Complex plasmas in Space: Experiments on the International Space Station — V. Molotkov
29 Nov 2012
Vladimir Molotkov, Ph.D., the head of laboratory «Complex discharge plasma», Joint Institute for High Temperatures of the Russian Academy of Sciences.
Being able to observe individual microparticles and their super-slow motion may be ideal for experimental studies of the strongly and weakly correlated systems. This, in turn, could lead to a better understanding of the fundamental principles that govern critical phenomena, such as phase transitions, self-organization of condensed matter, as well as the onset of cooperative phenomena.
However, the Earth’s gravity is so strong that it forces microparticles to sediment. Therefore, one can normally create only a thin horizontal layer of particles levitating in plasma. As a result, Earth-bound experiments have naturally concentrated on 2D systems (single continuous layers that are only one microparticle thick). In the absence of gravity, however, the microparticles can occupy the whole plasma, so that it is possible to obtain experimental conditions when the system is isotropic, homogeneous, and not stressed by the pull of gravity. For the precise studies of stress-free processes occurring in large 3D systems, microgravity experiments are absolutely essential.
The first long-term investigations of complex plasmas in microgravity, onboard the International Space Station (ISS), started 11 years ago with the Russian-German bilateral project. From 2001 to 2005, the first complex plasma lab on the ISS was the Russian-German “Plasma Kristall Experiment” (“PKE-Nefedov”, named for the Russian project scientist who died just before the lab was installed on the ISS). The improved next-generation laboratory, “PK-3 Plus”, was launched in 2005 and was built on the same principles as its predecessor but with a more advanced design, better manipulation capabilities, and improved particle and plasma diagnostics.
Plasma Kristall laboratories on the ISS over the last 11 years. Russian cosmonaut Sergei Krikalev (left inset) performed experiments with PKE-Nefedov Lab in 2001 and 2005, ESA astronaut Thomas Reiter (right inset) worked with PK-3 Plus Lab during his stay in 2006.
Qualitative properties of many generic processes have no critical dependence on the particular form of the interparticle interaction. However, there are very interesting new effects that occur when the interaction becomes anisotropic or/and multiscale. Hence, to “design“ particle systems with prescribed interactions is considered the “ultimate advance“ – and with complex plasmas it can be done. Preliminary experiments to test the feasibility (in one dimension so far) have already been successfully conducted, which will lead to the next big step of research on the ISS. In a current pre-development phase we are developing a plasma laboratory (“PlasmaLab”) that can tune the interaction potential in all three dimensions. This makes it possible to create and study a wealth of new “anisotropic“ solid and liquid states – with microgravity as the essential element for its success.
In this lecture I will review the whole period of complex plasma research on the ISS, presenting different examples of experiments carried out under microgravity, and making the special emphasis on a wonderful complementarity of such research to ground-based experiments.