Crystallization fronts in 3d complex plasmas in microgravity

Complex plasmas are low temperature plasmas with embedded microparticles. Under typical conditions, the microparticles acquire charges of some thousands of electrons. They interact with each other and can form “plasma crystals” [1]. Usually, on Earth, these crystals form above the plasma sheath, where the electric field compensates for gravity. Under these conditions, they are, however, compressed, and it is difficult to study extended 3d systems. Under microgravity conditions, the complex plasma is located in the bulk of the plasma.Then crystallization typically occurs by homogeneous nucleation [2]. Here, we present new experiments on crystallization by propagating fronts in a three-dimensional complex plasma in the PK-3 Plus laboratory on board the International Space Station.