Microplasmas

A microplasma is made by first applying electromagnetic fields to confine the ions to a specified region of space. A technique called laser cooling can then cool the trapped ions to temperatures of less than a hundredth of a kelvin. Because microplasmas can be built up practically one ion at a time, they provide an excellent opportunity to explore mesoscopic systems, that is, collections of ions too small to behave like a familiar, macroscopic system and yet too complex to be identified with the behavior of a single ion. Furthermore, microplasmas can serve as models for the dense plasmas in stellar objects. Like the atoms in liquids, the ions in some cold microplasmas can diffuse through a somewhat ordered state. In other cases, the ions can resemble the atoms in solids, diffusing very slowly through a crystal lattice. Yet the nature of microplasmas is quite different from that of conventional liquids and solids. Whereas common liquids and solids have densities of about 1023 atoms per cubic centimeter, microplasmas have concentrations of about 108 ions per cubic centimeter. Consequently, the average distance that separates ions in a microplasma is about 100,000 times greater than the distance between atoms in common liquids or solids. Furthermore, whereas internal attractive forces between the atoms hold a conventional liquid or solid together, external electric and magnetic fields hold the trapped ion microplasmas together. Indeed, the ions, which all have the same charge, actually repel each other and tend to disperse the microplasma