Turbulence with chaotic signatures in a collisional plasma.
Item
-
Title
-
Turbulence with chaotic signatures in a collisional plasma.
-
Identifier
-
AAI9417444
-
identifier
-
9417444
-
Creator
-
Castellanos, Angel.
-
Contributor
-
Adviser: Joseph Johnson, III
-
Date
-
1994
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Physics, Fluid and Plasma | Physics, Electricity and Magnetism | Engineering, Electronics and Electrical
-
Abstract
-
Turbulence and Chaos are investigated in a collisional plasma generated in a glow discharge tube with argon at medium pressures (1-1000 mTorr). The dynamics are studied via measurements on both ion density fluctuations (IDF) and neutral light emission fluctuations (NLEF). The principal diagnostic tools are: a discharge tube 2.5 cm in diameter, an array of three Langmuir probes, a thermal probe, neutral optical emissions and digital spectral analysis. The relationship between the standard turbulent and chaotic parameters as found in ion density fluctuations and the corresponding parameters in the collision induced emission fluctuations from neutrals is determined. Using standard turbulent and chaotic analytical procedures, the influence of the gas pressure, the temperature and the discharge current on the fluctuations is established. The pressure, the temperature and the current are found to be control parameters of the system. A critical pressure {dollar}p\sb{lcub}c{rcub} \approx 200{dollar} mTorr divides the behavior of the system into turbulent and quasiperiodic states. For {dollar}p\sb{lcub}c{rcub} < 200{dollar} mTorr the system exhibits chaotic behavior; otherwise the behavior is quasiperiodic. Increases in the temperature and in the current are found to drive the system into chaos. The different routes to chaos are discussed. Turbulent parameters such as the spectral index and correlation times are calculated. Fluctuation power spectra of both IDF and NLEF exhibit the same dominant modes and both signals have the power-law dependence on frequency of the form {dollar}P\propto\omega\sp{lcub}-n{rcub};{dollar} values of the spectral index n are compared with predicted values. Cross-correlation profiles between IDF and NLEF show that these fluctuations are correlated, indicating energy transfer from ions to neutrals via ion-neutral collisions and charge transfer interactions. From three-dimensional amplitude spectra surfaces the evolution and direction of energy flow in the fluctuations are observed. Phase space reconstruction and correlation dimension calculations show the system evolving from limit cycles with dimension one to strange attractors with fractal dimensions larger than two. The calculation of positive Lyapunov exponents with values greater than zero indicates that the chaotic behavior is governed by strange attractors. A simple two-dimensional model for quasiperiodic behavior is formulated and found to be in agreement with the experimental results. Correlation dimension analysis of our data requires that a dynamical model for the chaotic state be at least three-dimensional. The effect of chaotic and periodic fluctuations on the optical radiation from neutrals is investigated and compared with relevant theories of radiation. Measurements on neutral line emission profiles from the plasma under the influence of periodic and quasi-periodic fluctuations show that frequency shifts and excitation of satellites on the line profile are due to the Stark effect. Emissions under low frequency chaotic fluctuations exhibit typical normal pressure broadened profiles.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
