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Title: Experimental Studies of Direct-Drive, Low-Intensity, Low-Adiabat Spherical Implosions on OMEGA

Abstract

Low-adiabat (high-compressibility) implosions were performed with shells filled with 15 atm of D2 gas driven with ~12.5 kJ, 3-ns-square pulse shapes, and a laser intensity of ~2 x 10^14 W/cm^2. Initial target modulations, imprinted on the target surface by laser nonuniformities, were varied by using drive with and without smoothing by spectral dispersion. The performance of the spherical implosions was correlated with measured target modulations at the end of the acceleration pulse performed in a planar target with similar conditions using through-foil radiography. The neutron yield decreases sharply when target modulations become comparable with the target thickness at the end of the acceleration phase. The measured target areal densities are less sensitive to target modulations.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Laboratory for Laser Energetics, University of Rochester
Sponsoring Org.:
USDOE
OSTI Identifier:
899497
Report Number(s):
DOE/SF/19460-727
Journal ID: ISSN 1070-664X; PHPAEN; 1688; 2006-168; TRN: US0703513
DOE Contract Number:
FC52-92SF19460
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCELERATION; IMPLOSIONS; LASERS; NEUTRONS; PERFORMANCE; TARGETS; THICKNESS; DIRECT DRIVE LASER IMPLOSION

