Observation of metallic sphere - complex plasma interactions in microgravity

The PK-3 Plus laboratory [1, 2] on board the International Space Station is used to study the interaction between metallic spheres and a complex plasma. We show that the spheres significantly affect both the local plasma environment and the microparticles. The spheres charge under the influence of the plasma and repel the microparticles, forming cavities surrounding the spheres. At intermediate distances from the sphere surface, however, the interaction between the microparticles and the spheres is attractive. The spheres affect the plasma fluxes, which can lead to the excitation of dust-acoustic waves near the spheres

Recent Results from the Plasmakristall-4 (PK-4) Microgravity Complex Plasma Laboratory

Plasmakristall-4 (PK-4) is a Joint European-Russian microgravity complex plasma facility on the International Space Station [1]. In PK-4, the experiments are performed in a polarity-switched (with the frequency of hundreds Hz) dc discharge ignited between two electrodes in an elongated glass tube. Under microgravity conditions, plastic microspheres injected into this plasma form three-dimensional ordered structures. Miroparticles in the plasma are illuminated with a laser and observed by two videocameras. PK-4 offers many possibilities to manipulate the microparticle clouds. Many manipulation methods (modulation of the dc discharge, variation of the polarity-switching parameters, etc.) are plasma-mediated. Unlike those, manipulation laser allows to exert a radiation pressure force directly on the microparticles without influencing the background plasma. Also, several plasma diagnostic instruments are included into the system: e.g., glow observation camera and spectrometer. PK-4 was commissioned in June, 2015. Since then four experimental campaigns were performed with it. In this paper, the results obtained on PK-4 will be overviewed. Such topics, as microparticle charge and ion drag measurements, electrorheology, shear flows will be discussed. References [1] M.Y. Pustylnik et.al., Rev. Sci. Instrum. 87, 093505 (201

Plasmakristall-4: New complex (dusty) plasma laboratory on board the International Space Station

New complex-plasma facility, Plasmakristall-4 (PK-4), has been recently commissioned on board the International Space Station. In complex plasmas, the subsystem of μm-sized microparticles immersed in low-pressure weakly ionized gas-discharge plasmas becomes strongly coupled due to the high (103–104 e) electric charge on the microparticle surface. The microparticle subsystem of complex plasmas is available for the observation at the kinetic level, which makes complex plasmas appropriate for particle-resolved modeling of classical condensed matter phenomena. The main purpose of PK-4 is the investigation of flowing complex plasmas. To generate plasma, PK-4 makes use of a classical dc discharge in a glass tube, whose polarity can be switched with the frequency of the order of 100 Hz. This frequency is high enough not to be felt by the relatively heavy microparticles. The duty cycle of the polarity switching can be also varied allowing to vary the drift velocity of the microparticles and (when necessary) to trap them. The facility is equipped with two videocameras and illumination laser for the microparticle imaging, kaleidoscopic plasma glow observation system and minispectrometer for plasma diagnostics and various microparticle manipulation devices (e.g., powerful manipulation laser). Scientific experiments are programmed in the form of scripts written with the help of specially developed C scripting language libraries. PK-4 is mainly operated from the ground (control center CADMOS in Toulouse, France) with the support of the space station crew. Data recorded during the experiments are later on delivered to the ground on the removable hard disk drives and distributed to participating scientists for the detailed analysis