EXPERIMENT RECORD N° 9452
PK-4 Plasma Kristall
  1. 2014 • ISS Increments 41-42
  2. 2015 • ISS Increments 43-44
  3. 2015 • ISS Increments 45-46
  4. 2016 • ISS Increments 47-48
  5. 2016 • ISS Increments 49-50
  6. 2017 • ISS Increments 51-52
  7. 2018 • ISS "Horizons" - long-duration mission
  8. 2018 • ISS Increments 55-56
  9. 2018 • ISS Increments 57-58
  10. 2019 • ISS Increments 59-60
  11. 2019 • ISS Increments 61-62
  12. 2020 • ISS Increments 63-64
Physical Sciences:
  • Complex plasmas
  • Plasma physics
EPM (European Physiology module)
O. Havnes (1), J. Goree (2), G. Morfill (3), M. Thoma (4), V. Molotkov (5), A. Usachev (5), S. Ratynskaia (6), L. Boufendi (7), U. de Angelis (8), D. Samsonov (12), G. Kroesen (9), E. Thomas (10), H. Thomas (11), A. Lipaev (5), U. Konopka (10), M. Pustylnik (11), V. Fortov (5), A. Ivlev (12), S. Khrapak (3), M. Kretschmer (3), S. Mitic (3), O. Petrov (5), O. Vaulina (12), A. Zobnin (5), E. Lisin (12), M. Vasiliev (12), M. Myasnikov (12), X. Koss (12), V. Naumkin (12), M. Rosenberg (12), V. Yaroshenko (3), V. Nosenko (3), T. Antonova (12), M. Fink (12), M. Rubin-Zuzic (12), L. Couedel (12), J. Williams (12), R. Merlino (12), P. Tolias (12), Z. Donko (12), P. Hartmann (12), K. Takahashi (13), H. Totsuji (13), O. Ishihara (13), T. Mieno (13), N. Sato (13), S. Adachi (13), M. Takayanagi (13), Y. Hayashi (13)
(1)  
University of Tromsø
Institute for Physics and Technology
Nordlysobservatoriet
9037 Tromsø
NORWAY
(2)  
The University of Iowa
Department of Physics & Astronomy
512, Van Allen Hall
IA 52242 Iowa City
USA
Tel:  
+1.319.335.1843
Fax:  
+1.319.335.1753
e-mail:  
john-goree@uiowa.edu
(3)  
Max-Planck-Institut für extraterrestrische Physik - MPE
Gießenbachstr.
85748 Garching
GERMANY
Tel:  
+49(0)89.30000.3567
Fax:  
+49(0)89.30000.3399
e-mail:  
gem@mpe.mpg.de
(4)  
Justus-Liebig-Universität Gießen
I. Physikalisches Institut
Heinrich-Buff-Ring 16
35392 Gießen
GERMANY
Tel:  
+49(0)641.99.33110
Fax:  
+49(0)641.99.33109
e-mail:  
Markus.H.Thoma@exp1.physik.uni-giessen.de
(5)  
Joint Institute for High Temperatures
Russian Academy of Sciences - JIHT RAS
Izhorskaya 13/19
125412 Moscow
RUSSIA
Tel:  
+7.495.484.2455
Fax:  
+7.495.485.8055
e-mail:  
molotkov@ihed.ras.ru
lipaev@ihed.ras.ru
usachev@ihed.ras.ru
(6)  
School of Electrical Engineering, Space & Plasma Physics
Royal Institute of Technology - KTH
Teknikringen 31
10044 Stockholm
SWEDEN
Tel:  
+46(0)8.7909121
Fax:  
+46(0)8.24.54.31
e-mail:  
srat@kth.se
(7)  
Universite d´Orleans
GREMI
14, Rue d´Issoudun BP 6744
45067 Orleans Cedex 2
FRANCE
Tel:  
+33(0)2.38.49.48.73
Fax:  
+33(0)2.38.41.71.54
e-mail:  
laifa.boufendi@univ-orleans.fr
(8)  
University of Napoli - Federico II
Istituto Nazionale di Fisica Nucleare - INFN
Department of Physical Sciences
Complesso Univ. di Monte Sant´Angelo
via Cinthia
ITALY
Tel:  
+39(0)81.6.76.800
e-mail:  
Umberto.Deangelis@na.infn.it
(9)  
Eindhoven University of Technology
Department of Applied Physics
P.O Box 513
5600 MB Eindhoven
THE NETHERLANDS
Tel:  
+31(0)40.247.43.57
e-mail:  
g.m.w.kroesen@tue.nl
(10)  
Auburn University
Plasma Sciences Laboratory
Physics Department
Allison Lab 206
Auburn
Alabama 36849-5311
USA
Tel:  
+1(0)334.844.4126
e-mail:  
etjr@physics.auburn.edu
uzk0003@auburn.edu
(11)  
Deutsches Zentrum für Luft- und Raumfahrt e.V.
Forschungsgruppe Komplexe Plasmen
Oberpfaffenhofen
Postfach 11 16
82230 Weßling
GERMANY
Tel:  
+49(0)8153.28.0
Fax:  
+49(0)8153.28.2243
e-mail:  
hubertus.thomas@dlr.de
Mikhail.Pustylnik@dlr.de
(12)  
TBD
NIUE
(13)  
Kyoto I. T.
JAPAN
BACKGROUND
Plasma accounts for over 99% of visible material in space.
Plasmas are ionized gases produced by high temperatures, like in the sun, or by electric fields, i.e., low temperature discharge plasmas like in neon tubes. In the latter case the degree of ionization is small and a large amount of neutral gas is present.

