A career of chasing particle beams

Alex Bogacz, a senior scientist at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility since 1997, has spent his career in accelerator physics solving problems. From studying complex particle beam dynamics in particle accelerators to designing next-generation machines, his almost four decades of work have recently been recognized by his peers by being named a Fellow of the American Physical Society in October 2024.

“This is a very flattering and distinguished honor,” said Bogacz, who also leads the Accelerator Physics group in Jefferson Lab’s Center for Advanced Studies of Accelerators.

An APS fellowship recognizes those members who have made advances in physics research or significant innovations in the application of physics to science and technology. Bogacz, who was nominated by his professional peers and selected by the APS Council, was cited “For the development of a broadly adopted novel coupling formalism for accelerators, its application to innovative recirculating linac designs, and leadership in high-energy recirculating linac design for ERLs [energy-recovering linear accelerators], muon colliders, and CEBAF upgrades.”

A novel expression

The first accomplishment recognized by APS, a formalism, is a mathematical representation of particle beam motion with two degrees of freedom. This work began when Bogacz arrived at Jefferson Lab 27 years ago. His first job was to improve the Continuous Electron Beam Accelerator Facility (CEBAF) by redesigning the beam optics that governs the machine’s electron beam transport.

The horizontal and vertical motion of the electron beam are coupled, which makes its motion much more complex. When designing accelerators, it’s important to understand this complicated coupled motion, but back then, there was no suitable representation to study a machine like CEBAF. 

“In my quest, I needed to have a tool to easily study this,” Bogacz said.

Bogacz grew up in an academics-focused household in Wroclaw, Poland. His father was a chemistry professor, and his mother was a professor of linguistics. Early on, he was fascinated by prime numbers and attracted to the problem-solving aspect of math.

“Math was my first love,” said Bogacz, who participated in the Math Olympics in grade school. “I always found an underlying beauty in doing analytic calculations with paper and pencil.”

So, despite majoring in physics during graduate school at the Technical University of Wroclaw, Bogacz continued to pursue his first love, taking math classes that weren’t required. One such class was group theory. Knowledge acquired during this group theory class allowed him to gain new insight into a mathematical representation of coupled betatron motion. The results were published in October 2010.

Bogacz drew on his background in math, creating a Weyl-like group generated by 10 independent operators constructed from the eigen-vectors of the Hamiltonian. An irreducible representation of that group served as the new parametrization of the coupled betatron motion. 

“I consider that my single most important contribution to accelerator physics,” Bogacz said. “It has a very practical application to studying beam dynamics and is important to many researchers.”

Since publication, this formalism has been widely used by physicists to more accurately model and better design accelerators. CERN researchers, for example, coded the formalism into MADX, a program used to simulate and design accelerators. The result is an improving understanding of coupled beam motion’s effects.

This technique of combining seemingly unconnected advanced math with his understanding of accelerator physics to create new solutions for accelerators would prove to be a trend throughout Bogacz’s career.

Beam leadership toward multiple machines

Bogacz says that his interest in accelerators started while he was earning his Ph.D. at Northwestern University. His curiosity was sparked by an accelerator physics course taught by two scientists from DOE’s Fermi National Accelerator Laboratory. He eventually followed these inspiring teachers to Fermilab. During his eight years there, Bogacz worked on studying collective instabilities in different accelerators of the Tevatron complex, and he also got involved in a muon accelerator program.

Muons, a type of short-lived elementary particle, rapidly decay after they are produced, making it very challenging to produce a beam of muons for experiments. Scientists figured out that they need to accelerate muons very rapidly (close to the speed of light) to form a beam. Serving as a co-spokesperson, Bogacz pioneered muon cooling and acceleration experiments that used crystals to form muon beams for future muon colliders at TRIUMF, Canada’s national particle accelerator center,

However, using the classic racetrack-shape to accelerate muons would be costly. Another college math class, topology – the study of stretchable shapes – helped Bogacz design a more efficient shape for muon acceleration.

Thinking back to this course, Bogacz considered how different accelerator shapes would affect the amount of energy imparted to the particles racing around inside. He took the racetrack shape and squished the two linear accelerators together, closing the gap in between them to form one piece. He then closed the curves on the end to form droplets. When he calculated how much energy this would give to muons per lap, he was floored: this “dog bone”-shaped accelerator could accelerate muons twice as efficiently as the racetrack topology.

“The dogbone topology is a game changer for muons,” Bogacz said. “I consider this design my intellectual contribution to accelerating fast-decaying particles like muons.”

Bogacz originally proposed the dogbone design about 20 years ago. More recently, it has been revived by his peers at CERN and in the International Muon Collider Collaboration as a potential shape for a future muon collider in the U.S.

“It’s very rewarding for me when my ideas are used by other scientists,” said Bogacz, who is providing input to this project with his colleagues at Jefferson Lab.

After spending a year as a visiting scholar at the University of Tokyo, where he worked on designs for J-PARC, the Japan Proton Accelerator Research Complex at the High Energy Accelerator Research Organization (KEK) in Japan, Bogacz finally arrived at Jefferson Lab.

He says that he loves the lab’s smaller size and close-knit community.

“Within a year, I was pretty much able to learn about all the systems and know all the people from other departments,” Bogacz said. “Right away, I got involved in the most important things.”

At Jefferson Lab, Bogacz has served as a co-spokesperson for an energy recovery demonstration experiment at CEBAF. Using a system of magnets, Bogacz and his team were able to recover the same amount of energy as what was originally injected into the machine, a result working toward more sustainable accelerators.

And Bogacz isn’t done. He’s currently leading the accelerator design effort for a potential upgrade to Jefferson Lab’s main accelerator: the 22 GeV CEBAF upgrade project. CEBAF is currently a DOE Office of Science user facility with more than 1,900 scientific users worldwide. However, as nuclear physicists look to the future, they hope that an upgrade of the machine will allow exploration of new realms of physics that are currently inaccessible anywhere else.

Bogacz says that he will also continue to share his knowledge of particle accelerators built over a lifetime of learning and research. He plans to continue teaching for the annual U.S. Particle Accelerator School, a role he has enjoyed for the past decade.

“This is not the end of my work,” Bogacz said. “I still feel young at heart.”

By Chris Patrick

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Jefferson Science Associates, LLC, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science. JSA is a wholly owned subsidiary of the Southeastern Universities Research Association, Inc. (SURA).

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science