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Title: Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility

Abstract

When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm 3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm 3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out an exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed in this paper a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics at fill densities ≤0.3 mg/cm 3 (with backscattered and “missing” energies being of about 5% and 23% of the total laser energy, respectively). The capsule shape at stagnation was slightly oblate and improved with lowering the fill density. We also performed an implosion with a lower-picket, 12.6-ns pulse atmore » the hohlraum fill density of 0.15 mg/cm 3 to observe comparable hohlraum energetics (about 3% of backscattered and 27% of “missing” energy) but an even more oblate implosion shape. Finally, achieving symmetric implosions of 1.06-mm Be capsules in low-fill, 6.72-mm gold hohlraums with reasonably low-adiabat pulses may not be feasible. However, symmetric implosions have recently been successfully demonstrated in such hohlraums with 0.8-mm Be capsules.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1];  [1]; ORCiD logo [1];  [2];  [2];  [2]; ORCiD logo [2]; ORCiD logo [2];  [2];  [2];  [2];  [2]; ORCiD logo [2]; ORCiD logo [2];  [2];  [2] more »; ORCiD logo [2];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [3];  [3];  [3];  [3]; ORCiD logo [3];  [3];  [3];  [4] « less
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1357132
Report Number(s):
LA-UR-17-20756; LLNL-JRNL-734711
Journal ID: ISSN 1070-664X
Grant/Contract Number:
AC52-06NA25396; AC52-07NA27344; NA0001808
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Hohlraum; X-ray imaging; Radiosurgery; Stimulated Brillouin scattering; Implosion symmetry

Citation Formats

Simakov, A. N., Wilson, D. C., Yi, S. A., Loomis, E. N., Kline, J. L., Kyrala, G. A., Zylstra, A. B., Dewald, E. L., Tommasini, R., Ralph, J. E., Strozzi, D. J., MacPhee, A. G., Milovich, J. L., Rygg, J. R., Khan, S. F., Ma, T., Jarrott, L. C., Haan, S. W., Celliers, P. M., Marinak, M. M., Rinderknecht, H. G., Robey, H. F., Salmonson, J. D., Stadermann, M., Baxamusa, S., Alford, C., Wang, Y., Nikroo, A., Rice, N., Kong, C., Jaquez, J., Mauldin, M., Youngblood, K. P., Xu, H., Huang, H., and Sio, H. Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility. United States: N. p., 2017. Web. doi:10.1063/1.4983141.
Simakov, A. N., Wilson, D. C., Yi, S. A., Loomis, E. N., Kline, J. L., Kyrala, G. A., Zylstra, A. B., Dewald, E. L., Tommasini, R., Ralph, J. E., Strozzi, D. J., MacPhee, A. G., Milovich, J. L., Rygg, J. R., Khan, S. F., Ma, T., Jarrott, L. C., Haan, S. W., Celliers, P. M., Marinak, M. M., Rinderknecht, H. G., Robey, H. F., Salmonson, J. D., Stadermann, M., Baxamusa, S., Alford, C., Wang, Y., Nikroo, A., Rice, N., Kong, C., Jaquez, J., Mauldin, M., Youngblood, K. P., Xu, H., Huang, H., & Sio, H. Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility. United States. doi:10.1063/1.4983141.
Simakov, A. N., Wilson, D. C., Yi, S. A., Loomis, E. N., Kline, J. L., Kyrala, G. A., Zylstra, A. B., Dewald, E. L., Tommasini, R., Ralph, J. E., Strozzi, D. J., MacPhee, A. G., Milovich, J. L., Rygg, J. R., Khan, S. F., Ma, T., Jarrott, L. C., Haan, S. W., Celliers, P. M., Marinak, M. M., Rinderknecht, H. G., Robey, H. F., Salmonson, J. D., Stadermann, M., Baxamusa, S., Alford, C., Wang, Y., Nikroo, A., Rice, N., Kong, C., Jaquez, J., Mauldin, M., Youngblood, K. P., Xu, H., Huang, H., and Sio, H. 2017. "Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility". United States. doi:10.1063/1.4983141.
@article{osti_1357132,
title = {Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility},
author = {Simakov, A. N. and Wilson, D. C. and Yi, S. A. and Loomis, E. N. and Kline, J. L. and Kyrala, G. A. and Zylstra, A. B. and Dewald, E. L. and Tommasini, R. and Ralph, J. E. and Strozzi, D. J. and MacPhee, A. G. and Milovich, J. L. and Rygg, J. R. and Khan, S. F. and Ma, T. and Jarrott, L. C. and Haan, S. W. and Celliers, P. M. and Marinak, M. M. and Rinderknecht, H. G. and Robey, H. F. and Salmonson, J. D. and Stadermann, M. and Baxamusa, S. and Alford, C. and Wang, Y. and Nikroo, A. and Rice, N. and Kong, C. and Jaquez, J. and Mauldin, M. and Youngblood, K. P. and Xu, H. and Huang, H. and Sio, H.},
abstractNote = {When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out an exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed in this paper a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics at fill densities ≤0.3 mg/cm3 (with backscattered and “missing” energies being of about 5% and 23% of the total laser energy, respectively). The capsule shape at stagnation was slightly oblate and improved with lowering the fill density. We also performed an implosion with a lower-picket, 12.6-ns pulse at the hohlraum fill density of 0.15 mg/cm3 to observe comparable hohlraum energetics (about 3% of backscattered and 27% of “missing” energy) but an even more oblate implosion shape. Finally, achieving symmetric implosions of 1.06-mm Be capsules in low-fill, 6.72-mm gold hohlraums with reasonably low-adiabat pulses may not be feasible. However, symmetric implosions have recently been successfully demonstrated in such hohlraums with 0.8-mm Be capsules.},
doi = {10.1063/1.4983141},
journal = {Physics of Plasmas},
number = 5,
volume = 24,
place = {United States},
year = 2017,
month = 5
}

