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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".〔 This article incorporates material from LANL: © Copyright 2010 Los Alamos National Security, LLC All rights reserved. ''Copyright Notice''. Unless otherwise indicated, this information has been authored by an employee or employees of the Los Alamos National Security, LLC (LANS), operator of the Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies〕 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.〔Fleck, John. "Failure of Axis Plagues Labs", ''Albuquerque Journal'' (26 December 2005): A1.〕 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.〔(Los Alamos' DARHT aces first test ) November 9, 1999〕〔(DOE Says DARHT Fully Operational; Questions Remain ) May 26, 2008〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dual-Axis Radiographic Hydrodynamic Test Facility」の詳細全文を読む スポンサード リンク
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