skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: X-ray laser measurements of direct drive imprint on vulcan

Abstract

High gain direct drive inertial confinement fusion requires very uniform irradiation of a hollow spherical shell with a layer of fusionable deuterium and tritium on its inner surface. The intensity of laser irradiation builds up in several nanoseconds from an initial `foot` at {approximately}10{sup 13} W/cm{sup 2} to more than 10{sup 15} W/cm{sup 2} during the main drive pulse. Laser ablation of the capsule surface produces a high pressure, accelerating the shell radially inward, and resulting in Rayleigh-Taylor (R-T) growth of surface perturbations originating from both the initial surface roughness of the capsule and from imprint of spatial non- uniformities in the laser drive intensity early in the laser pulse. The uniformity of illumination on a direct drive implosion capsule is determined on a large scale by the multi-beam irradiation geometry, and on a small scale by beam smoothing techniques. By using a large number of beams (such as the 60 beams of the Omega laser or 48 beam clusters for the NIF), large scale non-uniformities due to the overlap of the laser focal spots are adequately reduced. Random phase plates (RPPs) are introduced to smooth the individual beam focal spots. The spatial intensity variations of the individual beam specklemore » patterns may be smoothed by spectral dispersion (SD) with induced spatial incoherence (ISI) or by using partially coherent light. We performed experiments to study the imprint under conditions simulating the low intensity foot of the pulse on an ignition target, such as designed for the NIF. We used a 0.53 micrometer laser wavelength, and considered the imprint in thin Al foils due to both a broadband distribution of modes such as those in smoothed speckle patterns, and a single mode optical intensity variation. We characterized the laser imprint using a Ge x-ray laser and multilayer imaging optics, as described previously. In this paper we summarize and compare the multiple and single mode imprinting results. 9 refs., 7 figs.« less

Authors:
; ;  [1]
  1. and others
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
632785
Report Number(s):
UCRL-ID-128006
ON: DE98051042; TRN: 98:008866
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Jul 1997
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; NONUNIFORM IRRADIATION; LASER TARGETS; FOILS; DIRECT DRIVE LASER IMPLOSION; ICF DEVICES; X-RAY LASERS; EXPERIMENTAL DATA

Citation Formats

Kalantar, D.H., Wolfrum, E., and Zhang, J. X-ray laser measurements of direct drive imprint on vulcan. United States: N. p., 1997. Web. doi:10.2172/632785.
Kalantar, D.H., Wolfrum, E., & Zhang, J. X-ray laser measurements of direct drive imprint on vulcan. United States. doi:10.2172/632785.
Kalantar, D.H., Wolfrum, E., and Zhang, J. Tue . "X-ray laser measurements of direct drive imprint on vulcan". United States. doi:10.2172/632785. https://www.osti.gov/servlets/purl/632785.
@article{osti_632785,
title = {X-ray laser measurements of direct drive imprint on vulcan},
author = {Kalantar, D.H. and Wolfrum, E. and Zhang, J.},
abstractNote = {High gain direct drive inertial confinement fusion requires very uniform irradiation of a hollow spherical shell with a layer of fusionable deuterium and tritium on its inner surface. The intensity of laser irradiation builds up in several nanoseconds from an initial `foot` at {approximately}10{sup 13} W/cm{sup 2} to more than 10{sup 15} W/cm{sup 2} during the main drive pulse. Laser ablation of the capsule surface produces a high pressure, accelerating the shell radially inward, and resulting in Rayleigh-Taylor (R-T) growth of surface perturbations originating from both the initial surface roughness of the capsule and from imprint of spatial non- uniformities in the laser drive intensity early in the laser pulse. The uniformity of illumination on a direct drive implosion capsule is determined on a large scale by the multi-beam irradiation geometry, and on a small scale by beam smoothing techniques. By using a large number of beams (such as the 60 beams of the Omega laser or 48 beam clusters for the NIF), large scale non-uniformities due to the overlap of the laser focal spots are adequately reduced. Random phase plates (RPPs) are introduced to smooth the individual beam focal spots. The spatial intensity variations of the individual beam speckle patterns may be smoothed by spectral dispersion (SD) with induced spatial incoherence (ISI) or by using partially coherent light. We performed experiments to study the imprint under conditions simulating the low intensity foot of the pulse on an ignition target, such as designed for the NIF. We used a 0.53 micrometer laser wavelength, and considered the imprint in thin Al foils due to both a broadband distribution of modes such as those in smoothed speckle patterns, and a single mode optical intensity variation. We characterized the laser imprint using a Ge x-ray laser and multilayer imaging optics, as described previously. In this paper we summarize and compare the multiple and single mode imprinting results. 9 refs., 7 figs.},
doi = {10.2172/632785},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1997},
month = {7}
}