Implosion experiments

X ray motion picture frames of implosion experiment. Note compression of core in final frames. 

One of the reasons why we did not push too hard in all these implosion experiments was that both the experimental results and a large amount of theoretical work indicated basic limitations both in the driving mechanisms and in the implosion process itself. 

Figure 8.16. Comparison of calculation and experiment for explosive implosion fragmentation data on uranium cylindrical shells.

Vessels under vacuum do not explode but implode, and the consequences may be significantly worse than the pressure difference of 1 atm suggests. Implosions are, however, very rare and usually result from apparatus being incorrectly designed or handled. The author, with 40 years of laboratory experience, has never seen an implosion. 

Ultrasonic wave clearly enhances the solubilization process (Figure 7, 8). Figure 8 also indicates that diffusion-controlled dissolution maintained even under ultrasonic pulses. The diffusivity under ultrasonic pulses was measured to increase about 3-4 times at the given geometry and power used in this experiment. There are two known effects of ultrasonic waves on solubilization i) acoustic streaming, and ii) cavitation/implosion[24,25]. 

Cavitation/implosion is the most effective mechanism known in ultrasonic cleaning. Cavity formation needs a negative pressure that is generated in the incompressible fluid. The isothermal compressibility of CO2 in the conditions of this experiment is about 2-4 orders higher than that of water at room temperature (Table 2). In other words, CO2 at the current experimental conditions seemed to be no longer an incompressible fluid nor did it induce cavitation/implosion. 

In the meantime Seth Neddermeyer, whose implosion experimentation group Parsons inherited, had visited a U.S. Bureau of Mines laboratory at Bruceton, Pennsylvania, to experiment with high explosives. Edwin McMillan, who was interested in implosion, went with the Caltech physicist ... 

No one doubted that Little Boy would work if any design would. Otto Frisch s Dragon experiments had proven the efficacy of the fast-neutron chain reaction in uranium. The gun mechanism was wasteful and inefficient but U235 was forgiving. It remained to test implosion. While doing so... 

Sunday morning another phone call came with wonderful news. Hans Bethe spent the whole night of Saturday analyzing the electromagnetic theory of this experiment and discovered that the instrumental design was such that even a perfect implosion could not have produced oscilloscope records different from what was observed. So I became again acceptable to local high society. 

Oppenheimer acted quickly to maximize the laboratory s efforts to master implosion. Only if the implosion method could be perfected would the plutoniiun produced at Hanford come into play. Without either a plutonium gun bomb or implosion weapon, the burden would fall entirely on uranium and the less efficient gun method. Oppenheimer directed a major reorganization of Los Alamos in July 1944 that prepared the way for the final development of an implosion bomb. Robert Bacher took over G Division (for gadget) to experiment with implosion and design a bomb George Kistiakowsky led X Division (for explosives) in work on the explosive components Hans Bethe continued to head up theoretic studies and Deke Parsons now focused on overall bomb construction and... 

There must be protections if a container might experience implosion due to a process failure. That may include changes in the process design and components or in the structural elements. The goal is to reduce or eliminate risks. 

Detonations in the cylindrical and spherical experiments were initiated in separate tubes and then allowed to diffract into the main chamber through a small connecting tube. Because of the tube opening at the center of symmetry, the implosion of cylindrical and spherical waves will be incomplete and distorted. Some energy will be directed into the initiator tube, and the gas motion within the main vessel and initiator tube will be coupled. These nonideal effects were not modeled in the numerical simulations or quantified in the experiments. Attempts to directly initiate the detonation within the main chamber did not result in clean waveforms. Failure to have an ideal geometry is one of the sources of uncertainty in the present experiments. 

Simulation of the present experiments with these dissipation models and the standaxd coefficient values made only a slight difference in the predictions in comparison to the observations. An ad hoc increase in the dissipation coefficient values by a factor of 10 yields much better agreement of the simulation with the experiments. The results of that simulation are shown in Fig. 8. We can only conclude that over long times, that is, following multiple reflections of the shock wave, dissipation mechanisms are greatly enhanced by the shock wave-turbulence interactions and, possibly, the nonideal nature of the implosion process at the center of the cylinder. The possibility of significant shock-wave turbulence interactions is consistent with the known turbulent nature of the flow and the observation of large-amplitude pressure fluctuations. 

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