Measurements of electron-ion collision rates and Rydberg atom populations in ultracold plasmas by using short electric field pulses
Date
2017
Authors
Chen, Wei-Ting, author
Roberts, Jacob, advisor
Robinson, R. Steve, committee member
Harton, John, committee member
Krapf, Diego, committee member
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Abstract
Ultracold plasmas are good tools for studying fundamental plasma physics. In particular, these plasmas are well-suited to study so-called strong coupling physics the physics of plasmas where nearest-neighbor Coulomb interactions become large enough to cause spatial correlations and break assumptions. An ultracold plasma makes such a good tool because it is it is free of interactions with neutral atoms, and has a well controlled and tunable initial conditions. The UCPs in this work were created from the photoionization of cold 85Rb atoms. The experiments described in this thesis are focused on the measurements of damping of electron center-of-mass oscillations. We developed a method that uses two short electric field pulses to map the temporal profile of the oscillation amplitude. We found that the damping of such oscillations can result from dephasing which is a collisionless mechanism or from electron-ion collisions or a combination of both. Thus, we separate the study of two pulse measurements into two parts. The first part of the two short electric field pulse measurement is about the measurements and modeling of in the collisionless damping regime. The second part will focus on the regime where the damping is dominated by electron-ion collisions where we not only observed strong coupling influence on electron-ion collision rates, but also saw break down of one or more standard assumptions used in plasma physics calculations. Rydberg atoms can be formed in ultracold plasmas through three-body recombination process. Our setup was capable of measuring Rydberg atoms in a energy range above the bottleneck energy. We measured the Rydberg populations at different temperatures, and our preliminary results agree well with a parameter-free calculation. However, there are some unexplained parts of our measurements on early time Rydberg populations. This means more studies are needed in the future in order to interpret our results and make use of them. Future work includes measurements of the strong coupling influence on electron-ion collision rates in a magnetized ultracold plasma, measurement of Rydberg population below the bottleneck energy, a detailed study of evaporations in ultracold plasmas.
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Subject
plasma
three-body recombination
electron-ion collision
ultracold plasma
Rydberg atom