ISSN:
1432-0630
Keywords:
Laser diagnostics
;
Rayleigh scattering
;
Sound
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Abstract The scattering mechanisms possible in weakly ionized plasmas are reviewed. The different cases can be discerned by means of the magnitude of three characteristic parameters: 2π/ωτ c being the ratio of scattering time and mean free collision time, y=1/kλ c being the scattering parameter defined as the ratio of scattering length and mean free collision path, and χω/c s, T 2 being the ratio between the product of thermometric conductivity and scattering frequency to the square of the adiabatic or isothermal sound velocity. For $${{2\pi } \mathord{\left/ {\vphantom {{2\pi } {\omega \tau _c〈〈 1}}} \right. \kern-\nulldelimiterspace} {\omega \tau _c〈〈 1}}$$ quantum mechanical formulae have to be used, whereas in the opposite case classical treatments are applicable. The classical methods are Boltzmann equation formalisms ify≪1, and fluid dynamics ify≫1. In the fluid dynamical case there appear two waves for low frequencies, $${{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-\nulldelimiterspace} {c_{s, T}^2 }}〈〈 1$$ , an adiabatic one which can propagate with weak damping and an isobaric one which cannot propagate, both wave types yielding together three scattered lines. In the opposite case of high frequencies, $${{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-\nulldelimiterspace} {c_{s, T}^2 }} 〉 〉 1$$ , the scattering behavior is different from ordinary hydrodynamics. Here also do exist two types of waves, isochoric and isothermal, but none of them can propagate. Since the intensity of the scattered isochoric wave can be neglected, there is only one scattered line. Local temperatures and particle densities can be determined from the scattered spectrum. On the other hand, transport coefficients like shear and bulk viscosity as well as thermometric conductivity can be derived from sound absorption or Rayleigh scattering experiments if an independent temperature measurement is performed at the same time. The general formalism is applied to a weakly ionized hydrogen arc plasma.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00898369
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