Particles Inside the Void of a Complex Plasma

Experiments with complex (“dusty”) plasmas in microgravity often show a particle-free region in the center of the discharge, which is the so-called “void.” The cause of this unexpected feature is assumed to be the ions streaming outward from the discharge center toward the radio-frequency electrodes and walls, dragging the microparticles with them out of the center. In several experiments onboard the International Space Station, single particles moving out of the void could be traced. The obtained trajectories reveal the distribution of the forces inside the void.