Date of Award

2012

Document Type

Honors Thesis (Open Access)

Department

Colby College. Physics and Astronomy Dept.

Advisor(s)

Duncan A. Tate

Abstract

The project was started with an objective to investigate the effect of radio fre- quency absorption in Ultra Cold Neutral Plasmas (UNPs). The plasma oscillation is density dependent and can be excited by using external radio frequency field. A homodyne circuit is used to detect direct absorption of the radio frequency waves. The radio frequency waves are applied to conducting meshes which lie on either side of the plasma. The meshes are effectively a capacitor, which together with inherent circuit resistance constitute a high pass filter. A small part of the gain and phase shift of the filter depend on the presence of the plasma. The gain change and phase change of the initial radio frequency signal by the high pass filter is observed using a digital oscilloscope. The gain change and the phase change signal can be used to identify the resonance point in the ultra cold neutral plasma. The resonant frequency is related to plasma expansion velocity, plasma temperature and plasma density. Therefore, by identifying resonant frequency various plasma parameters can be determined. The results of the experiment were used to identify various modes of plasma oscillations. Due to the limitation of time, only qualitative data analysis was performed. The results are in good qualitative agreement with the theory as well as previous exper- iments. The data obtained from this project as well as the understanding acquired here can be used in future experiments. In the future, a comprehensive quantita- tive analysis of the results is necessary to verify the underlying theories as well as accurately determine various plasma parameters.

Keywords

plasma, UNP

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