Doctoral Thesis
Refine
Year of publication
Document Type
- Doctoral Thesis (160) (remove)
Has Fulltext
- yes (160)
Is part of the Bibliography
- no (160)
Keywords
- Plasma (25)
- Plasmaphysik (25)
- Plasmadiagnostik (14)
- Stellarator (13)
- Komplexes Plasma (7)
- Polyelektrolyt (7)
- Cluster (6)
- Kernfusion (6)
- Wendelstein 7-X (6)
- Atmosphärendruckplasma (5)
- Hochfrequenzplasma (5)
- Ionenfalle (5)
- Massenspektrometrie (5)
- Metallcluster (5)
- Adsorption (4)
- Barrierenentladung (4)
- Diffusion (4)
- Divertor (4)
- Fusion (4)
- Fusionsplasma (4)
- Magnetron (4)
- Modellierung (4)
- Niedertemperaturplasma (4)
- Penningfalle (4)
- Physik (4)
- Plasma-Wand-Wechselwirkung (4)
- Plasmachemie (4)
- Plasmadynamik (4)
- Polyanion (4)
- Simulation (4)
- Spektroskopie (4)
- Turbulenz (4)
- Absorptionsspektroskopie (3)
- Aluminium (3)
- Clusterion (3)
- Dissertation (3)
- Ellipsometrie (3)
- Emissionsspektroskopie (3)
- FT-IR-Spektroskopie (3)
- Festkörperphysik (3)
- Flugzeitspektrometrie (3)
- Gasentladung (3)
- Glimmentladung (3)
- Kernphysik (3)
- Laser (3)
- Laserinduzierte Fluoreszenz (3)
- Laserspektroskopie (3)
- Leuchtstofflampe (3)
- Penning trap (3)
- Plasma Physics (3)
- Plasmamedizin (3)
- Plasmarandschicht (3)
- Polymere (3)
- Quantenoptik (3)
- Selbstorganisation (3)
- Tokamak (3)
- dusty plasma (3)
- mass separation (3)
- polyanion (3)
- stellarator (3)
- Abstimmbarer Laser (2)
- Alfvén-Welle (2)
- Anion (2)
- Atmosphärendruck (2)
- Beschichten (2)
- Beschichtung (2)
- Brennfleck (2)
- Cardiolipin (2)
- Clusterphysik (2)
- Computerphysik (2)
- Driftwelle (2)
- Dynamik (2)
- Emission (2)
- Festkörper (2)
- Floquet (2)
- Flugzeitmassenspektrometrie (2)
- Fragmentation (2)
- Fullerene (2)
- Fusionsreaktor (2)
- Graphen (2)
- Heißes Plasma (2)
- Helium (2)
- Impurities (2)
- Infrarotspektroskopie (2)
- Instabilität (2)
- Kaltes Plasma (2)
- Kathode (2)
- Kernstruktur (2)
- Lipide (2)
- Low Temperature Plasma (2)
- MR-ToF MS (2)
- MR-ToF device (2)
- Magnetfeld (2)
- Magnetic Confinement (2)
- Magnetische Rekonnexion (2)
- Magnetohydrodynamik (2)
- Monoschicht (2)
- Monte-Carlo-Simulation (2)
- Multi-reflection time-of-flight mass spectrometry (2)
- Nanopartikel (2)
- Neutronenbeugung (2)
- Nuclear Physics (2)
- Optisches Messgerät (2)
- Optomechanik (2)
- Oxidation (2)
- Plasma physics (2)
- ROS (2)
- Rasterkraftmikroskopie (2)
- Reflektometrie (2)
- Rekonstruktion (2)
- Röntgenreflektometrie (2)
- Sauerstoff (2)
- Sekundärelektronen (2)
- Stereoskopie (2)
- Stickstoff (2)
- Theoretische Physik (2)
- W7-AS (2)
- Weiche Materie (2)
- Xenon (2)
- atmospheric pressure (2)
- atomic clusters (2)
- barrier discharge (2)
- electrode (2)
- erosion (2)
- laser spectroscopy (2)
- laser-induced fluorescence (2)
- multi-reflection time-of-flight mass spectrometry (2)
- plasma (2)
- plasma diagnostics (2)
- plasma medicine (2)
- polyelectrolytes (2)
- surface charges (2)
- topologische Isolatoren (2)
- 7755384-6 (1)
- AFM (1)
- AFM-Kraft-Abstandskurven (1)
- AOM (1)
- ASDEX (1)
- Ab-initio-Rechnung (1)
- Abregung (1)
- Absorption Spectroscopy (1)
- Aktivität <Konzentration> (1)
- Alfven (1)
- Alfvén Waves (1)
- Algorithm (1)
- Algorithmen (1)
- Algorithmus (1)
- Aluminium Cluster (1)
- Aluminium cluster (1)
- Aminogruppe (1)
- Aminogruppen (1)
- Anode (1)
- Antikoagulans (1)
- Antrieb (1)
- Argon metastables (1)
- Artificial nerual networks (1)
- Astrophysik (1)
- Atmospheric pressure plasma (1)
- Atmosphärendruckentladung (1)
- Atomabsorptionsspektroskopie (1)
- Atomemissionsspektroskopie (1)
- Atomgewicht (1)
- Atomspektrum (1)
- Auftrittsgröße (1)
- BAM (1)
- Barium (1)
- Bayes'sche Datenanalyse (1)
- Bayes-Verfahren (1)
- Bayesian Data Analysis (1)
- Beam (1)
- Biasing (1)
- Binäres Gemisch (1)
- Biomembran (1)
- Blei (1)
- Bogenentladung (1)
- Boltzmann equation (1)
- Bootstrap current (1)
- Bose-Einstein Kondensation (1)
- Bose-Einstein condensation (1)
- Bose-Einstein-Kondensation (1)
- Brennstoffzelle (1)
- Brewster angle microscopy (1)
- Bündelbildung (1)
- Bürstenpolymere (1)
- CD Spektroskopie (1)
- Cadmium (1)
- Cavity Enhanced Absorption Spectroscopy (1)
- Cavity Ring-Down Spectroscopy (1)
- Cavity-Enhanced-Absorptionsspektroskopie (1)
- Cavity-Ring-Down-Spektroskopie (1)
- Cluster beam (1)
- Cluster charge (1)
- Cluster flow (1)
- Cluster formation (1)
- Coatings (1)
- Coil Optimization (1)
- Collisions (1)
- Colloidal Probe Technique (1)
- Complex plasma (1)
- Computersimulation (1)
- Connection length (1)
- Correlation Analysis (1)
- DBD (1)
- DNA (1)
- De-Excitation (1)
- Dense Plasmas (1)
- Density (1)
- Destabilisierung (1)
- Detachment (1)
- Diagnostik (1)
- Diamant (1)
- Dichte Plasmen (1)
- Dichtematrix (1)
- Dielectric Barrier Discharge (1)
- Dielektrische Entladung (1)
- Digital Ion Trap (1)
- Digitale Ionenfalle (1)
- Diodenlaser mit externem Resonator (1)
- Direct Force Measurement (1)
- Dispersionsrelation (1)
- Dissipation (1)
- Domänen-Wachstum (1)
- Doppler cooling (1)
- Drift-Diffusions-Modell (1)
- Driftwellen (1)
- Duennschichten (1)
- Durchbruch (1)
- Dusty Plasma (1)
- Dusty plasma (1)
- Dämpfung (1)
- Dünne Filme (1)
- Dünne Schicht (1)
- Dünne Schichten (1)
- Dünnes Plasma (1)
- ECDL (1)
- ECRH (1)
- EEDF (1)
- EEVF (1)
- EPR (1)
- Edelgas (1)
- Effluent (1)
- Einmodenlaser (1)
- Eisen-Polypyrrol (1)
- Elastizität (1)
- Electric Propulsion (1)
- Elektrische Polarisation (1)
- Elektrischer Strom / Messung (1)
- Elektrode (1)
- Elektron (1)
- Elektronegative Plasmen / negative Ionen (1)
- Elektronenbad (1)
- Elektronendichte (1)
- Elektronenemission (1)
- Elektronenkinetik (1)
- Elektronenparamagnetische Resonanz (1)
- Elektronenstreuung (1)
- Emission Spectroscopy (1)
- Emissionsentwicklung (1)
- Emitter (1)
- Empfindlichkeit (1)
- Energiereiches Teilchen (1)
- Entropie (1)
- Erosion (1)
- Escape factor (1)
- Ethylenglykol (1)
- ExB-Drift (1)
- ExB-drift (1)
- Expansion (1)
- Exziton (1)
- FCT-Verfahren (1)
- FT-ICR-Spektroskopie (1)
- FTIR (1)
- FTIR spectroscopy (1)
- FTIR-Spektrometrie (1)
- Far (1)
- Fast Particles (1)
- Feldlinienverschmelzung (1)
- Fernerkundung (1)
- Finite Systeme (1)
- Fluid-Modellierung (1)
- Fluktuationen (1)
- Fluoreszenz (1)
- Fluorkohlenstoffhaltigen Plasmen (1)
- Fluorocarbon Plasmas (1)
- Flüssigkeiten (1)
- Fusion , Plasma , Plasmaphysik (1)
- Fusion plasma (1)
- Fusion plasmas (1)
- GID (1)
- GaAs sputtering (1)
- Gallium (1)
- Gallium-Oxide (1)
- Galliumoxid (1)
- Gas Cell (1)
- Gasaufzehrung (1)
- Gaselektronik (1)
- Gasphasenabscheidung (1)
- Gastemperatur (1)
- Gaszelle (1)
- Glimmentladungsspektroskopie (1)
- Graphene (1)
- Green-Funktion (1)
- Group (1)
- Guided Streamer (1)
- Gyro-kinetic Theory (1)
- Gyrokinetik (1)
- Hamburg / Deutsches Elektronen-Synchrotron (1)
- Heat flux (1)
- Heat load (1)
- Heat-flux (1)
- Heparin (1)
- Heterostrukturen (1)
- HiPIMS (1)
- High-Precision Mass Spectrometry (1)
- High-Temperature (1)
- Hoch Performanz (1)
- Hochfrequenzentladung (1)
- Hochfrequenzplasma / Plasmadynamik / Interferometrie / Photodetachment / Sauerstoff Plasma (1)
- Hot plasma (1)
- Hy (1)
- Hybrid-Verfahren (1)
- Hybridisierungstheorie (1)
- Hydrogen peroxide (1)
- Hydroperoxyl (1)
- IR-TDLAS (1)
- ISOLTRAP (1)
- Impulsübertragung (1)
- Informationstheorie (1)
- Infrarot (1)
- Infrarotabsorption (1)
- Innere Energie (1)
- Intermittenz (1)
- Interpenetrierendes polymeres Netzwerk (1)
- Ion Thruster (1)
- Ion Traps (1)
- Ion thrusters (1)
- Ion traps (1)
- Ionenbeschuss (1)
- Ionendichte (1)
- Ionenfallen (1)
- Ionenimplantation (1)
- Ionenstrahlfalle (1)
- Ionentriebwerk (1)
- Ionthruster (1)
- Isothermal Titration Calorimetry (1)
- Jet (1)
- Kalorimetrie (1)
- Katalysator (1)
- Kernmassenmessungen (1)
- Kinetic Transport Theory (1)
- Kinetic simulation (1)
- Kinetische Gastheorie (1)
- Kinetische Theorie (1)
- Kinetische Transporttheorie (1)
- Kobalt-Polypyrrol (1)
- Kondo effect (1)
- Konformation (1)
- Kontaktmodell (1)
- Kontraktion (1)
- Kontrolle (1)
- Korrespondenzprinzip (1)
- Kraftmikroskopie (1)
- Kreuzkorrelationsspektroskopie (1)
- Kupfer-Release (1)
- Kupfer-T (1)
- Kupferoxid <Kupfer(I)oxid> (1)
- Kupferoxid <Kupfer(II)-oxid> (1)
- Künstliche Intelligenz (1)
- LE/LC phase transition (1)
- Laboratory experiment (1)
- Laborexperiment (1)
- Ladungsdichtewelle (1)
- Ladungstransfer (1)
- Lamellare Phase (1)
- Langmuir Monolayers (1)
- Langmuir-Sonde (1)
- Laser spectroscopy (1)
- Laser-Cluster-Wechselwirkung (1)
- Laser-cluster interaction (1)
- Laser-induced fluoresence (LIF) (1)
- Laserdiod (1)
- Laserdurchstimmung (1)
- Laserheizung (1)
- Laterale Selbststrukturierung, Polyelektrolyt, Multischicht (1)
- Least-squares method (1)
- Leuchtwerbung (1)
- Lichtstreuung (1)
