Implementation and performance of beam smoothing on 10 beams of the Nova Laser

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Recent simulations and experiments on Nova indicate that some level of smoothing may be required to suppress filamentation in plasmas on the National Ignition Facility (NIF), resulting in the addition of 1-D smoothing capability to the current baseline design. Control of stimulated Brillouin scattering (SBS) and filamentation is considered essential to the success of laser fusion because they affect the amount and location of laser energy delivered to the x-ray conversion region (hohlraum wall) for indirect drive and to the absorptive region for direct drive, Smoothing by spectral dispersion (SSD)[1], reduces these instabilities by reducing nonuniformities in the focal irradiance ... continued below

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14 pages

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Pennington, D. M.; Dixit, S. N.; Weiland, T. L.; Ehrlich, R. & Rothenberg, J. E. March 11, 1997.

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Recent simulations and experiments on Nova indicate that some level of smoothing may be required to suppress filamentation in plasmas on the National Ignition Facility (NIF), resulting in the addition of 1-D smoothing capability to the current baseline design. Control of stimulated Brillouin scattering (SBS) and filamentation is considered essential to the success of laser fusion because they affect the amount and location of laser energy delivered to the x-ray conversion region (hohlraum wall) for indirect drive and to the absorptive region for direct drive, Smoothing by spectral dispersion (SSD)[1], reduces these instabilities by reducing nonuniformities in the focal irradiance when averaged over a finite time interval. We have installed SSD on Nova to produce beam smoothing on all 10 beam lines. A single dispersion grating is located in a position common to all 10 beam lines early in the preamplifier chain. This location limits the 1{omega} bandwidth to 2.2 {angstrom} with sufficient dispersion to displace the speckle field of each frequency component at the target plane by one half speckle diameter. Several beam lines were modified to allow orientation of the dispersion on each arm relative to the hohlraum wall. After conversion to the third harmonic the beam passes through a kinoform phase plate (KPP) designed to produce an elliptical spot at best focus. The KPPs produce a focal spot having an elliptical flat-top envelope with a superimposed speckle pattern. Over 93% of the energy is contained in the central 400 km. Calculations indicate a 16% rms. intensity variance will be reached after 330 ps for a single beam.

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14 pages

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INIS; OSTI as DE00016346

Source

  • 2nd Annual International Conference on Solid-State Lasers for Applications to Inertial Confinement Fusion, Paris (FR), 10/22/1996--10/25/1996; Other Information: Supercedes report DE98050750; PBD: 11 Mar 97

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  • Other: DE98050750
  • Report No.: UCRL-JC--124503
  • Report No.: CONF-9610225--
  • Grant Number: W-7405-Eng-48
  • Office of Scientific & Technical Information Report Number: 16346
  • Archival Resource Key: ark:/67531/metadc619057

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  • March 11, 1997

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  • June 16, 2015, 7:43 a.m.

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  • May 6, 2016, 1:28 p.m.

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Pennington, D. M.; Dixit, S. N.; Weiland, T. L.; Ehrlich, R. & Rothenberg, J. E. Implementation and performance of beam smoothing on 10 beams of the Nova Laser, article, March 11, 1997; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc619057/: accessed November 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.