Plasma Crystal studies on the International Space Station
Dr. Hubertus Thomas (MPE)
For more than ten years, the International Space Station has been in operation as our manned outpost in space. It is one of the largest international cooperations, led by Russia and the US. While the main political force behind it was to overcome the cold war, the ISS now provides excellent opportunities for scientists to study the influence of gravity on humans and for materials sciences. It is also the technological driver for future manned and unmanned missions to space.
Fundamental research on the ISS is carried out in various fields, from medicine to materials science. The first major scientific laboratory was commissioned in a Russian-German cooperation in 2001 by the first permanent crew in operation: the plasma crystal laboratory PKE-Nefedov. While the other ISS partners NASA, ESA and JAXA had to wait for their laboratory modules, with our Russian partners we could accommodate this experiment in the Russian part of ISS and put it into operation. A perfect deal between DLR and ROSCOSMOS made this possible for the German partners, which have only indirect access to resources on the ISS via ESA: Germany was responsible for the design, manufacture and qualification of the laboratory, while Russia took care of the transport and accommodation on the ISS, crew training, organization and execution of the experiments. Scientists from both sides, the Max Planck Institute for Extraterrestrial Physics and the Academy for High Temperatures in Moscow, benefited from this deal because the scientific results were jointly analysed and published.
The plasma crystal research, or more generally the complex plasma research is a relatively young field in existence since 1994, which has grown considerably since then. A plasma is an ionized gas, the fourth and disordered state of matter – the others being solid, liquid and gas. A plasma crystal thus is a contradiction in itself – a crystallization in a normal plasma is not possible. However, if one adds small solid particles with a size of about one thousandth mm (or “dust”) the plasma can crystallize. Due to interactions with the free electrons and ions in the plasma, the dust particles get charged with sometimes up to several thousand charges on a single particle. If there are enough charged particles in the plasma, mutual electrostatic repulsion then causes this to be arranged in regular structures. Through this self-organization the particles can then form a liquid or a solid. The special benefit for physicists: individual particles, i.e. individual "atoms" can be tracked, and dynamic processes such as melting or the motion of lattice defects can be investigated directly. This is only possible as the particles are very large and distances in the ordered structures are measured in several tenths of a millimetre – huge for atomic standards. Observation is then possible already by simple microscopy with low magnification.
Since the particles are so large and therefore heavy, gravity plays a major role in the formation of plasma crystals. In ground-based laboratories only small and basically two-dimensional crystals can be studies. Larger systems require zero gravity; the ISS therefore provides perfect conditions. Other possibilities for experiments with zero gravity are given on parabolic flights, the drop tower in Bremen or scientific rocket flights.
PKE-Nefedov was in operation on the ISS until 2005 and is their most successful and profitable experiment scientifically. Since 2006 its successor laboratory PK-3 Plus operates on the ISS, and again provides outstanding results. This will be operated until 2013, when the third generation, the laboratory PK-4, will be commissioned, this time as a cooperation between ESA and ROSCOSMOS on the Columbus module.
In the next Café & Kosmos, Dr. Hubertus Thomas will report on the plasma crystal science and of course the international space station ISS.
Please note the special date for this Cafe&Kosmos on Wednesday 21. December.
letzte Änderung 2011-11-09 durch H. Steinle