Marching elephants

Sergei Nagaitsev

Sergei Nagaitsev, head of the Accelerator Division, wrote this column.

By most accounts, Hannibal’s Rome invasion force in 218 B.C. included 37 or 38 elephants. Nobody knows how he managed to march his army and his elephants over the Alps, but he ended up occupying much of the Roman homeland for many years.

Our invasion force into the neutrino empire includes 19 cavities in the Booster — Fermilab’s oldest synchrotron, built more than 40 years ago. This week we achieve a great milestone — we will install the 10th of these radio-frequency cavities, which accelerate bunches of protons needed for Fermilab’s neutrino experiments.

The cavities were originally constructed in the 1960s and installed in the Booster tunnel in the early 1970s. They were never designed to operate at beam intensities requested by proton-hungry neutrino experiments. Fermilab is currently executing a cavity refurbishment program as part of the Proton Improvement Plan project, led by William Pellico (AD) and Robert Zwaska (APC).

Refurbishing these 40-year-old accelerator cavities is an involved business. Once a cavity is removed from the Booster tunnel, it’s allowed to “cool down” to reduce its radio-activation levels, after which it is disassembled and inspected. The damaged parts are replaced or repaired, and others are cleaned. Then it is reassembled. The final step is to test the cavity at full power and the maximum repetition rate. After that, it is ready for installation in the tunnel.

Much like marching an elephant over the Alps (I would imagine), it takes about 10 weeks to refurbish one Booster cavity. It turns out that the Booster needs at least 17 cavities in order to operate reliably, so we are “marching” two elephants at a time. With the installation of cavity number 10, we are halfway over the Alps!

July 1970: A flatbed semitrailer delivers a pair of Booster radio-frequency cavities. Photo: Fermilab