John W. White’s research while affiliated with Lawrence Livermore National Laboratory and other places

Numerical solutions of the hydrodynamicequations of motion for a collapsing bubble have shown that shock waves can be generated during the collapse. It has been shown that these shock waves can supply and remove energy from the center of the bubble rapidly enough to account for the picosecond duration flashes that are observed experimentally. However, these solutions have not included energy loss mechanisms, so the calculated temperatures are excessively high. More accurate numerical simulations are discussed that (i) model the shocked gas as a plasma with distinct ion, electron, and radiation temperatures, and (ii) include energy losses by ion conduction, electron conduction, and radiant energy transport. As an example, a sonoluminescing bubble of deuterium is considered, whose sinusoidal driving amplitude is enhanced by a small pressure spike. Although the calculated radiation and electron temperatures are only tens of eV, the calculated peak ion temperatures are a couple hundred eV (≊2 000 000 K), which may be sufficient to initiate a very small number of thermonuclear reactions at the center of the bubble. [Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W‐7405‐Eng‐48.]

In support of the Comprehensive Test Ban, research is underway on the long?range propagation of signals from nuclear explosions in the deep underwater sound (SOFAR) channel. Our work has emphasized the variation of wave properties and source region energy coupling as a function of height or depth of burst. Initial calculations on CALE, a two?dimensional hydrodynamics code developed at LLNL by Robert Tipton, were linked at a few hundred milliseconds to a version of NRL?s weak shock code, NPE, which solves the nonlinear progressive wave equation [B. E. McDonald and W. A. Kuperman, J. Acoust. Soc. Am. 81, 1406?1417 (1987)]. The wave propagation simulation was then followed down to 5000?m depth and out to 10 000?m range. In the future, calculations on a linear acoustics code will extend the propagation to greater distances. Until recently our research has considered only explosions in or above the deep ocean. New results on energy coupling and signal propagation in shallow water and the effects of other improvements will be presented. [Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W?7405?ENG?48.] Standards Committee S2 on Mechanical Vibration and Shock. Working group chairs will present reports of their recent progress on writing and processing various shock and vibration standards. There will be a report on the interface of S2 activities with those of ISO/TC 108 (the Technical Advisory Group for ISO/TC 108 consists of members of S2, S3, and other persons not necessarily members of those committees), including a report on the activities of ISO/TC 108, with the plans for its September 1996 meeting in Sydney, Australia. Scope of S2. Standards, specifications, methods of measurement and test, and terminology in the fields of mechanical vibration and shock, and condition monitoring and diagnostics of machines, but excluding those aspects which pertain to biological safety, tolerance and comfort.

Hydrodynamic simulations of a collapsing bubble show that pure D2 cannot exhibit picosecond sonoluminescence, because of its large sound speed. The addition of D2O vapor lowers the sound speed and produces calculated results consistent with experiments. A pressure spike added to the periodic driving amplitude creates temperatures that may be sufficient to generate a very small number of thermonuclear D-D fusion reactions in the bubble.

Numerical hydrodynamic simulations of the growth and collapse of a 10 [mu]m air bubble in water were performed. Both the air and the water are treated as compressible fluids. The calculations show that the collapse is nearly isentropic until the final 10 ns, after which a strong spherically converging shock wave evolves and creates enormous temperatures and pressures in the inner 0.02 [mu]m of the bubble. The reflection of the shock from the center of the bubble produces a diverging shock wave that quenches the high temperatures ([gt]30 eV) and pressures in less than 10 ps (full width at half maximum). The picosecond pulse widths are due primarily to spherical convergence/divergence and nonlinear stiffening of the air equation of state that occurs at high pressures. The results are consistent with recent measurements of sonoluminescence that had optical pulse widths less than 50 ps and 30 mW peak radiated power in the visible.

The principal objective of the non-proliferation program is to discourage clandestine testing of nuclear explosives by maintaining an effective global surveillance system. The methods of detection include underwater and atmospheric acoustics, seismology and atmospheric photometry. The goals of the underwater acoustics are the identification and location of ocean acoustic signatures. The investigation is directed toward obtaining t quantitative correlation between the initial explosion source under various conditions and the final acoustical signatures received at a great distance for different paths. By computer simulations, we calculated the energy coupling and dissipation in the water and studied the signature patterns. In this paper, we report preliminary results of the study on the signals from 1 kt explosions after the signals have propagated a significant distance in the SOFAR channel. The third step in the model has not yet been addressed.

Artificial viscosity [Q] has been used for over 40 years [1] to simulate numerically the propagation of waves in a discretized continuum. It is composed typically of terms that are quadratic and linear in the gradient of the particle velocity, and switches (numerical representations of physical criteria) for turning the terms on and off. The quadratic term is active only in the region of a sharp discontinuity, e.g., a shock, where the velocity gradient is large, and spreads (smooths) the discontinuity over a few computational zones, or a fixed length. The linear Q was introduced to damp numerical noise, but it is active throughout the mesh. Consequently, it can be very dissipative. 6 refs., 5 figs., 1 tab.