Citation Formats

Smalyuk, V.A., Betti, R., Delettrez, J.A., Glebov, V.Yu., Goncharov, V.N., Li, D.Y., Meyerhofer, D.D., Regan, S.P., Roberts, S., Sangster, T.C., Stoeckl, C., Seka, W., Frenje, J.A., Li, C.K., Petrasso, R.D., and Seguin, F.H. Experimental Studies of Direct-Drive, Low-Intensity, Low-Adiabat Spherical Implosions on OMEGA. United States: N. p., 2006. Web.
Smalyuk, V.A., Betti, R., Delettrez, J.A., Glebov, V.Yu., Goncharov, V.N., Li, D.Y., Meyerhofer, D.D., Regan, S.P., Roberts, S., Sangster, T.C., Stoeckl, C., Seka, W., Frenje, J.A., Li, C.K., Petrasso, R.D., & Seguin, F.H. Experimental Studies of Direct-Drive, Low-Intensity, Low-Adiabat Spherical Implosions on OMEGA. United States.
Smalyuk, V.A., Betti, R., Delettrez, J.A., Glebov, V.Yu., Goncharov, V.N., Li, D.Y., Meyerhofer, D.D., Regan, S.P., Roberts, S., Sangster, T.C., Stoeckl, C., Seka, W., Frenje, J.A., Li, C.K., Petrasso, R.D., and Seguin, F.H. Wed . "Experimental Studies of Direct-Drive, Low-Intensity, Low-Adiabat Spherical Implosions on OMEGA". United States. doi:.
@article{osti_899497,
title = {Experimental Studies of Direct-Drive, Low-Intensity, Low-Adiabat Spherical Implosions on OMEGA},
author = {Smalyuk, V.A. and Betti, R. and Delettrez, J.A. and Glebov, V.Yu. and Goncharov, V.N. and Li, D.Y. and Meyerhofer, D.D. and Regan, S.P. and Roberts, S. and Sangster, T.C. and Stoeckl, C. and Seka, W. and Frenje, J.A. and Li, C.K. and Petrasso, R.D. and Seguin, F.H.},
abstractNote = {Low-adiabat (high-compressibility) implosions were performed with shells filled with 15 atm of D2 gas driven with ~12.5 kJ, 3-ns-square pulse shapes, and a laser intensity of ~2 x 10^14 W/cm^2. Initial target modulations, imprinted on the target surface by laser nonuniformities, were varied by using drive with and without smoothing by spectral dispersion. The performance of the spherical implosions was correlated with measured target modulations at the end of the acceleration pulse performed in a planar target with similar conditions using through-foil radiography. The neutron yield decreases sharply when target modulations become comparable with the target thickness at the end of the acceleration phase. The measured target areal densities are less sensitive to target modulations.},
doi = {},
journal = {Physics of Plasmas},
number = ,
volume = 14,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • Low-adiabat (high-compressibility) implosions were performed with {approx}860 {mu}m diam, 24- and 35-{mu}m-thick shells filled with 15 atm of D{sub 2} gas driven with {approx}12.5 kJ, 3-ns-square pulse shapes, and a laser intensity of {approx}2x10{sup 14} W/cm{sup 2}. Initial target modulations, imprinted on the target surface by laser nonuniformities, were varied by using drive with and without smoothing by spectral dispersion. The performance of the spherical implosions (with a gas fuel convergence of {approx}16) was correlated with measured target modulations at the end of the acceleration phase performed in a planar target with similar conditions using through-foil radiography. The neutron yieldmore » decreases sharply when target modulations become comparable with the target thickness at the end of the acceleration phase. The measured target areal densities are less sensitive to target modulations. Implosions with 35-{mu}m-thick shells produced neutron-averaged areal densities that are among the highest on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)].« less
  • Neutron yields of direct-drive, low-adiabat (alpha ~~ 2 to 3) cryogenic D2 target implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have been systematically investigated using the two-dimensional (2D) radiation hydrodynamics code DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)]. Low-mode (ell <- 12) perturbations, including initial target offset, ice-layer roughness, and laser-beam power imbalance, were found to be the primary source of yield reduction for thin-shell (5 um), low-alpha, cryogenic targets. The 2D simulations of thin-shell implosions track experimental measurements for different target conditions and peak laser intensitiesmore » ranging from 2.5 x 10^14–6 x 10^14 W/cm^2. Simulations indicate that the fusion yield is sensitive to the relative phases between the target offset and the ice-layer perturbations. The results provide a reasonable good guide to understanding the yield degradation in direct-drive, low-adiabat, cryogenic, thin-shell-target implosions. Thick-shell (10 um) implosions generally give lower yield over clean than low-ell-mode DRACO simulation predictions. Simulations including the effect of laser-beam nonuniformities indicate that high-ell-mode perturbations caused by laser imprinting further degrade the neutron yield of thick-shell implosions. To study ICF compression physics, these results suggest a target specification with a <-30 um offset and ice-roughness of sigma_rms < 3 um are required.« less
  • Neutron yields of direct-drive, low-adiabat ({alpha}{approx_equal}2 to 3) cryogenic D{sub 2} target implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have been systematically investigated using the two-dimensional (2D) radiation hydrodynamics code DRACO[P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)]. Low-mode (l{<=}12) perturbations, including initial target offset, ice-layer roughness, and laser-beam power imbalance, were found to be the primary source of yield reduction for thin-shell (5 {mu}m), low-{alpha}, cryogenic targets. The 2D simulations of thin-shell implosions track experimental measurements for different target conditions and peak laser intensities ranging from 2.5x10{sup 14}-6x10{supmore » 14} W/cm{sup 2}. Simulations indicate that the fusion yield is sensitive to the relative phases between the target offset and the ice-layer perturbations. The results provide a reasonable good guide to understanding the yield degradation in direct-drive, low-adiabat, cryogenic, thin-shell-target implosions. Thick-shell (10 {mu}m) implosions generally give lower yield over clean than low-l-mode DRACO simulation predictions. Simulations including the effect of laser-beam nonuniformities indicate that high-l-mode perturbations caused by laser imprinting further degrade the neutron yield of thick-shell implosions. To study ICF compression physics, these results suggest a target specification with a {<=}30 {mu}m offset and ice-roughness of {sigma}{sub rms}<3 {mu}m are required.« less
  • Effects of the intensity pickets on laser imprinting were investigated using laser-driven, planar plastic and foam targets on the OMEGA Laser System. Intensity pickets are used in adiabat-shaping techniques, designed to improve stability of inertial confinement fusion targets. The measurements were performed in planar foam targets using the decaying shock (DS) method of adiabat shaping and in planar plastic targets using the relaxation (RX) method.
  • Effects of the intensity pickets on laser imprinting were investigated using laser-driven, planar plastic and foam targets on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Intensity pickets are used in adiabat-shaping techniques designed to improve stability of inertial confinement fusion targets. The measurements were performed in planar foam targets using the decaying shock method of adiabat shaping and in planar plastic targets using the relaxation (RX) method. In foam targets, the picket reduced the target areal-density modulations by {approx}6 times at shorter spatial wavelengths of 30 and 60 {mu}m, while at a longermore » wavelength of 120 {mu}m there was no reduction. The ''imprint efficiency,'' the equivalent surface amplitude produced by imprinting, was reduced by the intensity picket by a factor of {approx}3 at a spatial wavelength of 60 {mu}m, while it was increased by a factor of {approx}2 at a 120-{mu}m spatial wavelength. In plastic targets, used to test the RX method, the imprint efficiency was reduced by the intensity picket by a factor of {approx}2 at spatial wavelengths of 30 and 60 {mu}m, while it was about the same at a 120-{mu}m spatial wavelength.« less