- Linienprofilfunktion (1)
- Lipid monolayers (1)
- Lipid-Monoschichten (1)
- Lipid-Oxidation (1)
- Lokale-Feld-Näherung (1)
- Lokale-Mittlere-Energie-Näherung (1)
- Low temperature plasma (1)
- Luftleuchten (1)
- MG-63 Zellen (1)
- MG-63 cells (1)
- MIR-Spektroskopie (1)
- Machine learning (1)
- Magnetfelddiagnostik (1)
- Magnetic edge properties (1)
- Magnetic field diagnostics (1)
- Magnetic fields (1)
- Magnetic reconnection (1)
- Magnetische Rekonnektion (1)
- Magnetischer Einschluss (1)
- Magnetischer Sensor (1)
- Magnetismus (1)
- Magnetized (1)
- Magnetron sputtering (1)
- Mass Specrtometry (1)
- Mass spectrometry (1)
- Massenspektroskopie (1)
- Master-Gleichung (1)
- Mathematische Modellierung (1)
- Matrix (1)
- Mechanik (1)
- Mehrfach negativ geladene (1)
- Mehrschichtsystem (1)
- Metall-Isolator-Phasenumwandlung (1)
- Metall-Polymer Verbindungen (1)
- Metalle (1)
- Microwave interferometry / Electron density / Laserphotodetachment (1)
- Mid-IR absorption spectroscopy (1)
- Mie-Theorie (1)
- Mikrofluidik , Mechanik , Zelle , Holographie , Hologramm , Deformation , Biomedizin , Bluttransfusion , Cytometrie , Viskoelastizität (1)
- Mikroplasma (1)
- Mikrowelleninterferometer (1)
- Mikrowellenplasma (1)
- Mineral (1)
- Model Membranes (1)
- Modell (1)
- Modellbildung (1)
- Moden (1)
- Modendynamik (1)
- Modenübergang (1)
- Molecular Kinetics (1)
- Molekulardynamik (1)
- Molekülkinetik (1)
- Multireflexionsflugzeitmassenspektrometrie (1)
- Multischicht (1)
- Multiterm (1)
- NBI (1)
- NIR-Spektroskopie (1)
- Nachstellungsszenarien (1)
- Nachtluftleuchten (1)
- Nanocluster (1)
- Nanokompositschichten (1)
- Nanoparticles (1)
- Nanoplasmamodell (1)
- Negative ion (1)
- Neoclassical transport (1)
- Neutral Beam Injection (1)
- Neutralisation (1)
- Neutralization (1)
- Neutrino (1)
- Neutronenreflektometrie (1)
- Neutronenschalenabschluss (1)
- Neutronenstern (1)
- Nichtgleichgewicht (1)
- Nichtisothermisches Plasma (1)
- Nichtlineare Dynamik (1)
- Niederdruckentladung (1)
- Niederdruckplasma (1)
- Niedertemperatur-Plasma (1)
- Nuclear Structure (1)
- Nuclear fusion (1)
- Nukleosynthese (1)
- Oberfläche (1)
- Oberflächenkräfte (1)
- Oberflächenladung (1)
- Oberflächenladungen (1)
- Oberflächenmodifizierung (1)
- Oberflächenstöße (1)
- Operante Konditionierung (1)
- P3M (1)
- PDADMA (1)
- PECVD (1)
- PECVD-Verfahren (1)
- PEI,PDADMA,PSS,surface forces,atomic force microscopy, colloidal probe (1)
- PIC (1)
- PSS (1)
- PVD (1)
- Parallelstrom (1)
- Particle flux (1)
- Particle in Cell Simulation (1)
- Particle-in-Cell (1)
- Particle-in-cell (1)
- Paul-Falle (1)
- Penning Trap (1)
- Penning-Falle (1)
- Permeationsbarriere (1)
- Phase transitions (1)
- Phasenübergänge (1)
- Phaseresolved Diagnostic (1)
- Phospholipide (1)
- Phospholipids (1)
- Photoströme (1)
- Plasma , Plasmaphysik , Laser , Fluoreszenz , Interferometer , Wakefield , CERN , Kielfeld-Beschleuniger , Teilchenbeschleuniger , Laserinduzierte Fluoreszenz (1)
- Plasma , Plasmaphysik , Tokamak , Stellarator , Magnetohydrodynamik , Kinetische Theorie , Simulation , Alfvén-Welle , Energiereiches Teilchen (1)
- Plasma / Turbulenz (1)
- Plasma Chemistry (1)
- Plasma Instability (1)
- Plasma Modeling (1)
- Plasma Surface Interaction (1)
- Plasma diagnostics (1)
- Plasma diagnostics techniques and instrumentation (1)
- Plasma dynamics (1)
- Plasma medicine (1)
- Plasma surface interaction (1)
- Plasma-Flüssigkeits-Wechselwirkung (1)
- Plasma-Immersions-Implantation (1)
- Plasma-Oberflächen-Wechselwirkung (1)
- Plasma-wall interaction (1)
- Plasmainstabilität (1)
- Plasmajet (1)
- Plasmanitrieren (1)
- Plasmaschwingung (1)
- Plasmasimulation (1)
- Plasmasonde (1)
- Plasmaspektroskopie (1)
- Plasmastrom (1)
- Plasmatheorie (1)
- Plasmatransport (1)
- Plasmawelle (1)
- Plasmonik (1)
- Pockels-Effekt (1)
- Pockels-effect (1)
- Polarisation (1)
- Polaron (1)
- Polyanionen (1)
- Polyanions (1)
- Polydimethylsiloxan (1)
- Polyelektrolytbürste (1)
- Polyethylenglykole (1)
- Polyethylenimin (1)
- Polymer (1)
- Polystyrolsulfonate (1)
- Potenzialhyperfläche (1)
- Power decay (1)
- Proteine (1)
- Präzisionsmassenmessung (1)
- QCLAS (1)
- Quantendot (1)
- Quantenkaskadenlaser (1)
- Quantenmechanik (1)
- Quantenphasenübergang (1)
- Quantenpunkt (1)
- Quantentheorie (1)
- Quantum Cascade Laser (1)
- Quecksilber (1)
- RF Plasma (1)
- RF-Entladung (1)
- RNS (1)
- ROS, cell and mitochondria mechanics (1)
- Radial axis shift (1)
- Radialverteilung (1)
- Radikal (1)
- Radioactive Ion Beams (1)
- Radioaktivität (1)
- Radiofrequenz (1)
- Radionuklide (1)
- Rasterkraftmikroskop (1)
- Reaktionsdynamik (1)
- Reaktive Sauerstoffspezies (1)
- Reaktives Sputtern (1)
- Reflektometer (1)
- Reinforcement learning (1)
- Relativistische Quantenmechanik (1)
- Relaxationskinetik (1)
- Renormalization (1)
- Robust (1)
- Rohstoffgewinnung (1)
- Rotational transform (1)
- Röntgen-Photoelektronens (1)
- Röntgenbeugung (1)
- Röntgendiffraktion (1)
- Röntgenreflektivität (1)
- S/XB coefficient (1)
- Schadstoffabbau (1)
- Schalenabschluss (1)
- Schaumflotation (1)
- Schlieren (1)
- Schnelles Teilchen (1)
- Schnittstelle (1)
- Schutzschicht (1)
- Schwerelosigkeit (1)
- Scrape-off layer width (1)
- Scraper (1)
- Secondary Electrons (1)
- Seebeck effect (1)
- Self-absorption (1)
- Self-patterning, polyelectrolyte, multilayers (1)
- Sheath transmission coefficient (1)
- Silber (1)
- Simulationsexperiment (1)
- Spectroscopy (1)
- Spin Trap (1)
- Spin Trapping (1)
- Spintronik (1)
- Spot (1)
- Sputterdeposition (1)
- Sputtering (1)
- Sputtern (1)
- Stark gekoppelte Systeme (1)
- Startverhalten (1)
- Staub (1)
- Staubdichtewelle (1)
- Staubige Plasmen (1)
- Staubiges Plasma (1)
- Stickstoff-Sauerstoff-Gemisch (1)
- Stickstoffgruppe (1)
- Stochstic Programming (1)
- Stoffwandlung (1)
- Stoß (1)
- Streutheorie (1)
- Strikeline (1)
- Strukturbildung (1)
- Sulfide (1)
- Supervised learning (1)
- Surface Collisions (1)
- Symmetrie (1)
- TDLAS (1)
- THz (1)
- TMCL (1)
- TOF (1)
- Teflon (1)
- Temperatur (1)
- Theoretical Physics (1)
- Thermografie (1)
- Thin films (1)
- Thrombozytopenie (1)
- Time-of-flight mass spectrometry (1)
- Titan Tholins (1)
- Titan-Tholine (1)
- Titanaluminide (1)
- Titanatom (1)
- Titandioxid (1)
- Titanlegierung (1)
- Titannitrid (1)
- Tomographie (1)
- Topologischer Isolator (1)
- Tracer particles (1)
- Tracerpartikel (1)
- Transport (1)
- Transporttheorie (1)
- Turbulente Strömung (1)
- UV-VIS-Spektroskopie (1)
- VUV-Strahlung (1)
- Velocity distribution (1)
- Verdampfung (1)
- Verlustprozess (1)
- Verschränkung (1)
- Verunreinigungstransport (1)
- Vielteilchensystem (1)
- Vielteilchentheorie (1)
- Vorionisation (1)
- W7-X (1)
- Wand-Abregung-Wahrscheinlichkeit (1)
- Waves (1)
- Wellen (1)
- Wellenmagnetfeld (1)
- Wellenwechselwirkung (1)
- Wendelstein (1)
- Wendelstein 7-x (1)
- Whistlerwelle (1)
- Widerstand <Elektrotechnik> (1)
- Wolfram (1)
- Wärmeschutz (1)
- X-ray diffraction (1)
- X-ray reflectivity (1)
- Zeeman and Stark effects (1)
- Zeeman- und Stark-Effekte (1)
- Zeitaufgelöste Diagnostik (1)
- Zelle (1)
- Zellmechanik (1)
- Zitterbewegung (1)
- absorption spectroscopy (1)
- adsorption (1)
- airglow (1)
- akusto-optischer Effekt (1)
- aminogroups (1)
- anomal transport (1)
- anomaler Transport (1)
- appearance size (1)
- atmospheric pressure discharge (1)
- atomic force microscopy (1)
- atomic spectra (1)
- barrier corona (BC) (1)
- binary mixture (1)
- bundle formation (1)
- cathode (1)
- cavity QED (1)
- cavity ring-down (1)
- cell mechanics (1)
- charge measurement (1)
- charge-density-wave (1)
- closed neutron shell (1)
- cluster (1)
- cobalt-polypyrrole (1)
- cold atmospheric pressure plasmajet (1)
- complex plasma (1)
- conductive (1)
- consistent (1)
- contact model (1)
- continuously tuning (1)
- control (1)
- copper release (1)
- cross-correlation spectroscopy (1)
- cylindrical wave (1)
- deposition (1)
- dice lattice (1)
- dielectric barrier discharge (1)
- dielectric barrier discharge (DBD) (1)
- dielektrisch behinderte Entladung (1)
- diffusion within multilayers (1)
- divertor (1)
- domain growth (1)
- drift waves (1)
- dust (1)
- dust charge (1)
- dust-density waves (1)
- edelmetallfreie Katalysatoren (1)
- electron bath (1)
- electron emission (1)
- electron kinetics (1)
- ellipsometry (1)
- energetic ion (1)
- entanglement (1)
- evaporation (1)
- external cavity diode laser (1)
- fast optical and electrical diagnostics (1)
- fdtd (1)
- finite difference in time domain (1)
- finite systems (1)
- fluctuations (1)
- fluid modelling (1)
- fluorescent lamp (1)
- fluorescent lamps (1)
- flüssig (1)
- forcing (1)
- froth flotation (1)
- ftir spectroscopy (1)
- full-wave (1)
- gas consumption (1)
