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Implosion experiments of gas-filled plastic-shell targets with [ell ] = 1 drive nonuniformity at the Gekko-XII glass laser

Published online by Cambridge University Press:  18 January 2002

MANABU HEYA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
HIROYUKI SHIRAGA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
ATSUSHI SUNAHARA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
MIKIO NAKASUJI
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
MASAHARU NISHIKINO
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
HIROSHI HONDA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
KAZUHISA FUJITA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
NOBUHIKO IZUMI
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
NORIAKI MIYANAGA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
HIROAKI NISHIMURA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
HIROSHI AZECHI
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
SHUJI NARUO
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
HIDEAKI TAKABE
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
TATSUHIKO YAMANAKA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
KUNIOKI MIMA
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Abstract

Effects of an implosion nonuniformity with [ell ] = 1 ([ell ]: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-Xll glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with [ell ] = 1 was observed in the shape of the accelerated target at the early stage of the implosion. At the final stage of the implosion, the resultant nonuniformity with [ell ] = 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 properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity with [ell ] = 1. The experimental results were compared with one-dimensional (1-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with [ell ] = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of [ell ] = 1 only but with multimode nonuniformities such as [ell ] = 1 coupled with some additional middle-mode ones (e.g., [ell ] = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark.

Type
Research Article
Copyright
© 2001 Cambridge University Press

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Implosion experiments of gas-filled plastic-shell targets with [ell ] = 1 drive nonuniformity at the Gekko-XII glass laser
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Implosion experiments of gas-filled plastic-shell targets with [ell ] = 1 drive nonuniformity at the Gekko-XII glass laser
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