The use of ultraviolet Thomson scattering as a versatile diagnostic for detailed measurements of a collisional laser produced plasma
Collective Thomson scattering from ion-acoustic waves at 266nm is used to obtain spatially resolved, two-dimensional electron density, sound speed, and radial drift profiles of a collisional laser plasma. An ultraviolet diagnostic wavelength minimizes the complicating effects of inverse bremsstrahlung and refractive turning in the coronal region of interest, where the electron densities approach n{sub c}/10. Laser plasmas of this type are important because they model some of the aspects of the plasmas found in high-gain laser-fusion pellets irradiated by long pulse widths, where the laser light is absorbed mostly in the corona. The experimental results and LASNEX simulations agree within a percent standard deviation of 40% for the electron density and 50% for the sound speed and radial drift velocity. Thus it is shown that the hydrodynamics equations with classical coefficients and the numerical approximations in LASNEX are valid models of laser-heated, highly collisional plasmas. The versatility of Thomson scattering is expanded upon by extending existing theory with a Fokker-Planck based model to include plasmas that are characterized by (0 {le} k{sub ia}{lambda}{sub ii} {le} {infinity}) and ZT{sub e}/T{sub i}, where k{sub ia} is the ion-acoustic wave number, {lambda}{sub ii} is the ion-ion mean free path, Z is the ionization state of the plasma, and T{sub e}, T{sub i} are the electron and ion temperatures in electron volts (eV), respectively. The model is valid for plasmas in which the electrons are approximately collisionless (k{sub ia}{lambda}{sub ei}k{sub ia}{lambda}{sub ee} {ge} 1), and quasineutrality holds, ({alpha} {much_gt} 1), where {alpha} = 1/k{lambda}{sub DE} and {lambda}{sub DE} is the electron Debye length. This newly developed model predicts the lineshape of the ion-acoustic Thompson spectra and when fit to experimental data provides a direct measurement of the relative thermal flow velocity between the electrons and ions.
- Research Organization:
- California Univ., Davis, CA (United States)
- OSTI ID:
- 136321
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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