DARHT gets kudos from headquarters

By ROGER SNODGRASS, Los Alamos Monitor Editor

During a recent trip to Los Alamos National Laboratory, a senior official of the National Nuclear Security Administration made a special point of visiting the hydrotest facility.

Steve Goodrum, assistant deputy administrator, science engineering and production, said that after his trip was scheduled, word came in that the second axis of the lab’s Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) had met and exceeded its requirements for beginning operations.

“When the e-mails and calls started coming in about DARHT’s success,” he told employees at the facility Wednesday, “the news permeated the (DOE headquarters) Forrestal Building.”

So Goodrum asked to make this special side trip. He passed along congratulations and formal certificates of appreciation to members of the team and took a tour of the newly proven second axis.

Accompanying Goodrum were LANL Director Michael Anastasio and Charles McMillan, associate director for weapons physics. The delegation from Washington also included NNSA science campaign manager Chris Deaney.

Ray Scarpetti, the DARHT second-axis project manager, conducted a tour of the accelerated hall and the complex electron beam that produces the x-rays which is expected, beginning in a few more months, to give multiple high-resolution images from inside exploding mock nuclear weapons.

The capability is considered essential for verifying the reliability of the nuclear weapons stockpile without testing actual weapons.

The second axis was thought to be complete in 2003, as JASON, the prestigious national security consulting team, pointed out in their project review in 2006. Scarpetti said JASON found the approach to be solid, but still saw the project as risky.

“There are uncertainties in the ability of a target to generate more than two satisfactory radiation pulses,” JASON wrote.

But they also recognized, “There are well-structured development programs aimed at curing both of these problems.”

As the recent results demonstrated, the problems have been cured. “I expected the results to be good,” said Scarpetti, “but they’re really good.

The second axis was expected to meet or exceed several criteria, including a certain voltage and a certain electrical current, as a prerequisite for breaking a powerful beam into four separate pulses.

The pulses enable the camera that shoots at 400 billionths of a second to capture an image and then download the data during the interval.

Another requirement had to do with the spot size, which relates to the sharpness of the image that the camera can capture.

The first axis of the facility was considered a benchmark, able to produce a 2.3 mm spot.

In its groundbreaking performance, the second axis came in at 1.6 mm, a substantial improvement.

A final criterion had to do with dose, the measure of the radiation of the x-ray intensity, and therefore how well the dense materials under investigation could be penetrated.

Trying to achieve a dose of 100 rad at 1 m., in the first 3 pulses and 300 in the final pulse, the team achieved 170, 185, and 170 rad on the first three pulses and 445 rad on the final test.

Again the goals were exceeded by more than 50 percent.

“We made it look easy,” Scarpetti said who attributed this and other achievements to teamwork and a practice of bringing in leading experts from around the country.
Scarpetti gave special credit to Subrata Nath, his deputy.

“I had on staff or as consultants the best team that could be assembled throughout the country,” he said. “Through the roughest times I never lost faith that we could get there.”