Physics & Astronomy

“Ultra-cold Neutral Plasmas”

Ultra-cold neutral plasmas (UNPs) are made by photoionization of cold atoms in a magneto-optical trap (MOT). The temperature of the ions is the same as that of the parent atoms, of order 100 microKelvin, while the electron temperature can be controlled in the range 0-1000 K by the frequency of the ionization laser.

On the other hand, the plasma electron density is determined by the ionization laser intensity. In a UNP, one therefore has the possibility of approaching the strongly coupled plasma regime, where the particle electrostatic potential energies become comparable with their kinetic energies, and where ion correlation phenomena may be manifested. Furthermore, experiments can be carried out with precisely controllable initial conditions, making UNPs useful test systems for evaluation of theoretical plasma modeling techniques.

At Colby, we are interested in two kinds of experiments. First, we are investigating the possibility of cooling UNPs using Rydberg atoms, and second, we are using radio-frequency waves to study plasma oscillations in the UNP with the goal of extracting information on the plasma expansion velocity. My talk will describe our progress in both these areas.