- gepulster Betrieb (1)
- glow-to-arc transition (1)
- guided streamer (1)
- gyrokinetic (1)
- gyrokinetics (1)
- gyrokinetisch (1)
- helicon, fluorescence, accelerator (1)
- high performance (1)
- high spatial resolution (1)
- hot spot (1)
- hybrid method (1)
- ignition behavior (1)
- in situ (1)
- in-situ Diagnostik (1)
- infrared spectroscopy (1)
- inhomogeneous plasma (1)
- inhomogenes plasma (1)
- instabilities (1)
- intermittency (1)
- internal energy (1)
- ion accelerator (1)
- ion drag (1)
- ion traps (1)
- ion-beam trap (1)
- ionenwind (1)
- ipf-fd3d (1)
- iron-polypyrrole (1)
- isotherms (1)
- jet (1)
- kinetic modelling (1)
- konsistent (1)
- lamellar phase (1)
- laser atomic absorption (1)
- laser heating (1)
- layer-by-layer (1)
- lebensdauerabhängige Auftrittsgrößen (1)
- leitfähig (1)
- lifetime-depentend appearance size (1)
- line profile function (1)
- lipid domain growth (1)
- lipid oxidation (1)
- liquid (1)
- local-field-approximation (1)
- local-mean-energy-approximation (1)
- loss process (1)
- low-temperature plasma (1)
- magic number (1)
- magische Zahlen (1)
- magnetic field (1)
- magnetic fields (1)
- mapping (1)
- mercury-free (1)
- metal polymer structures (1)
- metal-insulator transition (1)
- microfluidics, cell mechanics, cells, holography, hologram, deformation, biomedicine, transfusion medicine, cytometry, viscoelasticity (1)
- microinstabilities (1)
- microinstabilitäten (1)
- microplasma (1)
- mimic scenario (1)
- mixed-valence correlations (1)
- mode dynamics (1)
- modeling (1)
- monolayer (1)
- multilayer composition (1)
- multiterm (1)
- nanoparticles (1)
- nanowire (1)
- negative Ionen (1)
- negative ions (1)
- neoclassic (1)
- neoklassisch (1)
- neuron-rich calcium isotopes (1)
- neutron reflectometry (1)
- nicht-Hermitizität (1)
- nichtlinear (1)
- nightglow (1)
- nitrogen metastables (1)
- nitrogen-oxygen gas mixtures (1)
- non noble metal catalysts (1)
- non-Hermitian (1)
- non-equilibrium (1)
- nonlinear dynamics (1)
- nuclear mass measurements (1)
- numerical simulation (1)
- numerische simulation (1)
- offene Quantensysteme (1)
- open quantum systems (1)
- optical diagnostics (1)
- optomechanics (1)
- oxidation processes (1)
- oxygen (1)
- parallel current (1)
- partial discharge (PD) (1)
- permeation barrier (1)
- phase separation (1)
- photocurrent (1)
- photodetachment spectroscopy (1)
- phototdissociation (1)
- plasma chemistry (1)
- plasma current (1)
- plasma dynamics (1)
- plasma physics (1)
- plasma theory (1)
- plasma-liquid-interaction (1)
- platelet biomechanics (1)
- platelet cytoskeleton (1)
- pollution control (1)
- polyelectrolyte (1)
- polyelectrolyte multilayer (1)
- polymer (1)
- positive Säule (1)
- positive column (1)
- pre-ionization (1)
- precision mass measurements (1)
- pulsed operation (1)
- quantum cascade laser (1)
- quantum phase transition (1)
- quecksilberfrei (1)
- r-Prozess (1)
- radial distribution (1)
- radio frequency discharge (1)
- radioactive nuclei (1)
- radionuclides (1)
- reconstruction (1)
- remote (1)
- resonant state (1)
- resonanter Zustand (1)
- retrieval (1)
- schnelle optische und elektrische Diagnostik (1)
- scrape-off layer (1)
- secondary electron emission (1)
- secondary electrons (1)
- self-assembly (1)
- semi-empirical (1)
- sensitivity (1)
- short-lived nuclides (1)
- similarity scaling (1)
- single mode (1)
- soft matter (1)
- solid-state physics (1)
- space charge (1)
- species conversion (1)
- spin-polarized current (1)
- spot (1)
- stereoscopy (1)
- strain fields (1)
- superoxide anion (1)
- surface forces (1)
- surface physics (1)
- symmetry (1)
- teflon-like (1)
- temperatur (1)
- temperature (1)
- thermionische Emission (1)
- thermography (1)
- thin films (1)
- time-correlated single photon counting (TC-SPC) (1)
- topological insulator (1)
- topological insulators (1)
- transient spark (1)
- transport (1)
- tunable diode laser absorption spectroscopy (1)
- tungsten (1)
- turbulence (1)
- two-photon absorption laser-induced fluorescence (1)
- ultra-thin (1)
- ultradünn (1)
- valleytronics (1)
- voltage stabilization (1)
- wave interaction (1)
- wave magnetic field (1)
- wetted area (1)
- whistler wave (1)
- xenon (1)
- zylindrische Welle (1)
- Überwachtes Lernen (1)
Institute
- Institut für Physik (160) (remove)
Manipulating and utilizing plasmas becomes a more and more important task in various research fields of physics and in industrial developments. Especially in nowadays spacerelevant applications there are different ideas to modify plasmas concerning particular tasks.
One major point of interest is the ability to influence plasmas using magnetic fields. To study the underlying physical effects that were achieved by these magnetic fields for both scenarios Particle-in-Cell simulations were done. Two examples are discussed in this thesis.
The first example originates from an experiment performed by the European Space Agency ESA in collaboration with the German Space Agency DLR. To verify the possibility of heat-flux reduction by magnetic fields onto the thermal protection system of a space vehicle a simplified experiment on earth was developed. Most of the heat that is created during re-entry comes from compression of the air ahead of the hypersonic vehicle, as a result of the basic thermodynamic relation between temperature and pressure. The shock front, which builds up in front of the vehicle deflects most of the heat and prohibits the surface of the space vehicle from direct contact with the maximum flux. State of the art spacecrafts use highly developed materials like ceramics to handle the enormous heat. An attractive approach to reduce costs is to use magnetic fields for heat-flux reduction. This would allow the use of cheaper materials and thus reduce costs for the whole space mission. A partially-ionized Argon beam was used to create a certain heat-flux onto a target. The main finding of the experimental campaign was a large mitigation of heat-flux by applying a dipole-like magnetic field. The Particle-in-Cell method was able to reproduce experimental observations like the heat-flux reduction. An additionally implemented optical diagnostics module allowed to confirm the results of the spectroscopy done during the experiment. The underlying effect that is responsible for the heat-flux reduction was identified as a coupling between the modified plasma and the dominating neutral flux component. The plasma, that is guided towards the target, act as a shield in front of the target surface for arriving neutrals. These neutrals are slowed down by charge-exchange collisions. Furthermore the magnetic field induces an increased turbulent transport that is also needed to reach a reduction in heat-ux. The turbulent transport was also obtained by three-dimensional Direct Simulation Monte Carlo simulations. Unfortunately, such source driven turbulence can not be expected in space, so that a heat flux reduction in real space applications is questionable. Nevertheless, other effects like the induced turbulence by the rotating vehicle can compensate the missing source driven effect.
The second scenario in which a magnetic field is used to modify the heat flux of a plasma is the operation of the pulsed cathodic arc thruster. The same Particle-in-Cell code was used to simulate a typical pulse of this newly developed thruster of Neumann Space Pty Ltd. The typical behavior of the thruster could be reproduced numerically. The thrust is mainly produced by fast electrons. These electrons are accelerated by electric fields as a result of a plasma-beam instability. This plasma-beam instability was verified by a phase space diagnostics for the electrons. To demonstrate the influence of the magnetic field a simulation of the cathodic arc thruster without magnetic field and one with magnetic field were compared. It was shown that the use of a magnetic field leads to a ten times larger thrust by directing the heat ux. The resulting narrow plume is an additional Advantage of the particle guiding magnetic field. This narrowness of the plume reduces the danger of interaction with other components of the space vehicle.
Both scenarios demonstrate the different capabilities for electromagnetic fields to manipulate plasmas and especially the corresponding heat-flux with respect to certain tasks. The possibilities range from reducing the heat-flux onto a target to maximizing the thrust by directing the heat-ux. This thesis demonstrates that simulations are a great tool to support experiments and to deliver an improved physics understanding. They help to identify the basic physics principles in the different systems, because they can deliver information not accessible to experiments.
