A breakthrough in the development of fusion diagnostics and the creative use of radio frequency waves to heat the plasma that fuels fusion reactions earned the 2017 outstanding research and engineering awards from the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL). Physicist Brian Grierson and engineer Nevell Greenough received the honors from PPPL Interim Director Richard Hawryluk at a ceremony November 7 for their exceptional achievements.
Grierson received the Kaul Foundation Prize for Excellence in Plasma Physics Research and Technology Development for his groundbreaking measurements of the flow of the main atomic nuclei, or ions, in the DIII-D tokamak. DIII-D is a fusion plasma experiment operated by General Atomics for the Department of Energy in San Diego. The prize includes a $6,000 cash award endowed by former PPPL Director Ronald Davidson, who donated to Princeton University a portion of the gift he received as the 1993 recipient of the Award for Excellence in Science, Education and Physics from the Kaul Foundation in Tampa, Florida.
Greenough was named "Distinguished Engineering Fellow" for his creation of "high-power electrical and electronic engineering solutions to heat and diagnose plasmas with radio frequencies." Such heating works alongside the injection of powerful neutral beams to raise plasma temperature to the tens of millions of degrees that fusion reactions require. The honor, which is part of the PPPL Distinguished Research and Engineering Fellow Program, includes a $5,000 award supported by the DOE.
For Grierson, a member of the PPPL collaboration on the DIII-D tokamak, or fusion device, that General Atomics runs in San Diego, plasma physics holds intriguing mysteries that he seeks to unravel. "I find great excitement in discovering new things, figuring it out, achieving new insight," Griesrson said. "Physics research is a series of small discoveries that accumulate to new understanding through close collaboration with other equally inquisitive minds. Every day, we experience frustration, challenge conventional wisdom, solve complex problems and eventually get the satisfaction of accomplishment -- that never gets old for me."
Grierson holds a five-year DOE Early Career Research Program grant that he received in 2014. With it he runs DIII-D experiments, analyzes the data and manages two junior physicists in research related to the main ions in plasma. He divides his time between such Early Career Research work and general DIII-D research on the transport of heat, particles and momentum in plasma. "He's interested in everything and has great impact on everything that he touches," says Mike Zarnstorff, PPPL deputy director for research.
The Kaul Prize recognizes Grierson's "tour-de-force diagnosis and analysis system for main ion behavior that everybody thought was impossible," Zarnstorff said. "He managed to pull it off, and then used it to diagnose how main ions contribute to turbulence-driven rotation at the edge of the plasma and compare with theoretical predictions. This is a very important process that we as a laboratory and with DIII-D are very interested in understanding."
The findings, which Grierson achieved with a fast camera and spectroscopic measurement of light waves, marked a radical shift from previous analyses, which focused on ions from impurities in the plasma that are simpler to analyze. But such measurements relate to main ion flow only through assumptions that do not directly reveal the behavior of the essential main ions. "While data from the past was valuable," said Hawryluk, a research physicist, "measurements of the main ion species are far more relevant for comparison with theory, and accomplishing this task was extraordinarily difficult."
Grierson earned his doctorate from Columbia University in 2009 after receiving a bachelor of science degree in applied mathematics, nuclear engineering and physics from the University of Wisconsin-Madison. He joined PPPL as an associate research physicist on assignment to DIII-D and became a staff research physicist on the collaboration in 2012.
When not doing science Grierson enjoys backpacking, camping and exploring the California outdoors with his wife, Michele. The couple maintains a website with photos and videos taken during trips to a dozen places in California and around the world. "There's so much to see and do, so many great places to visit," said Grierson, "and after time spent away from the office I'm eager to jump back into solving the complex challenges of physics research."
Greenough, a 41-year veteran of PPPL, heads the tightly knit Radio Frequency (RF) group that runs and maintains the RF heating system for the National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL. His broad responsibilities range from overseeing RF operations to programming controls for the RF power transmitted from six generators to 12 antennas inside the tokamak. "I know a little bit about a whole bunch of things," Greenough says with more than a touch of modesty. "I'm an expert in none but maybe I can get it to work when it's needed."
Greenough's two supervisors take a more expansive view of his accomplishments. "Nevell is the consummate electrical engineer and has been an incredible asset to the Laboratory," says Timothy Stevenson, the head of Heating Systems at PPPL. "In recent years he has taken on many improvements for RF instrumentation and controls systems. Ever the student, Nevell's love of everything electrical, from antique radios to cutting-edge computer chips and programming techniques, makes him the very definition of an engineering distinguished fellow."
For Joel Hosea, a physicist who heads RF science and technology at the Laboratory, Greenough is a highly skilled manager of an expert group and a dedicated worker who takes on many tasks to keep the RF systems in pristine condition. His attention to detail is unwavering. "Maintaining RF systems takes quite a lot of effort even when they're down," Hosea says. "Water must always keep running through the main RF power tubes to keep them clean, for example. Nevell is responsible for making sure that the water is flushed so nothing grows in the tubes, which requires a great deal of work along with his other responsibilities."
Greenough joined PPPL in 1976 with a bachelor's degree in electrical engineering from Lehigh University. An expert in fields ranging from high-voltage and electromechanical design to programming and diagnostics, he has designed and installed RF components and control equipment for numerous PPPL projects. Included among them were the Tokamak Fusion Test Reactor (TFTR) and the National Spherical Torus Experiment (NSTX), the forerunner of the National Spherical Torus Experiment-Upgrade, which uses much of the same RF equipment.
Along the way Greenough has collaborated on RF systems for the Alcator C-mod tokamak at the Massachusetts Institute of Technology and the DIII-D tokamak in San Diego, with a knack for innovation that has been readily apparent. Randy Wilson, retired head of the ITER and Tokamaks Department who worked closely with Greenough for many years and considers him a friend, recalls the time when a DIII-D researcher noted that a circuit that calculated the dissipation of heat from an RF power tube needed improvement. "Nevell went to a computer flea market and found a circuit," Wilson said. "He programmed it over the weekend and brought it in on Monday, and sure enough it worked."
Greenough maintains his passion for electrical engineering when not on the job. He is a licensed amateur radio operator and enjoys fixing up old radios from the 1930s and 1940s and hearing them play. An outdoors enthusiast, he kayaks with friends in the Catskills and rows on other lakes. He also enjoys music from all eras and learning the bass guitar.
Looking ahead, Greenough wants to see the high harmonic system, which feeds megawatt power to the RF antennas on NSTX-U, remain productive. "The controls that I developed with a lot of help from others," he said, "will increase the reliability and accuracy of the system for many years to come."