MPE: PK-3 Plus - A successful story continues

"PK-3 Plus"

A successful story continues...

The Evolution of a Project

PK-3 Plus, as its precursor PKE-Nefedov, is a joint Russian/German scientific project. The collaborating science teams are from the Russian Academy Institute for High Energy Densities in Moscow and from MPE. The scientists and engineers from both institutions have been working since 2002 on the realisation of PK-3 Plus. In December 2005 this next-generation complex plasma experiment facility was launched to the International Space Station ISS with a russian Progress cargo spacecraft. First experiments were performed in January 2006. The science model, which was tested on two parabolic flight campaigns is kept with additional diagnostics at MPE for further laboratory investigations, and for the planning and tests of the experiments on board of the ISS. At the request of ESA, the Russian/German science team agreed to make PK-3 Plus available for research to other scientists from ESA, thus providing much-needed new science impulses to the community within ESA's interim ISS utilisation programme.

PK-3 Plus is - like PKE-Nefedov (Fig. 1, click here for a hardware description) - a symmetrical driven radio-frequency plasma discharge with special features for the investigation of complex plasmas under microgravity conditions. As a second generation laboratory, PK-3 Plus provides major new possibilities for these investigations due to its design improvements relative to the first long-term experiment PKE-Nefedov. The PK-3 Plus apparatus allows investigations at neutral gas pressures (Argon and/or Neon) between 0.05 - 2.5 mbar and rf-power of 0.01 - 1 W. The complex plasma can consist of monodisperse particles in a size range from 1 - 20 μm. Up to six particle sizes can be added to the experimental volume. It is possible to change the number of particles, the composition of particles, the plasma conditions and the neutral gas pressure during one experiment. The particle cloud can be excited by an electrical low frequency signal on the electrodes (0.1 - 100 Hz at a maximum amplitude of 50 V) or by a low frequency modulation of the rf-amplitude in different wave forms (sinusoidal, square, pulse, etc.).

The Components

Fig. 2 shows a 3-D drawing of the new plasma chamber. Shown are the basic features of the new plasma chamber design: larger electrodes, dispensers included into the ground shield, a new rf-electronic box allowing many new important housekeeping and experiment measurements and the mounting of the chamber on supporting legs for highest symmetry.

Fig.1: The overall design of PK-3 Plus
is very similar to PKE Nefedov.
(Click here for detailed description.)

Fig.2: Scheme of the heart of PK-3 Plus -
the (improved) RF plasma chamber.

The apparatus is divided into two units, the experimental block and the Telescience system (TS), as is PKE-Nefedov. The experimental part is housed in a closed container with electrical and vacuum connections to the outside. It contains the experiment itself, electronics and a computer. An internal turbomolecular pump has been added to reach High Vacuum (<10^-5 mbar) in the plasma chamber. This is needed for cleaning the plasma chamber after long-term storing on the ISS and to produce very high repeatability of the experiments due to repeatable experiment parameter settings. A valve to space is used to reach the necessary prevacuum.

The TS apparatus is the control console for the cosmonaut and allows the storage of the digital and video data. Digital data are available on ground 1 day after the performance of the experiment, the analogue videos are stored on harddrives and have to be transported back via Sojus capsule or the Space Shuttle with the crew change. Quicklook videos are available right after the experimental run and will be transported via S-band and a special hardware (ROKVISS) to the DLR centre in Weilheim.

Before performing experiments in orbit the experimental parameters are tested on the science model in Munich and on the equivalent Training Model at IHED. In order to define a sequential measurement an autonomous software procedure is written and uploaded onto the ISS experiment computer. If necessary the cosmonaut can interact or control the experiment by hand via the TS apparatus.

Progress en detail

The Major differences compared to the first laboratory (PKE-Nefedov) are:

a new chamber concept avoiding a temperature gradient across the plasma chamber (thermophoresis eliminated) and therefore producing a more homogenous and symmetric complex plasma.
larger electrodes and a wider ground shield produce an enhanced homogeneity and symmetry in the plasma chamber. The vortices which always appear with the PKE-Nefedov experiment (shown here) are no longer existent.
continuous gas flow added for stable high purity gas conditions allow high rereatability of the experiments.
up to six different particle sizes (previously 2).
rf-control enhanced for investigations at very low power levels (10 mW).
new function generator with enhanced performance (larger amplitude, different wave forms).
3rd camera added to monitor the whole volume in between the electrodes.
4th camera added to monitor the glow in the whole volume in between the electrodes.
an enhanced gas regulation for fine-tuning gas pressure.
gas reservoirs of more content to be filled with Argon and probably Neon.
A more sophisticated house keeping system data on many more interesting parameters in a high speed burst mode.
A turbomolecular pump inside the container provides high vacuum conditions in the 10^-6 mbar range.
progressive scan cameras to avoid interleaved images.
digital storage of analog video signals on hard disks
modular concept for experiment electronics

Fig.3: The hardware before being encapsulated
for the space station. (Click to enlarge.)

All of this makes PK-3 Plus an ideal laboratory for investigating complex plasmas on the ground and under microgravity conditions. The science model, which will stay at MPE is fully functioning and equipped additionally with more diagnostics and other features. For example, it requires only slight changes to the plasma chamber and a temperature gradient can be established between the lower and the upper electrode allowing particle levitation of a certain size through the thermophoretic force. This opens up a broad field of interesting scientific observations.

Updated: 2006-03-20
Contact: Michael Kretschmer