What is Complex Plasma?

Plasma, the fourth state of matter, is consisted of neutrals, ions (positively charged) and electrons (negatively charged). The neutrals and the ions are relatively bigger and heavier. So they tend to be less mobile. On the other hand, the electrons are relatively smaller and lighter. So they tend to be highly mobile. If we introduce dust particles (directly or chemically with the use of reactive gases) into plasma, the electrons will interact and charge up the dust particle. The dust will then levitate above a confinement electrode due to the balance of electric force and gravitational force. This is the story of the making of complex plasma.

Different people use different names for complex plasma, such as dusty plasma, plasma crystals, colloidal crystals, fine particle plasma, coulomb crystal, etc.
Because the dust particle are highly negatively charged, their presence will dramatically change the properties of the plasma. So complex plasma give us a unique opportunity to study strongly coupled system.

Moreover, unlike classical plasma system where we consider the charge to be constant on each particle, the charge of the dust particles in complex plasma system varies with time and position. And so complex plasma opens up an unexplored and facinating field in plasma physics.

Fig.1 - Complex Plasma (or Dusty Plasma) is compromised of dust particles submerged in plasma.

We can easily illuminate the particles in complex plasma with a laser and visualize the individual particle motions. Moreover the characteristic frequency of the particles with the plasma is low. So complex plasma is a useful model for us to study solid state physics and to understand the relationship between the plasma and solid in slow motion.