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TRR 24:  Fundamentals of Complex Plasmas

Subject Area Physics
Term from 2005 to 2017
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 5486308
 
Final Report Year 2018

Final Report Abstract

Plasma physicists in Greifswald and Kiel joined forces with the aim of establishing a common research strategy for new directions in the field of low-temperature plasma physics. Leading research groups at the Ernst- Moritz-Arndt-Universität Greifswald and the Christian-Albrechts-Universität zu Kiel, together with the Leibniz Institute for Plasma Science and Technology (INP) in Greifswald and the Max-Planck-Institut für Plasmaphysik (IPP), Greifswald branch, provided their expertise in plasma kinetics and dynamics, reactive plasmas as well as plasma theory. Physical plasmas, of course, are characterized by complex processes from microscopic to macroscopic scale in space and time. The considered plasma systems were thermodynamically open systems and, as a rule, in a non-equilibrium state. Therefore, the CRC-24 focused on low-temperature plasmas that become complex either by embedded microscopic, electrically charged, solid particles, which form a strongly-coupled subsystem, or by the presence of negative ions as well as reactive atoms and molecules interacting with surfaces. The core activities in these subfields initially defined two project areas, A: Dynamics and Order Phenomena and B: Reactivity and Surface Processes. The research activities included systematic investigations of the following fundamental aspects: (1) Forces, confinement, order phenomena and collective processes in dusty plasmas including three-dimensional (3D) particle ensembles in plasma confinement, waves, self-organization and plasma stability, and the ordering and dynamic behavior in the presence of wake fields, shielding and magnetic fields. (2) Chemical and physical processes of ions, atoms and molecules in the plasma and the interaction of the plasma with particles and solid surfaces with the focus on the dynamics of multi-component plasmas and plasma-surface interaction involving the plasma sheath dynamics, the build-up of surface charges at internal and external boundaries, the emission of secondary species, and the influence of negative ions and metastables on discharge operation modes. (3) Formation and properties of nanoparticles in plasmas with the focus on reactive processes in molecular plasmas and at surfaces leading to the synthesis of nano-sized particles, surface modification and deposition of functional thin films and nano-composites. The research activities of CRC-24 projects involved close cooperation between experiment, simulation and theory. The diagnostics of all relevant plasma species, such as atomic and molecular radicals, negative ions or metastable excited particles as well as particles in the mesoscopic range between nanometers and micrometers have been realized by application of innovative measurement methods including mass spectrometry, Gaussian beam microwave interferometry, various modern laser spectroscopic techniques, laser photo detachment, ellipsometry, and surface sensitive techniques with evanescent waves, x-ray diffraction or atomic force microscopy. On the macroscopic scale, where phenomena such as plasma crystallization, pattern formation, phase transition have been studied, novel diagnostic techniques were included such as high-speed video microscopy, stereoscopic imaging and digital holography for tracing particles in dusty plasmas. For investigations of waves and turbulence, Doppler-free spectroscopy for visualizing the ion motion was applied. The complexity of the various processes and different scales required the well-coordinated use and development of analytical methods and computational techniques. The applied methods included discharge modeling by fluid and particle-in-cell (PIC) approaches, fluid-kinetic description for reaction kinetics and electron energy distributions, stability analysis, ab-initio modeling of strongly coupled systems with molecular dynamics (MD) and Monte-Carlo (MC) techniques, and multi-scale simulations for plasma-surface interactions. During the CRC-24 funding 60 PhD students have completed their doctoral degree. The scientific results of the collaborative research on complex plasmas over twelve years have been published in 585 papers in peer-reviewed journals, including the topical issue “Fundamentals of Complex Plasmas” in European Physics Journal D 72(2018)5 with scientific results of the last funding period. Furthermore, results of the CRC-24 projects have been presented on important national and international plasma conferences including 28 invited plenary lectures.

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