Complex or dusty plasmas are plasmas which contain beside electrons, ions, and neutral gas in addition micro-particles, e.g., dust grains. Due to the high mobility of the electrons (compared to the ions) in low temperature discharge plasmas the micro-particles collect a large number of electrons on their surface.
For a particle with a diameter of a few microns this charge can be of the order of 10.000 electron charges. Therefore the micro-particles interact strongly with each other, and complex plasmas are an example for strongly coupled plasma in which the interaction energy between the plasma particles (or at least of one component) is larger than the kinetic energy of the particles. Such plasmas became of great scientific interest during the last years.

Due to the strong influence of gravity on the micro-particles, most experiments on complex plasmas are strongly distorted or even impossible on Earth and require microgravity conditions
as this avoids particle sedimentation.

PK-4 is an experiment for investigating complex plasmas. PK-4 generates complex plasma crystals in a glass tube filled with an inert gas. It is hoped that the data derived from various experiments will provide new insights into the physics of condensed materials (for which complex plasmas are used as models in crystallization), various astrophysical questions (such as the agglomeration of dust in the genesis of planets) and future applications in semiconductor technology and medicine.
 
Since 1998 prolonged experiments with complex plasmas have taken place in space, first, aboard the Russian Space Station MIR (PK-1, PK-2). The complex plasma experiments on the MIR Space Station were part of the Russian program. Then, later, plasma experiments were performed on the International Space Station (ISS: PKE 3 "Nefedov" and PK-3 Plus). Starting with the installation of PKE 3 "Nefedov" on the ISS in 2001 the project became a German-Russian collaboration. An upgraded version of this experiment "PK-3 Plus" was operating on-board the ISS .

PK-4 is a successor of the PK-3 "Nefedov" and "PK-3 Plus" space experiments.

A short history of PK
In 2002 the PK-4 project started as a collaboration between MPE (PI/Coordinator Prof. G. Morfill) and JIHT (formerly IHED, PI/Coordinator Prof. V. Fortov). The breadboard development for PK-4 has been performed in the period 2002 – 2006 by MPE and JIHT under financial support from the DLR and the Max-Planck Society. The two laboratory setups at MPE and at JIHT were developed at that time, and finally a PK-4 setup to be used for short microgravity experiments during parabolic flights was established, which has been successfully tested during 7 parabolic flight campaigns.

The PK-4 project benefits from the leading role of the two institutes MPE and JIHT in defining the scientific objectives and requirements and in the development and utilization of the experiment facility.

ESA initiated the Phase A/B project for PK-4 in January 2006 as a response to several scientific proposals submitted to the Announcement of Opportunity issued in 1999, 2000 and 2004 by ESA’s Directorate of Human Spaceflight for research in physical sciences using the ISS .

PK-4 entered the Phase C with ESA in September 2008.

SCIENTIFIC OBJECTIVES
PK-4 is not an apparatus dedicated for specific experiments but rather a laboratory which shall offer the possibility to perform a large variety of experiments with complex plasmas and to react to new developments in this field in a manner as flexible as possible.

The main interest lies in the investigation of the liquid phase and flow phenomena of complex plasmas for which PK-4 is especially suited thanks to a DC-discharge and its geometry (elongated glass tube with a large observational access).

The experiments for PK-4 can be divided into research in
three classes of fundamental questions:

1. Microscopic properties of complex plasmas
This category comprises the charging of the particles, the external forces on the particles (e.g. ion drag), the fundamental interactions between the particles, agglomeration, and particle growth.

2. Macroscopic properties of complex plasmas
In this category belong hydrodynamics (e.g. viscosity), thermodynamics (e.g. equation of state), and non-equilibriums aspects (e.g. lane formation, self-organisation) of complex plasmas.

