Only 40 feet underneath Cornell University’s football field, electron and positron beams race around a half-mile loop of narrow piping nearly as fast as the speed of light in a machine known as the Cornell Electron Storage Ring, or CESR.
Junior Laura Salo’s research involving CESR at Cornell this past summer helped move the team one step closer to achieving the goals of the Cornell Laboratory for Accelerator-Based Sciences and Education, CLASSE, to produce the brightest source of X-ray beams in the United States.
“As the particles pass through deflecting magnetic fields, X-rays are emitted and these are used for X-ray research at Cornell,” said Michael Billing, an accelerator physicist at Cornell and Salo’s research supervisor.
Salo worked in the Wilson Laboratory at Cornell where she used a computer program to determine how some proposed modifications, called the CHESS-U upgrade, would affect the stability of the particle beam in the machine. After electrons and positrons have been accelerated in a different ring, they are moved into CESR, where these beams are maintained near the speed of light, Salo said.
“When the beams get up to speed, they’ll exit the ring and go into the Cornell Electron Storage Ring, or CESR, and it’s in that storage ring that they are maintained at this speed,” Salo said. “That’s also where they oscillate the beam to produce X-rays.”
The X-rays can then be used in other research projects to study the characteristics of different samples as they interact with the destructive X-ray beams.
To improve the brightness of the X-ray beams produced using CESR, researchers at the laboratory proposed adding new components along the ring and replacing parts of the ring with narrow pipes that would require a more focused beam, Salo said.
Before they could make these modifications, however, the research team needed to know precisely how the upgrade would affect the stability of the particle beam..
“You’ve got to have a pretty focused beam to get particles moving near the speed of light to consistently shoot through a narrow pipe,” Salo said. “That’s what my project was doing. I was basically calculating how stable the beam was based on the impact from different factors in the ring, like undulators, wigglers, and collimators — just different things that they need to make the ring function or to generate X-rays.”
Salo’s work calculated how different components of the ring affected the oscillation of the beam as it travels around the ring. She focused on a particular characteristic of the beam’s motion: the tune shift, and what limits that characteristics places on the beam’s overall stability.
“They wanted to know how many electrons can be in the beam at one time, or basically how bright they can make the beams,” Salo said. “Tune shift is going to limit that.”
To calculate the impact of each individual component and the overall tune shift, Salo wrote a computer program that estimated their effect on the beam’s stability. She used undulators, a component of the ring where the beam pipe becomes much narrower, as a test case to make sure her program worked correctly.
“Undulators cause huge tune shifts, and they want to put about five more undulators in the ring,” Salo said. “They don’t quite know what the effect will be from them. That’s why I wrote a computer program to predict what the tune shift will be after the upgrade.”
Once she obtained estimates from the program, Salo compared the numbers to her mentor’s theoretical calculations and data from experimental runs done with the machine, and found them to be in good agreement, Salo said. After running another test with the collimators, she ran the program to predict results for the upgrade.
Then, she presented her findings to other researchers at Cornell who needed her results for their calculations. The other researchers incorporated her predictions into their own parts of the project, Salo said.
“My results made them reexamine some calculations based on my numbers, but it was cool to be able to influence what they were doing,” Salo said.
She said she also enjoyed working in an office in the CESR control room, where she was able to meet some of the operators and learn a lot about how the ring worked.
“It was really neat because I got firsthand knowledge of what was happening with the machine the entire summer,” Salo said. “First thing I did when I walked in in the morning was to check the status of the machine: whether it was on or down and how long the beam had been running. Of course, when something happened, you heard the alarms go off, so I got used to what all the different alarms meant. You’d hear one go off, and then a split second later you’d hear one of the operators running across the floor to go do something. It was fun to be right there in the control room.”
Physics department chair Ken Hayes said Salo was one of two Hillsdale students to conduct research at other colleges over the summer through a national program that provides undergraduate students with an opportunity to conduct research.
“We encourage all of our physics majors to apply for summer REU positions,” Hayes said in an email. “REU’s are very helpful for the students as they get to experience what graduate-level research is like at a research university. Also, having done an REU greatly strengthens a student’s application to graduate school…Hillsdale College physics majors have been quite successful in obtaining REU positions.”
Billing said future research will also use the same software Salo used over the summer.
“Laura’s results predicted a reasonable operating charge… and we will continue to utilize this software to optimize the maximum charge [for different parts of the beam],” Billing said in an email. “The higher charge per [section of the beam] allows enough decay time for the physicists to study the dynamics of molecules after being excited by X-rays before the X-rays from the succeeding [beam section] arrive on the sample.”
Billing said Salo was diligent and focused on the project, and sometimes worked long hours to achieve her research goals.
“Laura’s work during the summer was very successful, and my colleagues and I enjoyed working with her,” Billing said in an email.