A publication of the Office of Advanced Simulation & Computing, NA-114, NNSA Defense Programs
December 2007
NA-ASC-500-07—Issue
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First Demonstration of Predictive Capability for Weapon Systems in Hostile Nuclear Environments
A Sandia team has completed the first demonstration of a high-fidelity predictive capability for combined system-generated electromagnetic pulse (SGEMP) effects. Without underground testing, a robust SGEMP predictive capability such as that demonstrated by Sandia is needed to design and qualify new systems (e.g., RRW1).
SGEMP effects occur when intense x-rays generate a pulse of electrons in the re-entry vehicle/body (RV/RB) interior that generates strong electromagnetic (EM) fields inside the system. These fields can potentially disrupt electronics. For this milestone, the Sandia team modeled the SGEMP response of a cable, a small cavity, and an enclosed electronic component. For the first time, a prediction of the electrical insult delivered to a subsystem from the combined SGEMP effects was possible. The effects were self-consistently calculated using a lumped-parameter circuit model that integrated all the effects.
The cavity and component SGEMP effects are especially difficult to simulate. For cavity SGEMP, complex physical interactions occur between radiation, EM, and plasma, which are only partly understood. Further development is continuing of models for the physical response of cavity gases as well as component dielectrics and foams in intense radiation environments.
The computational demands for the radiation transport part of the cavity SGEMP analysis were very demanding, requiring up to 700,000 CPU-hours on Purple to resolve the distribution of photo-emitted electrons to the necessary precision. Predicting component SGEMP was also very challenging. For the radiation transport analysis, the electron current distribution across more than 30 million finite elements was resolved to micron resolution at material boundaries. Red Storm was extensively utilized, and each radiation transport calculation required 30,000 CPU-hours. This same mesh was the largest ever used for time-domain EM analysis.
The figure illustrates the calculated electric fields (left) induced in materials near a conducting post during an SGEMP event (side view) and the corresponding density of energetic electrons (right) near the post (top view).
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