Minimize ISS: Plasma Kristall

ISS Utilization: Plasma Kristall (PK) the longest-running Space Station experiment

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July 2021: As Europe celebrates 20 years of ESA astronauts on the International Space Station, a Russian-European experiment has been running quietly in the weightless research centre for just as long: the Plasma Kristall (PK) suite of investigations into fundamental science. 1) 2)

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Figure 1: Plasma Kristall parts on the International Space Station (image credit: ESA/NASA–T. Pesquet)

Plasma Kristall takes a plasma and injects fine dust particles in weightlessness, turning the dust into highly charged particles that interact with each other, bouncing off each other as their charge causes the particles to attract or repel. Under the right conditions, the dust particles can arrange themselves over time to form organized structures, or plasma crystals.

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Figure 2: Roscosmos cosmonaut Oleg Novitsky working on the Plasma Kristall-4 experiment in Europe's Columbus laboratory on the International Space Station, 18 June 2021 (image credit: ESA/NASA–T. Pesquet)

These interactions and forming of three-dimensional structures resemble the workings of our world on the atomic scale, a world so small that we cannot see move even with an electron microscope. Add a laser to the mix and the dust particles can be seen and recorded for observation by scientists on Earth for a sneak peak of the world beyond our eyes.

These surrogate atoms are a way for researchers to simulate how materials form on an atomic scale, and to test and visualize theories. The experiment cannot be run on Earth because gravity only makes sagging, flattened recreations possible; if you want to see how a crystal is constituted you need to remove the force pulling downwards – gravity.

Figure 3: Visualizing the laws of physics. Shear flow motion in a complex plasma fluid in weightlessness on the International Space Station. This image is part of the Plasma Kristall-4 (PK-4) experiment. PK-4 is an ISS experiment that injects microscopic dust particles into a neon or argon tube to act as atom substitutes. As they float in the charged gas, they will collect negative charges as positive ions accumulate around them. As a result, they will start to repulse each other – just like atoms do in a fluid state. Particle flow is induced through the radiation pressure from a laser beam aimed at the central part of the particle cloud. This manipulation causes the proxy atoms to interact strongly, leading sometimes to melting. The particles in PK-4 are made of plastic. A plasma is an electrically charged gas, a bit like lightning, that rarely occurs on Earth. It is considered to be the fourth state of matter, distinct from gas, liquid and solid matter (image credit: DLR)

On 3 March 2001, “PK-3 Plus” was turned on in the Zvezda module, the first physical experiment to run on the Space Station. Led by the German Aerospace Center DLR and the Russian space agency Roscosmos, the experiment was a success and later followed up by a fourth version, installed in 2014 in ESA’s Columbus laboratory, this time as an ESA-Roscosmos collaboration.

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Figure 4: Sergei Krikalev with the PKE-Nefedov experiment (PK-3) during Expedition 1 mission on the ISS in 2001 (image credit: RSC Energia)

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Figure 5: Roscosmos cosmonaut Elena Serove installing the Plasma Kristall-4 experiment in Europe's Columbus laboratory on the International Space Station in 2014 (image credit: ESA/NASA–T. Pesquet)


Planet conceptions

By changing the parameters in PK-4, such as adjusting voltage or using larger dust particles, the atom doppelgangers can simulate different interactions. Complex phenomena such as phase transitions, for example from gas to liquid, microscopic motions, the onset of turbulence and shear forces are well known in physics, but not fully understood at the atomic level.

Using PK-4, researchers across the world can follow how an object melts, how waves spread in fluids and how currents change at the atomic level.

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Figure 6: A plasma is an electrically charged (‘ionized’) gas. It is considered to be the fourth state of matter, distinct from gas, liquid and solid matter. The image shows the parabolic flight setup of PK-4 used as a test model for the ISS. The plasma (orange glow) is created in a U-shaped glass tube with an electric field. The microparticles trapped in the chamber are illuminated by a green laser light allowing the observation of the motion of the particles. PK-4 will inject microscopic dust particles into a neon and argon tube to act as atom substitutes. As they float in the charged gas, they will collect negative charges as positive ions accumulate around them. As a result, they will start to repulse each other – just like atoms do in a fluid state. Doing this research on Earth is not possible – the dust particles would fall with gravity and the simulated atoms would not behave realistically. This experiment is making the atomic scale visible for analysis and will help scientists to understand the interactions of atoms (image credit: Michael Kretschmer)

Using PK-4, researchers across the world can follow how an object melts, how waves spread in fluids and how currents change at the atomic level.

