Brown Theoretical Physics Center

In its 21-year history, the Summer Student Theoretical Physics Research Session (SSTPRS) led by Brown Theoretical Physics Center (BTPC) Director S. James Gates Jr. has been held at either the University of Maryland, the University of Iowa, or since 2017 at Brown University. SSTPRS had its origins as a joint collaboration between Gates and Professor Vincent G. J. Rodgers (University of Iowa). Every year up until 2020, this unique opportunity for undergraduate and graduate students was held in person.

The COVID-19 outbreak required various adjustments to the typically four-week long program, including making the program completely virtual on Zoom. “We ran the program five weeks as we felt it necessary to get the students to the usual point of readiness to engage authentic research that has been our tradition,” shared Gates. In addition to the extra days on the calendar, the daily schedules were adjusted to reduce the amount of online instruction to 12 hours per week, compared to 20 to 25 hours per week of in-person instruction in previous years.

In his 48 consecutive years of teaching, Gates never imagined having such a diverse group of students in his program. Participants this year included three from Brown University, three from Caltech, three from the Chinese University of Hong Kong, a participant in Abu Dhabi, one from UCDavis, and the remainder from the University of Maryland. This was possible because of the technology of Zoom.

This was Assistant Professor Kory Stiffler’s eighth year participating in the SSTPRS, and his fifth as an instructor. He discussed some of the challenges and resulting achievements of this new model. “The instructors had to be more efficient, and we were able to cover nearly as much material as the typical in-person sessions of the past. The students’ attentiveness and hard work was crucial in these successes. They were truly a remarkable group of students and were able to successfully meet all of the challenges along with the instructors,” added Stiffler.

Communicating real-time long and detailed calculations to students was one obstacle to overcome. The instructors were able to use writing tablets to solve this problem. They then had the students take still pictures of their handwritten calculations and use the share screen feature of Zoom.

From the perspective of the 22 students in this year’s program, this new virtual model for the SSTPRS was also a win. Brown University junior Laurel McIntyre had no previous experience with physics research. She applied to the program because she wanted to expand her skills and begin deciding which area of physics she would like to pursue. McIntyre notes, “I think the mentors handled the transition to virtual well. They often put us in Zoom breakout rooms and encouraged us to communicate with each other because collaboration is important in research.” As a student without research experience, this was a great platform for McIntyre and others to build a foundation for future research opportunities.

In the previous semester, third-year Brown PhD student Aleksander Cianciara attended Professor Gates’ research group meetings to learn more about supersymmetry and adinkras, pictures that encode the mathematics of how supersymmetric particles interact. His interest in adinkras inspired him to apply for the SSTPRS program this summer. “I was really impressed by how the mentors were able to create and facilitate an effective curriculum to take students with ranging knowledge of physics and get them up to speed with the essentials necessary for research in theoretical physics,” shares Cianciara. “I think it’s a powerful testament that physics isn’t about memorizing pages of equations and facts, but rather about learning to think through an idea logically and rigorously from start to finish. As the frontiers of knowledge continue to expand, I wonder if this program is perhaps providing a new paradigm for how physics could be taught in the future.”

Although it was an unexpected change to a summer program with two decades of in-person instruction under its belt, the adaptation to virtual was a success. When asked whether he thought future programs would be better in-person or virtual, Stiffler concluded, “I do see a hybrid of in-person events with virtual components added as a future possibility.”

Along with Gates and Stiffler, this summer’s SSTPRS instructors were Professor Kevin Iga (Pepperdine University), Dr. Konstantinos Koutrolikos (Brown), Ms. Yangrui Hu (Brown), and Ms. Sze-Ning Mak (Brown). Mr. Andrew Dewald (University of Iowa) worked as a Teaching Assistant and Dr. Pete Bilderback (Brown) and Ms. Mary Sutton (Brown) worked as Administrative Assistants.

A research team has predicted the presence of “topologically protected” electromagnetic waves that propagate on the surface of plasmas, which may help in designing new plasma systems like fusion reactors.

Nearly 50 years ago, Brown University physicist Michael Kosterlitz and his colleagues used the mathematics of topology — the study of how objects can be deformed by stretching or twisting but not tearing or breaking — to explain puzzling phase changes in certain types of matter. The work won Kosterlitz a share of the 2016 Nobel Prize in Physics and has led to the discovery of topological phenomena in all kinds of systems, from thin films that conduct electricity only around their edges, to strange waves that propagate in the oceans and atmosphere at the Earth’s equator.

Now a team of researchers, including another Brown physicist, has added a new topological phenomenon to that ever-growing list. In new theoretical research, the team shows that electromagnetic waves of topological origin should be present on the surface of plasmas — hot soups of ionized gas. If the theory proves true, those waves could provide a new way for scientists to probe the properties of plasmas, which are found in everything from fluorescent lightbulbs to stars.

The research was led by Jeffrey Parker, a research scientist at Lawrence Livermore National Laboratory, in collaboration with Brad Marston, a professor of physics at Brown, and others. The paper is published in Physical Review Letters.

The waves, called gaseous plasmon polaritons, propagate along the interface of a plasma and its surroundings when the system is exposed to a strong magnetic field. Marston says that what’s interesting about these waves is that they are “topologically protected,” meaning that they’re inherently present in the system and are resistant to being scattered by impurities.

“Any time you have a wave that’s protected against scattering, it means they can stay intact over a long distance,” Marston said. “As a practical matter, we’re hoping that these can be used to diagnose plasma states. One of the big problems in plasma physics is to figure out the state of a plasma without disturbing it. If you stick in a probe, you’re going to disrupt the system. We might be able to use these waves to discern the state of a plasma without disturbing it.”

One way to think about topological protection, Marston says, is something known as the hairy ball theorem. Imagine a ball covered in long hairs. If one were to try to comb those hairs down, there will always be at least one spot on the ball where the hairs won’t lie flat.

“This spot will always be there,” Marston said. “You can move it around, but the only way to get rid of it is to tear some hair out. But barring something violent like that, if you’re just manipulating it continuously without tearing anything, there’s always going to be a vortex.”

The ever-present vortex on the hairy ball is mathematically analogous to the waves on a plasma’s surface, Marston says.

“In this case, there’s always a vortex but it’s in the wave-number space, wavelengths of the different waves,” he said. “It’s a little more abstract than in real space, but the math is largely similar.”

Having fleshed out the theoretical basis for these waves, the next step is to perform experiments to confirm that they’re really there. Marston and his colleagues recently won a seed grant from Brown to help them do just that. With the help of researchers at UCLA’s Basic Plasma Physics Facility, Marston and his colleagues plan to perform experiments to detect these waves.

Ultimately, Marston hopes that the discovery of these waves could be a boon for plasma physics, helping scientists to better understand and control plasma systems. One major area Marston is interested in is plasma fusion reactors. Such reactors could one day harness nuclear fusion to produce an abundance of clean energy, but so far the plasma systems have proven hard to control.

“In the long term, we hope this can make an impact on fusion energy,” Marston said. “If we can use these waves to discern the states of plasmas, it might help in designing a fusion reactor that’s stable and able to produce energy.”

But for now, Marston and his colleagues are looking forward to performing their experiments.

“If we can demonstrate these things experimentally, people in the plasma community will hopefully start paying closer attention to this idea,” he said.

Other co-authors on the paper were Steven Tobias and Ziyan Zhu.

Original article: https://www.brown.edu/news/2020-05-14/plasma