Diagnosing direct-drive, shock-heated, and compressed plastic planar foils with noncollective spectrally resolved x-ray scattering

The electron temperature (T(e)) and average ionization (Z) of nearly Fermi-degenerate, direct-drive, shock-heated, and compressed plastic planar foils were investigated using noncollective spectrally resolved x-ray scattering on the OMEGA Laser System [T. R. Boehly , Opt. Commun. 133, 495 (1997)]. Plastic (CH) and Br-doped CH foils were driven with six beams, having an overlapped intensity of similar to 1x10(14) W/cm(2) and generating similar to 15 Mbar pressure in the foil. The plasma conditions of the foil predicted with a one-dimensional (1-D) hydrodynamics code are T(e)similar to 10 eV, Z similar to 1, mass density rho similar to 4 g/cm(3), and electron density n(e)similar to 3x10(23) cm(-3). The uniformly compressed portion of the target was probed with 9.0-keV x rays from a Zn He(alpha) backlighter created with 18 additional tightly focused beams. The x rays scattered at either 90 degrees or 120 degrees were dispersed with a Bragg crystal spectrometer and recorded with an x-ray framing camera. An examination of the scattered x-ray spectra reveals that an upper limit of Z similar to 2 and T(e)=20 eV are inferred from the spectral line shapes of the elastic Rayleigh and inelastic Compton components. Low average ionizations (i.e., Z < 2) cannot be accurately diagnosed in this experiment due to the difficulties in distinguishing delocalized valence and free electrons. Trace amounts of Br in the CH foil (i.e., 2% atomic concentration) are shown to increase the sensitivity of the noncollective, spectrally resolved x-ray scattering to changes in the average ionization. The experimentally inferred electron temperatures are comparable to the 1-D predictions. (c) 2007 American Institute of Physics.