In particular, a better understanding of the influence of electromagnetic fields on the heat-flux distribution in space-relevant applications was obtained. This can be the basis for further simulation-guided optimization, e.g. for the design of more effective cathodic arc thrusters. Here, the goal is to minimize costs for prototypes by replacing the hardware by virtual prototypes in the simulations. This allows to test basic design ideas in advance and get more highly-optimized designs at a fraction of time and costs.
The present experimental work investigates plasma turbulence in the edge region of magnetized high-temperature plasmas. A main topic is the turbulent dynamics parallel to the magnetic field, where hitherto only a small data basis existed, especially for very long scale lengths in the order of ten of meters. A second point of special interest is the coupling of the dynamics parallel and perpendicular to the magnetic field. This anisotropic turbulent dynamics is investigated by two different approaches. Firstly, spatially and temporally high-resolution measurements of fluctuating plasma parameters are investigated by means of two-point correlation analysis. Secondly, the propagation of signals externally imposed into the turbulent plasma background is studied. For both approaches, Langmuir probe arrays were utilized for diagnostic purposes. The main findings can be summarized as follows: Greatly elongated fluctuation structures exist in plasma edge turbulence. The structures are aligned along the confining magnetic field (k|| = 0). The correlation degree of fluctuations for a short connection length of 0.75m is greater than 80%. For much longer connection lengths of 23m and 66m, the correlation degree is reduced to approximately 40%. A conceptual interpretation of these observations is the coexistence of two different fluctuation components. One component has a correlation length parallel to the magnetic field below 20m and the other component a correlation length greater than 70m. Sine signals in the frequency range 1-100 kHz were injected into the turbulent plasma background. The propagation parallel and perpendicular to the magnetic field of the signals was studied. In poloidal direction, an asymmetry is observed, that can be explained by a copropagation of the signal with the background E × B-rotation of the plasma. The signal propagation parallel to the magnetic field shows no such asymmetry. As an advanced approach, spatio-temporal wave patters were injected into the edge plasma. The waves launched that way can be seen as test waves' in a turbulent background. The coupling strength of the imposed wave patterns to the background turbulence relies on the match of the imposed waves to the dynamics of turbulent structures. If the propagation direction of the imposed waves is parallel to the propagation direction of the background plasma, improved coupling is observed. This finding underlines the importance of the background plasma rotation for future attempts of controlling the plasma edge turbulence. Further optimization of frequency and wave vector of the imposed waves is probably a promising approach for achieving a significant and systematic influence of turbulence. Taking into account the present experimental state-of-the-art, for a deeper insight into the mechanism of the plasma edge turbulence of magnetized high-temperature plasmas a joint effort of numerical modeling and experimental results is a valuable approach. Such a cooperation should cover the explanation of the correlation observations as well as the experiments on signal injection into background turbulence. A quantitative comparison between the results presented in this work and a dedicated numerical drift wave simulation would be a significant step forward to a better understanding of plasma edge turbulence.
In the present work high density helicon plasma discharges are created and characterized as a promising concept towards the realization of plasma wakefield accelerators to build up electric fields in the order of GV/m to accelerate electrons to energies in the TeV range with proton driving bunches. For such a concept plasma sources are needed that are able to maintain discharges with plasma densities of n_e = 7E20 m^-3 over long distances with a low variation in plasma density. Measurements at the PROMETHEUS-A device are performed for variable parameters, like magnetic induction, RF heating power and filling gas pressure. A CO2 laser interferometer, a laser induced fluorescence (LIF) diagnostic and a reaction rate model are combined to give a full picture. It is shown that in most cases the plasma density is centrally peaked with a high density region +- 5 mm from the center. The peak plasma density increases with increasing filling gas pressure, RF heating power and magnetic induction, limited by the number of neutral particles in low pressure discharges, by the transferred heating power and the increasing recombination and electron quenching rates of argon ions in high filling pressure cases. The increase in plasma density with increasing magnetic induction correlates to the direct proportionality in the helicon dispersion relation. For all investigated operational parameters the time evolution of the helicon discharge shows the same characteristics and is reliably reproducable inside the error bars. The electron temperature is determined by combining the collisional radiative model with line ratio measurements of two spontaneously emitted LIF lines. The low electron temperature regime of 1.2 eV < T_e < 1.4 eV and the electron temperature profiles are consistent with helicon wave heating via collisional power dissipation. The maximum plasma density of n_e = (6 +- 1)E20 m^-3 is measured at high RF power of P_RF = 24 kW, p_0 = 9 Pa filling gas pressure and a magnetic induction of B = 105 mT with a maximum electron temperature at 1.4 eV. At these operational parameters the plasma density peaking time and width are determined to be 270E-6 s and 50E-6 s, respectively. This shows that specific plasma density requirements for the use of a wakefield accelerator are reachable and the duration of the peak plasma density is more than sufficient for a relativistic particle to pass a 1 km long plasma cell. Additionally time-resolved LIF profile measurements for neutral and singly ionized argon were conducted to complement the previously evaluated measurements. The time resolution of the LIF diagnostic was chosen in a way to adequately represent the evolution of densities and to allow full profile measurements over one day. A resolution of 200E-6 s was chosen. The time-resolved neutral and ion metastable densities show hollow profiles with high densities at the edges over the first ms indicating higher ionization levels and increasing electron quenching rates. The metastable densities are highly determined by electron temperature, RF heating power and filling neutral gas pressure and do not reflect the neutral argon evolution. To investigate the influence of neutral depletion on the density evolution and maximum plasma density, the argon neutral and ion ground state densities are determined. Both time-resolved density profiles show a hollow profile with highest densities at the edges over a longer time interval of 3-4 ms. The penetration depths (ionization mean-free paths) indicate increased ionization of neutral argon while dissipating inwards, corresponding well to the theoretical value of lambda = 20 mm. This results in a depletion of neutrals in the center of the discharge, leading to a limitation and a fast decrease of plasma density after the neutrals are partially ionized. The shown refilling effect of neutral argon is too slow to have an important impact. At operation parameters for highest plasma density, the calculated ground states also show a fast increase in density at the end of the discharge after the RF-heating is switched off. This indicates recombination effects to these atomic states and higher ionization levels than ArII in the helicon discharge.
This thesis describes experiments with clusters stored in an electrostatic ion trap called Multi-reflection time-of-flight (MR-ToF) analyzer. These devices are established as mass separators and analyzers with high resolving powers and fast processing times. The objective was to characterize an experiment that utilizes such analyzer for cluster research, to this end a laser-ablation ion source was combined with an MR-ToF analyzer.
In the first part, an experiment scheme that combines two operating modes, namely in-trap lift operation and mirror operation, is presented and characterized for the present setup. For ion capture in-trap lift switching was employed and exit-side mirror switching for ejection with higher information content. Measurements were performed with small lead clusters to illustrate individual advantages of both techniques and the gain of combining them with focus on the ions’ ToF ejection window.
In the second part, a recently introduced method of ion separation by transversal ejection of unwanted species inside the trap was studied for the present setup. The ejection is performed by appropriate pulses of the potentials of deflector electrodes located in the trap. The various parameters affecting the selection effectivity and resolving power are illustrated with tin-cluster measurements, with resolving powers of up to several tens of thousands.
The third part presents the experiment in detail, with the construction of each component and measurements for its various performance parameters. Because the heart of the setup is the MR-ToF analyzer the characterization focuses on the trap. In addition, cluster ions were mass selected in the MR-ToF device and photodissociated. The charged fragments were stored and mass analyzed in a proof-of principle MS/MS experiment where both MS steps were performed in the MR-ToF operation mode.
This work studies different alternatives for parallelization of ground-state DMRG, with a focus on shared memory multiprocessor systems. Exploiting the parallelism in the dominant part of a DMRG calculation (diagonalization of the superblock Hamiltonian), speedups of 5 to 6 on 8-CPU machines can be achieved. A performance analysis gives hints as to which machine is best siuted for the task. The parallelized DMRG code is then applied to current problems in theoretical solid state physics with electronics, bosonic and spin degrees of freedom. Stripe-like modulations of the hole density in the ground state of doped Hubbard with cylindrical boundary conditions are idenficied in the thermodynamic limit using extrapolation techniques. In the 1D Holstein model of spinless fermions at half filling, Luttinger parameters and the charge structure factor are determinde in order to derive the phase diagram that had previously been established only on small lattices. For the 1D half-filled Holstein-Hubbard model, a finite size analysisof spine and charge excitation gaps in the relevant sectors (Mott insulator, Peierls band insulator and bipolaronic Peierls insulator) is able to yield the phase diagram as well. Finally, is the Heisenberg spin chain with dynamical phonons is considered as a relevant model for a spin-Peierls transition in Copper Germanate. Using DMRG, the relation between singlet-triplet excitation gap and dynamical dimeriaztion is calculated for the first time.
