How a Despatch Oven Is Helping Produce Ultra-Pure Copper a Mile Underground

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Matt Kapust

Matt Kapust

A process known as a “quench” results in batch after batch of the world’s purest copper several times a month in the Majorana Demonstrator experiment’s clean-room machine shop.

Crazy enough, the shop is actually located a mile underground for safety reasons and some of the copper is designated to be used as part of a 2-inch-thick shield that will protect Majorana from background radiation.

However, the copper must be purified first since its surface is polluted by cosmic radiation.

Extremely pure copper nuggets are brought 4,850 feet underground, to a clean room near the Ross Shaft, where the copper is then dissolved in acid baths and eventually electroformed onto cylindrical stainless steel molds, called “mandrels.”

The next step is transporting the copper-coated mandrels, each about 23 inches tall by 13 inches in diameter, over half a mile from the electroforming lab to the Majorana machine shop.

A lathe is used to eliminate the rough copper surfaces before finally getting to the quench.

In preparation for the quench process, the mandrels are baked in a Despatch oven at 600 degrees F. for six hours.

After a waiting period, machinists using insulated mitts open the oven and roll in a small counterweighted crane.

The hot mandrel is rolled out of the oven by attaching a hook, where a stainless steel tank of deionized water is then positioned underneath the mandrel.

From here, a hand lever lowers the hot mandrel into the room-temperature water which generally results in a startling CRACK as the hot copper comes into contact with cold water.

Eventually, the mandrel is submerged until the stainless steel at the top hits the water and it shrinks enough to allow a hollow drum of ultra-pure copper to slide off the mandrel into the tank.

Boom! New plate stock that Majorana Project Engineer Matthew Busch of Duke University says will be used to help shield the experiment from radiation.

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