3. Generic properties of classical many-body systems
Complex plasmas are ideal model systems for studying various problems of strongly coupled many-body systems in solid state physics, fluid physics, plasma physics, nano-technology and even nuclear physics because complex plasmas can easily be produced and observed in real time on the microscopic and kinetic level. Hence dynamical processes can be investigated on the level of single particles which is not possible in most systems.
Therefore new insights in the dynamics of those processes can be provided. Typical examples are crystallization and melting, phonons in plasma crystals, dust waves, Mach cones, nozzles, turbulence, and nano-fluidics.


RELATED RESEARCH :
57
th ESA Parabolic Flight Campaign - 2012
Complex Plasma Experiments with PK-4

53rd ESA Parabolic Flight Campaign 2010
Plasma crystal experiment on ISS: Test of the PK-4 experiment facility
 
14th DLR PFC - 2009
Tests of the PK-4 Experiment on Board the ISS

13
th DLR PFC - 2009
Complex plasma in microgravity - the next generation

49th ESA Parabolic Flight Campaign 2008
Test of PK-4 for ISS
 
11th DLR PFC - 2007
Tests of the PK-4 Experiment on Board the ISS

45th ESA Parabolic Flight Campain 2006
Plasma crystal experiment on ISS: test of the PK-4 experiment facility
 
ISS 12S (Soyuz TMA-8) + Increment 13 2006
ISS "Astrolab" Long Duration Mission 2006
Plasma crystal research on the ISS (PK-3 Plus)


41st ESA Parabolic Flight Campaign 2005
Preliminary tests of the PK-4 experiment on board of the ISS

39th ESA Parabolic Flight Campaign 2005
PK-3 Plus - The Successor experiment to PKE-NEFEDOV on the ISS
 
36th ESA Parabolic Flight Campaign 2004
Plasma crystal experiment on ISS: test of the PK3-Plus experiment facility

Plasma crystal experiment on ISS: test of the PK4 experiment facility

35th ESA Parabolic Flight Campaign 2003
PS-35/3(Plasma Crystal: PK3 Plus) and PS-35/4 (Plasma Crystal: PK4) 
 
31
st ESA Parabolic Flight Campaign 2001
Preliminary Tests for the International Mirogravity Plasma Facility
 
ISS 3S (Soyuz TM-33) French "Andromede" Mission 2001
PKE-Nefedov extended research programme Growth of particles under microgravity conditions 
 
29th ESA Parabolic Flight Campaign 2000
Preliminary tests for the International Microgravity Plasma Facility-IMPF 

Note: Prof. Ove Havnes and Prof. Gregor Morfill are retired.

The PK-4 plasma crystal laboratory was launched from Baikonur cosmodrome on 29 October 2014 on board of Progress 57P. It was installed into the European Physiology Module (EPM) and went into operation in space for the first time in December 2014. In June 2015 first reference experiments were conducted, seeing the begin of scientific operation. Research work with the PK-4 will be spread over at least four years starting in autumn 2015.

EXPERIMENT FACILITY
The PK-4 experiment facility on the ISS shall consist of four basic components: experiment apparatus in a sealed container (similar as in the case of PKE-"Nefedov" and "PK-3 Plus"), Control and Video Management Unit (CVMU) unit, the external power supply, and the external gas supply. In addition a tele-science unit will be used to operate the experiment by the cosmonauts/astronauts. MPE is responsible for the development and construction of the experiment apparatus on an integrated base plate (IBP), whereas the other components are developed and constructed by industry partners, including the container. The heart of the PK-4 facility, the IBP, shall contain the following components:

1. Plasma chamber
The plasma chamber consists of a glass tube of about 35 cm length and 3 cm diameter containing ports for the DC-electrodes, up to six particle injectors, and vacuum and gas connections.

2. Vacuum pump
To evacuate the chamber and to control the working pressure a vacuum pump (turbo molecular) together with a vent-line (pre-vacuum) to open space is used.

3. Gas filling system
The gas filling system consists of gas bottles (neon, argon, argon-oxygen mixture), vacuum pipes, and valves. The gas system is automated to deliver the user requested pressure and gas flow values, which can be varied independently. The operational pressure range is between about 5 and 250 Pa, the gas flow between 0.06 and 10 sccm.

4. Dispensers
Up to six particle injectors (dispensers) are used to inject mono-disperse microparticles with diameters in the range 1 to 20 microns. Two concepts are available based either on a mechanical shaker as used in PKE-Nefedov and PK-3 Plus or a new gas-jet dispenser.

5. DC high voltage power supply
The DC power supply provides the required voltage at the electrodes to ignite and maintain the plasma (voltage range: +/- 3 kV). The DC current in the plasma can be chosen between 0.4 and 3 mA. The DC voltage can be modulated with frequencies from 1 to 300 Hz for particle manipulation. A fast polarity switching with a frequency in the kHz range can be used to create a stable (without flow), homogeneous, and extended particle system.

