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Using a cryogenic linear 22-pole rf ion trap, rate coefficients for H/D exchange reactions of OH− with D2 (1) and OD− with H2 (2) have been measured at temperatures between 11 K and 300 K with normal hydrogen. Below 60 K, we obtained k1 = 5.5 × 10−10 cm3 s−1 for the exoergic reaction (1). Upon increasing the temperature above 60 K, the data decrease with a power law, k1(T) [similar] T−2.7, reaching ≈1 × 10−10 cm3 s−1 at 200 K. This observation is tentatively explained with a decrease of the lifetime of the intermediate complex as well as with the assumption that scrambling of the three hydrogen atoms is restricted by the topology of the potential energy surface. The rate coefficient for the endoergic reaction (2) increases with temperature from 12 K up to 300 K, following the Arrhenius equation, k2 = 7.5 × 10−11 exp(−92 K/T) cm3 s−1 over two orders of magnitude. The fitted activation energy, EA-Exp = 7.9 meV, is in perfect accordance with the endothermicity of 24.0 meV, if one accounts for the thermal population of the rotational states of both reactants. The low mean activation energy in comparison with the enthalpy change in the reaction is mainly due to the rotational energy of 14.7 meV contributed by ortho-H2 (J = 1). Nonetheless, one should not ignore the reactivity of pure para-H2 because, according to our model, it already reaches 43% of that of ortho-H2 at 100 K. Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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.

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.

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

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

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

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.

In this thesis we explore numerical methods that could be used to solve La- place's equation. We compare the boundary element method (BEM), implemen- ted in Bempp library, and the finite element method (FEM), implemented in FEniCS library, by using them to solve Laplace's equation in the cases of a mul- tipole and a rf ion trap, which we create a model of through the use of Gmsh. In order to gauge effectiveness of a method, we measure the time of evaluation, me- mory usage and the squared deviation from theoretical values (if we know them) summed over the points of evaluation. In the end, we use the known values of electric field to simulate a charged particle moving within the trap, comparing evolution of its position and velocity for BEM and FEM. 1 2

The aim of this work was to create a computer model that would simulate the process of the experiment performed on the apparatus SA CRDS. The program has two resuls. The first is determination of the concentrations of plasma's species in the active discharge. The second result is electron temperature in the afterglow. To create the model we needed to determine ongoing interactions and their rate constants. The method of chemical kinetics is important in this work. 1