Astrophysically Relevant Experiments on Radiation Transfer through Plasmas with Large Velocity Gradients

Details Astrophysically Relevant Experiments on Radiation Transfer through Plasmas with Large Velocity Gradients Astrophysically Relevant Experiments on Radiation Transfer through Plasmas with Large Velocity Gradients

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aps..dpp4ifa06w&link_type=abstract

American Physical Society, Division of Plasma Physics Meeting, November 10-15, 1996, abstract #4IFA.06

Physics

Plasma Physics

Scientific paper

The transfer of radiation through plasmas with large velocity gradients is of relevance to several astrophysical situations, such as supernovae explosions, maser operation, and stellar winds. In dimensionless units, similar conditions often prevail in laser-produced plasmas, with velocity gradients of order 10^9s-1 significantly altering the effective optical depth and line shape. Some of the simplest cases to study experimentally are the hydrogenic resonance lines. We have used a novel double-crystal high-resolution high-dispersion x-ray spectrometer to study the shape and intensity of the Lyman-alpha transition of hydrogenic aluminum in both planar and cylindrical geometry laser-plasma experiments.(This work has been performed in collaboration with Pravesh Patel of the University of Oxford, Steven Rose and Abdeslem Djaoui of the Rutherford Appleton Laboratory, Oldrich Renner of the Czech Institute of Physics, and Allan Hauer of Los Alamos National Laboratory.) The observed line shape and intensity agree well with detailed modelling. The experiment is modelled using a one-dimensional Lagrangian hydrocode, incorporating average-atom non-LTE atomic physics. The opacity effects on the ion populations are treated within the escape factor approximation, taking into account the effects of the velocity gradient. The hydrocode gives time and space-dependent values of the electron and ion densities, excited state fractions, electron and ion temperatures, and velocities. The hydrodynamic output is post-processed with a radiative transfer routine to construct the simulated line shape. Details of the experiments and results will be presented, and relevance to the astrophysical situations discussed.

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