Computational chemical physics can give important input to astrophysical modelling and other fields of physics, where molecular properties are of importance. Understanding of spectroscopic and reactive behaviour is crucial for many systems of astrophysical interests like stars, interstellar medium and comets. Especially stellar atmospheres are of interest, because the complex physics of stars are not yet completely understood. Stars are in an unstable balance of gravitation and radiation pressure and the atmospheric dynamics have been subject of extensive modelling. Complete and accurate spectroscopic information of the atoms and molecules in these atmospheres is necessary for this attempt. In addition, the only information we have about astrophysical systems is light which is emitted or absorbed by particles in these media. This is not only true for astrophysics. In plasma physics sometimes the usage of invasive diagnostics, like Langmuir probes, is not wanted because they disturb the system. In these cases some information of the system can be regained by passively measuring infrared spectra of the plasma or by active induction of electronic transition like the laser-induced fluorescence method. Another remote sensing application is the measurement of the atmospheric composition on earth. Here, larger particles in the atmosphere as well as greenhouse gases are of current interest. Unfortunately, the experimental spectroscopic data, which is needed for the understanding and interpretation of the measured spectra, is often incomplete. This gap can be, to some extend, filled by computational chemical physics. The aim of this work was to investigate the capabilities and limitations of ab initio based potential energy surfaces for spectroscopic and reactive studies and to apply these methods to problems of rovibrational and rovibronic spectroscopy and reaction dynamics. The choice of ab initio methods and the potential fitting methods is critical for the computational chemical physics, as all further quantities directly depend on their quality. In this work modified versions of the Braams polynomial potential energy surface were used. A high level coupled cluster ab initio method was used to build potentials for a series of small hydrocarbons. Hydrocarbons can be found almost everywhere on earth and in the universe. They exist in laboratory plasmas, stellar and planetary atmospheres and interstellar gases. In all these cases, light emitted or absorbed by the molecules is an important diagnostics of the system. The potential constructed in this work partly included a cluster expansion, which adds reactant configuration spaces to the fits. This could not be done for CH_3 and higher hydrocarbons, because of the limitations of the Coupled Cluster ab initio method, which is well suited for the potential wells, but not for the dissociation regions. The examples of methyl and methane show how the potentials can be used for rovibrational spectroscopy. Results of radiation transport simulations illustrate the importance of as complete-as-possible line lists for radiation transport calculations.\\ The rovibronic spectroscopy of diatomic molecules is another important aspect for the stellar atmospheric modelling. Metal hydrides and oxides add opacity to the atmosphere in the visible light and ultraviolet frequency regions, as well as do the hydrocarbons in the infrared one. In addition the spectra of metal hydrides/oxides can be used to gather information about metal and their isotope abundances. They are used as markers for the conditions in the atmospheres of stars. In this work a new code was developed, that efficiently calculates bound-bound transitions between electronic states and bound-continuum cross sections for diatomic molecules. It also offers an adequate treatment of quasi-bound rovibrational states. One important representative of the diatoms is magnesium hydride, MgH. Before this work, line lists and photodissociation cross section were available involving the three lowest doublet states of MgH. In this work new potential energy curves were calculated and adapted to updated experimental data. This causes changes in the relative energies between the electronic states and therefore shifts in the line lists. These are important, because accurate line positions are needed for the identification of spectral lines. In addition two further electronic states were included in the calculations. This expands the spectral range of MgH into the near ultraviolet region. Radiation transport models showed significant absorption by MgH from the newly added electronic states. A second usage of the diatomic potential energy curves are photodissociation cross sections. As interstellar environments are chemically active, such data is necessary for a complete picture of the ongoing processes. The photodissociation cross sections of MgH reveal a stronger dependence of the underlying potential than the bound-bound lines. In the case of MgH the cross sections are rather weak, besides occasional resonance lines which can be several orders of magnitude stronger. As mentioned, not only spectroscopic, but also reactive behaviour of molecules is important in astrophysics. A current problem connected with this is the abundance of CH^+ in interstellar clouds. Its measured abundances do not fit the predictions from theoretical models. In addition Gerlich and co-workers recently measured low temperature H + CH^+ -> C^+ + H_2 reaction rates, which diverge from the theoretical picture and which could not be explained. In this work a reactive potential energy surface was built for the CH_2^+ system, which was then used to perform extensive calculations with quasi-classical trajectory and quantum scattering methods. It was found out, that the potentials used in previous works are not accurate enough to allow low temperature calculations. Results from these potentials must be taken with care. Furthermore, the results from the new potential energy surface indicate significantly reduced reaction rates compared to previous numerical studies. This is in agreement with the new results of Gerlich and co-workers. Nevertheless, the large error bars in the low temperature range for experimental as well as numerical results strongly suggest refined methods to be developed for both, before a final conclusion can be made. This work demonstrated the possibility of modern computational chemical physics to supply consistent data for spectroscopy and reaction dynamics. These are necessary and important inputs for fields like astrophysics, plasma physics and chemistry.
In this work, spatial distributions for reactive stable and transient species that are involved
in the reaction cycle of H2O2, a key species for biomedical applications, were
determined directly in the effluent of a kINPen-sci plasma jet. The small diameter
of cold atmospheric pressure plasma jets and their operation at atmospheric pressure
that causes strong quenching reactions make diagnostics challenging. Here, various diagnostic
techniques have been employed and adapted for the use in the effluent of a
cold atmospheric pressure plasma jet, which were laser atomic absorption spectroscopy
(LAAS) at 811.5 nm for the detection of Ar(3P2), picosecond two-photon absorption
laser-induced fluorescence spectroscopy (ps-TALIF) at 225 nm and 205 nm for the
detection of O and H atoms, respectively, and continuous wave cavity ring-down spectroscopy
(cw-CRDS) at 1.506 µm for the detection of HO2, and cw-CRDS at 8000 µm
for the detection of H2O2. All these methods provide absolute number densities. In
this work, spatial distributions within the small diameter of the effluent of a CAPJ
were obtained, which have not been reported so far literature. In order to overcome the
line-of-sight limitations of CRDS, radial scans were performed and transformed into a
spatial distribution by using Abel inversion.
Based on the determined spatial density distributions for H atoms, O atoms, HO2
radicals, and H2O2 molecules, together with the investigated impact of humidity in the
feed gas on the excitation dynamics and the production of Ar(3P2), and finally on a
comparison of the experimental results to a plasma chemical and reacting flow model,
three different zones with varying reaction kinetics were identified. The densities close
to the nozzle of the kINPen-sci plasma jet were dominated by reactions within the
plasma zone including the dissociation of H2O added to the Ar feed gas and O2 that
was presumably transferred into the plasma zone by counter-propagating ionisation
waves. Notably, also the larger molecules, such as HO2 and H2O2 were mainly formed
within the plasma zone of the plasma jet. Between 1.5 mm and 5 mm below the nozzle,
the atomic species and molecular radicals generated in the plasma zone were consumed
by chemical reactions with the surrounding gas, whose composition was controlled by
applying a gas curtain. At further distances from the nozzle, where typically biological
samples are positioned, only H2O2 and HO2 were observed.
With this work, it is successfully demonstrated that even for the small diameters of
cold atmospheric pressure plasma jets the determination of spatial profiles for reactive
transient and stable species is possible within the effluent. By combining the experimental
results, important insights into the formation and consumption of H2O2 and its
precursors were gained, which are essential for the understanding of use of plasmas in
biomedical applications.
Tunable Diode Laser Absorption Spectroscopy in the mid InfraRed spectral range (IR-TDLAS) has been applied to investigate the behaviour of CF, CF2 and C2F4 species produced in pulsed CF4/H2 capacitively coupled radio frequency plasmas (13.56 MHz CCP). This experimental technique was shown to be suitable for temporally resolved measurements of the absolute number density of the target molecules in the studied fluorocarbon discharges. The temporal resolution of about 20…40 ms typically achieved in the standard data acquisition mode (“stream mode”) was sufficient for the real-time measurements of CF2 and C2F4, but not of CF whose kinetics was observed to be much faster. Therefore, a more sophisticated approach (“burst mode”) providing a temporal resolution of 0.94 ms was established and successfully applied to CF density measurements. In order to enable the TDLAS measurements of the target species, preliminary investigations on their spectroscopic data had been carried out. In particular, pure C2F4 has been produced in laboratory by means of vacuum thermal decomposition (pyrolysis) of polytetrafluoroethylene and used as a reference gas. Therefore, an absorption structure consisting of several overlapping C2F4 lines around 1337.11 cm-1 was selected and carefully calibrated, which provided the first absolute measurements of the species by means of the applied experimental technique. The absolute number density traces measured for CF, CF2 and C2F4 in the studied pulsed plasmas were then analysed, in which two differential balance equations were proposed for each of the species to describe their behaviour during both “plasma on” and “plasma off” phases. Analytical solutions of the balance equations were used to fit the experimental data and hence to deduce important information on the kinetics of the studied molecules. In particular, during the “plasma off” phase, the self-recombination of CF2 (CF2 + CF2 (+M) → C2F4 (+M)) was found to be dominant in the kinetics of the radical, but of minor importance for C2F4 production. A rapid consumption of CF observed within 7…25 ms after switching off the plasma was explained mainly by volume reaction with other species (most likely with CF3), whereas diffusion of the radical towards the reactor walls followed by sticking on the surfaces was found to contribute only at relatively low pressures (<10 Pa). Under certain discharge conditions, measured CF density traces exhibited significant overshoots in 50…150 ms after the plasma ignition, which had not been known from literature before. The electron impact fragmentation of C2F4 was shown to be essential for CF production at the beginning of the “plasma on” phase and therefore for formation of the observed CF density overshoots. Finally, the broad band FTIR spectroscopy was applied in order to better characterize the gas phase composition of the studied plasmas. Thus, absorption bands of CF4, C2F4, C2F6, C3F8, CHF3 and HF stable molecules were detected in the FTIR spectra recorded between 400 and 4000 cm-1. The spectra were then successfully deconvolved and the absolute concentration of the detected species was estimated. In particular, the absolute number density of C2F4 obtained from the FTIR measurements was in a good agreement with that achieved by means of the IR-TDLAS technique. The work was supported by the German Research Foundation (DFG) within the framework of the Collaborative Research Centre Transregio 24 “Fundamentals of Complex Plasmas” (SFB/TRR24, project section B5).
Turbulence is a state of a physical system characterized by a high degree of spatiotemporal disorder. Turbulent processes are driven by instabilities exhibiting complex nonlinear dynamics, which span over several spatial as well as temporal scales. Apart from fluids and gases, turbulence is observed in plasmas. While turbulent mixing of a system is sometimes a desired effect, often turbulence is an undesired state. In hot, magnetically confined plasmas, envisaged for energy generation by thermonuclear fusion, plasma turbulence is clearly a problem, since the magnetic confinement time is drastically deteriorated by turbulent transport. Hence, a control mechanism to influence and to suppress turbulence is of significance for future fusion power devices. An important area of plasma turbulence is drift wave turbulence. Drift waves are characterized by currents parallel to the ambient magnetic field, that are tightly coupled to a coherent mode structure rotating in the perpendicular plane. In the present work, the control of drift waves and drift wave turbulence is experimentally investigated in the linear magnetized helicon experiment VINETA. Two different open-loop control systems - electrostatic and electromagnetic - are used to drive dynamically parallel currents. It is observed that the dynamics of the drift waves can be significantly influenced by both control schemes. If the imposed mode number as well as the rotation direction match those of the drift waves, classical synchronization effects like, e.g., frequency locking, frequency pulling, and Arnold tongues are observed. These confirm the nonlinear interaction between the control signal and the drift wave dynamics. Finally, the broadband drift wave turbulence, and thereby turbulent transport, is considerably reduced if the applied control signal is sufficiently large in amplitude.
Ion traps such as Paul traps and MR-ToF (multi-reflection time-of-flight) devices are indispensable tools at radioactive ion beam facilities for the preparation of high-quality radioactive ion beams for subsequent experiments or for precise measurements of the properties of radioactive ions, such as nuclear binding energies or nuclear charge radii.
Within the work of this thesis, Doppler- and sympathetic cooling is implemented in a linear Paul-trap cooler-buncher enabling a reduction of the longitudinal emittance of radioactive ion beams resulting in a significant improvement of the ion beam quality. Moreover, a next-generation MR-ToF device is conceptualized in order to achieve isobaric pure beams with a higher ion intensity than state-of-the-art MR-ToF devices can provide. Once fully constructed and commissioned, it will operate at an unprecedented ion beam energy of 30 keV. Both of these advances are expected to become important for a wide range of experimental programs pursued at low-energy branches of RIB facilities ranging from fundamental symmetry studies, nuclear structure, rare isotope studies with antimatter, searches of physics beyond the standard model to material science and the production of medical isotopes.
