Puzzling together Fermilab’s ASTA beam dump

An ironworker positions a structural component of the beam dump. Photo: Curtis Baffes, AD

At the back of the facility housing Fermilab’s Advanced Superconducting Test Accelerator is an elaborately constructed cube of steel and concrete, meticulously pieced together in Tetris fashion using many pieces gleaned from laboratory grounds.

The recycled-steel and -concrete cube will serve as the high-energy beam dump for the future ASTA electron beam. The beam dump stops the particle beam after it has passed through the accelerator and the test beamlines. Last December, Fermilab completed the construction of the dump and installed the beam absorbers at its core. Its completion was the realization of a year of design and engineering work, led by Curtis Baffes from AD’s mechanical support department.

“It was fun putting it together,” Baffes said. “I tried to puzzle together the re-used steel as well as I could, making sure that the blocks, which varied widely in size and shape, would end up fitting tightly.”

At the heart of the two-story-high dump are two beam absorbers, each about the size and shape of a lateral filing cabinet. Nestled deep inside the dump, the absorbers are surrounded by steel plates, which in turn are surrounded by concrete blocks. Together, they stop the beam, contain its energy and shield the outside world from radiation.

To make economical use of the laboratory’s resources, Baffes and his team built much of the beam dump from spare parts. They scavenged through hundreds of steel and concrete blocks on the laboratory’s grounds and in its property database to find the collection of pieces that required a minimum number of cuts to fit into the prescribed space.

The space is a 28-foot by 24-foot by 26-foot high dedicated room at the end of the future beam line’s path. Over the course of several weeks and with the help of a crane, Fermilab’s Craig Rogers guided ironworkers as they lowered 1,200 tons of shielding in the prescribed order into the facility.

The dump needs to be able to stop a beam in its tracks. Using a configuration developed by Fermilab scientists Mike Church and Igor Rakhno, Baffes implemented a beam absorber design that would catch the beam and effectively dissipate its 75 kilowatts of power.

Permanently surrounded by shielding, the absorbers had to be tested at every step of their construction to minimize any chance of having to break it open later to fix an overlooked error.

“We tried to have quality assurance at every step so we wouldn’t send anything to the next level of assembly that we hadn’t tested pretty exhaustively, or that we didn’t develop a high level of confidence in,” Baffes said. Fermilab technicians Chris Exline, Dave Franck, Wayne Johnson and Ron Kellett were instrumental in this absorber assembly and testing program.

Now that construction of the beam dump is finished, it awaits beam tests, which will occur near the end of the calendar year.

—Leah Hesla