Turbulent magnetized plasmas from ionizing shock waves.
Item
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Title
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Turbulent magnetized plasmas from ionizing shock waves.
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Identifier
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AAI9224832
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identifier
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9224832
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Creator
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Liang, Zuohua.
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Contributor
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Adviser: Joseph A. Johnson, III
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Fluid and Plasma
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Abstract
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Turbulent argon plasmas produced behind hypersonic shock waves (10 {dollar}<{dollar} M {dollar}<{dollar} 60) are studied in the presence of weak magnetic fields at various strengths between 0 and 600 gauss, parallel and antiparallel to the shock tube's axis. The experiment is performed in a cylindrical arc discharge shock tube of 5 cm diameter and 210 cm overall length. Laser induced fluorescence and an electric probe are used as diagnostics of the ion density. Turbulent fluctuations behind the shock front are observed which persist for a time in the order of 10 {dollar}\mu{dollar}s. Using standard turbulent and chaotic analytical procedures, the influence of the magnetic field on the characterizing parameters is determined under circumstances of changing Mach number and pressure. These parameters include spectral index, correlation time scales, turbulent intensity and chaotic dimensionality. The parameters of turbulence obtained from the two diagnostics are quite consistent. Fluctuation power spectra follow a P {dollar}\sim{dollar} f{dollar}\sp{lcub}\rm -n{rcub}{dollar} behavior with 1.3 {dollar}<{dollar} n {dollar}<{dollar} 2.8; this agrees with theoretical predictions as well as the results of other investigators. An increasing magnetic field increases the characterizing correlation time, the turbulent intensity, and the chaotic dimension but decreases the small correlation time. Therefore the magnetic field decreases the order (increases the dimensionality) in the turbulent plasma, independent of the direction of the field parallel or antiparallel to the direction of the shock wave. A turbulent velocity-field-coupling model is proposed. A dispersion relation shows that, in the presence of an external magnetic field, varieties of new modes in a turbulent plasma are generated. The model predicts an increasing complexity of the turbulent system with increasing strength of the field and is in very good qualitative agreement with our experiment results.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
