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Title: Report of visit to LLNL 26 June to 10 July 2010

Abstract

On this visit my principal activity was focused on the capsule and in particular to ascertain whether the heat-flow-driven electrothermal (ET) instability would occur in NIF indirect-drive experiments. Filamentary structures, assumed to be associated with the ET instability, have been observed years ago in the coronal plasma of direct-drive and more recently by proton probing of targets irradiated directly with an intense short-pulse (~1ps.) laser. A different proton probing diagnostic based on a subsidiary exploding pusher source has also shown filamentary structures in direct drive experiments at 10 13 – 10 15 W cm -2 intensity, but with only 47μm resolution. Recently measurements have been made on indirectly driven capsules on OMEGA and no filamentary structures were observed. During my visit 1-D numerical simulations from HYDRA were studied. The method was to employ Lagrangian plots of density, temperature etc. for many cells and to test whether the two conditions necessary for growth of the ET instability would simultaneously be satisfied. These conditions are that the electron temperature should be less than a critical temperature and that the electron heat flow should be greater than 0.02 times the free-streaming value. We found that for all of the 16 zones considered nonemore » should be unstable, though in some cases it could be marginal. A further development of the heat-flux condition is contained in Appendices A and B, giving a lower threshold, but still indicating that the NIF indirect-drive will be stable to ET. Other subjects briefly studied included the validity of the non-local model of transport in the hohlraum gas; the inclusion of magnetic fields in HYDRA; the electric field in capsules and shocks; the proposed theta pinch for the LIFE project; the importance of ion viscosity, thermal conduction, and Maxwellisation at the final implosion; the question of an electric field and hence a return current generated in radiation transport due to photon momentum deposition; the physical appropriateness of numerical viscosity; and the magnetic field generation on the gold wall.« less

Authors:
 [1]
  1. Imperial College, London (United Kingdom)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1124810
Report Number(s):
LLNL-SR-454996
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING

Citation Formats

Haines, M. G. Report of visit to LLNL 26 June to 10 July 2010. United States: N. p., 2010. Web. doi:10.2172/1124810.
Haines, M. G. Report of visit to LLNL 26 June to 10 July 2010. United States. doi:10.2172/1124810.
Haines, M. G. Tue . "Report of visit to LLNL 26 June to 10 July 2010". United States. doi:10.2172/1124810. https://www.osti.gov/servlets/purl/1124810.
@article{osti_1124810,
title = {Report of visit to LLNL 26 June to 10 July 2010},
author = {Haines, M. G.},
abstractNote = {On this visit my principal activity was focused on the capsule and in particular to ascertain whether the heat-flow-driven electrothermal (ET) instability would occur in NIF indirect-drive experiments. Filamentary structures, assumed to be associated with the ET instability, have been observed years ago in the coronal plasma of direct-drive and more recently by proton probing of targets irradiated directly with an intense short-pulse (~1ps.) laser. A different proton probing diagnostic based on a subsidiary exploding pusher source has also shown filamentary structures in direct drive experiments at 1013 – 1015 W cm-2 intensity, but with only 47μm resolution. Recently measurements have been made on indirectly driven capsules on OMEGA and no filamentary structures were observed. During my visit 1-D numerical simulations from HYDRA were studied. The method was to employ Lagrangian plots of density, temperature etc. for many cells and to test whether the two conditions necessary for growth of the ET instability would simultaneously be satisfied. These conditions are that the electron temperature should be less than a critical temperature and that the electron heat flow should be greater than 0.02 times the free-streaming value. We found that for all of the 16 zones considered none should be unstable, though in some cases it could be marginal. A further development of the heat-flux condition is contained in Appendices A and B, giving a lower threshold, but still indicating that the NIF indirect-drive will be stable to ET. Other subjects briefly studied included the validity of the non-local model of transport in the hohlraum gas; the inclusion of magnetic fields in HYDRA; the electric field in capsules and shocks; the proposed theta pinch for the LIFE project; the importance of ion viscosity, thermal conduction, and Maxwellisation at the final implosion; the question of an electric field and hence a return current generated in radiation transport due to photon momentum deposition; the physical appropriateness of numerical viscosity; and the magnetic field generation on the gold wall.},
doi = {10.2172/1124810},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2010},
month = {9}
}

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