Double-shell target design for the NIF: Noncryogenic ignition and nonlinear mix studies for Stockpile Stewardship
Double-shell ignition is complementary to the baseline approach by virtue of not requiring: (1) cryogenic preparation and fielding, (2) high-contrast pulse-shaping for shock-timing, and (3) demanding x-ray flux symmetry control. The use of simpler low-contrast pulse-shaping potentially allows more benign hohlraum conditions by reducing the risk of laser backscatter. In addition, the associated higher laser fluence threshold for optics damage initiation allows the possibility of more routine high-fluence shots with 2{omega} on the NIF. Based on LDRD-sponsored research in FY01-03 on NIF double-shell ignition target designs, the feasibility of this approach was advanced through both a highly successful implosion campaign on the Omega laser facility and a variety of design improvements for mitigating instability. The double-shell implosion campaign on Omega achieved the important milestone of repeatably demonstrating dominant primary (2.45 MeV) neutron production from the mix-susceptible compressional phase of a double-shell implosion, using fall-line design optimization and exacting fabrication standards. Showing effective control of fuel-pusher mix during final compression is an essential element for achieving ignition. In our studies to control mix by reducing hydrodynamic instability a new pathway for destructive Rayleigh-Taylor growth on the outer surface of the inner shell at ignition scales was identified. However, highly resolved multi-mode simulations showed that with use of a graded dopant in the inner shell and material-matching with an exterior metallic foam, this instability was significantly reduced. In addition, the resulting density-gradient stabilization was seen to quench small-wavelength growth, thereby avoiding the computationally challenging turbulent regime. A major goal of future research for realizing double-shell ignition on the NIF is experimental validation of this instability mitigation approach using the Omega laser facility.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15013925
- Report Number(s):
- UCRL-TR-202361; TRN: US200803%%959
- Country of Publication:
- United States
- Language:
- English
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