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DARHT temporarily sidelined

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By Roger Snodgrass

The dual axis X-ray facility, described as a come-from-behind success story for Los Alamos National Laboratory this year, has suffered an accident and is back on the injured list.

Having been declared fully operational by the National Nuclear Security Administration in May and on track toward its first ever experiment using its second axis, the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility misfired last week.

DARHT is meant to be one of the ultimate tools for analyzing the condition of nuclear weapons in the nuclear stockpile, by peering inside mock nuclear devices under near-test pressures with a double barrel of penetrating X-rays.

A laboratory official blamed the resulting internal damage on an unexpected result while the beam of high-energy electrons was being tuned. During the process, the beam is focused on a graphite stopper, until the beam is properly configured. At that point, the stopper is removed and the beam strikes a tungsten target producing X-rays. But on July. 31 the system to backfired before getting to that point, causing a “backstream” of atomized carbon from the stopper to flow back into the internal workings of the beam line.

DARHT’s first axis has been working since 1999, but the second axis has had a rougher road. The project history reveals a significantly expanded concept followed by equipment failures. New technologies had to be developed and budgets ballooned.

The purpose of the second axis was expanded to produce a more powerful beam that could be “kicked” into four separate x-ray shots to record the sequence of events inside an imploding object.

“It’s an unwelcome thing, but when you’re doing something for the first time and you’re putting together a highly complex machine, you do expect things like this to happen,” said Laboratory spokesman Kevin Roark Tuesday. “You’d like it better if they didn’t happen, but it’s a setback, not a disaster.”

The facility will now begins a clean-up phase of “fewer than 20 out of the 74” accelerator cells, Roark said, along with some other scheduled maintenance.

Corrective action, depending on the analysis of the problem, could include administrative controls or adding a procedural step.

“Or they might consider some kind of engineered control,” Roark said.

“The good news is that when they redesigned the second axis, they took into account that there might be a time a cell would fail, or a problem with a group of cells, so it was designed not to have to take the whole thing apart like axis one,” he said.

A full test of the duel axis system was scheduled for August, but that schedule was already slipping into the fall. With an additional delay, the test is now projected for early 2009.