LLE Review 128

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Highlights

This volume of the LLE Review, covering July–September 2011, features “Hot-Spot Mix in Ignition-Scale Inertial Confinement Fusion Targets.” In this article, mixing of ablator material into the hot spot of ignition-scale inertial confinement fusion implosions by hydrodynamic instabilities is diagnosed with x-ray spectroscopy at the National Ignition Facility. The experimentally inferred values of hot-spot mix mass, based on the absolute spectral brightness of the emergent Ge K-shell emission, range from 2 to 400 ng. Most implosions have less than 75 ng of hot-spot mix, consistent with the requirements for ignition.

Additional highlights of research presented in this issue include the following:

• The differential cross section for the elastic neutron–triton (n–³H) and neutron-deuteron (n–²H) scattering at 14.1 MeV using an inertial confinement fusion (ICF) facility is measured. By measuring elastically scattered ³H and ²H ions from a deuterium–tritium gas-filled ICF capsule implosion, the differential cross section for the elastic n–³H scattering was obtained. Significantly higher accuracy was achieved than in previous accelerator experiments. The results compare well with calculations that combine the resonating-group method with an ab initio no-core shell model, which demonstrates that recent advances in ab initio theory can provide an accurate description of light-ion reactions.
• Direct-drive, Rayleigh–Taylor (RT) growth experiments are performed in liquid deuterium (D₂) on the OMEGA laser with planar cryogenic targets at a laser intensity of ~4 × 10¹⁴ W/cm². These are the first RT measurements in deuterium at conditions relevant to inertial confinement fusion (ICF) using a mass-preimposed initial modulation. The measured modulation optical depths are in agreement with the 2-D hydrodynamics code DRACOusing flux-limited local thermal transport, providing an important step in the experimental validation of simulations for direct-drive ignition.
• A highly efficient pulsed-diode–pumped, room-temperature Yb:YAG ceramic laser with a slope efficiency of 78% and an optical-to-optical efficiency of 51% is demonstrated. This is the highest slope efficiency for a room-temperature Yb:YAG ceramic laser reported to date. A regenerative amplifier with +15-mJ output energy and fourth-order super-Gaussian beam profile based on this laser has been demonstrated.
• A summary of LLE’s Summer High School Research Program, the FY11 Laser Facility Report, and the National Laser Users’ Facility and External Users’ Programs are presented.
• This volume concludes with R. D. Petrasso’s (Plasma Science and Fusion Center, MIT) report on the Third Omega Laser Facility Users’ Group Workshop (27–29 April 2011). LLE hosted more than 115 researchers from 25 universities and laboratories and 9 countries. The goal for the three-day workshop was to facilitate communications and exchanges among individual OMEGA users and between users and LLE; to present ongoing and proposed research; to encourage research opportunities and collaborations that could be undertaken at the Omega Laser Facility and in a complementary fashion at other facilities; to provide an opportunity for students and postdoctoral fellows to present their research at LLE in an interactive and informal atmosphere; and to provide feedback to LLE about ways to improve the facility and future experimental campaigns.