Implosion experiments of gas-filled plastic-shell targets with l=1 drive nonuniformity a the Gekko-XII glass laser

Citation
M. Heya et al., Implosion experiments of gas-filled plastic-shell targets with l=1 drive nonuniformity a the Gekko-XII glass laser, LASER PART, 19(2), 2001, pp. 267-284
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
LASER AND PARTICLE BEAMS
ISSN journal
0263-0346 → ACNP
Volume
19
Issue
2
Year of publication
2001
Pages
267 - 284
Database
ISI
SICI code
0263-0346(200106)19:2<267:IEOGPT>2.0.ZU;2-B
Abstract
Effects of an implosion nonuniformity with l = 1 (l: Legendre polynomial mo de number) on the hot spark formation were investigated in a series of dire ct-drive implosion experiments at the Gekko-XII glass laser (Yamanaka et al ., 1987). The implosion dynamics and the performance from the early to fina l stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with l = 1 was observed in the shape of the accelerated target at the early stage of the i mplosion At the final stage of the implosion, the resultant nonuniformity w ith l = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission prope rties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity, with l = 1. The experimental re sults were compared with one-dimensional (I-D) and two-dimensional (2-D) hy drodynamic simulations. As a result, it was found that the implosion nonuni formity with l = 1 shifts the whole implosion dynamics towards its directio n and prevents the confinement of the gas fuel considerably. However, the e xperimentally observed degradation in the hot spark formation, such as redu ctions in neutron yield and features in X-ray emission, can be reproduced i n 2-D simulations not with an asymmetric perturbation of l = 1 only,but wit h multimode nonuniformities such as l = 1 coupled with some additional midd le-mode ones (e.g., l = 6). Such a complex spike structure caused by the mu ltimode nonuniformities was found to be essential for the experimentally ob served rapid cooling of the hot spark.