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Relations between geomagnetic activity and magnetopause locations
Mokrý, Adrián ; Němeček, Zdeněk (advisor) ; Grygorov, Kostiantyn (referee)
The magnetopause separates the area in which all phenomena are influenced by the Earth's magnetic field from the interplanetary space filled with the solar wind. Our ability to predict its location is a measure of our understanding of the processes that take place in this space. The present thesis is focused on the analysis of a database of roughly 30,000 magnetopause passes observed from the subsolar region to the tail of the magnetosphere with the aim of clarifying/verifying the influence of magnetospheric electric currents represented by geomagnetic indices. A linearly decreasing dependence of the magnetopause position on the AE index was found from the subsolar point down the tail. Furthermore, a correlation analysis of the influence of the Dst index was performed and we have found the delay of about 5 hours between the Dst peak and magnetopause displacement in the subsolar region, while the results are contradictory on the night side and more observations would be collected to clarify them.
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Solar Wind Modification in the Earth Foreshock
Urbář, Jaroslav ; Němeček, Zdeněk (advisor) ; Souček, Jan (referee) ; Vandas, Marek (referee)
Title: Solar Wind Modification in the Earth Foreshock Author: Jaroslav Urbář Department: Department of Surface and Plasma Science Supervisor: Prof. Zdeněk Němeček, Department of Surface and Plasma Science Abstract: The thesis presents statistical studies of the solar wind deceleration and deflection in the foreshock and its potential causes. The multi-point observa- tions from the THEMIS mission in the foreshock are compared with a Wind solar wind monitor with motivation to estimate different factors influencing evolution of solar wind speed and its deflection. We have found a systematic deceleration of the solar wind mainly due to its proton component with a decreasing distance to the bow shock that is controlled by the compressibility and the level of magnetic field fluctuations in the ULF wave range associated with the flux of reflected and accelerated particles. We can conclude that the reflected particles excite waves of large amplitudes that decelerate the solar wind protons throughout the foreshock as well as in front of the Moon. Keywords: Earth foreshock; reflected protons; solar wind proton velocity recon- struction; deceleration; ULF waves 1
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Functional simulator of the energetic electron detector from the TARANIS project
Enžl, Jakub ; Přech, Lubomír (advisor) ; Němeček, Zdeněk (referee)
Over a signi cant period of time there have been observations of storm-connected phenomena - so called Transient Luminous Events (TLE). In order to perform new measurements, a microsatellite is being developed under a project called TARANIS. The microsatellite is to carry a device designed to measure high-energy electrons IDEE. Its analyser developed at the Department of Surface and Plasma Science (Faculty of Mathematics and Physics, Charles University) should perform overall control of the detector and processing of registered data. The analyzer will also generate an Alert signal to inform other TARANIS devices whenever TLE-related event such as Relativistic Runaway Electon burst is observed. In order to test the analyzer an 4IDEE detector simulator is being developed. It's task is to generate data and send it to the analyzer. The data should be consistent with the ones expected to be measured during TLE. Another phenomenon to be studied by TARANIS is lightning-induced electron precipitation. Registration of such data will be simulated as well.
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Dynamics of the bow shock and magnetopause
Jelínek, Karel ; Němeček, Zdeněk (advisor) ; Kudela, Karel (referee) ; Vandas, Marek (referee)
viii Title: Dynamics of the bow shock and magnetopause Author: Karel Jelínek Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc. Department of Surface and Plasma Science e-mail address: zdenek.nemecek@mff.cuni.cz Abstract: The interplanetary space is a unique laboratory which allows us to dis- cover (i) a behavior of the plasma under different conditions, (ii) origin of its insta- bilities, and (iii) its interaction with obstacles such as the Earth's magnetosphere. The present thesis analyzes the outer Earth's magnetosphere. The results are based on the in situ sensing by a variety of the spacecraft (e.g., IMP-8, INTERBALL-1, MAGION-4, Geotail, Cluster-II and Themis). The solar wind curently monitored by the WIND and ACE spacecraft near the La- grange point L1 affects by its dynamic pressure the Earth's magnetic field which acts as a counter-pressure and the boundary where these pressures are balanced is the magnetopause. Due to supersonic solar wind speed, the bow shock forms in front of the magnetopause and a region in between, where plasma flows around an obstacle is named the magnetosheath. The thesis contributes to a deaper understanding of the dependence of magnetopause and bow shock shapes and positions, especially, (1) on the orientation of the inter-...
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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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MHD nestability plazmatu pozorované ve výbojích tokamaku COMPASS
Kripner, Lukáš ; Němeček, Zdeněk (advisor) ; Havlíček, Josef (referee)
Compass tokamak (R = 0.56 m, a = (0.23 × 0.38) m, Ip = 200 − 400 kA, BT = 1.2 − 2.1 T and pulse length up to 1 s) is the smallest device with ITER-relevant plasma geometry with scale 1:10 to the ITER size. A tokamak plasma confinement is strongly limited by an occurrence of magnetohydrodynamic (MHD) instabilities occurring during the discharge. In the thesis, theoretical considerations and a typical behaviour of the tokamak plasma MHD instabilites are summarized based on the lite- rature overview. This discussion is complemented with an overview of the Compass diagnostics and different data analysis techniques. Finally, the examples of the Compass plasma behaviour influenced by sawtooth instability and tearing modes are shown and discussed. 1
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Numerical modelling of plasma jet generated by plasma torch
Hirka, Ivan ; Němeček, Zdeněk (referee)
," The thesis and attached papers deal with some aspects of numerical modeling of plasma jet generated by plasma torch and also with numerical modeling of processes in thennal plasma reactor. All tlows are considered to be turbulent in all simulations except for special cases. First part of the thesis is dedicated to short introduction to the topic and to description of turbulent physical models that are used later in all next simulations. Second part is dedicated to description of physical experiment itself and to results that were obtained from numerical simulations. More details are given in following papers that concem 2D and 3D simulations of mixing of steam plasma jet with steam atmosphere, with nitrogen and simulation of gasification of wooden particles by steam plasma jet in thennal plasma reactor. Standard, RNG and realizable k-E models, and standard k-O)model were used for most of the simulations. Steam plasma and nitrogen transport and thennodynamic coefficients used in the computations were detennined under the assumption of existence of LTE. Results for temperature, velocity and density distributionsare discussedin each modelingand presented as images obtained from the FLUENT code, for currently used reactor geometry setup and plasma jet characteristics. Centerline temperature of steam...
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