The use of ultraviolet Thomson scattering as a versatile diagnostic for detailed measurements of a collisional laser produced plasma

Thesis/Dissertation · Fri Jan 08 00:00:00 EST 1993

DOI:https://doi.org/10.2172/10139130· OSTI ID:10139130

Tracy, Mark David ^[1]

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1. Univ. of California, Davis, CA (United States)

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_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 ≤ k_iaλ_ii ≤ ∞) and ZT_e/T_i, where k_ia is the ion- acoustic wave number, λ_ii is the ion-ion mean free path, Z is the ionization state of the plasma, and T_e. T_i are the electron and ion temperatures in electron volts respectively. The model is valid for plasmas in which the electrons are approximately collisionless, (k_iaλ_ei, k_iaλ_ee ≥ 1), and quasineutrality holds, (α ≥1), where α = 1/kλ_DE and λ_De is the electron Debye length. This newly developed model predicts the lineshape of the ion-acoustic Thomson spectra and when fit to experimental data provides a direct measurement of the relative thermal flow velocity between the electrons and ions.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 10139130
• Report Number(s): UCRL-LR-115173; ON: DE94009273
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: 8 Jan 1993
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
74 ATOMIC AND MOLECULAR PHYSICS
LASER-PRODUCED PLASMA
PLASMA DIAGNOSTICS
ION-ION COLLISIONS
THOMSON SCATTERING
EXPERIMENTAL DATA
FOKKER-PLANCK EQUATION
ULTRAVIOLET SPECTRA
700320
664300
700380
PLASMA DIAGNOSTIC TECHNIQUES AND INSTRUMENTATION
COLLISION PHENOMENA
ELEMENTARY AND CLASSICAL PROCESSES IN PLASMAS