6. RF-generator
The RF-generator (power: 0 - 5 W, frequency: e.g. 81.36 MHz) is used to operate the two RF-coils (one movable by motor drive) located outside of the glass tube. These coils are used to confine and manipulate the micro-particles in the chamber. Pulses of different shapes, length, and amplitudes can be produced for further manipulation of the particles, e.g. for creating shocks in a particle cloud.

7. Diagnostics
A diode laser is used for particle illumination. Ideally the laser wavelength should be in the region where the camera CCD is the most sensitive, for example 532 nm with a power up to 150 mW.
The reflected light from the particles is observed by two CCD cameras with up to 200 frames per second and a maximum resolution of about 10-15 microns. Cameras and laser are mounted on a motor-driven translation stage, which allows us to observe the particles in different locations inside of the tube. The images are processed in the CVMU and stored on hard disks similar as in PK-3 Plus. In addition, an overview camera will record the plasma glow in the plasma chamber. The plasma glow will be observed through narrow-band IF-filters centred on two Ne spectral lines and one Ar spectral line. By using this filter combination and deriving the relative line ratios it is possible to estimate the electron temperature distribution within the gas discharge plasma (including dust cloud areas). Finally, a spectrometer will analyse the light emission from the plasma.

8. Manipulation laser
The beam from a laser diode can be attached to the glass tube to accelerate the micro-particles by light pressure (in the laboratory model an infrared laser diode with a wave length of 915 nm and a maximum output power of 20 W is installed). A more efficient diode will be used on the ISS. The choice of laser wavelength is not driven by science. What is needed is a small sized laser with high efficiency and a maximum output power of 20 W.

9. Thermal manipulators
A thermal manipulator (heating wire) shall be attached to the glass tube from outside to create a temperature gradient which can be used to manipulate, e.g. to stop the microparticles, without changing the plasma parameters.

10. EM electrode
A DC electrode (wire) shall be attached to the inner wall of the glass tube, allowing a manipulation of the micro-particles, e.g. creating a nozzle for the particle flow. In the last EM-version of PK-4 the electrode has a “grid-like” design.

11. Spectrometer
A spectrometer is mounted above the particle observation cameras allowing the local measurement of spectral lines along the line of sight and in the field of view of the particle observation cameras.

All these components are used at the moment already in laboratory and parabolic flight experiments, where in the latter case the apparatus is integrated in a rack.

OPERATIONS OVERVIEW
The basic experimental protocol starts with an evacuation of the plasma chamber for several hours (a minimum of 20 hours; base pressure: <10-3 Pa) to guarantee good plasma conditions, e.g. no striations.

Then neon or argon gas is filled in with a gas flow of typically 2 sccm reaching pressures between 5 and 250 Pa.

Afterwards the plasma is ignited by the high-voltage (about 1000 V) of the DC electrodes corresponding to a DC current of the order of 1 mA and a longitudinal electric field of about 2 V/cm.

Then the micro-particles are injected. They get quickly charged in the plasma and drift from the cathode to the anode with a typical velocity between 1 and 10 cm/s.

In addition, the electric fields from the two RF coils/electrodes or the fast polarity switching can be used to manipulate the particles, e.g. to capture and confine them.

Gas flow, modulation of the DC and RF fields, the powerful manipulation laser, the thermal manipulator, and the EM electrode can also be used to manipulate the particles, e.g. to accelerate them or to introduce oscillations.

A sketch of the PK-4 experiment is shown in Figure 1. The micro-particles are made visible by illumination with a laser beam, which is widened into a sheet by a cylindrical lens. The scattered light is recorded by one or two CCD cameras (e.g. up to 200 frames per second, with a maximum resolution of about e.g.10 microns/pixel). The light emission (“plasma glow”) from the plasma will be measured using the narrow band IF-filters.

The basic measurements comprise the positions of the particles, their velocities (extracted from the track length of the particles or from their positions in consecutive images), and correlations between the particles. These quantities are determined from the images by using a dedicated IDL program or other methods for image analysis.

At the end of each experiment run the particles will be removed by gas flow before the plasma is switched off in order to avoid the contamination of the glass walls.

Basic Experiment Run
1. Evacuation of chamber to base pressure
2. Filling of chamber with gas up to the working pressure (various pressures)
3. Start glow camera & spectrometer
4. Start recording
5. Creation of DC plasma (various currents)
6. Injection of micro-particles (various sizes)
7. Cleaning of chamber by gas flow.
8. Switch off plasma
9. Stop recording
Extended Run (after step 6)
- Trapping of particles by polarity switching (PS), RF-coil (DC off) (RF), thermal manipulator (TM), or EM-electrode (EM)
- Manipulation by gas flow (GF), laser (LM), DC-modulation (DCM), movable RFcoil (MRF), RF pulses (RFP), EM-electrode (EM), or thermal manipulator (TM)
- Further injections of particles
 
OPERATIONS DETAILS

To guarantee the requested scientific performances, the level of microgravity disturbances at the level of the Plasma Chamber shall not exceed 10-3 g for frequencies between 0 Hz and 100 Hz. The experiments with PK-4 inside Columbus should be scheduled in such a way as to avoid additional g-disturbances. The micro-gravity level shall be monitored during the operation of PK-4.

