Time- and space-resolved X-ray spectroscopy for observation of the hot compressed core region in a laser driven implosion

Fusion pellet implosion by direct laser irradiation was investigated by mea ns of time- and space-resolved X-ray spectroscopic measurements. Fusion pel lets filled with a deuterium fuel gas including a small amount of Ar dopant were irradiated with 12 beams of intense partially coherent light and line emissions from the dopant were observed. There were two type of implosion studies. First, experimental conditions were carefully chosen to provide im plosions that were as stable as possible, these we refer to as the "balance d" cases. Second, the energy balance was manipulated so that two specific b eams, diametrically opposed to each other, had relatively large energy diff erences. This imposes additional low-modal non-uniformity on the pellet! an d these experiments are called that the "unbalanced" cases. Experimental re sults were compared with hydrocode simulations, which were post-processed b y the aid of X-ray spectrum analysis code. The experimental results in term s of temporal variations of the Ar He-beta line and their spatial profiles obtained with an X-ray monochromatic imager were well replicated by one-dim ensional (1-D) simulation for the balanced case, whereas those for the unba lanced case showed large discrepancies. Furthermore, a clear difference was found in the emission of Li-like satellite lines between two cases: In the unbalanced case, the satellite lines became much more intense than the He- beta line at late time in the implosion. These experimental results suggest that the imposed low-modal non-uniformities assisted in the quenching of h ot, compressed core formation. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.