Science Seminars

3/18/2010 – Complex Plasmas – From the Laboratory to Experiments on the International Space Station

Speaker: U. Konopka Max-Planck-Institut f”ur extraterrestrische Physik, Giessenbachstrasse, 85740 Garching, Germany
Date: Thursday, Mar 18, 2010
Time: 4:00 PM
Location: Duane D-142

Seminar Abstract:

Dusty plasmas, or often called ”complex plasmas” have been studied for decades mainly related to plasma processing or astrophysical environments. 1994 an unfamiliar, ordered state of micro particles in a low temperature plasma environment, the so called ”plasma crystal” was discovered. As a result, the investigation of dusty plasmas was strongly intensified. The behavior of the charged particles within any kind of plasma environment, like low temperature rf, dc or atmospheric pressure plasma is now looked at. Especially the collective effects of larger particle systems with millions of fine particles, distributed isotropically in three dimensions gained much interest. Investigations include the study of wave phenomena, instabilities, particle flows, crystal structures as well as phase transitions, to name a few examples. All those phenomena can be studied, due to the nature of the complex plasmas, on the fundamental kinetic scale of individual particles. Compared to colloidal systems, which have a similar nature, complex plasmas cover also the hole dynamic range from over-damped to undamped system, what makes them unique. A significant knowledge in various research fields might be gained as a result of the interdisciplinarity of complex plasmas experiments. However, due to anisotropic forces acting on the negatively charged fine particles under earthbound conditions, it is difficult to establish an isotropic three dimensional system in the laboratory. In general, the fine particles are confined within the plasma volume due to strong electric fields that push the particles towards the plasma bulk out of the plasma sheath region. In balance with the ”strong” gravitational force, large particles tend to settle close to a lower sheath boundary, leading to vertically compressed particle clouds. For particles in the tens of micro meter range gravity can lead to a complete collapse of the particle cloud towards a mono-layer system, which of course is also of fundamental interest and thus studied extensively too. But, to study isotropic homogeneous fine particle plasmas, it is necessary either to use small sub-micro meter particles, which have the disadvantage that in general conditions their dynamic is over-damped, or to avoid the gravitational influence by performing experiments in microgravity environments, as are supported for example by drop tower experiments, parabolic flights or on the International Space Station (ISS). In the course of the talk, I will show examples of earth bound complex plasma experiments as well as some that were performed in parabolic flights or the Space Station experiments PKE-Nefedov or its successor PK-3Plus, that is operational since 2006.