A joint Fermilab/SLAC publication

Tabletop ATLAS assembly, no hardhat required


Physicist Sascha Mehlhase may have missed the actual construction of the ATLAS detector at CERN, but he found another way to experience the joy of building it – a way reminiscent of his childhood and the contents of a particularly good toy box he once had. He made the detector out of Legos.

Two colleagues at Mehlhase’s office at the Niels Bohr Institute in Copenhagen put forward the idea of building the detector out of Legos for a public event last year, but they never got around to doing it themselves. Last month as a similar event approached, Mehlhase decided to go for it. To the displeasure of his wife, he spent an entire weekend using the free digital designer software on Lego.com to translate photos and 3D renderings from the ATLAS website into a plan for plastic.

He scaled the model to a Lego man, a few centimeters in height, corresponding to a two-meter tall human, which made the finished masterpiece nearly a half-meter in height. The fixed selection of blocks, however, meant that everything didn’t scale with exactly 100 percent accuracy.

“Sometimes in LEGO you get these pieces in lengths of two, four, six or eight when a seven would be perfect,” Mehlhase said.

He convinced the head of his group to buy the 10,000 pieces his design called for, which arrived in a huge package with about two-thirds of its contents in need of sorting. Mehlhase and a few students started doing this by color and then by type – a task he estimates took about a quarter of the total time.

Soon Mehlhase discovered that the project was more formidable than he’d foreseen. An instruction manual created by the Lego software yielded “4,500 pages of almost useless material,” Mehlhase said. Because the detector is a symmetrical machine, inside-out assembly makes more sense than bottom-to-top, which the computer didn’t realize.

So he abandoned the manual. Instead, over the course of a few weeks, he spent 33 hours comparing the digital Lego design he’d made with his bins of sorted pieces, figuring out by sight where things should go.

“So far I’ve managed everything without glue,” he said.

The public event passed, but Mehlhase was on a mission. Brick by primary-colored brick he toiled. A few challenges scientists faced in creating the real ATLAS detector proved challenging in the LEGO model as well. For example, the outer magnets in both structures are much heavier than some internal pieces, yet they need to support themselves without breaking.

Mehlhase finished the mini-detector, complete with tiny technicians and red block “ATLAS” sign, in early November. His group at Copenhagen plans to use it for outreach. A few other institutions have emailed him about the designs, and he said he’d gladly share. He says he’d like to see his Lego ATLAS design at CERN one day.

For now Mehlhase plans to display the model in a glass case in the hallway outside his office. The real ATLAS detector may belong to the thousands of physicists who built and run it, but this one is all Copenhagen’s.

Image courtesy of Sascha Mehlhase.

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