Douglas B. Clarke

Sonoluminescence and the prospects for table-top micro-thermonuclear fusion

Abstract 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.

Star in a Jar

A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized two-component plasma. The use of accurate equations-of-state, plasma physics, and radiation physics distinguishes our model from all previous models. The model provides an explanation of many features of single bubble sonoluminescence that have not been collectively accounted for in previous models, including the origin of the picosecond pulse widths and spectra. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains only argon, in agreement with a recent theoretical analysis.

Sonoluminescence, shock waves, and micro-thermonuclear fusion

We have performed numerical hydrodynamic simulations of the growth and collapse of a sonoluminescing bubble in a liquid. Our calculations show that spherically converging shock waves are generated during the collapse of the bubble. The combination of the shock waves and a realistic equation of state for the gas in the bubble provides an explanation for the measured picosecond optical pulse widths and indicates that the temperatures near the center of the bubble may exceed 30 eV. This leads naturally to speculation about obtaining micro-thermonuclear fusion in a bubble filled with deuterium (D2) gas. Consequently, we performed numerical simulations of the collapse of a D2 bubble in D2O. A pressure spike added to the periodic driving amplitude creates temperatures that may be sufficient to generate a very small, but measurable number of thermonuclear D-D fusion reactions in the bubble.

Acoustic source calculations for nuclear bursts

Research has been conducted on the source term for long‐range underwater propagation of signals from nuclear explosions in and above the ocean, in support of CTB monitoring objectives. A suite of source‐region simulations is reviewed to study the variation of wave properties and source‐region energy partition as a function of height or depth of burst. The multistep calculation combines LLNL’s CALE hydrodynamics code in the strong shock region with NRL’s weak shock code, NPE, at intermediate ranges. The source term calculations are intended as a starter field for long‐range linear propagation models to obtain signature estimates at normal observational ranges. Calculations are presented to examine the effect of sea ice below an air burst on acoustic coupling into the water column. The ice was modeled as a continuous elastic layer 5‐m thick at the water surface, and the source as a 1‐Kt explosion 50 m above the ice. Calculations with and without the ice layer predict a moderate, but noticeable reduction in coupled acoustic energy in signals observed at the 10 000‐m range. [Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.]

Validation of source region energy partition calculations with small‐scale explosive experiments

The decrease in signal energy as the location of a nuclear explosion varies from deep in the ocean to above the ocean surface is a concern for the planned ocean monitoring component of the Comprehensive Test Ban Treaty. Small‐scale experiments were designed to validate predictions of energy coupling by nuclear explosions in the ‘‘source region,’’ the origin of the signals that propagate in the deep underwater sound (SOFAR) channel. The experiments were performed in a biologically dead lake at a scale length of 1/50 (1/125 000 in explosive energy) relative to one kiloton using 6.82‐kg charges of Pentolite 50/50. The acoustic energy coupled into the water was monitored at a 60‐m range by a hydrophone string with eight piezoelectric sensors spaced from near‐surface to a 30‐m depth. Useful data were obtained at five burst locations: 5, 2, 0, −2, and −15 m. Results from the experiments and new calculations support the predicted energy partitioning for above‐surface explosions with model and experiment peak pre...

Calculated pulse widths and spectra of sonoluminescing nitrogen and argon bubbles

By modeling the hot compressed gas in a sonoluminescing bubble as a thermally conducting plasma it is shown that the measured picosecond pulse widths are due to electron conduction and the rapidly changing opacity of the plasma at the onset of ionization. The model shows that these mechanisms are also responsible for the absence of an ‘‘afterglow’’ subsequent to the sonoluminescent flash, as the hot bubble expands and cools. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains only argon, in agreement with a recent theoretical analysis. [This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W‐7405‐Eng‐48.]

Hydrodynamic simulations of an imploding bubble

Numerical solutions of the hydrodynamic equations 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), whi...

Propagation of signals from strong explosions above and below the ocean surface.

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 impro...

Investigation of the ocean acoustic signatures from strong explosions at a long distance in the ocean sound channel by computer simulation

The identification and location of ocean acoustic signatures are the principal objectives of a program to discourage clandestine testing of nuclear explosives. Difficulties arise primarily from variations in the water column. In turn, these variations affect acoustic propagation in the SOFAR channel. In this study, the path effects on the signals generated by strong explosions (1 and 10 kn) are investigated. The goal is to make a quantitative correlation between the initial source description and the final acoustical signatures received at a great distance under various conditions. The study is performed entirely by computer simulations applying two computer programs in succession. First, the explosions are simulated by a 2‐D hydrodynamic computer program, CALE, which was originally developed to calculate astrophysical problems. The computed signals have reached more than 700 m deep approaching the SOFAR channel. At this point, the CALE output is linked to a hydro‐acoustic computer program, the NPE code, ...

Hydrodynamic simulations of bubble collapse and picosecond sonoluminescence

Numerical hydrodynamic simulations of the growth and collapse of a 10‐μm 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 μm of the bubble. The reflection of the shock from the center of the bubble produces a diverging shock wave that quenches the high temperatures (≳30 eV) and pressures in less than 10 ps (FWHM). 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 peak temperature at the center of the bubble is affected strongly by the ionization model used for the air. 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...