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8Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2016
EXPERIMENTAL STUDY OF PHASE TRANSITIONS IN THREE-DIMENSIONAL
COMPLEX PLASMA
V.I. Molotkov, A.M. Lipaev, V.N. Naumkin, D.I. Zhukhovitskii, A.D. Usachev,
H.M. Thomas*, S.A. Khrapak*
Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russia,
e-mail: molotkov@ihed.ras.ru *Forschungsgruppe Komplexe Plasmen, DLR, Oberpfaffenhofen, Germany, e-mail: Hubertus.Thomas@dlr.de
Complex (dusty) plasmas are composed of weakly ionized gas and charged microparticles and represent the plasma state of soft matter. The investigations which are not available on ground have been performed onboard the International Space Station (ISS) with the help of the "Plasma Crystal-3 Plus" (PK-3 Plus) laboratory. A number of interesting phenomena has been observed. The phase transition from isotropic plasma into electrorheological plasma (string fluid plasma) was initiated. The formation of such string fluids, or general electrorheological plasmas, is possible due to the manipulation of the interaction potential between the microparticles along the field line. It can be changed from an isotropic screened Coulomb to an asymmetric attractive potential through accelerating ions by the ac voltages at frequencies above the dust plasma frequency applied to the electrodes.
The crystal-liquid phase transition was obtained in large 3D isotropic dusty plasma. These phase changes are driven by manipulating the neutral gas pressure. Detailed analysis of complex plasma structural properties allows us to quantify the extent of ordering and accurately determine the phase state of the system. It is observed that the system of charged particles can exhibit melting upon increasing the gas pressure.
The slow compression of the dust particle subsystem has been investigated. We performed experiments to demonstrate a change of the structural properties of the dusty plasma system due to a change of the particle charge. There have been used two-species complex plasmas with one species composed of small (1.55 p,m) and the other composed of big (14.9 p,m) particles. The bigger particles can be added to the system. This effectively increases the strength of the confinement and compresses the small particle system. Fig.1 demonstrates a change of the pair correlation function for the initial dusty plasma system (only small particles are present) and for the compressed system (with an addition of bigger particles that increases a confinement of the small particles system). This demonstrates the phase transition for the compressed system.
The authors gratefully acknowledge the support from the Russian Science Foundation, Grant No. 14-12-01235 and the support from DLR/BMWi (Grants No. 50WM0203 and 50WM1203).
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Fig.1: Change of pair correlation function due to compression by bigger particles
