Experimental studies of strongly-coupled dusty plasmas
Abstract
Experiments were conducted in the new cross-disciplinary field of strongly-coupled dusty plasmas. These plasmas, which consist of small particles embedded in the sheath of a radio-frequency discharge plasma, facilitate the study of non-equilibrium phase transitions. The particles are highly charged due to collection of electrons and ions in the plasma and confined by the strong electric fields in the sheath. Under the influence of their mutual repulsion and the surrounding plasma, the particles form highly ordered, quasi-two-dimensional structures, which are frequently called "plasma crystals". The non-equilibrium phase transitions were induced by changing external experimental parameters, in this case, the neutral gas pressure. From a detailed static structural analysis, it was found that the melting of the plasma crystal was correlated with a proliferation of topological lattice defects. Translational and orientational correlation functions were also computed. While the correlation function results agree well with the predictions of a 2D, second order melting theory, an analysis of the defects contradicts certain assumptions underlying the theory. The kinetic temperature of the particles was measured during another melting experiment, and found to be much higher than that of the neutral gas, to which the particles were collisionally coupled. A simple model is presented to explain this phenomenon. The model is used along with an experiment to show that electrostatic fluctuations present in the plasma above the particle layer could not be responsible for heating the particles. Finally, a new technique for characterizing the particle interaction potential directly from observed particle dynamics is presented. The mean-square displacement of the particles is measured as a function of time which, in turn, yields the lattice Einstein frequency. By assuming that the interaction potential is Yukawa in form, the particle charge is determined. Along with a separate measurement of the particle kinetic energy, the Coulomb coupling parameter is found during a melting transition.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 2000
- Bibcode:
- 2000PhDT........16Q