Void Closure in Complex Plasmas under Microgravity Conditions

Abstract

We describe the first observation of a void closure in complex plasma experiments under microgravity conditions performed with the Plasma-Kristall (PKE-Nefedov) facility on board the International Space Station. The void--a grain-free region in the central part of the discharge where the complex plasma is generated--has been formed under most of the plasma conditions and thought to be an inevitable effect. However, we demonstrate in this Letter that an appropriate tune of the discharge parameters allows the void to close. This experimental achievement along with its theoretical interpretation opens new perspectives in engineering new experiments with large quasi-isotropic void-free complex plasma clouds in microgravity conditions.

Successive Generations of Dust in Complex Plasmas: A Cyclic Phenomenon in the Void Region

“…They are experimentally observed in various dusty plasmas both under microgravity conditions or in the laboratory. They have been observed in sputtering discharges [19,[22][23][24][25] or with calibrated injected dust particles [26,27]. In reactive plasmas, dust voids have not really been observed until now.…”

Complex Plasma Research under Microgravity Conditions: PK‐3 Plus Laboratory on the International Space Station

“…This is very important for many dedicated experiments. With the PK-3 Plus setup three ways of void closure have been detected: by adjusting lowest rf-power (like in the PKE-Nefedov laboratory [4]), by using a symmetrical gas flow, and by low frequency electric excitation [8]. The latter can be used additionally to initiate a phase transition from an isotropic fluid into a so-called electrorheological string fluid.…”

“…The first laboratory, PKE-Nefedov, has already provided great insight into the behavior of complex plasma under microgravity conditions [3][4][5][6]. Fundamental investigations, like the formation of a particle free void in the center of the microparticle cloud induced by the ion drag force underestimated by the state of the art theory, which has been improved by the adaption to the new experimental results [7], or the first observation of bcc structures in plasma crystals [3] are only a few of the interesting results obtained there.…”

Non-equilibrium phase transitions in complex plasma

“…Particles 'inside' ('outside') R are pushed away from (pulled toward) the center. This results in a dust free region at the center of the discharge chamber, the so-called 'void' [37][38][39].…”