Complex (dusty) plasma research under microgravity conditions complements the research in the laboratory. Due to reduction of the main force on microparticles in the lab — gravity — it is possible to form complex plasmas in the bulk region of plasmas in homogeneous large 3D systems and to investigate other phenomena than those accessible on Earth in detail. Therefore, PK-3 Plus was operated as a long-term microgravity facility from 2006 to 2013 on the International Space Station ISS. It was perfectly suited for the formation of large stable liquid and crystalline systems and provided interesting insights into processes like crystallisation and melting, laning and phase separation in binary mixtures, electrorheological effects due to ac electric fields and projectile interaction with a strongly coupled complex plasma cloud.
International collaboration on complex plasmas was established in 2007. Since then, the Japanese science team joined microgravity experiments using PK-3 Plus on the International Space Station (ISS). Our main objective is to investigate the critical phenomena of charged systems. Operational conditions, based on the original theory and ground-based experiments, were proposed to the international science team. As a result, we successfully obtained opportunities of microgravity experiments. The operation on the ISS was terminated in 2013. The Japanese team continued analyzing the data to summarize the microgravity experiments by the end of March, 2014. A new apparatus PK-4 has already installed on the ISS and the operation begins. We are now seeking new objectives suitable for PK-4.
In this study, we investigate the deformation of the levitated droplet using a YAG pulsed laser and the possibility of the measurement of its thermo-physical properties. The sample was levitated by using an electrostatic levitator (ESL). The behavior of levitated droplet was observed by high-speed camera that has been installed on the side of ESL chamber. A hole on the droplet was provided by the laser radiation pressure. During the relaxation of deformation, a small liquid drop (satellite) jumped out from the levitated sample. The size of satellite drop depends on the power of the YAG-laser. Weber number was estimated when the satellite droplet was formed. The Weber number at satellite formation was similar to the experiment on the International Space Station.