is focussed on dust grain modification through ion implantation and its destruction via sputtering process. Two compu- ter models are presented - first for computing the ion implantation profile in the grain and second, for the shape of the sputtered grain lying on the surface of a bigger object. The resulting shape of the grain is compared with that obtained experimentally. Important results of the thesis are measured sputtering yields for spherical SiO2 grains at several surface potentials obtained by simultaneous ion and electron bombardments. Keywords: ions, dust grains, sputtering, sputtering yield, implantation profile 1
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Study of plasma in tokamak-type devices with spectroscopic methods
Naydenkova, Diana ; Stöckel, Jan (advisor) ; Plašil, Radek (referee) ; Svoboda, Vojtěch (referee)
In Tokamak department of Institute of Plasma Physics, radiation of high-temperature plasma is investigated using spectroscopic methods in visible, ultraviolet and infrared regions. The radiation gives information regarding tokamak plasma parameters and their changes, which is necessary for future realization of fusion reactor. In the frame of this doctoral thesis the development of spectroscopic diagnostics for observing of plasma radiation and its temporal evolution in COMPASS tokamak was performed. The absolute calibration of developed systems in order to recalculate measured signal to units of radiation was done. The sources of imprecisions of absolute measurements in tokamak conditions are properly discussed in the first part of the dissertation. Plasma radiation in the range 257-1083 nm was measured and interpreted using NIST database and FLYCHK code. Ion density for the most significant impurities was estimated. IDL code for effective ion charge estimation as a ratio of real and hydrogen plasma Bremsstrahlung radiation near 523 nm was developed. Profiles of electron density and temperature measured by Thomson scattering system were used for hydrogen plasma Bremsstrahlung radiation calculations. The example of applying of spectroscopic data for studying of COMPASS plasma heating using neutral beam...
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Laboratory Study of Field Ion Emission from Dust Grain
Jeřáb, Martin ; Šafránková, Jana (advisor) ; Stöckel, Jan (referee) ; Nehasil, Václav (referee)
Title: Laboratory study of field ion emission from dust grains Author: Martin Jeřáb Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc., KFPP Abstract: Dust particles are common objects in space environment. As a dust particles, we call objects with typical sizes of several atoms up to approximately 100 µm. However, a total mass of dust particles is only about 1% of total mass of our galaxy, the presence of dust particles significantly affects environment. The most interesting is dynamics of dust particles and attached dust charging processes. The presented thesis consists of two main parts. The first part deals with the experimental study of field ion emission. Our measurements have been performed using gold and carbon spherical dust grains. It has been found that during the charging of dust particle using ion gun are the primary ions implanted under the surface of the dust particle from where they are release in the form of neutral gas. This releasing of implanted ions affects field ion emission for several hours. The second part of the thesis describes a development of new experimental apparatus determined to the study of photoemission dust charging and con- sequently to the "true" field ion emission study. Keywords: dust, dusty plasmas, charging properties, field...
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Additional plasma heating of tokamak plasma by powerful beam of deuterium atoms on the COMPASS tokamak
Bogár, Klára ; Stöckel, Jan (advisor) ; Berta, Miklós (referee) ; Kappatou, Athina (referee)
Two neutral beam injectors (NBIs) were installed on the COMPASS tokamak as a main upgrade after its move from the UK to Prague. The thesis deals with general experimental specifications of additionally heated plasmas by the NBI under the wide range of conditions on the COMPASS tokamak. The geometrical parameters of the beams are determined from the spectro- scopic measurements. Consequently, the NBI power passing through the narrow duct connecting NBI and tokamak chamber is investigated. The passing fraction of the NBI power is confirmed by the power balance analysis, which provides information about the delivered power into the plasma based on the plasma parameters. Once the delivered power is well known a description of beams interaction with plasma via global parameters such as the plasma temperatures, the plasma density, the energy confinement time and neutron yield is given. It is shown, that the NBIs heat mostly ions, which can reach ∼ 1 keV in the plasma core. Moreover, the impact of the fast ions presence on the commonly observed MHD activities, the sawtooth instability and the edge localized modes (ELMs), is discussed and compared with results from other tokamaks. The sawtooth period is prolonged by the influence of the NBI from 2 ms up to 4.5 ms. The knowledge of the NBI passing power into...
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