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Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy
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- Journal:
- High Power Laser Science and Engineering / Volume 3 / 2015
- Published online by Cambridge University Press:
- 08 July 2015, e19
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Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (
${>}1$ keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (
${\it\delta}R=\pm 1.15~{\rm\mu}\text{m}$), image-to-image timing (
${\it\delta}({\rm\Delta}t)=\pm 2.5$ ps) and absolute timing (
${\it\delta}t=\pm 10$ ps) are presented. Angular averaging of the images provides an average radius measurement of 
${\it\delta}(R_{\text{av}})=\pm 0.15~{\rm\mu}\text{m}$ and an error in velocity of 
${\it\delta}V/V=\pm 3\%$. This technique was applied on the Omega Laser Facility [Boehly et al., Opt. Commun. 133, 495 (1997)] and the National Ignition Facility [Campbell and Hogan, Plasma Phys. Control. Fusion 41, B39 (1999)].
