UNIVERSITY PARK, Pa. — Camila López Pérez, a doctoral student in nuclear engineering at Penn State, supported by the Princeton Plasma Physics Laboratory (PPPL)’s Dr. Robert A. Ellis Fellowship, has conducted fusion energy research on-site at Princeton for the past year and a half.
The fellowship is awarded to "doctoral thesis students and postdoctoral researchers who are enthusiastic, passionate and have a deep interest and strong desire to pursue a career in plasma and/or fusion science, computation, engineering or a related field,” and who are interested in collaborating with PPPL, according to the fellowship webpage. PPPL is a U.S. Department of Energy national laboratory managed by Princeton University and awards the fellowship to a small number of students in the United States per year.
The two-year fellowship is directly supporting López Pérez’s dissertation research on developing and evaluating materials for nuclear fusion, a process in which two atomic nuclei combine to form a heavier nucleus and release energy. These reactions occur in plasma, a state of matter comparable to extremely hot gas, which can degrade the materials used to contain it. López Pérez’s research focuses on developing materials that can withstand the extreme heat and particle fluxes inside fusion reactors — a key challenge in fusion research, she said.
“I specifically study how plasma interacts with ‘self-healing’ plasma-facing components (PFCs),” López Pérez said. “I study a PFC design in which liquid lithium is used in combination with a refractory metal such as tungsten.”
She said lithium is attractive because it can help improve plasma performance since it has a low atomic number and bonds easily with impurities, while tungsten has exceptional thermal and mechanical properties but can be cooled and destabilize plasma if it erodes and enters the reaction.
“Understanding how these materials retain hydrogen and behave under fusion-relevant conditions is crucial to advancing reactor designs,” she said.
López Pérez is advised by Martin Nieto-Perez, an associate teaching professor of nuclear engineering.
“I encouraged Camila to apply for the PPPL Robert Ellis Fellowship because I believe she would be an excellent candidate that would fulfill the lifelong desire of Dr. Ellis as an educator: the support of enthusiastic, passionate graduate students with a deep interest and a strong desire to pursue a career in plasma physics or fusion science,” Nieto-Perez said. “Camila has proven to be a committed, talented, and dependable student in multiple occasions since I started advising her three years ago.”
López Pérez has been physically working at PPPL for the past year and a half as part of the fellowship, contributing to the Lithium Tokamak Experiment–Beta. This is a unique small tokamak — a doughnut-shaped fusion device that confines plasma with magnetic fields — and the only tokamak in the world whose inner walls are fully coated with lithium. Her work explores how hydrogen is retained in lithium coated porous tungsten, and how improved techniques for applying lithium on the PFCs can enhance reactor performance.
At Penn State, López Pérez helped develop liquid-metal droppers — syringe-like tools designed to deposit precise amounts of lithium — that she used to study how lithium wets and spreads across porous tungsten by placing controlled droplets onto experimental samples. At PPPL, she adapted and integrated these droppers into the lithium evaporators used in this experiment, enabling lithium to be loaded in a clean, controlled atmosphere and allowing the evaporators to deposit lithium more consistently while also increasing their fill capacity.
"Doing this makes the lithium application cleaner,” López Pérez said. “Doing “between shot” evaporations help to evaporate Lithium between each plasma shot, which can improve plasma performance. These upgrades will help inform the design basis for the newer generation of evaporators on the National Spherical Torus Experiment Upgrade and on the ST-40, which is owned and operated by Tokamak Energy in the U.K.”
Another major component of López Pérez’s dissertation work at PPPL involves upgrading the Sample Exposure Probe (SEP), a tool used to study materials’ change in chemistry after being exposed to plasma. She modified the SEP to incorporate electron beam-assisted temperature programmed desorption — a technique that heats samples using an electron beam and measures the species that desorb from the sample — to measure how much hydrogen the materials retain.
“This information is important for making reactors safer and improving their performance,” Lopez Perez said.
Using the upgraded SEP, López Pérez is currently testing lithium coated porous tungsten materials developed at Penn State to evaluate their stability, hydrogen retention and overall behavior in fusion-relevant plasma conditions.
“With my work, I aim to advance lithium-wall tokamak technologies by improving lithium application methods and helping optimize advanced materials for use as plasma-facing components,” López Pérez said. “This experience has helped me further develop my research skills, learn about tokamak operations, and it has connected me with exceptional scientists who have guided and supported my research.”
López Pérez presented early findings from her lithium evaporator upgrades and porous tungsten testing at the IEEE Symposium on Fusion Engineering in June and, more recently, at the American Physical Society Division of Plasma Physics meeting in November.