FOR 1123:  Physics of Microplasmas

Microplasmas have gained very high attention recently. They are operated at around atmospheric pressure in small volumes with a scale length of typically 100 µm. They are thus highly collisional. 
Still, due to the confinement in narrow space, microplasmas have pronounced non-equilibrium properties with hot electrons but cold gas temperature. They are most useful for a variety of applications. Though the absolute power may be small their power density is enormous. They are characterised by high electron densities and very high electric fields close to the surface. The Debye length contracts below 1 µm, the mean free paths of species become very small and the classical separation between bulk and sheath disappears. Microplasmas can have extreme properties. 
Subject of this Research Unit is a systematic investigation of selected microdischarge configurations in order to better understand their complex dynamics from breakdown to full evolution of the discharge, understand the space- and time dependent transport of energy, radiation and reactive species, and the plasma surface interactions under these extreme conditions. Finally, we investigate prototypical applications of microplasmas. 
The key physics questions we want to address are:

1. understanding the space- and time dependent energy coupling, energy flow, radiation, transport and the reactive particle balance inside and outside of the microdischarge
2. understanding the discharge dynamics from ignition to discharge evolution during rf-phases
3. understanding what governs their stability
4. understanding and controlling plasma surface interactions of microdischarges.

Within this Research Unit we will address the following work packages:

1. investigation of the discharge breakdown and of the control and modification of plasma surface interactions with its implications on discharge properties using intense photon fields
2. diagnostics of microplasmas with cutting edge, partly unique techniques such as phase resolved optical emission spectroscopy, multi-photon laser based spectroscopy using nanosecond lasers, broadband absorption spectroscopy employing femto second lasers, Thomson scattering and CARS-type measurements and molecular beam mass spectrometry
3. modelling of microdischarges focussing on non-linear sheath phenomena and on "global" approaches as well as the treatment of the kinetics by PIC methods in very close connection to experiments
4. exploration of two selected applications of microplasmas in areas with particularly high potential based on the improved understanding of the complex discharge mechanisms.

Projects

• Spectroscopic investigations of transient processes in self-pulsing microdischarges (Applicant Schulz-von der Gathen, Volker)
• Investigation of transient phenomena in microplasmas by absorption spectroscopy and by laser-assisted "pump-probe"-experiments (Applicant Böke, Marc)
• Laser spectroscopic determination of electric fields, electron densities, and electron temperatures in atmospheric pressure microdischarges (Applicant Czarnetzki, Uwe)
• Breakdown, stability and similarity laws of microplasmas (Applicant Stefanovic, Ilija)
• Numerical simulation of microplasma jets and their interaction with surfaces (Applicant Mussenbrock, Thomas)
• Spatial and temporal structures in microplasmas (Applicant Brinkmann, Ralf-Peter)
• Reaction chemistry in reactive microplasma jets (Applicant Benedikt, Ph.D., Jan)
• Investigation of atmospheric pressure filamentary discharges and its application for film deposition on inner surface of tubes, cavities and flat surfaces (Applicant Awakowicz, Peter)
• Central tasks of the Research Unit (Applicant von Keudell, Achim)

Spokesperson

Professor Dr. Achim von Keudell
Ruhr-Universität Bochum 
Fakultät für Physik und Astronomie 
Institut für Experimentalphysik II 
Arbeitsgruppe Reaktive Plasmen
Universitätsstraße 150 
44801 Bochum 
Telephone: +49 234 3223680 
Fax: +49 234 3214171 
E-Mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Deputy spokesperson

Professor Dr. Jörg Winter

Ruhr-Universität Bochum 
Fakultät für Physik und Astronomie 
Institut für Experimentalphysik II 
Arbeitsgruppe Reaktive Plasmen
Universitätsstraße 150