Physicist Duncan Tate to Develop New Techniques for Plasma Physics Experiments

Natural Sciences4 MIN READ

National Science Foundation grant to fund cutting-edge Colby research on ultracold plasmas

Professor of Physics and Astronomy Duncan Tate's optical table holds sophisticated instrumentation that he and his student researchers keep finely tuned in order to obtain precise results for his cutting-edge research on ultracold neutral plasmas.
August 24, 2020

The National Science Foundation has awarded Professor of Physics and Astronomy Duncan Tate nearly $200,000 to deepen his research on ultracold neutral plasma, which has potential implications for the pursuit of relatively clean nuclear fusion power.

The three-year grant will allow Tate to conduct experiments that physicists can draw upon to develop new theoretical techniques potentially useful in large-scale plasma fusion research. Tate, an atomic, molecular, and optical physicist, will conduct the experiments in his Colby lab with the help of student researchers. 

The ultracold neutral plasma state has not yet been extensively studied by plasma physicists, he said. “It’s a field with a lot of promise that’s reached its midpoint. People are trying to figure out where to go with it, and I’m happy to get funding from NSF to look at some ideas about where to go next.”

In the plasma state, atoms are ionized and the resulting electrons and ions are bound by their mutual attraction. This situation is ubiquitous in the universe, such as in stars (including the Sun), interstellar glass clouds, lightning, the aurora borealis, and even in fluorescent light bulbs. A typical plasma environment is hot and disorderly with electrons and ions zipping around and bumping into each other. It’s an environment, Tate explained, with weak forces between the electrons and ions that is difficult to control and study.

In the ultracold neutral plasma that Tate studies, electrons and ions are both very cold, and the forces between them are relatively significant. Such plasmas are often strongly coupled, making this environment unlike most other known plasmas. In addition, the experimental techniques used make them easier to both study and control than in conventional plasma experiments.

In his research, Tate first employs a relatively new technique using five lasers to cool atoms in a vacuum chamber. Next, he uses a powerful infrared laser and a dye laser to remove electrons from the cold atoms—a process called photoionization—to create the ultracold neutral plasma. Using a pulsed laser, he can conduct controlled experiments in this environment about 20 times a second. “Surprisingly,” Tate said, “during that short amount of time—if you have electronics that are fast enough—you can make measurements of what’s happening in the plasma.”

He has those electronics in his lab, plus a plethora of other instrumentation—charged particle detectors, oscilloscopes, a laser wavemeter, for example—that he and students have assembled on a 4-foot by 8-foot optical table. 

Tate is in search of tricks in atomic physics to slow down the heating process in plasma and maybe even reverse it in some circumstances, he said. “It’s essentially like changing the local plasma environment by adding atoms into it in such a way that those atoms can be used as little ice cubes to remove heat from the electrons.“

In previous research, Tate has demonstrated that this process works at higher initial electron temperatures. Now, he wants to see if it works on electrons that are initially much cooler, a property that is controlled by the photoionization laser. 

This grant marks the fourth NSF grant Tate has received in the last 18 years. His strong record of including students in his research earns him marks with the foundation. 

Students working in Tate’s lab connect theoretical topics learned in the classroom with hands-on experimental physics. “They’re theories, but what makes us think that they’re correct? How do they apply in atoms? The experiments I do only work because quantum mechanics is a good theory, it’s a correct theory,” he said. 

It can also work in the other direction, where experimental results such as those from Tate’s lab add to theoretical physicists’ understanding of certain phenomena. “I have very precise control of the initial conditions, and that enables us to test ideas quite quickly to see what will work and what won’t.

His research on ultracold neutral plasma has the potential to advance general plasma physics research, which is primarily driven by fusion research in search of a relatively clean variant of nuclear power without heavy radioactive waste.

By its nature, plasma physics research is done at large, expensive scales that move relatively slowly. Tate’s ability to conduct experiments quickly will advance this research at a faster, more efficient pace.