The following gas/mixtures shall be considered for design:
- experiment gases: Ar, Ne
- cleaning gas: mixture of Ar (or Ne) and O2 (O2 max 24%)

The materials for the particles are:
- melamine-formaldehyde (spheres)
- silica (spheres)
For one experiment run, particles of different sizes and in a quantity of up to 10-6 particles should be used per injection.

The light source shall be a laser, with a wavelength ±150 nm with respect to the maximum sensitivity of the camera chip.

The data will be images (particle and glow observation) and house keeping files.

The number of experiment days to be performed during the lifetime of the Plasma Crystal Facility PK-4 is expected to be: 4 years operation x 4 missions per year x 3 days per mission = 48 experiment days.
Therefore, the maximum number of micro-particles to be consumed during the lifetime of PK-4 is expected to be:
50 experiment days x 100 injections per day x 106 particles per injection (max.) = 5 x 109 particles
For a detailed description of the results, please, consult the paper (which is also attached in the "Attachments" section - see below)
H.M. Thomas, M. Schwabe, M.Y. Pustylnik, C.A. Knapek, V.I. Molotkov, A.M. Lipaev, O.F. Petrov, V.E. Fortov, S.A. Khrapak, (2019), "Complex plasma research on the International Space Station", Plasma Physics and Controlled Fusion - Special Issue Featuring the Invited Talks from the 45th EPS Conference on Plasma Physics, Prague, 2-6 July 2018611, DOI: https://doi.org/10.1088/1361-6587/aae468, pp. 014004.

