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Building a Cyclotron on a Shoestring

Starting when he was an undergrad, Tim Koeth built a 12-inch cyclotron. Now he is in grad school and his creation is used in a senior-level lab class.

I was immediately obsessed,” says Timothy Koeth, who, as a sophomore in physics in 1995 at Rutgers Univer- sity, got the bug to build a cyclotron. “I was sitting in Tom Devlin’s modern physics lecture,” recalls Koeth. “He described the principle of the cy- clotron. He said it required a lot of RF power. I was—and am—a ham radio operator, so RF was no problem. It needed a big magnet; I knew I could find one of those. How tough could a vacuum system and chamber be?” Some six years later, Koeth’s 12-inch machine became part of an under- graduate lab course.

Building the cyclotron required a combination of hands-on and theoret- ical skills, says Mark Croft, Koeth’s undergraduate adviser. “High-voltage engineering, vacuum systems, ma- chining skills, computer program- ming—the whole gamut. To have one person who could do all that, and ded-

the shape of the pole pieces.”

The cyclotron is much more com- plex than “a typical experimental setup in the class—the photoelectric effect, lasers, and so on,” says Michael Gershenson, who has taught the class. “Having it in the lab demonstrates to students that somebody can do this.” So far, he adds, working on the cy- clotron has counted either as multiple experiments or as independent study. Either way, Gershenson says, the stu- dents “have been in permanent con- tact with Tim.”

But Koeth plans to phase out his own involvement. The aim, he says, is to have a standalone experiment “where students can turn on the ma- chine and do canned experiments, such as measuring the charge-to-mass ratio of the proton or the mass of a neutron.” To that end, Koeth and his friend Stu- art Hanebuth, who has worked on the

cyclotron from the start, are writing a user’s manual. At Hanebuth’s initia- tive, they are also exploring rigging the cyclotron to be remotely operable by high-school classes.

Free labor, cheap parts

The cyclotron was Koeth’s brainchild, says Hanebuth. “I was his free labor. I fabricated the table, tested software, tightened screws. I must have crimped a thousand terminations. At one point, I had a full working duplicate of the control rack in my bedroom.”

The two friends met when Koeth responded to Hanebuth’s online ad for used Geiger counters. They discov- ered not only that they shared a love for surplus goods, but that Koeth was the guy Hanebuth had been wanting to meet for about six years: As a high- school student in Minnesota, Hane- buth had read in Science World, a pub- lication for teens, about an eighth grader who discovered a radioactive source in a New Jersey school.

“That was me!” says Koeth. “I had

icate so much time, is unheard of.” Adds particle physicist Mohan Kalelkar, head of Rutgers’ undergrad- uate physics program, “Tim has such creative ideas and puts them into play. Even though I myself am an ex- perimentalist, I don’t know the inner workings of a cyclotron. To actually construct one—Tim is a very remark- able individual.”

Teaching tool

Koeth is now in Rutgers’ PhD pro- gram doing research in accelerator physics at Fermilab. When he started graduate school, he had to find a new home for the cyclotron—which by then had migrated from his parents’ garage to a warehouse on campus. “I sold the idea of using the cyclotron in the senior lab,” says Koeth. “It may be the only fully functioning 1-MeV cy- clotron dedicated to teaching in the US, or the world.”

The first students to work on the cyclotron in the lab setting modified the magnet to better focus the proton beam. Others have worked on im- proving the ion source and, most re- cently, on a robotic measuring device to map the magnetic field in two di- mensions. “We expect there is an az- imuthal distortion,” says Koeth. “We think we might have to further adjust

The cyclotron built by Timothy Koeth (above, left) and Stuart Hanebuth is now part of an undergraduate lab course. The dark brown cylinders are the coils that ex- cite the 12-inch magnet (beige central cylinder). The ion beam, visible through the small central window (inset), can con- sist of pure protons from hydrogen gas (blue tank) or protons and neutrons from deuterium (green tank).


November 2004

Physics Today

© 2004 American Institute of Physics, S-0031-9228-0411-340-9



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