Hydrodynamics, which literally means ‘water motion’, is the science of forces acting on or exerted by fluids.
It’s a key field of investigation for AWE scientists because when the primary stage of a nuclear warhead is explosively compressed, components experience extremely high rates of strain – causing them to behave like fluids.
Prediction of the dynamic behaviour of materials as they flow under the influence of high pressure and stress is of considerable importance to understanding weapons. Without recourse to underground testing, above ground experiments have an important role in providing data to assess weapon safety and performance.
AWE conducts hydrodynamic experiments where small amounts of material are subjected to explosive shocks in specially sealed chambers. These experiments are photographed by giant X-ray machines and data is collected from a range of diagnostics.
The experiments carried out at AWE involve explosive compression of materials to observe how compression and shock waves develop, and how materials behave at interfaces between components.
Two approaches are followed in order to obtain the necessary experimental data. Firstly, complicated integrated experiments are carried out on devices as closely resembling the real warhead as practically possible. Secondly, simplified experiments are carried out to gain a more fundamental understanding of individual aspects of hydrodynamics.
Given the nature of these experiments, it is necessary to have specialised experimental facilities and diagnostics capable of performing under extreme conditions. Explosive experiments take place within reinforced firing chambers designed to safely contain the experiment. Simulant materials such as tantalum or lead are normally used in these experiments, but due to the unique properties of plutonium, a small number of experiments involve plutonium itself. In these cases, the amount of fissile material used is far below the quantity necessary to produce nuclear yield, and as a further precaution, tests involving toxic or fissile materials are completely contained within a further leak-light vessel.
To study the movements of shockwaves through high density material, AWE has developed a technique using powerful X-ray machines to record snapshots of the experiment. Data is then collected using a suite of diagnostics capable of performing under extreme conditions.
It’s important to obtain data to the highest possible accuracy, therefore much effort goes into improving the existing diagnostics and developing new ones. Work is underway to develop the next generation of experimental facilities, which will ensure AWE’s world-leader status is maintained in this important field of science.