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PV: Plenarvorträge

PV IX

PV IX: Plenarvortrag

Mittwoch, 20. März 2002, 19:00–20:00, HZO 30

Complex Plasmas - The way from the laboratory to space — •Uwe Konopka et al. — Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany

Microspheres that are injected into a plasma charge up due to the impact of electrons and ions on their surface. The particles interact with each other mainly via a screened electrostatic repulsion leading to local homogeneous distributions of charged microspheres. When the particle density is high enough the plasma behavior is strongly changing. The system is then called complex plasma. Low frequency perturbations, waves, instabilities, regular and even crystalline structure formation of the microspheres can arise. These effects have been studied already in many ground-based experiments since the plasma crystal has been discovered in 1994. The main advantage of the complex plasma systems is that the dynamic behavior of the large particle systems can be studied easily on their fundamental scale, the motion of individual particles, by recording the scattering of laser light with commercial camera systems.
Taking into account the electrostatic interaction only, the negatively charged particles should be confined where the plasma potential in the used plasma vessel has its maximum - the center of the plasma for typical setups. Under earth bound laboratory condition this ideal situation cannot be reached, since the gravitational force push the particle cloud towards the lower electrode/wall so that the complex plasma can only exists in the sheath regions close to the lower electrode/wall. In addition, the structure of the confined particles is vertically compressed. Thus, only 2- and 2 1/2-dimensional systems can be studied in these situations. To overcome anisotropy and to be able to get large homogeneous 3-dimensional complex plasmas, a program for experiments under microgravity conditions was established shortly after the plasma crystal discovery.
First microgravity experiments have been performed during parabolic flights, where about 20..25 seconds of microgravity can be reached for each parabolic maneuver. These experiment together with tests during flights on TEXUS-rockets were performed as a preparation for a long term complex plasma experiment on the international space station (ISS). This experiment, the PKE-Nefedov that is supported by DLR and perfomed in a collaboration with Russia, was launched in the beginning of 2001 as the first physical experiment on the ISS. During the experiment time many new phenomena like vortex flows, shear motion, coalescence of plasma clouds and coagulation of particles in a complex plasma have been observed.
To keep continuity in the field of complex plasma under optimal conditions, the microgravity program that is leaded by MPE is extended to the development of an international microgravity plasma facility (IMPF). This platform, supported by DLR and ESA, hopefully will be operational in about 2005 and lead to a better insight in many parts of physics.