PPPL By Jeanne Jackson DeVoe | September 9, 2016
When Hanna Schamis packed her bags for graduate school this summer, she already had two summers of hands-on research under her belt as an intern at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and had decided on a career in plasma physics.
Schamis recently began graduate school at the University of Illinois at Urbana-Champaign (UIUC) after completing her second Science Undergraduate Laboratory Internship (SULI) at PPPL. She plans to study in the Department of Nuclear, Plasma, and Radiological Engineering, and continue the research she started at PPPL on the effect of plasmas on materials that could be used for the walls of fusion devices to protect them from the intense heat and high flux of particles that emanate from plasmas, which can reach temperatures of up to 100 million degrees – hotter than the sun.
A change in career path
Schamis’ first summer at PPPL changed her career path, and the current project is more in line with her research interests. “When I first arrived at SULI last year I wasn’t very aware of everything going on in plasma research,” Schamis said. “Through the lectures and seminars, I started getting really interested in plasma material interactions so I ended up choosing that path.”
She may have chosen wisely, as finding a wall material that is long lasting and won’t affect the behavior of the ultra-hot plasma inside a reactor is one of the greatest challenges of fusion energy research. Such research, on the National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL and on other tokamaks, can help in understanding how once a burning plasma is achieved – such as that planned at the international fusion experiment under construction in France, ITER – a fusion reactor can be built with a durable wall.
A physics major as an undergraduate at the University of Michigan-Ann Arbor, Schamis said she liked the hands-on nature of the SULI program. “I like that it’s applied research and it has applications in the real world,” she said.
Schamis’ research this summer focused on an alloy of molybdenum (TZM), a substance that will be used to line the divertor, a part of the machine that collects heat and particles from the plasma. TZM could eventually be used to line the walls of the NSTX-U. TZM is a strong, heat-resistant material. It would avoid the problem of the plasma eroding the carbon that makes up graphite walls like those presently in the NSTX-U. This would be a serious problem in a reactor that runs for long periods of time like ITER.
Research on device attached to NSTX-U
Schamis used a device called the Material Analysis and Particle Probe (MAPP), developed by the University of Illinois at Urbana-Champaign, to conduct her experiment and analyze the results. MAPP is attached to the bottom of NSTX-U in the divertor, and inserts samples of plasma into the machine during experiments. The samples can then be retracted into a vacuum chamber that is part of MAPP. This chamber is fitted with an apparatus for x-ray photoelectron spectroscopy (XPS). XPS is performed by shooting x-rays at the sample, and measuring the energies of the electrons emitted by the elements on the surface. This allowed Schamis to analyze the effect of the plasma on the chemical composition of the TZM over time.
“This is the first time measurements of this kind have been performed on a large fusion device like NSTX-U. Since they were made while the samples were still in a chamber that was connected to NSTX-U, changes of the chemistry of the wall could be more readily correlated to changes in the plasma itself,” said PPPL physicist Robert Kaita, Schamis’ mentor on the project.
The TZM samples exposed to plasma were first coated with boron in a process called “boronization.” The process prevents oxygen, which is an impurity in the graphite walls of NSTX-U, from entering the plasma and cooling it. Schamis found that boronization worked for TZM as well. Boronization succeeded in binding the oxygen to the surface of the sample. but as with graphite, the boron wore off with plasma exposure over time.
While Schamis was analyzing the TZM sample, Felipe Bedoya, a graduate student at UIUC was investigating the effects of boronization and exposure to the plasma on a graphite sample. Studies of graphite continue to be important as the wall material of NSTX-U, and they are being conducted for the first time with MAPP. The two graduate students will continue analyzing the MAPP samples as part of their graduate work at the university. “Felipe is trying to understand the present NSTX-U wall in more detail, and Hanna’s job was to do the analysis to predict what would happen with a new material that we want to use in NSTX-U in the future,” Kaita said.
An exceptional intern
Kaita, who has mentored more than 70 students from high school through graduate school over his long career at PPPL, said Schamis was an exceptional intern. “Hanna was very interested and engaged. She really took ownership of her project,” he said. “She wanted to do a very good job in doing the detailed analysis and trying to look for answers to questions she didn’t understand. This made advising Hanna challenging and rewarding. I would tell her how to get started, and she would come back with tough questions.”
In her first summer as a SULI student, Schamis worked with physicist Igor Kaganovich on a simulation of a type of instability that could potentially disrupt a plasma experiment. She adopted an existing software code to create the simulation.
Schamis credits Kaganovich, deputy head of the PPPL Theory Department, with introducing her to graduate students and physicists who offered advice on graduate school. Kaganovich said one of the main points of the SULI program is to spark an interest in plasma physics research that could lead students like Hanna to pursue a career in the field. “That’s the whole point of the program, to get students experience with research,” Kaganovich said. “It’s important that they enjoy the project. I look at the students: what they can do and what they are interested in and try to match the project to them.”
That effort was not wasted on Schamis. “I feel like everyone helped a lot,” she said. “The main thing is I found what field of physics I wanted to be in and that’s really important.”
PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov (link is external).