Dual, orthogonal, backlit pinhole radiography in OMEGA experiments

Backlit pinhole radiography used with ungated film as a detector creates x-ray radiographs with increased resolution and contrast. Current hydrodynamics experiments on the OMEGA Laser use a three-dimensional sinusoidal pattern as a seed perturbation for the study of instabilities. The structure of this perturbation makes it highly desirable to obtain two simultaneous orthogonal backlighting views. We accomplished this using two backlit pinholes each mounted 12 mm from the target. The pinholes, of varying size and shape, were centered on 5 mm square foils of 50 m thick Ta. The backlighting is by K-alpha emission from a 500 m square Ti or Sc foil mounted 500 m from the Ta on a plastic substrate. Four laser beams overfill the metal foil, so that the expanding plastic provides radial tamping of the expanding metal plasma. The resulting x-rays pass through the target onto ungated direct exposure film DEF . Interference between the two views is reduced by using a nose cone in front of the DEF, typically with a 9 mm Ta aperture and with magnets to deflect electrons. Comparison of varying types of pinholes and film exposures will be presented from recent experiments as well as an analysis of the background noise created using this experimental technique. © 2006 American Institute of Physics. DOI: 10.1063/1.2351870