[1]  
S. Ratynskaia, M. Ratynskaia, S. Khrapak, R.A. Quinn, M.H. Thoma, G.E. Morfill, A. Zobnin, A. Usachev, O. Petrov, V. Fortov, (2004), "Dust mode in collisionally dominated complex plasmas with particle drift", IEEE Transactions on Plasma Sciences, 32, pp. 613.
[2]  
S. Ratynskaia, S. Khrapak, A. Zobnin, M.H. Thoma, M. Kretschmer, A. Usachev, V. Yaroshenko, R.A. Quinn, G.E. Morfill, O. Petrov, V. Fortov, (2004), "Experimental determination of dust particle charge at elevated pressures", Physical Review Letters, 93, pp. 085001.
[3]  
A. Usachev, A. Zobnin, O. Petrov, V. Fortov, M.H. Thoma, M. Kretschmer, S. Ratynskaia, R.A. Quinn, H. Höfner, G.E. Morfill, (2004), "The project", Czech Journal of Physics, Supplement: Proceedings of 21st Symposium on Plasma Physics and Technology (Praha, Czech Republic, 14-17 June 2004), C 54, pp. 639.
[4]  
M.H. Thoma, H. Höfner, S.A. Khrapak, M. Kretschmer, R.A. Quinn, S. Ratynskaia, G.E. Morfill, A. Usachev, A. Zobnin, O. Petrov, V. Fortov, (2005), "Measurement of the ion drag force in a complex dc plasma using the PK-4 experiment", Ukrainian Journal of Physics: International Conference on Dusty Plamas in Applications (Odessa, Ukraine, 25-29 August 2004), 50, pp. 179.
[5]  
V. Yaroshenko, S. Ratynskaia, S. Khrapak, M.H. Thoma, M. Kretschmer, H. Höfner, G.E. Morfill, A. Zobnin, A. Usachev, O. Petrov, V. Fortov, (2005), "Determination of the ion drag force in a complex plasma", Physics of Plasmas, 12, 9, DOI:10.1063/1.1947027, pp. 093503.
[6]  
V. Yaroshenko, S. Ratynskaia, S. Khrapak, M.H. Thoma, M. Kretschmer, G.E. Morfill, (2005), "Measurements of the dust-ion momentum transfer frequency and ion drag force in complex plasmas", Contributions To Plasma Physics, 45, 3-4, DOI: 10.1002/ctpp.200510024, pp. 223-228.
[7]  
S. Khrapak, S. Ratynskaia, A.V. Zobnin, V.V. Yaroshenko, M.H. Thoma, M. Kretschmer, A.D. Usachev, H. Höfner, G.E. Morfill, O.F. Petrov, V.E. Fortov, (2005), "Particle charge in the bulk of gas discharges", Physical Review E, 72, 1, DOI: 10.1103/PhysRevE.72.016406, pp. 016406.
[8]  
V.E. Fortov, A.V. Ivlev, S.A. Khrapak, A.G. Khrapak, G.E. Morfill, (2005), "Complex (dusty) plasmas: Current status, open issues, perspectives", Physics Reports, 421, 1-2, DOI: 10.1016/j.physrep.2005.08.007, pp. 1-103.
[9]  
S. Khrapak, S. Ratynskaia, A. Zobnin, M. Thoma, M. Kretschmer, A. Usachev, V. Yaroshenko, R. Quinn, G.E. Morfill, O. Petrov, V. Fortov, (2005), "Measurement of dust grain charge in a weakly ionized plasma of a dc discharge", Ukrainian Journal of Physics: Contributions to the International Conference on Dusty Plamas in Applications, (Odessa, Ukraine, 25-29 August 2004), 50, pp. 151.
[10]  
V. Fortov, G.E. Morfill, O. Petrov, M. Thoma, A. Usachev, H. Höfner, A. Zobnin, M. Kretschmer, S. Ratynskaia, M. Fink, K. Tarantik, Y. Gerasimov, V. Esenkov, (2005), "The project "Plasmakristall-4" (PK-4) - a new stage in investigations of dusty plasmas under microgravity conditions: first results and future plans", Plasma Physics and Controlled Fusion: 32nd EPS Plasma Physics Conference (Tarragona, Spain, 27 June-1 July 2005), 47, pp. B537.
[11]  
M.H. Thoma, H. Höfner, M. Kretschmer, S. Ratynskaia, G.E. Morfill, A. Usachev, A. Zobnin, O. Petrov, V. Fortov, (2006), "Parabolic Flight Experiments with PK-4", Microgravity Science and Technology: ELGRA Biennial Meeting (Santorini, Greece, 21-23 September 2005), 18, pp. 47.
[12]  
M.H. Thoma, M.A. Fink, H. Höfner, M. Kretschmer, S. Khrapak, S. Ratynskaia, V. Yaroshenko, G.E. Morfill, O. Petrov, A. Usachev, A. Zobnin, V. Fortov, (2007), "PK-4: Complex Plasmas in Space - the next Generation", IEEE Transactions on Plasma Sciences: 11th Workshop on the Physics of Dusty Plasmas (Williamsburg, USA, 28 June-1 July 2006), pp. 255.
[13]  
A.V. Ivlev, V. Steinberg, R. Kompaneets, H. Höfner, I. Sidorenko, G.E. Morfill, (2007), "Non-Newtonian viscosity of complex plasma fluids", Physical Review Letters, 98, 14, DOI: 10.1103/PhysRevLett.98.145003, pp. 145003.
[14]  
S. Mitic, B.A. Klumov, U. Konopka, M.H. Thoma, G.E. Morfill, (2008), "Structural Properties of a Complex Plasma in a Homogeneous DC Discharge", Physical Review Letters, 101, 12, DOI: 10.1103/PhysRevLett.101.125002, pp. 125002.
[15]  
V. Yaroshenko, M.H. Thoma, H.M. Thomas, G.E. Morfill, (2008), "Double layer formation at the interface of complex plasmas", Physics of Plasmas, 15, 8, DOI: 10.1063/1.2966119, pp. 082104-082104-6.
[16]  
S. Mitic, R. Sütterlin, A.V. Ivlev, H. Höfner, M.H. Thoma, S. Zhdanov, G.E. Morfill, (2008), "Convective dust clouds in a complex plasma", Physical Review Letters, 101, 23, DOI: 10.1103/PhysRevLett.101.235001, pp. 235001.
[17]  
A. Usachev, A.V. Zobnin, O.F. Petrov, V.E. Fortov, B.M. Annaratone, M.H. Thoma, H. Höfner, M. Kretschmer, M. Fink, G.E. Morfill, (2009), "Formation of a Boundary-Free Dust Cluster in a Low-Pressure Gas-Discharge Plasma", Physical Review Letters, 102, 4, DOI: 10.1103/PhysRevLett.102.045001, pp. 045001.
[18]  
A.V. Zobnin, (2009), "A Nonlocal Model of Spatially Nonuniform Positive Column of DC Discharge", High Temperature, 47, 6, DOI: 10.1134/S0018151X09060017, pp. 769-776.
