Materials Science and Engineering Seminar Series: Mark E. Koepke
Friday, February 25, 2011
1:00 p.m.-2:00 p.m.
Room 2108, Chemical and Nuclear Engineering Bldg.
Modulation of Wave-Mode Dynamics in Neon Glow Discharge Plasma
Mark E. Koepke
Robert C. Byrd Professor of Physics
West Virginia University
Modulation is observed in the dynamics associated with the interaction between a spatiotemporal oscillator (at frequency ω0) and a spatiotemporal driving force (at frequency ωi). The spatiotemporal oscillator is a p neon-ionization wave of a neon glow discharge plasma tube. The driving-force dynamics is either spatiotemporal, from another p neon-ionization wave, or temporal, from chopped neon-resonant laser light. The mode-amplitude normalization of the driving force term in the periodic-pulling equations is evident during the dynamics modulation, as validated by experimental observations.
Specifically, two ionization wave modes in a driven neon glow discharge alternate as the dominant mode as their response to the driving force alternates between spatiotemporal and temporal periodic pulling. This phenomenon is termed dynamics modulation [1, 2]. Dynamics modulation is reproduced experimentally in a neon glow discharge plasma. The system is periodically driven near a non dominant mode using a narrow band ring dye laser tuned to a wavelength near the metastable neon transition at 588.35 nm. A spatially fixed photodiode with a narrow band filter that selectively passes the primary neon spectral line at 640 nm is used to acquire the time series of luminosity oscillations. These experimental data are used to verify the proposed mechanism of dynamics modulation in a periodically driven neon glow discharge plasma and explore the resulting implications for spontaneous unidirectional mode transitions that occur with a change in discharge current.
 M. E. Koepke, K. D. Weltmann, and C. A. Selcher, Bull. Am. Phys. Soc. 40, 1716 (1995).
 K. D. Weltmann, M. E. Koepke, and C. A. Selcher, Phys. Rev. E 62, 2773, (2000).