Over the next decade, new particle physics experiments will come online at Fermilab—and they will all be hungry for particle beams. The lab is upgrading its accelerator complex to meet the heightened demand. Each experiment may have different beam requirements, including the timing of the beam delivery. A device called a chopper plays a key role in this timing. It divides the beam according to the pattern set by the experiment. Accelerator experts developed a prototype that successfully met every one of the stringent requirements placed on it.
The nimble, precise, and hardy chopper is vital to creating a versatile particle accelerator that can ship and sort beams of various intensities to various sites. Its development is a significant leap forward in accelerator technology that opens doors in discovery science. Also, it may have uses in industry and medicine.
If you were to zoom in on a beam in Fermilab’s accelerators, you would see not a continuous flow of particles but rather a queue of discrete particle packets. Scientists call these packets “bunches.” Scientists create custom particle beams by removing select bunches from the queue. For example, experts can adjust settings to eject every third bunch, with the remaining bunches forming a particular pattern that’s optimized for an experiment. The device that carries out the high-precision task of bunch removal is the beam chopper.
When, several years ago, a team of Fermilab accelerator experts set out to design the chopper that would become part of the lab’s upgraded accelerator complex as part of the Proton Improvement Plan II project, called PIP-II, nothing even close to what they needed existed. The difficulty was that the chopper needs to remove each unneeded bunch carefully, without perturbing its neighbors. In PIP-II, the millimeter-long bunches of negative hydrogen ions (a proton with two electrons) follow each other within only six billionths of a second—not much time to cleanly remove ion bunches. Novel solutions allowed the design of chopper prototypes that meet PIP-II’s exacting specifications. The chopper tests were resoundingly successful. Further work remains, but given the promising results of these first tests, the accelerator team concluded the beam chopper will work in Fermilab’s upgraded accelerator complex.
This work was supported by Fermi Research Alliance, LLC under contract with the Department of Energy, Office of Science, Office of High Energy Physics.
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