[19]  
S. Zhdanov, R. Heidemann, M.H. Thoma, R. Sütterlin, H.M. Thomas, H. Höfner, K. Tarantik, G.E. Morfill, A. Usachev, O.F. Petrov, V.E. Fortov, (2010), "Dissipative Dark Solitons in DC Complex Plasmas", Europhysics Letters, 89, 2, DOI: 10.1209/0295-5075/89/25001, pp. 25001.
[20]  
U. de Angelis, G. Regnoli, S. Ratynskaia, (2010), "Long-range Attraction of Negatively Charged Dust Particles in Weakly Ionized Dense Dust Clouds", Physics of Plasmas, 17, 4, DOI: 10.1063/1.3368797, pp. 043702.
[21]  
P. Tolias, S. Ratynskaia, U. de Angelis, (2010), "Regimes for experimental tests of kinetic effects in dust acoustic waves", Physics of Plasmas, 17, pp. 103707.
[22]  
M.H. Thoma, S. Mitic, A. Usachev, B.M. Annaratone, M.A. Fink, V.E. Fortov, H. Hofner, A.V. Ivlev, B.A. Klumov, U. Konopka, M. Kretschmer, G.E. Morfill, O.F. Petrov, R. Sutterlin, S. Zhdanov, A.V. Zobnin, (2010), "Recent Complex Plasma Experiments in a DC Discharge", IEEE Transactions on Plasma Sciences: 12th Workshop on the Physics of Dusty Plasmas (Boulder, USA, 2009), 38, 4, pp. 857.
[23]  
V. Yaroshenko, M.H. Thoma, H.M. Thomas, G.E. Morfill, (2010), "Generation of a Double Layer at the interface of complex plasmas", IEEE Transactions on Plasma Sciences: 12th Workshop on the Physics of Dusty Plasmas (Boulder, USA, 2009), 38, pp. 869.
[24]  
M.A. Fink, M.H. Thoma, G.E. Morfill, (2011), "PK-4 Science Activities in Micro-gravity", Microgravity Science and Technology: ELGRA Biennial Symposium and General Assembly (Bonn, Germany, 2009), 23, pp. 169.
[25]  
P. Tolias, S. Ratynskaia, U. de Angelis, (2011), "Kinetic models of partially ionized complex plasmas in the low frequency regime", Physics of Plasmas, 18, pp. 073705.
[26]  
A.V. Ivlev, M.H. Thoma, C. Räth, G. Joyce, G.E. Morfill, (2011), "Complex plasmas in external fields: The role of non-Hamiltonian interactions", Physical Review Letters, 106, pp. 155001.
[27]  
R. Heidemann, M. Kretschmer, S.K. Zhdanov, K.R. Sütterlin, H.M. Thomas, M.H. Thoma, G.E. Morfill, (2011), "Dissipative Dark Soliton in a Complex Plasma", IEEE Transactions on Plasma Sciences, 39, pp. 2720.
[28]  
S. Mitic, M.Y. Pustylnik, G.E. Morfill, E. Kovacevic, (2011), "In-situ characterization of nanoparticles during growth by means of white light scattering", Optics Letters, 36, pp. 3699.
[29]  
L. Wörner, E. Kovacevic, J. Berndt, H.M. Thomas, M.H. Thoma, L. Boufendi, G.E. Morfill, (2012), "Formation and Transport Phenomena of Nanometre-Sized Particles in a DC Plasma", New Journal of Physics, 14, pp. 023024.
[30]  
S.A. Khrapak, P. Tolias, S. Ratynskaia, M. Chauduri, A. Zobnin, A. Usachev, C. Rau, M.H. Thoma, O. Petrov, V. Fortov, G.E. Morfill, (2012), "Grain Charging in an Intermediately Collisional Plasma", Europhysics Letters, 97, 3, doi:10.1209/0295-5075/97/35001, pp. 35001.
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M.A. Fink, S.K. Zhdanov, M.H. Thoma, H. Höfner, G.E. Morfill, (2012), "Pearl-necklace-like Structures of Microparticle Strings Observed in a DC Complex Plasma", Physical Review E, 86, pp. 065401(R).
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S. Khrapak, M.H. Thoma, M. Chaudhuri, G.E. Morfill, A. Zobnin, A. Usachev, O. Petrov, V. Fortov, (2013), "Particle flows in a dc discharge in laboratory and microgravity conditions", Physical Review E, 87, pp. 063109.
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"http://www2011.mpe.mpg.de/theory/plasma-crystal/PK4/index.html", PK-4 home page by MPE.
[34]  
V.N. Naumkin, D.I. Zhukhovitskii, V.I. Molotkov, A.M. Lipaev, V.E. Fortov, H.M. Thomas, P. Huber, G.E. Morfill, (2016), "Density distribution of a dust cloud in three-dimensional complex plasmas", Physical Review E, 94, 3, DOI: https://doi.org/10.1103/PhysRevE.94.033204, pp. 033204.
[35]  
V.N. Naumkin, A.M. Lipaev, V.I. Molotkov, D.I. Zhukhovitskii, A.D. Usachev, H.M. Thomas, (2018), "Crystal-liquid phase transitions in three-dimensional complex plasma under microgravity conditions", Journal of Physics: Conference Series, 946, 1, DOI :10.1088/1742-6596/946/1/012144, pp. 012144.
[36]  
C.A. Knapek, P. Huber, D.P. Mohr, E. Zaehringer, V.I. Molotkov, A.M. Lipaev, V.N. Naumkin, U. Konopka, H.M. Thomas, V.E. Fortov, (2018), "Ekoplasma - Experiments with grid electrodes in microgravity", AIP Conference Proceedings, 1925, 1, DOI: https://doi.org/10.1063/1.5020392, pp. 020004.
[37]  
H.M. Thomas, M. Schwabe, M.Y. Pustylnik, C.A. Knapek, V.I. Molotkov, A.M. Lipaev, O.F. Petrov, V.E. Fortov, S.A. Khrapak, (2019), "Complex plasma research on the International Space Station", Plasma Physics and Controlled Fusion - Special Issue Featuring the Invited Talks from the 45th EPS Conference on Plasma Physics, Prague, 2-6 July 2018, 61, 1, DOI: https://doi.org/10.1088/1361-6587/aae468, pp. 014004.
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Components of the PK-4 plasma crystal laboratory prior to transportation to the International Space Station: experiment unit, rack drawers for electricity supplies, communications and data collection (courtesy: OHB System AG)

