Measurements of Direct-Drive Illumination Uniformity on OMEGA*

Experiments performed on the OMEGA Laser System have measured the 60-beam, direct-drive illumination uniformity. The UV illumination variations are inferred from images of x-ray emission from Au-coated spherical targets. The experiments are performed with spheres having diameters ranging from 800 to 980 microns, mounted on stalks identical to those used on cryogenic target experiments (17-micron-diam SiC fibers), and are diagnosed with an array of 11 digitally recorded x-ray pinhole camera images that sample the entire surface flux of x rays emitted by the target. Both 100-ps and 1-ns pulses are used in these experiments. The various effects that are important to the direct-drive, low-mode illumination uniformity (l < 30) such as beam overlap, target positioning, and stalk shadowing are all well measured with this method.