The next-generation MR-ToF mass separator is based on MIRACLS’ 30-keV MR-ToF device for highly sensitive and high-resolution collinear laser spectroscopy. By storing the ions in the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), the same ion bunch is probed by a spectroscopic laser for thousands of times compared to a single passage in traditional collinear laser spectroscopy (CLS). Dedicated simulation studies show that the accuracy and resolution will be close to traditional single-passage CLS while the sensitivity is significantly enhanced. Hence, measurements of nuclear properties via fluorescence-based CLS of very rare radionuclides as well as highly sensitive and high-precision measurements of electron affinities via laser-photodetachment-threshold spectroscopy of negatively-charged (radioactive) ions will become possible.
First measurement campaigns employing MIRACLS’ 1.5-keV MR-ToF device confirm the outstanding boost in signal sensitivity and provide confidence in the application of the MIRACLS technique for the measurement of scarcely produced radioactive ions that have been so far beyond the reach of conventional techniques. Furthermore, the electron affinity of 35Cl was measured, which is in perfect agreement with the literature value. These measurements will serve as important benchmarks for modern atomic and nuclear theory, especially in its description of nuclear charge radii.
In summary, the implementation of Doppler and sympathetic cooling at RIB facilities, the conceptualization of a 30-keV MR-ToF apparatus for highly selective and high-flux mass separation as well as for highly sensitive and high-resolution fluorescence-based laser spectroscopy and the expansion of the MIRACLS technique for the study of negatively-charged ions will enable unprecedented new measurement opportunities at RIB facilities.
Bei moderaten sinusförmigen Betriebsspannungen tritt in reinem Stickstoff der diffuse Townsend-Modus (APTD) auf. Das elektrische Feld ist hier über den Entladungsspalt annähernd konstant, weshalb ein anodengerichteter exponentieller Anstieg der Intensität der Emission beobachtet wird. Dementsprechend ist das Intensitätsmaximum direkt vor der Anode lokalisiert. Überraschenderweise lässt sich die APTD unter den gegebenen experimentellen Bedingungen (Breite des Entladungsspalts d_Spalt=1 mm und sinusförmige Betriebsspannung) ebenfalls in einer Helium-BE genieren. Für gewöhnlich wird jedoch in einer Helium-Entladung der diffuse Glimmentladungs-Modus (APGD) beobachtet, wobei der Entladungsspalt zwischen 2-5 mm breit ist. Das Emissionsmaximum einer solchen Entladung befindet sich durch die Ausbildung eines Kathodenfallgebiets vor der Kathode. Die geringe Breite des Entladungsspalts verhindert hier jedoch die Ausbildung der APGD. Entsprechend kann sich das Kathodenfallgebiet nicht entwickeln, wodurch die Spaltspannung nur schwach einbricht. Das Intensitätsmaximum der Emissionsentwicklung befindet sich wie bei der diffusen Stickstoff-BE direkt vor der Anode. Die Zünd- und Brennspannung ist in Stickstoff größer als in Helium, da die Vibrationszustände des Stickstoffs effizient durch Elektronen angeregt werden und diesen dabei Energie entzogen wird. Helium hat jedoch keine Vibrationszustände, weshalb die Elektronentemperatur ansteigt und die Zünd- und Brennspannung deutlich geringer ist. Eine Erhöhung des Spannungsanstiegs dU/dt beeinflusst signifikant die Entladungsentwicklung in der diffusen Helium-Entladung. So führt eine Variation von der Sinus- zur Rechteckspannung zu einem Wechsel des Entladungsmodus, nämlich von der APTD zur APGD. Die Ursache hierfür ist der deutlich höhere Energieeintrag, was sich auf die Ionisationsprozesse auswirkt. Die Verwendung einer Sägezahnspannung stellt in Bezug auf den Spannungsanstieg dU/dt eine Kombination aus der Sinus- und der Rechteckspannung dar. Mit dieser Betriebsspannung war es erstmals möglich, in einer Entladungsperiode entsprechend der Spannungsgradienten beide Entladungsformen (APTD und APGD) zu beobachten und zu studieren. Durch die Oberflächenladungsmessung konnte nachgewiesen werden, dass die während eines elektrischen Durchbruchs im Entladungsvolumen transferierte Ladung vollständig auf den Dielektrika akkumuliert wird. Der Vergleich der phasenaufgelösten Oberflächenladungsdichtemessung mit der zeitlichen Integration der Stromdichte zeigt, dass die Akkumulation von Oberflächenladungen instantan mit dem Auftreten eines Strompulses stattfindet. Nach einem Entladungsstrompuls bleiben die Oberflächenladungen unabhängig vom Entladungsmodus auf dem Dielektrikum konstant, bis die Entladung in der nächsten Halbwelle erneut zündet. In der filamentierten Entladung markieren die Oberflächenladungen den Auftreffpunkt der einzelnen Mikroentladungen. Die Oberflächenladungen sind an diesen Stellen stark lokalisiert. Die gemittelten radialen Oberflächenladungsdichteprofile haben gezeigt, dass diese sowohl für die negativen als auch für die positiven Oberflächenladungen einer Gauß-Verteilung folgen. Die volle Halbwertebreite der entsprechenden Oberflächenladungsdichteprofile unterscheidet sich. Die negativen Oberflächenladungen nehmen eine größere Fläche ein als die positiven Oberflächenladungen. Es konnte erstmals gezeigt werden, dass Mikroentladungen über viele Entladungsperioden immer wieder an der gleichen Stelle zünden, wo sich aus einer vorhergehenden Entladung ein lokalisierter Oberflächenladungsfleck entgegengesetzter Polarität befand. Dieses Phänomen wird als Memory-Effekt bezeichnet. Durch zeitlich definiertes Abschalten der Entladung konnten die Lebensdauern von Oberflächenladungen beider Polaritäten auf dem BSO-Kristall gemessen werden. Es konnte gezeigt werden, dass der Abbau der Oberflächenladungen in zwei Zerfallsprozesse k_1 und k_2 unterteilt ist. Während des Prozesses k_1 nimmt die Oberflächenladungsdichte innerhalb einiger weniger Sekunden deutlich ab. Die Zeitkonstante k_1 ist trotz der photoleitenden Eigenschaft des BSO-Kristalls unabhängig von der Beleuchtungsfrequenz des Kristalls ist. Der zweite deutlich langsamer ablaufende Prozess zeigte hingegen eine starke Abhängigkeit von der Beleuchtungsfrequenz der BSO-Kristalls. Wurde der Kristall kontinuierlich beleuchtet, verschwanden die Oberflächenladungen unabhängig von ihrer Polarität nach wenigen Sekunden vollständig. Je kleiner die Beleuchtungsrate des Kristalls ist, desto länger waren die Oberflächenladungen nachweisbar. Der Zerfallsprozess k_2 beruht auf intrinsischen Transportprozessen. Hierbei wird davon ausgegangen, dass die negativen Oberflächenladungen durch Elektronen nahe der Oberfläche gebildet werden. Die positiven Oberflächenladungen sind Löcher im Valenzband, die durch Elektronen-Ionen-Rekombination entstehen.
In the framework of the current work has been the plasma initiated and surface catalysed species conversion studied in low pressure and atmospheric plasmas. The aim of the work is to improve the understanding of the internal processes in order to increase the energy efficiency as well as the selectivity of the reaction products of future plasma devices. Beside many technical applications of plasmas, air purification shows great potential. Over the last decades, plasma based pollution control has proofed its ability to remove harmful contaminants or annoying odours from an air stream. However, the energy efficiency and the selectivity of the products are a remaining challenge.
Motivated by these issues, a multi stage packed-bed reactor has been used to remove admixed ethylene and toluene from an air stream. It has been found that the maximum toluene destruction has been 60%, whereas ethylene has been nearly completely removed. The specific energy β has been between 120 and 1600 JL-1. Fourier Transform Infrared spectroscopy, FTIR spectroscopy, has been used to identify and quantify the species H2O, CO2, CO, O3, HNO3, HCN, CH2O, CH2O2, N2O and NO2. However, none of these experiments led to the detection of NO.
The embedment of packing material into a plasma volume leads to increased surface effects. In order to study them, the inner side of a tube reactor, made of Pyrex, served as the surface under study and has been exposed to a rf plasma for 1h. The surface effects of the plasma treatment have been investigated indirectly by studying the oxidation of NO into NO2. After the plasma exposure, the reactor has been evacuated and filled with a gas mixture of 1% NO in N2 / Ar. Both species have been measured using quantum cascade laser absorption spectroscopy, QCLAS. It has been found that, using oxygen containing plasmas, the NO concentration decreased whereas the NO2 concentration increased. Therefore, oxygen containing plasmas are able to deposit oxygen on the surface. The filling with NO leads to the oxidation via the Eley-Rideal mechanism. A simplified model calculation supports these assumptions.
For a more comfortable application of the QCLAS, a compact multi channel spectrometer has been developed, TRIPLE Q. It combines the high time resolution with the possibility to measure the concentration of at least three infrared active species simultaneously. Due to the high time resolution, a huge number of spectra have to be analysed. In order to calculate absolute number densities, an algorithm has been developed which automatically treats typical phenomena like pulse jitter, rapid passage effect or variations of the intensity of the laser pulses.
The gas temperature is an important parameter in plasma physics. Using the TRIPLE Q system, the gas temperature has been determined for pulsed dc plasmas. For this case, NO has been used as a probe gas. From the spectra, the temperature has been calculated using the line ratio method. The relative intensity of the absorption structures of NO at 1900.5cm-1 and 1900.08cm-1 depend on the temperature. Therefore, the ratio has been used to calculate the gas temperature with a time resolution in the μs range.
Vibrationally excited nitrogen can be an energy reservoir that plays an important role in plasma chemistry. In N2 / N2O plasmas, vibrationally excited N2 can undergo relaxation via a resonant vibration vibration coupling between vibrationally excited N2 and N2O. Due to such an efficient energy transfer, the method allows one to study the relaxation of vibrationally excited N2. Using this method, molecules, which are not infrared active, can be monitored. This approach has extended the field of scientific and commercial applications of the QCLAS.
In this thesis, it was the subject to build a setup to study the interaction of clusters with intense laser light. A magnetron sputter cluster ion source was built to create metal clusters for the planned investigations. Furthermore, a linear Paul trap setup was built in order to allow the investigation of the mentioned interaction at one specific cluster size. The whole apparatus was characterized and first experiments were performed.
This work presents the first experimental investigation of the gas balance on the optimized modular stellarator Wendelstein 7-X (W7-X). A balance of all injected and removed particles and a measurement of internal particle reservoirs allows inference of the bound particle reservoir in the wall, which is of interest due to its effects on plasma density control and fuel retention. Different scenarios of the gas balance are presented with data from the operation campaign 1.2 with an inertially cooled graphite divertor. Both net outgassing and net retention scenarios are presented and W7-X is found to operate stable in a wide range of scenarios with varying wall conditions.
Since fusion experiments are conducted in ultra-high vacuum, suitable gauges are required for total and partial pressure measurement. The challenges and opportunities of the operation of pressure gauges in the steady magnetic field extending beyond plasma pulses are discussed. The performance of newly improved neutral pressure gauges, based on crystal cathode emitters is quantified. These provide improved operational robustness since they can be operated for long periods of time in strong magnetic fields. A crystal cathode setup and and its operation performance is presented along with a fast calibration scheme.
