First demonstration of new particle beam technology at Fermilab

Physicists love to knock particles together and study the chaos that results. Herein lies the discovery of new particles and strange physics that are created in tiny fractions of a second and reproduce conditions often unseen in our universe for billions of years. But for the magic to happen, two beams of particles must first collide.

Researchers at the U.S. Department of Energy’s Fermi National Accelerator Laboratory have announced the first successful demonstration of a new technique that improves particle beams. Future particle accelerators could potentially use this method to create better, denser beams of particles, increase the number of collisions, and give researchers a better chance to probe the rare physical phenomena that help us understand our universe. The team published their findings in the latest issue nature.

Each of the beam’s particles emits ultrafast light pulses as they pass through a special magnet called an undulator sensor (bottom right). Information about the energy or trajectory error of each particle is encoded in its light pulse. Light pulses are captured, focused and adjusted by various light optics. The particles then interact with their own momentum inside the identical kicker undulator (center). The interaction can be used to cool the particles or even control them depending on the system configuration. Image: Jonathan Jarvis, Fermilab

Particle beams are made up of billions of particles that move together in groups called beams. Condensing the particles in each bundle so that they are packed tightly together makes it more likely that particles in colliding clumps will interact—just as several people trying to walk through a doorway at the same time are more likely to push each other , than when passing through it. a wide open room.

Packing the particles together into a bundle requires something similar to what happens when you put an inflated balloon in the freezer. Cooling the gas in the balloon reduces the chaotic motion of the molecules and causes the balloon to shrink. “Cooling” of the beam reduces the chaotic movement of particles and makes the beam narrower and denser.

Scientists at Fermilab used the lab’s newest storage ring, the Integrable Optics Test Accelerator, known as IOTA, to demonstrate and explore a new kind of beam cooling technology with the potential to greatly speed up that cooling process.

“IOTA was created as a flexible R&D machine for accelerator science and technology,” said Jonathan Jarvis, a research scientist at Fermilab. “This flexibility allows us to quickly reconfigure the drive ring to focus on different promising opportunities. That’s exactly what we’ve done with this new cooling technique.”

The new technique is called optical stochastic cooling. This was first proposed in the early 1990s, and while significant theoretical progress has been made, an experimental demonstration of the technique has remained elusive until now.

This cooling system measures how the particles in the beam deviate from their ideal course and then uses a special configuration of magnets, lenses and other optics to deliver corrective jolts. This works because of a special feature of charged particles such as electrons and protons: when the particles move along a curved path, they emit energy in the form of light pulses, providing information about the position and speed of each particle in the group. The beam cooling system can collect this information and use a device called a kicker magnet to bring them back into line.

Traditional stochastic cooling, for which its inventor Simon van der Meer received a share of the Nobel Prize in 1984, works with light in the microwave range with a wavelength of several centimeters. In contrast, optical stochastic cooling uses visible and infrared light with wavelengths around a millionth of a meter. The shorter wavelength means that scientists can more accurately sense particle activity and make more precise corrections.

To prepare the particle beam for experiments, accelerator operators pass it through a cooling system. The improved resolution of optical stochastic cooling allows for more precise impacts of smaller groups of particles, so fewer revolutions around the accumulation ring are required. As the beam cools faster, researchers can spend more time using these particles to obtain experimental data.

“This is exciting because this is the first cooling technique demonstrated in the optical mode, and this experiment allows us to study the most important physics of the cooling process.” – Jonathan Jarvis

The cooling also helps preserve the bunches, constantly reigning in the particles as they bounce off each other. In principle, optical stochastic cooling can increase current cooling rates up to 10,000 times.

This first demonstration on IOTA used a medium-energy electron beam and a configuration called “passive cooling” that does not amplify the light pulses from the particles. The team successfully observed the effect and achieved about a tenfold increase in the cooling rate compared to the natural “radiation damping” experienced by the beam in IOTA. They were also able to control whether the beam cooled in one, two, or all three dimensions. Finally, in addition to cooling beams with millions of particles, the scientists also conducted experiments studying the cooling of a single electron stored in the accelerator.

The optical stochastic cooling device occupies the entire six-meter length of the long experimental line of IOTA. The system, designed and built by the IOTA/FAST team and industry partners, was recently used for the world’s first OSC demonstration. Photo: Ryan Postel, Fermilab

“This is exciting because this is the first cooling technique demonstrated in the optical mode, and this experiment allows us to study the underlying physics of the cooling process,” Jarvis said. “We’ve already learned a lot, and now we can add another layer to the experiment that will bring us much closer to real-world applications.”

After completing the initial experiment, the team is developing an improved system in IOTA that will be key to the development of the technology. It will use an optical amplifier to amplify the light from each particle by about 1,000 times and apply machine learning to add flexibility to the system.

“Ultimately, we will explore different ways to apply this new technique in particle colliders and beyond,” Jarvis said. “We think it’s pretty cool.”

To learn more about IOTA and optical stochastic cooling, read this article.

This work was supported US Department of Energy Office of Science, SC High Energy Physics, and the National Science Foundation.

Fermi National Laboratory is supported by the US Department of Energy’s Office of Science. The Office of Science is the largest supporter of basic research in the physical sciences in the United States and works to address some of the most pressing challenges of our time. For more information visit science.energy.gov.

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