PPPL By John Greenwald | July 12, 2016
Plasma – the hot ionized gas that fuels fusion reactions – can also create super-small particles used in everything from pharmaceuticals to tennis racquets. These nanoparticles, which measure billionths of a meter in size, can revolutionize fields from electronics to energy supply, but scientists must first determine how best to produce them.
After more than two years of planning and construction, the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) has commissioned a major new facility to explore ways to optimize plasma for the production of such particles. The collaborative facility, called the “Laboratory for Plasma Nanosynthesis,” is nearly three times the size of the original nanolab (link is external), which remains in operation, and launches a new era in PPPL research on plasma nanosynthesis. Experiments and simulations that could lead to new methods for creating high-quality nanomaterials at relatively low cost can now proceed at an accelerated pace.
The facility will host a number of different experiments using advanced diagnostics to observe nanosynthesis in situ, or as the experiments take place. “We should be able to simultaneously characterize and correlate the plasma and nanosynthesis processes,” said physicist Yevgeny Raitses, who heads the new laboratory. “This will help take our research to the very top level needed for fundamental studies in this interdisciplinary field.” All research will be conducted under the aegis of the Plasma Science and Technology Department, headed by physicist Philip Efthimion.
Nanomaterials exhibit remarkable strength, flexibility and electrical conductivity. Carbon nanotubes, found in sporting goods, body armor, transistors and countless other products, are tens of thousands of times thinner than a human hair and stronger than steel on an ounce-for-ounce basis.
Plasma could serve as an ideal substance for synthesizing — or producing — nanomaterial. The new 1,500-foot laboratory will study so-called low-temperature plasmas that are tens of thousands degrees hot, compared with fusion plasmas that are hotter than the 15-million degree core of the sun. These low-temperature plasmas contain atoms and free-floating electrons and atomic nuclei — or ions — that can be shaped by magnetic fields to provide reliable, predictable and low-cost synthesis of tailored nanoparticles.
However, achieving these goals requires a fuller understanding of plasma nanosynthesis than is currently available. One method of synthesis first turns a rod of iron or other material into plasma by vaporizing it with an electric arc. The plasma then condenses into solid nanomaterial. New understanding is needed to explain the chemical, kinetic and electrical interactions that accompany these changes and must be controlled to ensure the quality and purity of the nanomaterial.
Advanced laser systems
The new laboratory will use a collection of diagnostic systems to measure these processes as the synthesis takes place. A number of advanced laser systems developed specifically for this research are among the instruments employed. “The hope is that these measurements will give us physical insight into the whole chain of synthesis process,” said Raitses. The chain extends from the generation of plasma to the formation — or “nucleation” —of nanoparticles and their growth.
Overseeing the diagnostics is physicist Brent Stratton, who directs all diagnostic systems at PPPL. Mikhail Shneider, a senior research scientist at Princeton University, developed the diagnostic concepts and proposed a key laser system for measuring nanoparticles in a gas.
Once the synthesis is complete, researchers will evaluate the material with electron microscopes and other devices in facilities outside the laboratory. Participants will include the Princeton Institute for the Science and Technology of Materials (PRISM) at Princeton University, and Bruce Koel, a Princeton chemical and biological engineer with offices at PPPL and the University.
Researchers will also produce theoretical models of plasma nanosynthesis and compare the results to actual measurements. Models that correctly predict the data could deliver a precise understanding of the processes involved. Leading these simulations is Igor Kaganovich, deputy head of the PPPL Theory and Computation Department.
The diagnostic developments and synthesis experiments are conducted in close collaboration with Princeton theorists Roberto Car, a professor of chemistry, and Biswajit Santra, a postdoctoral fellow in the chemistry department. Also actively engaged in theoretical research is Predrag Krstic of the Institute for Advanced Computational Science at Stony Brook University.
PPPL engineer Andrei Khodak and postdoctoral fellow Alexander Khrabry are modeling use of an arc plasma reactor for synthesis of nanoparticles. They work in collaboration with an arc expert, Prof. Valerian Nemchinsky.
Major new topics for the overall project include plasma synthesis of nanotubes made from boron nitride, a compound that could become an efficient vehicle for drug delivery. Successfully designed boron nitride nanotubes could be loaded with drugs and directed to carefully targeted points in the body.
Plasma as synthesizing agent
Exploration of plasma as a synthesizing agent is a natural development for PPPL, the only national laboratory dedicated to research in fusion energy and plasma science. Findings of the existing PPPL nanolab, a two-room 600-square-foot facility that opened in 2013, give strong indications of improved methods for producing carbon nanomaterial.
The new facility can build on such findings. “The inclusion of this increased capability positions PPPL for expanded future opportunities in nanotechnology,” said Charles Gentile, lead engineer for operations and a designer of the facility. Contributing to the design was electrical engineer John Lacenere. Also helping to plan the facility were PPPL engineers Craig Shaw and Alex Merzhevskiy.
Both new and old laboratories provide attractive research opportunities for students and for postdoctoral fellows who are starting their careers. Postdocs Alexandros Gerakis, Vlad Vekselman, and Shurik Yatom at PPPL are developing advanced laser diagnostics and conducting plasma nanosynthesis experiments, together with James Mitrani, a graduate student in the Princeton Program in Plasma Physics. Yao Wen Yeh, a graduate student in the Princeton University School of Engineering and Applied Science, is working with Koel on evaluating materials.
The postdocs participate in many collaborations. They work on diagnostic developments with Stratton and Shneider and conduct experiments with Raitses and collaborators from George Washington University, led by Prof. Michael Keidar, and Case Western Reserve University led by Prof. Mohan Sankaran. Also engaged in experiments is Sophia Gershman, a research scientist at PPPL.
Attractive research opportunities
A number of other scientists are consulting or working on diagnostic development. They include PPPL physicists Benoit LeBlanc, Ahmed Diallo and postdoctoral fellow Jorge Munoz Burgos, and research scholar Arthur Dogariu of the Princeton Department of Mechanical and Aerospace Engineering.
The new facility occupies a former storage area that had to be thoroughly remodeled and carefully engineered to ensure health and safety, like its smaller cousin. Features include a ventilation system that takes in outdoor air and pipes it back through ultra-low particulate filters instead of recycling it. The system also generates negative air pressure that is a few degrees below atmospheric pressure to keep laboratory air from circulating into hallways.
Construction of the Laboratory for Plasma Nanosynthesis was supported by the DOE Office of Science.
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).