Partial pressure measurements provide additional important information complementing the total neutral pressure measurements, and allowing additional physics insights. As part of this thesis work, a new diagnostic of this kind was implemented on W7-X, the so-called diagnostic residual gas analyzer (DRGA). It provides a wealth of information on various neutral gas species, with a relatively high time resolution - of order a few seconds. The diagnostic setup and its first results are presented in this thesis.
The biomechanical (Young's modulus, adhesion force, deformability) properties of platelets depend on the cytoskeleton and have an undisputed influence on physiological and pathological processes such as hemostasis and thrombosis. The alterations of these biomechanical properties can be used as label-free diagnostic markers in initiation or progressive diseases such as MYH9-inherited disease. Therefore, the focus of my thesis was to investigate the relationship between the changes in platelet cytoskeleton proteins and the resulting biomechanical properties using biophysical methods.
In the first chapter of my thesis I focused on my review of the biophysical methods that are most commonly used to assess and quantify the biomechanical properties of platelets. In this review, I provide an in-depth insight into the governing principles and instrumentation setup and discuss relevant examples applied to platelet mechanics. In addition, my review also summarizes the limitations of these biophysical methods and highlight latest improvements. The review covers the following techniques: micropipette aspiration, atomic force microscopy (AFM), scanning ion conductance microscopy (SICM), tensile force microscopy on hydrogel substrates, microcolumns, and deformable 3D substrates, and real-time deformability cytometry (RT-DC). This review is directed toward clinician scientists who are interested in exploring applications of single-cell based biophysical approaches in unraveling the role of platelet biomechanics in hemostasis and thrombosis research.
In the second chapter of my thesis, I present my research paper on the influence of commonly used ex vivo anticoagulants on the intrinsic biomechanical properties and functional parameters (e.g. activation profils) of human platelets. To comprehensively assess this, platelets obtained in different ex vivo anticoagulants such as ACD-A, Na-Citrate, K2-EDTA, Li-Heparin, and r-Hirudin were used, and their biomechanical properties were determined by real-time fluorescence and deformability cytometry (RT-FDC). Flow cytometry, and confocal laser scanning fluorescence microscopy were used to determine platelet function properties. K2-EDTA and Li-Heparin were found to affect platelet biomechanics by increasing actin polymerization of non-stimulated human platelets. This increased actin polymerization results in decreased platelet deformation. It is recommended that an ex vivo anticoagulant such as ACD-A, Na-Citrate, or r-Hirudin be chosen for the study of the cytoskeleton of human platelets and, if possible, that it not be exchanged, because comparability of results is not assured. Furthermore, I demonstrate the significance of choosing correct ex vivo anticoagulants in RT-FDC by showing that platelets from a healthy donor and a MYH9 patient with the E1841K point mutation differ in their deformation. This paper is the first comprehensive investigation at the single platelet level to establish the relevance of preanalytical standardization in platelet sample preparation for biomechanical studies.
The third chapter of my thesis is focused on the biomechanical analyses of platelets and thrombi from MYH9-related disease. Here I studied three Myh9 mouse lines with a point mutation in the Myh9 gene at positions 702, 1424, or 1841. Furthermore, two MYH9 patients (MYH9 p.D1424N, MYH9 p.E1841K) were examined. MYH9-related disease (MYH9-RD) presents with macrothrombocytopenia with a moderate bleeding tendency. It is caused by mutations in the MYH9 gene that lead to alteration of non-muscle myosin heavy chains type IIA (NMMHC IIA), resulting in disruption of the platelet cytoskeleton. Western blot analysis, flow cytometry, in vitro aggregometry, and transmission electron microscopy demonstrated that Myh9 point mutant mice have comparable primary function compared to the control group. The heterozygous point mutations in the Myh9 gene resulted in decreased platelet deformation (RT-FDC), decreased platelet adhesion to collagen (single platelet force spectroscopy-SPFS), and decreased platelet-platelet interaction forces (SPFS). Decreased platelet force (Micropost Arrays) results in softer thrombi (colloidal probe Spectroscopy), impaired clot retraction, and thus prolonged bleeding time. The R702C, D1424N, and E1841K mutations have a similar effect on platelet biomechanical functions, although the E1841K mutation had less impact on thrombus formation and stiffness. MYH9-RD patients have an increased risk of bleeding, and the antifibrinolytic drug tranexamic acid (TXA) is one way to control bleeding complications in these patients. It was shown that TXA treatment significantly reduced bleeding time in the three Myh9 mouse models, confirming that the enhanced bleeding phenotype due to decreased platelet forces in Myh9 mutant mice can be compensated by the addition of TXA.
With the biophysical methods and research results presented in my thesis, it is clear that it is essential to study the altered response of the platelet cytoskeleton by cytoskeletal mutations, biochemical, physical stimuli, or by pharmacological aspects. This will provide us with an opportunity to better understand the underlying mechanisms and thus contribute to better clinical treatment.
Abstract Atmospheric Pressure Discharges have attracted much interest in recent years. The development of a new processes based on this discharge needs a clear understanding of plasma and discharge physics and chemistry. At the present time much attention is paid to the chemical processes in barrier discharge plasma in various gas mixtures, since the understanding of these processes is necessary for the development of industrial reactors. Besides these, hydrocarbons are being used for the formation of diamond like or amorphous carbon (DLC) films. Specially, hydrogenated amorphous carbon (a-C: H) and plasma polymerization. In this work we have used Dielectric Barrier Discharge (DBD) a plasma device used to investigate simple hydrocarbon reactions in a plasma phase. Our aim of plasma phase chemical reaction studies is to form molecular hydrogen, higher order hydrocarbons CnHm up to n ≥ 12 series and nitrogen - containing organic complexes using simple hydrocarbons. Deposition of thin organic films or DLC films were carried out using the DBD. In this study we have chosen certain combination of gases such as C2Hm/N2 (m = 2, 4, 6) and C2Hm/Ar (m = 2, 4, 6); the purpose of using N2 and Ar gases are to dilute and stabilize the hydrocarbon plasma and to investigate plasma chemical reactions with nitrogen gas. All reactions were carried out under an atmospheric pressure (300 mbar) with gas ratio 1:2; Experiments were performed by applying high voltage with a frequency 5.5 kHz. The plasma phase diagnostics have been investigated using mass spectrometry and FTIR spectroscopy. Formation of molecular hydrogen, N-containing organic complexes and higher order hydrocarbons with C ≥ 12, have been investigated with mass spectrometry. FTIR spectroscopy reveals the formation of substituted alkanes (sp3), alkenes (sp2) and alkynes (sp) and nitrogen containing functional groups from the individual gases which are used in this work. Abundant formation of acetylene occurs with C2H6 and C2H4 as precursor gases. Amorphous hydrogenated carbon nitride (a-CNx:H) films have been deposited on Si (100) and glass substrates using gas mixtures C2Hm/N2 (m = 2, 4, 6). Surface chemical compositions have been derived from Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) and X-ray Photo electron Spectroscopy (XPS). FT-IRRAS and XPS show the presence of sp, sp2 and sp3 bonds of carbon and nitrogen for C2Hm/N2 thin films. Various functional groups such as amines, saturated and unsaturated alkyl groups have been identified. Thin films obtained from C2H2/N2 and C2H4/N2 gas mixture had a larger N/C ratio when compared to the film obtained from C2H6/N2. Thickness, refractive index and extinction co-efficient were investigated by ellipsometry. Rate of deposition have been investigated. Different surface morphology has been derived using Scanning Electron Microscopy. Amorphous hydrogenated carbon (a-C:H) films or diamond like carbon (DLC) films have been deposited on Si (100) and glass substrates using gas mixtures C2Hm/Ar (m = 2, 4, 6). Diagnostics for the deposited films have been done using different spectroscopic techniques. Surface chemical compositions have been derived from Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) and X-ray Photo electron Spectroscopy (XPS). FT-IRRAS show the presence of sp, sp2 and sp3 bonds of carbon and hydrogen for C2Hm/Ar (m = 2, 4, 6) thin films. The characteristic peak for C1s has been observed from XPS. Thickness, refractive index and extinction co-efficient were investigated by ellipsometry. Rate of deposition have been investigated.
Die vorliegende Arbeit liefert Beiträge zur optischen und elektrischen Charakterisierung des dynamischen Verhaltens von Plasmaspezies in Atmosphärendruck-Plasmen insbesondere mit Hinsicht auf den Einsatz in der Plasmamedizin. Dabei wurde ein breites Spektrum verschiedener Diagnostiken angewandt, um die Zugänglichkeit zur Bestimmung weiterer Plasmaparameter an Atmosphärendruck zu prüfen. Diese Arbeit stellt eine neue Methode zur Bestimmung der Ionendichte bei Atmosphärendruck- Bedingungen vor, bei der elektrische Oszillationen ausgewertet werden, deren Ursprung ionenakustische Wellen im Plasma sind. Weiterhin wurden neben relativen optischen Messungen wie der phasenaufgelösten optischen Fotografie (PROI) und der Kreuz- Korrelations-Spektroskopie (CCS) auch absolute optische Messungen mit der interferometrischen Hakenmethode und dem Pockels-Effekt durchgeführt. Anhand von elektrischen Messungen wurde ferner gezeigt, dass mit einer Strom- und Spannungs-Charakteristik der Einfluss von Aufbauparametern, wie der Kapillarposition oder dem Gasfluss, auf das Plasma untersucht werden kann. Gegenstand der Untersuchungen waren verschiedene Plasmaquellen, die für eine Nutzung in der Plasmamedizin entwickelt wurden. Sowohl die elektrischen Messungen des Parametereinflusses als auch die Bestimmung der Ionendichte erfolgten an der selbstpulsenden transienten Funkenentladung in Argon an offener Atmosphäre. Der geringe Filamentdurchmesser und der dennoch hohe Entladungsstrom ermöglichen die Detektion der ionenakustischen Instabilität. Darüber hinaus wurde diese erratisch zündende Entladung räumlich und zeitlich aufgelöst mit der CCS spektroskopisch untersucht. Dabei wird insbesondere die Selbst-Triggerung der CCS ausgenutzt, um einen Zeitbezug trotz des großen Entladungsjitter zu erhalten. Für die PROI wurden die räumlich und zeitlich stabilen Entladungsanordnungen der Nadel-Platte-Geometrie und des Kapillarjets in Helium gewählt. Die Anordnungen wurden mit einer periodischen Sinusspannung betrieben und wiesen Entladungsspalte von d = 5 - 15 mm auf. Eine besondere Anforderung der Messung mit dem Pockels-Effekt ist zu der räumlichen und zeitlichen Stabilität eine dielektrische Gegenelektrode, welche bei der Anordnung des Kapillarjets möglich war. Bei der Anwendung der interferometrischen Hakenmethode kam neben einem Erdgas-Sauerstoff-Mischgasbrenner sowohl eine Mikrowellen-Entladung (Plexc) als auch ein MHz-Plasmajet (kINPen) zur Anwendung. Die Bedeutung der elektrischen Messungen, besonders der Strom- und Spannungscharakteristik einer Entladung, wurde an dem Parametereinfluss der Kapillarposition einer erratisch zündenden transienten Funkenentladung vorgestellt. Es konnte gezeigt werden, dass der Zeitunterschied zwischen dem Stromsignal eines Vorstreamers und der Hauptentladung durch das Einbringen einer Kapillare in den Entladungsspalt deutlich verringert wird. Insbesondere der Beitrag der lokalen elektrischen Feldstärkeerhöhung an der Kapillarkante und der Diffusionsanteil der Umgebungsluft wurden als Ursachen, durch Vergleich einer Feldsimulation mit der Beobachtung der Vorphase an der Kapillarkante in den CCS-Messungen, diskutiert. Anschließend konnte gezeigt werden, dass der Leistungseintrag in die Vorphase durch die Platzierung der Kapillare deutlich reduziert werden kann. Ein wesentliches Ergebnis dieser Arbeit ist die Beobachtung von ionenakustischen Wellen als Oszillationen im Abklingen des Stromsignals einer erratisch zündenden transienten Funkenentladung. Hierzu war es nötig, elektrische Störungen zu erkennen und zu eliminieren. Es konnte ein Erdschleifen-freier Aufbau realisiert werden. In diesem Aufbau zeigt sich, dass die Signale der ionenakustischen Welle ausschließlich in einem bestimmten Gasflussbereich beobachtet werden. Die gemessene Frequenz der Oszillationen wurde als Ionenplasmafrequenz f_{pl ,i} identifiziert und enthält daher Angaben zu den Ionendichten im Bereich von n_{Ar_2^+} = 3•10^{14} cm^{-3} bis 1•10^{12} cm^{-3}. Nach einer Abschätzung der zu erwartenden Elektronendichte, die der gemessenen Ionendichte sehr nahe kommt, wurde die Dispersionsrelation für die vorhandenen Entladungsbedingungen aufgestellt und gelöst. Dabei zeigt sich eine starke zeitliche Dämpfung über die Ionen-Neutralteilchenstöße sowie eine räumliche Verstärkung für die Ionenplasmafrequenz. Aus der Dämpfung der Oszillationsamplituden konnte die Ionen- Neutralteilchen-Stoßfrequenz nu_i = 3•10^7 Hz ermittelt werden. Weiterhin ergibt sich aus der Lösung der Dispersionsrelation ein Existenzbereich für die ionenakustischen Wellen in Abhängigkeit von der Ionendichte und der elektrischen Feldstärke.