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  • When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm 3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm 3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out anmore » exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics at fill densities ≤0.3 mg/cm 3 (with backscattered and “missing” energies being of about 5% and 23% of the total laser energy, respectively). The capsule shape at stagnation was slightly oblate and improved with lowering the fill density. We also performed an implosion with a lower-picket, 12.6-ns pulse at the hohlraum fill density of 0.15 mg/cm 3 to observe comparable hohlraum energetics (about 3% of backscattered and 27% of “missing” energy) but an even more oblate implosion shape. Thus, achieving symmetric implosions of 1.06-mm Be capsules in low-fill, 6.72-mm gold hohlraums with reasonably low-adiabat pulses may not be feasible. However, symmetric implosions have recently been successfully demonstrated in such hohlraums with 0.8-mm Be capsules.« less
  • Room temperature or “warm” (273 K) indirect drive hohlraum experiments have been conducted on the National Ignition Facility with laser energies up to 1.26 MJ and compared to similar cryogenic or “cryo” (~20 K) experiments. Warm experiments use neopentane (C 5H 12) as the low pressure hohlraum fill gas instead of helium, and propane (C 3H 8) to replace the cryogenic DT or DHe3 capsule fill. The increased average Z of the hohlraum fill leads to increased inverse bremsstrahlung absorption and an overall hotter hohlraum plasma in simulations. The cross beam energy transfer (CBET) from outer laser beams (pointed towardmore » the laser entrance hole) to inner beams (pointed at the equator) was inferred indirectly from measurements of Stimulated Raman Scattering (SRS). These experiments show that a similar hot spot self-emission shape can be produced with less CBET in warm hohlraums. The measured inner cone SRS reflectivity (as a fraction of incident power neglecting CBET) is ~2.5× less in warm than cryo shots with similar hot spot shapes, due to a less need for CBET. The measured outer-beam stimulated the Brillouin scattering power that was higher in the warm shots, leading to a ceiling on power to avoid the optics damage. These measurements also show that the CBET induced by the flow where the beams cross can be effectively mitigated by a 1.5 Å wavelength shift between the inner and outer beams. A smaller scale direct comparison indicates that warm shots give a more prolate implosion than cryo shots with the same wavelength shift and pulse shape. Lastly, the peak radiation temperature was found to be between 5 and 7 eV higher in the warm than the corresponding cryo experiments after accounting for differences in backscatter.« less
  • The first 96 and 192 beam vacuum hohlraum have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr representing a 20 times flux increase over NOVA/Omega scale hohlraums. The vacuum hohlraums were irradiated with 2 ns square pulses with energies between 150 - 635 kJ. They produced nearly Planckian spectra with about 30 {+-} 10% more flux than predicted by the current radiation hydrodynamic simulations after careful verification of all component calibrations (which included an {approx} 10% downward correction to Center X-Ray Optics opacities just below the Cu L edgemore » at 50-750 eV), cable deconvolution, and analysis software routines. To corroborate these results, first a half hohlraum experiment was conducted using a single 2 ns-long axial quad with an irradiance of {approx} 1-2 x 10{sup 15} W/cm{sup 2} for comparison with NIF Early Light experiments completed in 2004. Second, we completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1 x 10{sup 14} W/cm{sup 2} over 5 ns) to avoid sensitivity to modeling uncertainties for non-local heat conduction and non-linear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere and the calculated Au conversion efficiency agree to {+-}5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we concluded the 30 {+-} 10% higher than expected radiation fluxes from the 96 and 192 beam vacuum hohlraums are attributable to differences in physics when we transitioned to large hot hohlraums. Specifically, using variants in the atomic physics models and electron heat conduction, newer simulations show that nonlocalization of energy deposition leads to less energy being stored in the coronal plasma leading to higher x-ray conversion efficiency. Since the larger volume-to-area ratio hohlraums have large coronal plasmas which scale volumetrically, the reduction in energy losses to the corona become more pronounced than for smaller NOVA/Omega scale hohlraums. The higher conversion efficiencies are also consistent with observations from other 1 ns gold sphere experiments conducted at Omega with 1 x 10{sup 15} W/cm{sup 2} laser irradiances.« less
  • The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an {approx}20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30{+-}10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. Inmore » addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of {approx}2x10{sup 15} W/cm{sup 2} for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1x10{sup 14} W/cm{sup 2} over 5 ns) to avoid sensitivity to modeling uncertainties for nonlocal heat conduction and nonlinear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-Hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere, and the calculated Au conversion efficiency agree to {+-}5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we conclude that the 30{+-}10% higher than expected radiation fluxes from the 96 and 192 beam vacuum Hohlraums are attributable to differences in physics of the larger Hohlraums.« less