Machining ultra-pure copper begins

Machinist Randy Hughes uses a press to flatten one half of a copper cylinder that was electroformed at the Majorana Temporary Clean Room.
Credit: 
Matt Kapust

Ultra-pure copper grown on the 4850 Level is finally being machined into parts for the Majorana Demonstrator experiment, and it’s happening in a clean-room machine shop also on the 4850 Level. “It’s going extremely well,” says experiment spokesman Steve Elliott of Los Alamos National Laboratory.

For more than a year copper has been electroformed in the Machinist Randy Hughes uses a press to flatten one half of a copper cylinder that was electroformed at the Majorana Temporary Clean Room. Temporary Clean Room (TCR) near the Ross Shaft. The process is simple but slow. Copper slug are dissolved in acid baths, then an electric current is run through the baths. Copper atoms adhere to stainless steel forms, called “mandrels,” to a thickness of about 5/8ths of an inch. Trace impurities in the original copper remain in the acid bath. Protected from the corrupting effects of cosmic radiation by nearly a mile of rock, TCR copper has no detectable radioactive isotopes. It’s the world’s cleanest, quietest copper.

The first copper-coated mandrels from the TCR were delivered to the Majorana machine shop, a kilometer away in the Davis Campus, on July 28. Machinist Randy Hughes of Adams IFC in Rapid City, had actually begun machining copper there in mid-July, but those first batches came from Pacific Northwest National Laboratory in Washington. The most sensitive parts of the Majorana experiment will use TCR copper.

Turning raw copper into scientific instruments is a multi-stage process. First, Hughes puts a copper-coated mandrel on a lathe to remove rough spots. Then he bakes the mandrel in an oven, then dunks it into water. The stainless steel mandrel shrinks in the cool water, allowing its copper coating to drop off—in the form of a hollow copper cylinder.

Hughes cuts the cylinders in half, then uses a press to squash them flat. He mills the flattened copper to “just a hair under half an inch,” and he means that literally. The copper plates are shy of half an inch by one five-thousandth of an inch—about the thickness of a human hair.

Then Hughes can machine the copper plates into the variety of parts, and he’ll be at it for awhile. Only about half the 5,000 pounds of copper that Machinist Randy Hughes uses a press to flatten one half of a copper cylinder that was electroformed at the Majorana Temporary Clean Room. will need has been electroformed, and Elliott said the machining could take two more years.

Hughes welcomes the challenge. He has 30 years’ experience as a machinist and toolmaker, much of it in Detroit, and he’s worked on complicated, demanding projects with tolerances measured in millionths of an inch. Still, he calls this job “the chance of a lifetime.” The Majorana Demonstrator will look for a yet-to-be-observed phenomenon called “neutrinoless double-beta decay” that could shed light on how the universe evolved. “This whole project’s a tad over my head,” Hughes admits, but he gave up his position as a supervisor at Adams IFC to work on it. “There are not many machinists who are going to be able to put on their resume that they worked in a clean-room machine shop 4,850 feet underground,” he said.