History
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.
When completed in 1999, the first-axis accelerator could produce one short electron pulse lasting 60 billionths of a second with an intensity of 2,000 amps and an energy of 20 million electronvolts. The beam could be focused to 2-millimeter diameter spot on the target. It was the smallest spot size and shortest pulse length ever achieved at that intensity. As a result, image quality was about three times higher than at Livermore's x-ray facility.
The second machine (second axis) is more complicated and, when first completed in 2003, was found to be unusable due to electrical breakdown. The origin of the electrical breakdown turned out to be unexpectedly high electric fields between the high-voltage plate and the oil-insulated magnetic cores and at sites where metal, high-voltage insulator, and vacuum meet inside the cells. After much analysis, the error in design was tracked to be due to faulty equipment used when doing voltage calibrations.
An extensive design overhaul and rebuild was required, which was completed in 2008. The project was initially expected to cost $30 million in 1988, but costs ultimately rose to $350 million.
Read more about this topic: Dual-Axis Radiographic Hydrodynamic Test Facility
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