Configuration of the two diagnostic instrument manipulators for the first SGEMP experiments, showing the test objects mounted on the equatorial DIMs being driven by the x-ray emission from the target.
(Download Image)NIF Experiments Help Validate Electromagnetic Pulse Codes
An important element of NIF’s National Security Applications mission is helping validate simulation codes designed to determine the effects of system-generated electromagnetic pulses (SGEMP) on various materials. Recently the NIF Team conducted three experiments for the SGEMP campaign, which is led by Sandia National Laboratories (SNL) and the UK’s Atomic Weapons Establishment (AWE).
The experiments were a continuation of the first SGEMP campaign performed last year. In those shots, the NIF laser created 7-keV (thousand-electron-volt) x-ray sources that drove electromagnetic current pulses similar to those generated at Sandia’s Z pulsed power facility in Albuquerque, New Mexico. About 500 kilojoules of ultraviolet laser energy produced the x-ray sources that created electromagnetic responses in various test objects mounted on two NIF diagnostic instrument manipulators (DIMs). Some of the test objects shared the target chamber vacuum, while others were filled with gas.
Five separate experiments contained in the SGEMP diagnostics cassettes spanned a range of conditions important to code validation. Local x-ray environments were diagnosed by calorimeters built into the cassettes, and NIF facility diagnostics provided additional details about the x-ray output from the laser-driven target. The SGEMP team staged a large amount of diagnostic and data acquisition equipment in the Target Bay for the tests. Excellent SGEMP data were recorded in both experiments, and the gas-fill system and in-situ calorimeters performed excellently. Small changes in the diagnostics between the first and second shots greatly improved facility diagnostic data quality.
The recent SEGEMP campaign used new x-ray sources at higher photon energies to get data from a unique x-ray environment. Experience gained in the first campaign enabled the team to optimize set-up of diagnostic and data acquisition systems as well as transactions between the shots. The x-ray sources for the recent tests included the 7-keV source as well as a 13-keV x-ray source created by a plasma formed from a krypton gas target with a unique x-ray spectrum to drive test-article effects. Both the 7-keV and 13-keV x-ray sources were developed and qualified in a series of dedicated shots in previous years. Two upcoming SGEMP shots using stainless steel instead of krypton gas will have 50 percent more laser power and significantly enhanced x-ray flux compared to the earlier shots.
“The known output from the x-ray sources allows SGEMP modelers and designers to develop precise experiments to isolate the physical phenomena of interest to their code validation program,” said LLNL Program Manager Kevin Fournier. “The team is looking ahead to the next set of trials this year that will use the 13-keV source again, but potentially with more than one megajoule of laser drive energy, as well as a new x-ray source with even higher x-ray energies.”
Along with researchers from AWE, members of the SGEMP Team include co-team leader Tim Flanagan of SNL; Program Manager Kevin Fournier of LLNL; Tom Zarick, Randall Romero, and Kate Blesener of SNL; and Marty Yeoman, Charles Brown, Fred Holdener, Steve Compton, Klaus Widmann, and Mark May of LLNL.
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