Semester

Summer

Date of Graduation

2009

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Mark E. Koepke.

Abstract

In dynamics modulation, two 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 was first noted by Koepke, Weltmann, and Selcher (Bull. Am. Phys. Soc. 40, 1716 (1995)), who saw two limited but representative cases and proposed a mechanism (Phys. Rev. E 62, 2773 (2000)) by which it occurs. The intent of this dissertation is to document experimentally and test the dynamics modulation mechanism they proposed. Using a new extension of a previous mathematical treatment of periodic pulling, the resulting experimental data are used to verify the predicted mechanism. A numerical model is also presented that reproduces the signature of dynamics modulation and further supports the validity of the mechanism.;For two pairs of mode frequencies, three complete data series as driving frequency is increased are presented. Each of these data series shows the progression of the system from pure spatiotemporal behavior, through dynamics modulation, and ending at entrainment in the upper mode. Ionization wave modes are examined using time series recorded using a photodiode with a narrow band filter that selectively passes the primary neon spectral line at 640 nm. The system was periodically driven using a narrow-band ring dye laser tuned to a wavelength near the metastable neon transition at 588.35 nm. The amplitude of the driving force was decreased (increased) by tuning the laser away from (nearer to) the center of the neon line, while the driving frequency was controlled by an acousto-optic modulator chopping the laser beam at the desired frequency. Arnol'd tongue boundaries identifying the edges of frequency entrainment regions in the driving amplitude-driving frequency plane were established for four different discharge currents. The (upward) dynamics modulation behavior seen by Koepke, Weltmann, and Selcher was reproduced and additional data were acquired for two additional representative cases of downward modulations, previously undocumented. The upward modulations are used to verify the mechanism, while the downward modulations exhibit qualitatively different behavior. These differences are discussed.;Two coupled van der Pol equations were chosen to model the mechanism described by Koepke, Weltmann, and Selcher, and the resulting time series was solved with a Runge-Kutta routine whose parameters could be adjusted as the simulation proceeded. The model successfully reproduces the qualitative behavior of dynamics modulation and reinforces the experimental verification of the proposed mechanism, but lacks sufficient complexity for a complete quantitative comparison.

Download

Share

COinS