Around 100 papers have been published based on the Plasma Kristall experiments and the knowledge gained is helping understand how planets form too. At its origin our planet Earth was probably two dust particles that met in space and grew and grew into our world. PK-4 can model these origin moments as they are during the conception of planets.

The huge amount of data that PK-4 creates is so vast it cannot be downloaded through the Space Station’s communication network, so hard disks are physically shipped to space and back with terabytes of information. The experiment is run from Toulouse, France, at the CNES space agency operating centre Cadmos.

Astrid Orr, ESA’s physical sciences coordinator notes “PK-4 is a great example of fundamental science done on the Space Station; through international collaboration and long-term investment we are learning more about the world around us, on the minute scale as well as on the cosmic scale.

“The knowledge from the PK experiments can be directly applied to research on fusion physics – where dust needs to be removed – and the processing of electronic chips, for example in plasma processes in the semiconductor and solar cell industry. In addition, the miniaturization of the technology required when developing Plasma Kristal is already being applied in plasma-based medical equipment for hospitals.

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Figure 7: The CADMOS control centre during the 12th campaign of the PK-4 experiment. CADMOS Human Spaceflight Department of France's space agency (CNES) and one of Europe's User Support Operations Centers that control and monitor experiments and hardware on the ISS (image credit: CNES)

Plasma care

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Figure 8: The plasma care® uses a unique technology to produce cold atmospheric plasma, the so-called Surface Micro-Discharge (SMD) technology. Battery-driven and easy to use, it has the size and weight of an old telephone handset (photo credit: terraplasma medical)

When cosmonaut Sergei Krikalev took the first plasma chamber onto the International Space Station (ISS) in 2001, to investigate complex dusty plasma crystals, nobody imagined that this would one day help the struggle against multi-drug resistant organisms.

Krikalev's experiments on the ISS were conducted under the guidance of Professor Gregor Morfill from the Max-Planck-Institute for Extraterrestrial Physics (MPE) in Garching, Germany. Morfill took advantage of weightlessness in orbit to study the complex plasmas, which on Earth would have been rather difficult because gravity causes the plasma crystals to be flat.

The initial 2001 tests were followed by a long series of experiments on the ISS, with the most recent fourth version of the experiment still working on the space station.

This makes the plasma study experiment the longest-running in space and it also provided the impetus to develop cold plasma technology.

Plasma is usually a hot, electrically charged gas but MPE developed a method for generating ‘cold plasmas’ at room temperature.


Some background on international cooperation in space

The PK-4 plasma crystal laboratory is a European-Russian collaboration between the European Space Agency (ESA) and the Russian space agency, Roskosmos , with scientific leadership from the DLR Research Group Complex Plasmas at the DLR Institute of Materials Physics in Space (formerly at the Max Planck Institute for Extraterrestrial Physics, MPE) and the Russian Academy of Sciences Joint Institute for High Temperatures (JIHT). The experimental hardware was developed in-house by the group during their time at MPE, and by OHB System AG (formerly Kayser-Threde GmbH). PK-4 is funded by ESA and Roscosmos. Additional funding for the project in Germany was provided by the The German Space Agency at DLR and the Max Planck Society. 3)

One of the most frequently-used physics laboratories on the International Space Station recently completed its final set of experiments. The Plasma Kristall Experiment (PK-3 Plus) lab, a Russian-German cooperation in operation since January 2006, has provided new insight into an unusual type of matter called plasma crystals. Though the experiment runs came to a close on June 14, the research continues to open an exciting world of potential technological spin-offs in medicine, agriculture and general science. 4)

The unique environment of microgravity allows physicists to study how these crystals form inside dusty plasmas — a type of matter with unique properties found everywhere — in ways not possible on Earth.



1) ”From atoms to planets, the longest-running Space Station experiment,” ESA Science & Exploration, 02 July 2021, URL:https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration
/Research/From_atoms_to_planets_the_longest-running_Space_Station_experiment

2) ”Twenty years of plasma research on board the ISS,” DLR, 3 March 2021, URL: https://www.dlr.de/content/en/articles/news/2021/01/
20210303_twenty-years-of-plasma-research-on-board-the-iss.html

3) ”Plasma crystal research on the ISS,” DLR News, 11 November 2019, URL: https://www.dlr.de/content/en/articles/news/2019/04/20191108_plasma-crystal-research-on-the-iss.html

4) ”Space Station Illuminates Dusty Plasmas For A Wide Range of Research,” NASA News, 10 July 2013, URL: https://www.nasa.gov/content/
space-station-illuminates-dusty-plasmas-for-a-wide-range-of-research/stationresearch/



The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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