Lab ‘accelerates’ physics learning

One might think that a warning alarm in a nuclear lab would send people running. But Larry Cerrito, a physics research support specialist, did not budge last week during a Physics 206 lab, and stayed nonchalant while the students around him anxiously asked for answers.

“It’s being unstable at 1 million electric volts, but we are going to persist,” Cerrito said. “It’s being very fussy today.”

“It” is a particle accelerator, a device which creates an imbalance of positive and negative charges that is used to drive a positively charged proton across a space at high speed. Though some professors and graduate students use this accelerator for their research projects, what sets this particular device apart is that it is used almost exclusively by undergraduates.

Cerrito commemorated the students’ completion of the lab with a Polaroid photograph of the lab group, which he distributes to each of the students.

“Traditionally, every group that comes through gets photographed,” Cerrito said. “We’re not quite up to the digital age on cameras yet.”

Unique experiences abound at Yale, from classes taught by world-renowned scholars to Masters’ Teas with famous and sometimes infamous figures. But Yale physics students at the undergraduate level have the opportunity to work with sophisticated equipment that puts them in the realm of professional scientists.

In the recesses of Sloane Physics Lab, at the end a circuitous network of corridors, lies Room 3E — the home the University’s Van de Graaff accelerator. The accelerator is now almost a relic of the technological past, but physics professor Moshe Gai said it has retained its charm through the years.

“I have an old affair with this old machine, a 25-year-old affair,” he said. “Those accelerators don’t exist. Forty years ago, they were the state-of-the-art. Today, they only exist in hidden places.”

Last summer, Gai worked on the machine with four undergraduate students, an experience he termed “a beautiful exercise” that resulted in the publication of a paper that was presented last October at a meeting of the American Physical Society. Gai said the machine proved optimal for the kind of research he was doing and also was preferable to the three-month wait for the WNSL accelerator.

The accelerator is a required lab instrument for students in Physics 206 and 381. Physics 206, a second semester physics lab, offers students the chance to work on the accelerator for two weeks as one of eight possible lab options.

“This was my first-choice lab,” Anna Mandel ’07 said. “We get to go in there and actually adjust everything ourselves. It was exciting.”

This particular accelerator has a storied past dating back to 1976, prior to which it was used as an irradiator to sterilize food for the U.S. Navy, Instructional Laboratories director Stephen Irons said. It is now a learning tool that allows Yale undergraduates to perform advanced scientific experiments.

“It was initially an electron accelerator,” Irons said. “The accelerator went on surplus. We took it and converted it to a proton accelerator and basically added the beam line.”

At the time of the accelerator’s dedication in the 1970s, the U.S. Energy Research and Development Administration and the National Science Foundation, along with supplementary University funds, paid for the device and its operating costs. The installation of the equipment seemed both logical and useful, said former physics chair Allan Bromley.

“I felt that it could serve a useful purpose if it could be devoted to purely undergraduate activities and research, so we cleaned it up and put in a set of ancillary equipment so that it could be used in sensible, interesting experiments,” he said.

Bromley said that the history of accelerators at Yale is long and varied. Ernest Lawrence, inventor of the cyclotron — the precursor of today’s electrostatic generators — was an assistant professor at Yale before going to the University of California, Berkeley, Bromley said.

The accelerator facilitates the understanding of basic physics concepts while demystifying nuclear physics machinery, physics professor Andreas Heinz said.

“The physics is really more straightforward because you have lower energies and you are restricted to nuclei which have a small number of protons and neutrons,” Heinz said. “This accelerator is a pretty remarkable thing because accelerators are usually somewhat of a mystery.”

Heinz said that the accelerator can be used for a multitude of experiments — including the Rutherford scattering experiment, which proves the existence of a super-dense nucleus at an atom’s core — as well as demonstrations that explain how stars work.

The Sloane accelerator is one of two on campus. The other is a larger and more powerful accelerator housed in Wright Nuclear Structure Laboratory about a block up Science Hill. What separates the accelerators, Cerrito said, is their power.

“[The Sloane accelerator] does work basically the same way as the Van de Graaff at WNSL, only on a much smaller voltage,” he said.

Cerrito has been the primary accelerator operator for seven years. He said the opportunity that the accelerator experiment presents is unparalleled and is a salient experience for the students involved.

“They all seem to enjoy it, enjoy doing the lab,” Cerrito said. “I think it’s a lot of fun. I think they have a lot of fun doing it. This may be the only time that they will ever get to work on an accelerator. It’s a good opportunity for them.”

The accelerator’s two components occupy distinct, separate levels in the lab room. On the bottom level is the beam line, where energy is “selected, shaped and aimed” at the target, Irons said. The dome, where the electric charge builds up, resides on the upper level.

Maintenance on the Sloane machine, which draws from the annual $40,000 University allocation for instructional labs in the Physics Department, is of an entirely different scale from that of the WNSL accelerator, Irons said. The larger device receives an annual $3 million grant from the of Energy.

Physics 206 student Eleanor Millman ’07 said the prospect of working on this level of sophisticated equipment is intriguing.

“The cool thing is that most people wouldn’t have the opportunity to use this instrument at the undergraduate level. This at a miniature level is what real nuclear physicists do, as evidenced by [WNSL],” Millman said.

Allan Bromley (top) was physics chair when Yale purchased the particle accelerator in 1972. On bottom from left to right are former physics professors Paul McGrath, William Callender and Howard Schultz.
Courtesy LawrenceCerrito
Allan Bromley (top) was physics chair when Yale purchased the particle accelerator in 1972. On bottom from left to right are former physics professors Paul McGrath, William Callender and Howard Schultz.