In a March 26 memorandum, Everet Beckner, deputy administrator for Defense Programs at the National Nuclear Security Administration, officially approved completion of the Dual Axis Radiographic Hydrodynamic Test Facility project and authorized close out of the construction phase of the project.

DARHT is a high-explosive firing site equipped with two flash X-ray machines that record interior details of dense metal objects to create time-resolved, stereoscopic images of mock-ups of nuclear weapon components at the moment of implosion.

DARHT's first axis, the world's most advanced hydrodynamic test facility, began providing high-quality images to NNSA's stockpile stewardship program in fall 2000.

"Completing this cornerstone of the national stockpile stewardship program is a major event for the Laboratory and a tribute to the outstanding work done by so many dedicated, hardworking people here and at our partner laboratories," said Ray Juzaitis, Los Alamos' associate director for Weapons Physics. "This is a fitting highlight to celebrate the Laboratory's 60 years in the nation's service."

DARHT's second axis, set at right angles to the first X-ray machine, will capture four images that can be combined with one first-axis image to produce a quasi-three-dimensional image. After commissioning of the second axis is completed in late 2004, these images will help validate the computer models needed for continued certification of aging stockpile weapons.

Modern nuclear weapons consist of two stages - a primary, or fission weapon, and a secondary, which provides thermonuclear yield. Of these, the most critical component is the primary, so a thorough understanding of its performance is essential for confidence in the stockpile.

Hydrodynamic experiments that measure the implosion characteristics of primary systems using simulated nuclear materials permit the evaluation of some crucial aspects of nuclear weapon performance.

Since the United States stopped underground testing of nuclear weapons in 1992, the stockpile stewardship program depends heavily on DARHT to provide insight about how aging stockpile components behave.

To understand whether the safety, reliability and performance of weapon components have been affected by aging, researchers must use radiographs to visually monitor the critical sequences inside a test detonation.

Electron accelerators produce intense, penetrating X-ray beams that, like a flash bulb, can freeze the motion of objects moving at explosively driven speeds of more than 2,000 miles an hour.

Electrons used for the snapshot are accelerated to energies of 20 million volts, and expend that energy in just 60-billionths of a second. The resulting radiographic images are compared with computer models, and differences are examined so researchers can refine their models to more accurately represent weapon behavior.

Using DARHT's first axis, researchers have performed six major hydrodynamic experiments and dozens of smaller high-explosives experiments that provided images of unprecedented resolution and clarity, said Rollin Whitman, DARHT project director.

The complex, four-pulse second-axis accelerator was designed, tested and built through a major collaboration among three national laboratories managed by the University of California - Los Alamos, Lawrence Livermore and Lawrence Berkeley - and the Department of Defense's MIT Lincoln Laboratory.

"We're extremely proud of the hard work of everyone involved with the DARHT project, and grateful for all the help of our colleagues at the other laboratories and our NNSA advisers at NNSA and Department of Energy headquarters and at the Los Alamos Site Office," Whitman said.

"Now that the construction phase is complete, we can focus on testing the various components and the other challenges of commissioning the second axis."

After commissioning, the second axis will give researchers stereoscopic and time-sequenced views of hydrodynamic experiments, which are vital to extending the life of aging nuclear weapon components, proving that remanufactured weapon pits are suitable for the stockpile, and validating new simulations that are now the key to certifying weapons safety and reliability in the absence of underground testing.

DARHT will be the stockpile stewardship program's primary experimental facility for the coming decade.

Because the new technology built into DARHT's state-of-the-art second axis was highly experimental, the Laboratory used reviews by an external panel of top technical and project management experts to assure its approach was sound.

The outside experts provided recommendations that helped the Laboratory and NNSA complete the engineering, baseline budget and multiple technical milestones needed to complete the project.

DARHT's first axis met all technical criteria; it was completed on time and for slightly less than its budget of $105 million. Construction of DARHT's second axis was completed recently within its capital budget of $154.6 million.

In December, DARHT's second-axis accelerator successfully transported an electron beam that met all the major technical criteria for close-out approval of the project, approval that was granted by Beckner last week.

All four major milestones have now been met, on schedule, as follows: demonstration of the second-axis injector (July 2, 2002); demonstration of the second-axis accelerator (Dec. 21, 2002); delivery of the second-axis gamma-ray camera system for imaging of X-ray data (Feb. 6, 2003); completion of the vessel preparation facility for clean-out of single-walled steel vessels. (Feb. 10, 2003).

Laboratory management and federal representatives will formally dedicate the DARHT facility in ceremonies scheduled for April 22, as part of the Laboratory's 60th anniversary celebrations. Media representatives are invited to attend.

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