Equilibration and Correlations in Strongly-Coupled Plasmas

William Marsh Rice University, Houston TX

Investigators

Abstract

Ultracold neutral plasmas provide an ideal environment in which to study fundamental processes such as the establishment of spatial correlations, phase transitions, heat transport, and non-equilibrium dynamics. In ultracold plasmas the relevant time scales are long, powerful optical diagnostics exist, and initial density profiles, energies, and ionization states are accurately known and controllable. All of which make it possible to study phenomena that are difficult to access in other experiments. This proposal centers around two diagnostics that are relatively straightforward but can be applied to ultracold neutral plasmas to study equilibration and correlations in unique ways. Fluorescence imaging will provide a spatially-resolved light-scattering spectrum that is Doppler broadened and shifted due to ion velocity. With proper choice of the excitation and detection geometry, ion velocity due to plasma expansion will be distinguishable from thermal ion velocity, which has not been possible before and is crucial for studying equilibration and thermal transport at later times after photoionization. Small-angle light scattering is a well established technique to study spatial correlations in liquids. Typically this is done with x-rays when the particle spacing is on the order of angstroms. But in ultracold neutral plasmas, the spacing is on the order of microns, allowing use of visible light that is resonant with the principle ion transition and takes advantage of the enormous resonant scattering cross-section. The angular dependence of forward scattered light will provide the static structure factor of the ions and a measurement of spatial correlations. This proposal will have impact well beyond the field of ultracold neutral plasmas because of the connection to fast-pulse laser plasmas, and it will also foster substantial training and outreach efforts. graduate students working in the research group leverage Rice's geographical location and educational philosophy to contribute greatly to diversity in science. Support of undergraduate researchers, especially from historically under-represented groups, is also a priority. An optics summer school at Rice for REU students is being developed. There are also research opportunities for gifted high school students in a local school district.