National Repository of Grey Literature 18 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Elementary Processes at Low Temperatures - Reactions of H3+ and N2H+ in Afterglow Plasmas
Kálosi, Ábel ; Plašil, Radek (advisor) ; Rubovič, Peter (referee) ; Španěl, Patrik (referee)
Electron-ion recombination and ion-neutral interactions play a piv- otal role in the chemical evolution of molecules in the Interstellar Medium (ISM). Physical conditions under which these processes un- dergo in the ISM include a wide range of temperatures and particle number densities. This work contributes to the experimental study of named low temperature phenomena in the range of 30 K to 300 K focusing on the reactions of hydrogen-containing light molecules. The employed experimental techniques are based on a combination of a Stationary Afterglow (SA) instrument with a Continuous Wave Cavity Ring-down Spectrometer (cw-CRDS). The main contributions of this work can be split into three topics. (1) The proton and deuteron con- taining isotopic system of H3 + ions. The isotopic fractionation process in collisions with hydrogen and deuterium gas was investigated in low temperature discharges, nominal ion temperatures of 80 K to 140 K, to deduce relative ion densities in the experiments. These are necessary for afterglow studies of isotopic effects in electron-ion recombination of the studied ions. (2) Vibrational spectroscopy of N2H+ ions focusing on first overtone (2ν1 band) transitions and ion thermometry, the first step towards studies of electron-ion recombination. (3) The role of para/ortho spin...
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...
Recombination of molecular ions with electrons at low temperatures
Kálosi, Ábel ; Plašil, Radek (advisor) ; Kudrna, Pavel (referee)
The aim of this work is the experimental study of recombination of molecular ions with electrons at low temperatures (< 300 K). The work gives an overview of the diagnostic methods, modelling of chemical kinetics, and experimental ap- paratuses Cryo-FALP II and SA-CRDS used in the undertaken measurements. Two processes were studied in the course of this work: state-selective binary disso- ciative recombination of H+ 3 ions in para-H+ 3 and ortho-H+ 3 states, and H2-assisted ternary recombination of H+ 3 . The main result of the state-selective dissociative recombination study is that the rate of recombination in the para-H+ 3 state is at least three times higher than in the ortho-H+ 3 state at 60 K. The study of H2- assisted recombination gave a better understanding of ternary processes of H+ 3 ions and removed further discrepancies between results of afterglow experiments.
Reactions of cations with hydrogen atoms and molecules at low temperatures
Tran, Thuy Dung ; Plašil, Radek (advisor) ; Kaňka, Adolf (referee)
This thesis is concerned about ion-molecular reactions at low temperatures, which are important the fully understand the chemical evolution in interstellar medium. For realization of experimental part of thesis has been used the apparatus of 22-pole radiofrequency ion trap, which allows study the rate constant of reactions at temperatures 10 - 100 K. Thesis contains measuring results of reaction NH+ + H → N+ + H2, which follows the previous study of reaction N+ + H2 → NH+ + H on the same apparatus, description of the apparatus and the general introduction.
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+ .
Study of reactions of simple ions in low temperature plasma
Kálosi, Ábel ; Plašil, Radek (advisor) ; Picková, Irena (referee)
The subject of this thesis is the study of the probe diagnostic method of low temperature plasma. The basis of Langmuir probe diagnostics in terms of appli- cation on apparatus CryoFALP II for the study of reactions of simply particles, the principle of the FALP technique and the experimental method of undertaken measurements are described. As a part of the thesis a package of evaluation pro- grams were compiled, which are ready to be a part of the measuring system as described in the thesis. Main results concern verification of the proper application of Langmuir probe technique in conditions characteristic for the apparatus, argon plasma was chosen as the medium of the measurements, where the characteristic loss process is ambipolar diffusion of charged particles. The application of the acquired knowledge is shown on recombination in oxygen plasma.
A source of cold hydrogen atoms
Podolník, Aleš ; Plašil, Radek (advisor) ; Kaňka, Adolf (referee)
Vodík v molekulární a atomární formě je nejčastější prvek ve vesmíru a proto jsou chemické reakce, ve kterých vystupuje, důležité pro pochopení nejen formace prvních hvězd a galaxií, ale i pro studium současných dějů v mezihvězdném plynu. Studium například reakce H- + H -> H2 + e- (asociativní odtržení) ujasňuje náhled na proces tvorby molekul vodíku a umožňuje upřesnění kvantově-mechanických modelů. Pro tento a další experimenty je na KFPP přítomen zdroj chladného atomárního vodíku. V práci je popsána aparatura zdroje a její operace, navrhováno a částečně realizováno zlepšení uspořádání vnitřní konstrukce a jsou proměřeny základní charakteristiky zdroje.
Laser absorption spectroscopy
Vyhlídka, Štěpán ; Plašil, Radek (advisor) ; Hrubý, Vojtěch (referee)
Study of recombination of molecular ionts in cold plasma plays a key role in our understanding of chemical kinetics in interstellar space or in upper layers of planetar atmospheres. Various metods are used for its study of which important part is laser absorption spectroscopy. Concentration or temperature of measured ionts can be found from their absorption spectra. In the presented work two spectroscopic techniques are briefly introduced - Cavity ringdown spectroscopy and Laser induced reaction technique. Main me- chanisms for spectral linewidth broadening are described and from absorption spectra of H+ 3 and N+ 2 ionts measured by above-mentioned techniques their kine- tic temperature is discovered. Because it is affected by spectral width of applied laser diodes, a part of this work also deals with description of its measurement by self-heterodyne method or Fabry-Pérot interferometer. The spectral width is found for infrared diode DFB laser. 1
Modelling of glow discharge positive column of oxygen in the middle pressures region
Laca, Marek ; Hrachová, Věra (advisor) ; Plašil, Radek (referee)
The aim of the presented work was to create model of the glos discharge positive column of the oxygen in the middle pressures (in range 100-1000 Pa) with the methods of the computer physics, specifically with the method of the chemical kinetics. I have focused on the existence of two forms of the discharge positive column in the oxygen, low and high gradient form with axial electrical field about 100 V/m and 1 kV/m. I developed continuous model of the low temperature plasma as the steady state solution of the continuity equation with the neglected divergent member. The model involves twelve different kinds of the particles and reactions among them: electrons, ground and excited states of the atomic and molecular oxygen, of course negative and positive ions. I had numerically solved time evolution of the particle concentration at constant pressure, until the system reached equilibrium state. My numerical results were compared with experimental measurements of the electron density, which had been done in the Department of Surface and Plasma Science. To get a consistency between my results and experimental ones for electron density, I had to variate reaction coefficients of the reactions in which charged particles are produced.

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1 Plášil, Roman
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