Figure 1: Sketch of the PK-4 experiment.

DLR website with further information on PK-4 in German language. http://www.dlr.de/dlr/desktopdefault.aspx/tabid-10337/1345_read-10069/#/gallery/14683

Russian cosmonaut is conducting the first reference experiments with PK-4 inside the European Columbus module of the ISS. Padalka is observing the first, perfectly captured particles on the laptop monitor (left). credits: ESA/Roscosmos

Plasma is an electrically neutral gas made up of charged particles. If particles that are electrically charged are present in the plasma, plasma crystals and complex plasmas can arise. Only in microgravity does it become visible how the charged particles behave and influence one another. This image shows complex plasma in an orderly and fluid state - as the plasma particles propagate freely in the test chamber. They arrange themselves in a three-dimensional lattice structure. credits: DLR (CC-BY 3.0)

For the scientific commissioning of the PK-4 laboratory on the International Space Station (ISS), initial tests were carried out. This image shows a test with plasma crystals in the fluid phase (see previous image of the lattice structure). Influenced by a powerful laser beam, the charged particles at the centre move in the direction of the laser. As they interact with their neighbouring particles, a shear flow is created. credits: DLR (CC-BY 3.0)

How atoms interact and behave is common high-school knowledge, but what we know is based on assumptions or snapshots. Electron microscopes have taken images of atoms so we know how they settle, but we have never recorded atoms moving. The ESA-Roscosmos Plasma Kristall-4 (PK-4) experiment is recreating atomic interactions in a fluid on a larger scale on the International Space Station. The proxy atoms in PK-4 are microparticles, which are suspended and charged in plasma (an ionised gas with electrons and ions). The microparticles interact with each other via the high electrical charges, forming a strongly coupled liquid or solid – a classical model system for condensed matter. This image shows the typical purple glow of an argon plasma in the PK-4 hardware on Earth. Microparticles are introduced into the plasma to observe how they behave. On Earth the particles are influenced by gravity but in space the particles will behave similarly to charged atoms in a fluid or crystal structure allowing researchers to understand better the hidden interactions of our world. PK-4 is installed in the European Physiology Module on the European space laboratory Columbus and runs for up to four days, four times a year.

Plasma (credit: DLR/MPE)

Roscosmos astronaut Sergei Prokopyev during the installation and commissioning of the new hardware in Europe´s Columbus laboratory on the International Space Station in July 2018. Sergei carried out the fifth campaign of Plasma Kristall-4 in November 2018. credit: ESA/Roscosmos
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DLR news article on the occasion of the first reference experiment conducted in June 2015. http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10293/427_read-13963/#/gallery/19777

project history of the PK-4 project on the DLR website (in German)

Online report from 30 November 2016 by the German Aerospace Centre on PK-4 "Plasma research on the ISS": http://www.dlr.de/dlr/presse/en/desktopdefault.aspx/tabid-10172/213_read-20253/#/gallery/25127
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H.M. Thomas, M. Schwabe, M.Y. Pustylnik, C.A. Knapek, V.I. Molotkov, A.M. Lipaev, O.F. Petrov, V.E. Fortov, S.A. Khrapak, (2019), "Complex plasma research on the International Space Station", Plasma Physics and Controlled Fusion - Special Issue Featuring the Invited Talks from the 45th EPS Conference on Plasma Physics, Prague, 2-6 July 2018, 61, 1, DOI: https://doi.org/10.1088/1361-6587/aae468, pp. 014004.

ESA webstory, dated 18 December 2018: "Fake Plastic Atoms"
 
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