Diese Dissertation präsentiert experimentelle Untersuchungen zu vertikalen und lateralen Strukturen von Polyelektrolytmultischichten (PEM) adsorbiert auf festen Oberflächen. Zur Herstellung von PEM werden Polykationen (Poly-(allylamin)hydrochlorid (PAH) oder Poly-(diallyldimethylammonium)chlorid, PDADMAC) und Polyanionen (Polys-(styren)sulfonat (PSS)) aus einer wässrigen Lösung auf eine hydrophile Siliziumdioxid-Oberfläche sequentiell adsorbiert. Um nicht–elektrostatische (sekundäre) Kräfte während der Adsorption zu untersuchen, wird Reichweite und Stärke der elektrostatischen Wechselwirkung durch eine definierte Konzentration monvalenten Salzes (c_ads) in den Polyelektrolyt (PE)-Lösungen eingestellt. Schichtdicke, und Homogenität der Multischichten entlang der PEM-Normalen werden mit Röntgenreflexion gemessen. Dies ist in Übereinstimmung mit veröffentlichten Daten und wird auf die elektrostatische Abschirmung, beschrieben durch die Debye-Hückel Theorie zurückgeführt. Komplementär wird Neutronenreflexion genutzt, um die Interpenetration einzelner Polyelektrolytschichten zu quantifizieren. Hierzu wird ein PEM aus zwei Blöcken unterschiedlicher Streulängendichte (SLD) hergestellt. Der SLD-Kontrast wird durch Verwendung von protonierten und deuterierten PSS realisiert. Durch Variation der Anzahl protonierter und deuterierter PE-Schichten wird die Breite der inneren Grenzflächen positionsabhängig entlang der PEM-Normalen vermessen. So ist erstmals eine eindeutige Bestimmung der Interpenetration (inneren Rauigkeit, sigma_int) benachbarter Polykat-/Polyananiondoppelschichten möglich. Die PEM-Dicke skaliert mit der Wurzel der Salzkonzentration in der Adsorptionslösung. Sowohl für PAH/PSS als auch für PDADMAC/PSS-Multischichten ist sigma_int nahe an der Film/Luft-Grenzfläche am geringsten und steigt mit zunehmendem Abstand. Für das PAH/PSS-System ist die Zunahme monoton, während beim PDADMAC/PSS-System sigma_int zunächst anwächst und sich dann eine konstante innere Rauigkeit (sigma_int, max) einstellt. Bei PADMAC/PSS steigt sigma_int,max mit zunehmendem c_ads. Erklärt wird diese Beobachtung durch eine höhere extrinsische Ladungsträgerkompensation der Polyelektrolytketten und eine verringerte elektrostatische Wechselwirkung, letzteres führt zu einer erhöhten Flexibilität der Polyelektrolytketten. Die Änderung von sigma_int wird über ein 1-dimensionales Diffusionsmodell quantifiziert. Zusätzlich wird der Polymerisationsgrad (Anzahl Monomere pro Kette) des Polykations variiert. Bei einer Vergrößerung des Polymerisationsgrades und großem c_ads nimmt die maximale innere Rauigkeit ebenfalls zu. Dies weist auf kooperative Effekte zwischen Polykat- und Polyanion hin, da nur das PSS deuteriert ist. Bei geeignetem c_ads nimmt die Dicke pro adsorbierter Polykation/Polyanion-Doppelschicht (d_Bl) zu. Während für den salzfreien Fall (c_ads = 0) die Parameter d_Bl und Polymerisationsgrad entkoppelt sind, wird die Kopplung mit steigendem c_ads immer deutlicher. Dies wird mit einer PE-Schicht erklärt, in der die PE-Ketten bei der Adsorption eine flache (c_ads = 0) bzw. geknäulte (c_ads > 0) Konformation einnehmen. In diesem Fall steigt sigma_int bei großem Polymerisationsgrad rapide nahe der PEM/Luft-Grenzfläche, d.h. die Diffusionskonstante wächst. An dieser Stelle wird die These aufgestellt, daß entropische Kräfte und Stressrelaxation die Interpenetration verursachen. sigma_int, max stellt einen metastabilen Gleichgewichtszustand dar. Da die Diffusionskonstante einer Kette invers mit der Anzahl der Segmente skaliert, erklärt Stressrelaxation warum die Diffusionskonstante mit steigendem Polymerisationsgrad zunimmt.
This thesis investigated dielectric barrier discharges (DBDs) in N2-O2 gas mixtures at atmospheric pressure, with a focus on the gas discharge physics. The main goal was to evaluate whether possible control mechanisms exist that can manipulate the breakdown and the development of DBDs, especially for pulsed operation. To examine the pre-breakdown phase, the actual breakdown and the main DBD development, DBDs in a double-sided, single filament arrangement with a 1 mm discharge gap were investigated by means of electrical and optical diagnostics with high resolutions. Spectrally- and temporally-resolved iCCD pictures (2D in space), spectrally- and spatio-temporally-resolved streak camera and CCS images (1D in space) were simultaneously recorded accompanied by a full electrical characterisation with fast voltage and current probes. Sinusoidal- and pulsed-driven DBDs were found to have a qualitatively similar spatio-temporal development, i.e. a cathode-directed ionisation front (v ~ 10^6 m/s, positive streamer mechanism), followed by a transient glow-like phase in the gap. For sinusoidal operation, the slope of the applied voltage is flat (dU/dt ~ 1 V/ns) compared to pulsed operation (dU/dt ~ 100 V/ns). Thus, during the longer pre-phase of the sine-driven DBD, many more charge carriers were generated, in contrast to the pulsed-driven DBDs, where the pre-phase is limited by the short voltage rise time. Consequently, just before the breakdown occurs, the charge carrier density is higher for sine-driven DBDs, i.e. the positive streamer starts in a highly pre-ionised environment, which leads to a lower propagation velocity. In addition to limiting the pre-phase (lower pre-ionisation), the steep voltage slope of the pulsed DBD amplifies the streamer breakdown because the applied voltage rises significantly during its propagation. Therefore, the transferred electrical charge and the electrical power of a single DBD can be controlled by the applied voltage amplitude, but only in pulsed operation. In addition to the effects of different voltage slope steepness, the pulse width is an excellent parameter in the pulsed operation to set the pre-ionisation, by shifting the DBDs into the after-glow of the previous discharge using asymmetrical HV pulse waveforms. The subsequent DBDs ignite in different pre-ionised conditions, defined by the residual charge carrier densities in the gap that originated from the previous DBD. The breakdown characteristics of these DBDs could be controlled down to the fundamental level. This thesis has described for the first time four different breakdown regimes in single filament DBDs for 0.1 vol% N2 in O2 and connected them to the processes during their pre-phases. The “classic” DBD development (a cathode-directed streamer followed by a transient glow discharge) could be controlled in a certain range, followed by a transition first to a breakdown regime featuring a simultaneous propagation of a cathode- and an anode-directed streamer, and finally to a reignition of the previous DBDs without any propagation, just by reducing the pulse width (time between two subsequent DBDs), i.e. increasing the pre-ionisation level. All differences between the DBDs at rising and falling slopes could be explained by the different pre-conditions in the gap. The O2 concentration in the N2-O2 gas mixtures offers another way of controlling the pre-ionisation. Due to the electron attachment as a consequence of the electronegativity of oxygen, the electron density decreases for higher O2 admixtures. Furthermore, the differences in the first Townsend ionisation coefficient and in the photo-ionisation between N2 and O2 influence the DBD behaviour as well. To some extent, some of the reported effects achieved by varying the pulse width at a fixed O2/N2 ratio were also observed for a fixed pulse width and changing O2 concentration. Hence, the response of the DBD properties to changing pre-ionisation levels seems to be a general principle of DBD control. Additional effects of the O2/N2 ratio, such as an increasing DBD inception jitter or higher streamer velocities, were also reported. Finally, a reverse of the effects induced by the O2 admixture such as DBD emission duration or DBD inception delay, was observed for O2 concentrations below 0.01 vol%, and were especially pronounced at a pressure of 0.5 bar. For 0.1 vol% O2 in N2, a minimal electron recombination rate was found, which can be explained by the different decay and recombination rates of positive nitrogen and oxygen ions. These different rates effect the charge carrier dynamics and consequently, the pre-ionisation in the gap. In conclusion, this investigation has highlighted the importance of volume memory processes on the breakdown and development of single filament DBDs at elevated pressures.