Dusty plasma

A complex or dusty plasma consists of a physical plasma in which additionally are particles in the size to about 100 microns. These microparticles, due to their small size, often referred to as dust shall be taken by the ions and electrons of the plasma and charge accordingly to the physical conditions in the plasma electrically on. In space under UV irradiation as electrons are removed by the photoelectric effect of the dust particles, the dust loads positively on. In the laboratory outweighs another effect: Since the electrons in a plasma is usually a much larger thermal velocity own than the ions, these often meet with the dust particles, so that their (negative ) charge - depending on the size of the particles - between a few and several thousand electron charges is.

As in a normal plasma, this charge will be the mobile charge carriers in the plasma, so that ions and electrons shielded. Are the dust particles at a sufficiently high density close to each other enough, they still feel the charges of other particles and begin to interact with each other. The complex plasma may then, depending on choice of plasma parameters that occur in the gaseous, liquid or solid state (plasma crystal), as well as in intermediate states. It is present in various states of aggregation.

In the study of complex plasmas in the laboratory is of unique advantage that you can make the dust particles individually visualized by illumination with a laser and observation with a camera. The movement of the microparticles can be individually monitored and analyzed. Basic processes, such as phase transitions and wave propagation, can such quasi with the naked eye, at the kinetic, ie the fundamental level, are made visible, which at the atomic level is hardly possible with real crystals. From the trajectories and the known mass of the microparticles can be closed directly to the active forces.

On Earth, the dust particles are in the electric field of the plasma boundary layer kept suspended ( levitated ), as they would otherwise fall to the bottom of the plasma chamber under the action of gravity. An exception is nanometer-sized particles, in which case the influence of gravity compared with other forces is low. Despite the levitation form on the earth usually only a few layers of dust systems. Therefore, experiments are often under microgravity, such as parabolic flights or on the International Space Station, carried out. Thus, the plasma crystal experiment ' PKE- Nefedov ' MPE Garching, 2001 was the first physical experiment on the ISS at all.

On the dust particles act in various plasma powers. In addition to the gravity and the electric or magnetic forces, the dust particles to be taken, for example, from the neutral gas particles. The ions exert a significant force on the dust particles. The friction with the electrons can usually be neglected in contrast. Additionally can be applied to the dust particles with a strong laser force. Another role played by the thermophoretic force, the microparticles to the colder side drives in the presence of a temperature gradient. In order to study the weak forces on the particles better, experiments are also helpful in microgravity.

Complex plasmas exist in nature in many circumstances, they play a role in the Earth's atmosphere, the rings of Saturn and the tail of comets among others. Especially in space are many types of dusty plasmas, since 99 % of the matter present as a plasma, which often comes in contact with the interstellar and interplanetary dust rare. Thus, the study of complex plasmas in the laboratory provides important information, such as arise from a dust and gas disk around a young star planet.

Not always dust is desired in the plasma. In the manufacture of microchips, for example, destruction of the sensitive structures. On the ( disturbing ) effects of dust in the planned ITER fusion reactor is currently being discussed. Also are often undesirable (eg soot ) particles in hot combustion gases. Methods, inter alia, were developed with the study of complex plasmas, can help here.

• Plasma Physics