LLE Review 92

Review 92


This volume of the LLE Review, covering July to September 2002, features an investigation of the radial structure of shell modulations near peak compression of spherical implosions. The structure of shell modulations at peak compression of implosions is measured using absorption of titanium-doped layers placed at various distances from the inner surface of 20-μm-thick plastic shells filled with D3He gas. Results show that the peak-compression, time-integrated areal-density modulations are higher at the inner shell surface, which is unstable during the acceleration phase of an implosion, than in the central part of the shell. The outer surface of the shell, which is unstable during the acceleration phase of an implosion, has a modulation level comparable to that of the inner shell surface.

Additional highlights of research presented in this issue includethe following:

  • Measurements of the neutron emission from inertial confinement fusion (ICF) implosions are providing important information about target performance that can be compared directly with numerical models. For room-temperature target experiments on OMEGA, the neutron temporal diagnostic (NTD), originally developed at Lawrence Livermore National Laboratory (LLNL), measures the neutron burn history with high resolution and good timing accuracy. Because the NTD is mechanically incompatible with cryogenic target experiments because of the standoff required to remain clear of the OMEGA Cryogenic Target Handling System (CTHS), a new cryogenic-compatible neutron temporal diagnostic (cryoNTD), which provides high-resolution neutron emission measurements for cryogenic implosions, has been designed for LLE's standard ten-inch manipulator (TIM) diagnostic inserters.
  • The yield of tertiary neutrons with energies greater than 20 MeV has been proposed as a method to determine the areal mass density of ICF targets. The use of carbon activations as a suitable measurement technique is discussed because of its high reaction threshold and the availability of high-purity samples.
  • The development of polyimide shells suitable for ICF cryogenic experiments on OMEGA is described along with the associated mechanical properties needed to define the processing conditions for operating the OMEGACTHS.
  • A linear model of anomalous stimulated Raman scattering from electron-acoustic (EA) waves in laser-produced plasmas is presented.
  • A 65(±5)-ps time delay in the onset of a resistive-state formation in 10-nm-thick, 200-nm-wide NbN superconducting stripes exposed to single photons has been measured. This delay in the photoresponse decreased down to zero when the stripe was irradiated by multi-photon (classical) optical pulses. The NbN structures were kept at 4.2 K, well below the material's critical temperature and were illuminated by 100-fs-wide optical pulses. This time-delay phenomenon is explained within the framework of a model based on photon-induced generation of a hotspot in the superconducting stripe and, subsequent, supercurrent-assisted resistive-state formation across the entire stripecross-section.
  • Reports on LLE's Summer High School Research Program, the FY02 Laser Facility Report, and the National Users' Facility News.

Table of Contents