Dual-Axis Radiographic Hydrodynamic Test Facility

The Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) is a facility at Los Alamos National Laboratory which is part of the Department of Energy's program. It uses two large X-ray machines to record three-dimensional interior images of materials. In most experiments, materials undergo hydrodynamic shock to simulate the implosion process in nuclear bombs and/or the effects of severe hydrodynamic stress. The tests are described as "full-scale mockups of the events that trigger the nuclear detonation". The powerful pulsed X-ray beams allow for an ultra-fast motion picture to be constructed showing the details of the process being studied in three dimensions. The tests are often compared with computer simulations to help improve the accuracy of the computer code. Such testing falls under the category of sub-critical testing.

Planning for DARHT began in the early 1980s.Lawrence Livermore National Laboratory in California had already developed an advanced electron accelerator for its own x-ray hydrotest facility, and that machine, known as a linear induction accelerator, met many of DARHT's requirements. In 1987 Los Alamos chose the same type of accelerator for its facility.

The project became an important priority after the United States stopped testing nuclear weapons in 1992. Approval for an overhaul and new axis came in stages, with the first axis approved for construction in 1992 and the second axis (initially to be a twin of the first) in 1997. This plan was changed when the Department of Energy decided it wanted the second axis to deliver not one view of the implosion, but a series of views in rapid succession.

Construction was halted between 1995 and 1996 due to lawsuits by Los Alamos Study Group and Concerned Citizens for Nuclear Safety, two anti-nuclear weapons organizations demanding that the laboratory produce an Environmental Impact Statement for its construction and operation. It has also been argued by activists that DARHT is a violation of the Comprehensive Test Ban Treaty and potentially the Nuclear Non-Proliferation Treaty, though the lab and the DOE reject this view.

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