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New Staff Research Physicists at PPPL

The Laboratory has announced the hiring of six postdoctoral researchers as staff research physicists. The researchers are Ahmed Diallo, Brian Grierson, Michael Jaworski, Walter Guttenfelder, Mario Podesta, and Erik Spence. “Please join us in congratulating each of them for their strong achievements and deserved advancement,” said Stewart Prager, Director of PPPL, and Michael Zarnstorff, Deputy Director for Research at PPPL, in their announcement to staff. Below are short biographies of the researchers.

Ahmed Diallo joined PPPL in 2009 as a post-doctoral researcher to conduct experiments on NSTX using the Thomson scattering system, a diagnostic tool for measuring electron temperature and density in plasmas. Diallo, an expert in laseraided plasma diagnostics, contributed to the recent upgrade of the Thomson diagnostic and was involved in daily NSTX operations. He studies pedestal physics and associated instabilities at the edge of tokamak plasmas. Understanding the physics governing a narrow width at the edge of the plasma — the pedestal — is important for the successful prediction of fusion gain in future fusion reactors, such as ITER. Diallo also develops advanced diagnostics for measuring plasma parameters. Before joining PPPL, Diallo had been a research fellow at Australia National University. He received a Ph.D. in experimental plasma physics from the University of Iowa in 2005. Diallo has authored and co-authored more than 20 scientific papers and presented more than 10 talks. “I was drawn to fusion research because of its huge potential for improving our ability to use clean energy sources,” Diallo said. “I also enjoy being part of a research group working toward this common goal to make it a reality.”

Brian Grierson has been on permanent assignment to the DIII-D tokamak at General Atomics in San Diego since receiving a Ph.D. in applied physics with distinction from Columbia University and joining PPPL in 2009. Grierson is currently engaged in measuring the main ion properties of deuterium plasmas. He gave an invited talk on this subject to the 2011 annual meeting of the American Physical Society Division of Plasma Physics in Salt Lake City. “One of the things I try to do when developing tools and programs is to share them with as many people as possible,” Grierson said. “This is a big part of collaborative research.” As a researcher, “I’m very happy to be in the community of plasma physicists as we’re getting ready for ITER,” he adds. “This is a great time to be a fusion scientist.”

Walter Guttenfelder tests the ability of gyrokinetic computer codes to simulate plasma turbulence inside the NSTX. “I’m stressing and straining these codes for the NSTX parameters, which are really extreme compared to conventional tokamaks,” says Guttenfelder, who received a Ph.D. in electrical engineering from the University of Wisconsin-Madison in 2008. He conducted post-doctoral research at the Centre for Fusion, Space & Astrophysics at the University of Warwick in England before joining PPPL in 2010. Guttenfelder has coauthored 31 refereed papers since 2000 and keeps a baseball glove and a football in his office to toss around with senior research scientist Rajesh Maingi for outdoor recreation. “I like to approach science problems where things look peculiar and weird,” Guttenfelder said of his research, “then break them down to where one-plus-one equals two, and then re-build them to help understand how the complex behavior that you observe arises.”

Michael Jaworski is deputy leader of the lithium research topical science group for the NSTX. His research focuses on probes of the density and temperature of plasma near the plasma-lithium interface. “Plasma-facing components are one of the most pressing issues for fusion,” said Jaworski, who gave an invited talk on electron energy distributions to the 2011 annual meeting of the American Physical Society Division of Plasma Physics in Salt Lake City. Jaworski earned a Ph.D. in nuclear engineering from the University of Illinois at Urbana-Champaign in 2009, and spent six months as a post-doctoral researcher there before joining PPPL in 2010. He views liquid lithium as a strong candidate for material for the plasma-material interface, since liquid lithium can be flowed in and out of a tokamak without shutting the machine. Solid materials, on the other hand, are subject to erosion and require periodic shutdowns to replace.

Mario Podesta is a researcher on NSTX whose work focuses on charge-exchange recombination spectroscopy (including real time measurements of plasma velocity), fast ion physics and fast ion-driven instabilities. Charge-exchange recombination spectroscopy is a technique for inferring ion density, temperature and velocity based on measurements of light emitted by impurities that are diluted in the plasma. Podesta joined PPPL’s staff as a postdoctoral researcher in 2009 after conducting research on NSTX as a postdoctoral researcher for the University of California-Irvine. Podesta studied nuclear engineering at the Politecnico di Milano University in Italy, and received a Ph.D. from the Plasma Physics Research Centre at the Ecole Polytechnique Fédérale de Lausanne in Switzerland. “Knowing plasma properties such as ion density, temperature and velocity is crucial for a correct interpretation of the plasma behavior. In particular, velocity plays a big role in the stability of tokamak plasmas,” Podesta said. “My studies also focus on understanding the interaction between fast ions and a particular class of plasma instabilities called ‘Alfvén modes’.”

Erik Spence, who joined PPPL in 2009 as an associate research physicist, conducts research on the MagnetoRotational Instability Experiment (MRI) and the Liquid Metal Experiment (LMX). He received a Ph.D. in physics from the University of Wisconsin-Madison in 2006 for his research on a liquid-sodium dynamo experiment, and received the Marshall N. Rosenbluth outstanding doctoral thesis award for this work. Spence was an NSERC Postdoctoral Fellow at the University of Toronto in Canada and a postdoctoral researcher at ETH Zürich, Institut für Geophysik in Switzerland prior to coming to PPPL. His research interests focus on the use of liquid-metal experiments to study magnetohydrodynamic instabilities and astrophysical objects. “Liquid metals are cooler than plasmas,” Spence said.

U.S. Department of Energy
Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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