Dual success for DARHT test

Physics Today : Los Alamos National Laboratory has conducted its first-ever double-viewpoint hydrodynamic test of a nuclear weapon component mockup at LANL’s Dual Axis Radiographic Hydrodynamic Test (DARHT) facility.DARHT has been operational for 10 years on one axis, but using a second axis simultaneously is a milestone for the facility. The test is part of the National Nuclear Security Administration’s stockpile stewardship program to continue to maintain the viability of US nuclear weapons without having to resort to underground nuclear tests."This is an important development,” said Brig. Gen. Garrett Harencak , NNSA principal assistant deputy administrator for military application. “The multiple X-ray images provided by [DARHT] will inform the critical work of our scientists and engineers across the nuclear security enterprise.""Initial indications show excellent data return,” said the hydrodynamic experiments division leader, David Funk. “The baseline experiment captured five time-dependent X-ray images and a variety of data from other diagnostics of pressure, temperature, and timing. This data provides the nation with one of the most rigorous tests of our capability to predict [nuclear] weapons performance."Conducted inside a specially designed double-walled containment vessel, the test used high explosives to drive an implosion of a duplicate of a W78 nuclear warhead made from non-nuclear surrogate materials. As the mockup is imploding, the DARHT facility fires two electron accelerators positioned at a 90-degree angle from one another to generate high-power x-rays that are used to create multiple images of the imploding device’s inner workings, which are then compared with computer predictions.The DARHT team solved a variety of technical challenges in the months and years leading up to this experiment. “While the first axis of DARHT has been functioning nearly flawlessly for more than 10 years, the second axis is still an operational prototype of the world’s longest pulsed electron linear accelerator, so the challenges have been monumental,” said Funk. “Just fitting the accelerator in the building had its challenges, leading to the use of a novel material with an exceptionally high magnetic field strength. Using standard materials would have required the accelerator to be five times bigger than it is, and it would not have fit in the building."Other challenges included designing a cathode injector system that would supply enough electrical current to the accelerator and developing a target that is robust enough to survive four pulses from the extremely high-energy electron beam of the second axis."I couldn’t be more proud of our team’s accomplishments preparing and conducting this first test,” said Funk. “The test marks the beginning of what will be a very long operational lifetime for this important diagnostic tool in support of national security.”