Secondary Physics
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AWE’s Secondary Design Group is responsible for the second stage of a nuclear device, known as a secondary. Our major responsibilities are to maintain design capability and to underwrite the operation of the secondary, and hence the overall nuclear functioning of the UK nuclear deterrent, Trident.
The physics-based understanding of how such systems perform is confirmed by experimentation, which in the past (before the Comprehensive Nuclear Test Ban Treaty) could involve the detonation of nuclear explosions and measurement of the resulting outputs.
Nuclear explosions were often carried out in the United States at the Nevada Test Site, where such tests – carried out underground – were known as UGTs (underground tests).
Such a test involved the boring of a deep hole in the rock into which the device was lowered. Above the device would be a large diagnostic rack connected to dozens of cables which carried vital information quickly from the detectors to recording instruments above ground. A thorough understanding of the physics involved in the actual diagnostic techniques is also crucial to the interpretation of the data.
The interpretation of UGT data requires a deep understanding of many branches of physics. These include: high and low temperature plasma physics, hydrodynamics, nuclear reactions, thermonuclear reactions, and the transport of energy by radiation and conduction.
The tested devices are modelled with complex simulations using large computer codes, which have been written in-house at AWE and are still being improved. The results of such simulations are compared with the diagnostic measurements in order to understand the operation and performance of nuclear weapons. This enables us to maintain and develop capability, as well as assure the safety and integrity of the current stockpile.
The modelling of a secondary stage involves the challenging areas of shock phenomena, radiation physics, material properties such as Equation-of-State (EoS) and opacity, plasma physics, nuclear physics and hydrodynamics (involving turbulence and the mixing of materials). One, two and three dimensional hydrodynamic, radiation and neutronic codes are used to model these processes, using AWE's Supercomputing facilities.
The Secondary Design Group uses innovative mathematical techniques and analysis tools to produce an assessment capability at the system, sub-system, and component levels. The continued reliability of the UK nuclear deterrent depends heavily on this capability.
Now that international treaties forbid underground testing, the design and assurance of the UK national deterrent has to be maintained using computer simulation and permitted non-nuclear above ground experiments (AGEX).
Opportunities exist to design new AGEX; both laser driven plasma experiments (in collaboration with our Plasma Physics department) and explosively driven materials experiments (in conjunction with our Hydrodynamics department), specify the data to be collected and carry out the analysis of the results.
Such experiments are a means of validating existing computer models, identifying any shortcomings in physics understanding, and developing improved models. Challenges also exist to analyse the full scale nuclear explosion experiments conducted in the past, in order to resolve the issues which were not fully understood at the time they were fired, and to develop new insights.
The physics-based understanding of how such systems perform is confirmed by experimentation, which in the past (before the Comprehensive Nuclear Test Ban Treaty) could involve the detonation of nuclear explosions and measurement of the resulting outputs.
Nuclear explosions were often carried out in the United States at the Nevada Test Site, where such tests – carried out underground – were known as UGTs (underground tests).
Such a test involved the boring of a deep hole in the rock into which the device was lowered. Above the device would be a large diagnostic rack connected to dozens of cables which carried vital information quickly from the detectors to recording instruments above ground. A thorough understanding of the physics involved in the actual diagnostic techniques is also crucial to the interpretation of the data.
The interpretation of UGT data requires a deep understanding of many branches of physics. These include: high and low temperature plasma physics, hydrodynamics, nuclear reactions, thermonuclear reactions, and the transport of energy by radiation and conduction.
The tested devices are modelled with complex simulations using large computer codes, which have been written in-house at AWE and are still being improved. The results of such simulations are compared with the diagnostic measurements in order to understand the operation and performance of nuclear weapons. This enables us to maintain and develop capability, as well as assure the safety and integrity of the current stockpile.
The modelling of a secondary stage involves the challenging areas of shock phenomena, radiation physics, material properties such as Equation-of-State (EoS) and opacity, plasma physics, nuclear physics and hydrodynamics (involving turbulence and the mixing of materials). One, two and three dimensional hydrodynamic, radiation and neutronic codes are used to model these processes, using AWE's Supercomputing facilities.
The Secondary Design Group uses innovative mathematical techniques and analysis tools to produce an assessment capability at the system, sub-system, and component levels. The continued reliability of the UK nuclear deterrent depends heavily on this capability.
Now that international treaties forbid underground testing, the design and assurance of the UK national deterrent has to be maintained using computer simulation and permitted non-nuclear above ground experiments (AGEX).
Opportunities exist to design new AGEX; both laser driven plasma experiments (in collaboration with our Plasma Physics department) and explosively driven materials experiments (in conjunction with our Hydrodynamics department), specify the data to be collected and carry out the analysis of the results.
Such experiments are a means of validating existing computer models, identifying any shortcomings in physics understanding, and developing improved models. Challenges also exist to analyse the full scale nuclear explosion experiments conducted in the past, in order to resolve the issues which were not fully understood at the time they were fired, and to develop new insights.