More than 1000 citations for plasma crystal paper

October 26, 2012

Complex (dusty) plasmas exist in space, such as in the interstellar medium, the rings of Saturn or the dusty tail of comets. This is why scientists at the Max Planck Institute for Extraterrestrial Physics originally started to investigate complex (dusty) plasmas in the laboratory in detail – but this is not where it ended. The first paper about crystallisation in a dusty plasma has now passed the milestone of 1000 citations, impressively demonstrating how active this new field of basic physics research has become.

View of a two-dimensional plasma crystal in the MPE laboratories. Due to electrical interactions the charged micro-particles in the plasma form regular structures, such as the lattice seen here.

A plasma is the most disordered state of matter - crystals are the most ordered. Therefore it came as a major surprise when in 1994 MPE scientists discovered that under special conditions plasmas can become liquids, and may even spontaneously crystallise. These so called ‘plasma crystals’ can form when charged micro-particles are added to the plasma. Even though these particles are tiny, they are still many billion times heavier than an atom. This makes it possible to study basic physical processes with unprecedented resolution and in slow motion, as if one could see atoms individually.


Earth’s gravity allows the scientists to study complex plasmas in a thin, horizontal layer of free-floating micro-particles or in stressed 3D structures. Many basic physical processes and in particular phase transitions can thus be investigated in great detail. After the first intriguing results in the MPE labs (and more or less at the same time by groups in Taiwan and Japan), the scientists soon started to plan for plasma crystal experiments under microgravity conditions, where the system is isotropic and homogeneous. A series of experiments on the International Space Station (ISS) started in 2001, and became the most successful natural science experiment on the ISS to date.


This visualization illustrates how many scientific publications refer to the first plasma crystal paper (see text) in 1994. There are now more than 1000 citations and the research field keeps growing and diversifying.

The first observations of plasma crystals in the laboratory can be regarded as a milestone in the development of the field and the transition from dusty to complex plasma. In the 1980s only a few publications emerged with solar system or astrophysical topics. Nowadays, about 600-700 publication per year appear with a very broad interdisciplinary spectrum of topics – from plasma over fluid to solid state physics – and the first paper from 1994 is still cited.


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