TR24-A2 Dynamics of magnetized complex plasmas

Project objectives

In this project the low-frequency waves and instabilities in dusty magnetized plasmas are studied. The investigations concern dispersion relations, destabilization by ion flow, formation of shocks or solitary waves, and turbulence. The wave types of primary interest are dust acoustic and dust ion-acoustic wave as well as dust dissipative and dust acoustic drift wave.

Project leader

Prof. Dr. A. Piel
Dr. Franko Greiner

Approach

The investigations are performed in three different experimental arrangements. Dust acoustic waves are studied in the MATILDA 2 device, a linear magnetized plasma with an rf-plasma source. Ion-acoustic waves are generated in the DODO double plasma device. For drift wave investigations a water-cooled magnet with a maximum field of B=0.7T and large volume (110cm long, 30cm bore) is used. This magnet can be tilted at an arbitrary angle from horizontal to vertical for changing the angle between magnetic field and gravity.


Project status

Experiment 1 The experiment DODO became operative for wave investigations in October 2005. Ion acoustic waves are generated by means of a double grid, which is symmetrically excited. The waves are detected by a plane probe in ion saturation mode, which can be positioned axially by a stepper motor. The wave signal is processsed by synchronous detection with a balanced mixer, which amplitude and phase of the signal as a function of position. In this way the real and imaginary part of the wavenumber are determined.

Experiment 2 The experiments on dust acoustic waves in Matilda2 began in December 2005. Dust acoustic waves are recorded as dust density fluctuations by means of a fast digital video camera. The dust grains with typical diameters of 1µm are illuminated by a sheat of laser light. The naturally unstable dust acoustic waves are synchronized with a superimposed sine-wave modulation of the anode voltage. This allows to operate the camera in a stroboscopic mode at the synch frequency. In this way we can study the three-dimensional shape of wave-fronts by moving the horizontal laser sheet vertically through the dust cloud

Matilda II

Experiment 3  After more than half a  year of planning and construction the christening of our new tildeable Magnet Experiment was on  August, 20  2006. It recieved the name "DUSTWHEEL",  because it is a 0.7 Tesla  resistive magnet in a wheel shaped cage and is intended to investigations of dusty magnetized plasma. DUSTWHEEL acts as the magntic field source for different plasma chambers.  The first experimental campaign started with a  circular stainless steel chamber of 1m length. Different  RF  Plasma Sources  were tested and it was shown,  that the equilibrium profile can be formed from deeply  hollow to nearly gaussian like shape with different antenna architectures. Even at very low density the plasma column shows drift wave dynamics.  To see a CCF reconstruction of  density structures, click on the figure beside.
In Summer 2007 the new plasma chamber PLEKA was taken into operation (see photo beside). It is completely made of plexiglas, i.e. video-oberservation of dust is possible at every axial position.
Compared to the drift wave dynymics in the stainless steel chamber, different drift modes are observed in PLEKA.

christening dustwheel




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