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 stockpile stewardship 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 . 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 . Description . During a weapon ' s crucial triggering phase , explosive charges that surround the nuclear fuel are detonated at multiple points . The result is a shock wave that moves inward ( implosion ) at supersonic speeds , compressing the fuel to higher and higher density . Implosion ends when the fuel reaches a supercritical density , the density at which nuclear reactions in the fuel build up an uncontainable amount of energy , which is then released in a massive explosion . To make the mockup non - nuclear , a heavy metal surrogate ( such as depleted uranium or lead ) stands in for the nuclear fuel , but all other components can be exact replicas . Sub - critical masses of plutonium may also be used . Under such extreme implosion forces materials tend to behave like fluids , so this mock implosion is called a hydrodynamic test , or hydrotest . Standard practice is to take a single stop - action snapshot of the weapon mockup ' s interior as the molten components rush inward at thousands of meters per second . X - rays that can penetrate the heavy metal in a weapon mockup are made with an electron accelerator . An electron beam moving at near the speed of light is smashed into a tungsten target . The electrons are yanked off course by the strong electrostatic pull of the positively charged nuclei in the tungsten atoms , and their sudden change in direction causes them to give off energy in the form of high - energy x - rays . Scientists already knew how to use a short burst ( pulse ) of high - energy electrons ( rather than a continuous beam ) to make a short pulse of high - energy x - rays . The new challenge was for the accelerator to deliver a very large number of electrons in an extremely powerful pulse to generate a x - ray flash that can penetrate the mockup during the ultra - dense implosion . Specifications call for a pulse of 100 billionths of a second , about a million times shorter than exposures achieved with a high - end conventional camera . As with the hole in a pinhole camera , the smaller the beam spot , the more point - like the area producing x - rays , and the sharper the resulting image . Each electron accelerator consists of a long row of doughnut - shaped magnetic induction cell s , each connected to a high - voltage generator . There are 74 in total in each accelerator but not all may be used . At the instant of firing , each generator discharges its power , creating a pulse of electric current through its induction cell , which in turn creates a large voltage difference across the gap separating that cell from its neighbor . The electron beam - pulse travels through the central bore of the cells , receiving a 200 keV energy kick each time it passes though a gap . One of the design problems was designing the new induction cores to fit in the confines of the previous facility . The design team had to replace the ferrite used in the first axis cores with " metglass " — paper - thin ribbons of amorphous iron tape . The maximum magnetic field strength ( saturation point ) in metglas is five times higher than in ferrite . The magnetic tape was insulated by thin layers of mylar and wound up into a roll of 20 , 000 turns to make mammoth six - foot - diameter cores , each four inches wide and weighing more than one and a half tons . Four cores fit into each induction cell .