High Resolution Measurement and Modeling of Ion Dynamics in an Ultracold Neutral Plasma
Author
McQuillen, Patrick Clark
Date
2015-04-22Advisor
Killian, Thomas C
Degree
Doctor of Philosophy
Abstract
Using high-resolution laser-induced fluorescence spectroscopy, ion dynamics in
an expanding ultracold neutral plasma (UNP) have been studied in unprecedented
detail. The evolution of the ion temperature is of great interest because the ions in
an ultracold neutral plasma are strongly coupled, meaning their Coulomb interaction
energy exceeds the thermal energy. This leads to novel plasma properties that are
hard to describe theoretically. Understanding all the factors that contribute to ion
temperature evolution is critical for designing schemes to cool the ions and achieve
even stronger Coulomb coupling.
This work has also observed several phenomena that have not previously been
studied in ultracold plasmas. Ion adiabatic cooling has been observed in a UNP for
the first time, resulting in ion temperatures as low as 100mK and up to a tripling of
the Coulomb coupling parameter. The importance of electron-ion energy transfer is
demonstrated with the first observations of electron-ion collisional heating. Inclusion
of this effect into existing numerical models provides better agreement with experimental
results. Results of molecular dynamics simulations of equilibrating plasmas
have been compared to early time experimental data, which provides a new method
of density determination that is much less sensitive to experimental systematics and
is accurate to within 10%. This improved certainty in the density allows accurate
comparison between data and a theoretical model of the plasma dynamics. The
agreement is excellent, but on a hydrodynamic time scale a small amount of extra
heat (on order of 100mK), not ascribable to electron-ion collisions or other sources in
the model, is detected in the ion component. Potential sources are discussed within
as well as proposals for further studies and improvements.
Keyword
ultracold plasma; neutral plasma; ion temperature; numeric modeling