Department of Nuclear Science and Engineering (NSE) junior Victoria Winters recently won one of three Undergraduate Poster Awards at the 54th Annual Meeting of the American Physical Society's Division of Plasma Physics.
The award, given for research at the student's home institution, recognizes Winters' research at Alcator C-Mod this past year as part of the MIT Undergraduate Research Opportunities Program program. Her winning poster, titled "Exponential Spectra in Alcator C-Mod Edge Turbulence" was co-authored with Assistant Professor Anne White (of NSE and the MIT Plasma Science and Fusion Center), David Pace (General Atomics), Jim Terry, Arturo Dominguez, NSE Assistant Professor Felix Parra and Jerry Hughes (MIT Plasma Science and Fusion Center).
The research proposes that exponential power spectra seen in edge turbulence of fusion plasmas is the result of deterministic chaos, and is associated with the presence of Lorentzian pulses in the time series data. Using reflectometer and Gas Puff Imaging (GPI) data in the Alcator C-Mod tokamak, the team analyzed exponential power spectra in Ohmic and L-mode plasmas. They found that both reflectometer homodyne signals and GPI signals measuring density fluctuations just inside or at the Last Closed Flux Surface exhibit exponential power spectra. Theoretically, the characteristic slope of the data on a semi-log plot gives the full width of the underlying Lorentzian pulses. Using a separate fitting routine, individual Lorentzian pulses in the reflectometer time series data have been identified, and the widths of the Lorentzian pulses match the inverse characteristic frequency of the exponential spectra. Preliminary analysis of the waiting times and pulse amplitudes indicate these are randomly distributed, yet the pulse widths have a narrow distribution. This is consistent with the deterministic chaos model, and further work is in progress to assess the robustness of the results.
Winters was also the recipient of the department’s 2012 Outstanding UROP Award for her research on this same topic.