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Neilson visits German stellarator to pave way for U.S. researchers

Gates serves as Interim Head of Advanced Projects

Hutch Neilson, PPPL’s head of Advanced Projects, is saying “auf wiedersehen” to the Lab for the next nine months as he travels to Greifswald, Germany, where he will be paving the way for future U.S. researchers to participate on the Wendelstein 7-X (W7-X) program as the experiment begins preparing for operations next year.

David Gates, a principal research physicist and the stellarator physics leader at PPPL, will be serving as Interim Head of Advanced Projects in Neilson’s absence.

Neilson’s new position comes after the U.S. Department of Energy and the European Atomic Energy Commission signed an agreement in June establishing a long-term partnership with the Max Planck Institute for Plasma Physics (IPP) and PPPL, Oak Ridge National Laboratory and Los Alamos National Laboratory. The agreement names PPPL as the lead institute for the U.S. collaboration on the W7-X.

The device will be the largest stellarator in the world. Stellarators are fusion devices that are different from the more prevalent donut-shaped tokamaks like PPPL’s National Spherical Torus Experiment (NSTX). Both stellarators and tokamaks create a highly charged, super-hot gas called a plasma to cause a fusion reaction. But in tokamaks, researchers drive a current through the plasma to create the magnetic field lines that contain the plasma. The current can produce chaotic swirls called “disruptions” that can halt a fusion reaction. Stellarators, on the other hand, are built with twisting, cruller-shaped magnetic field coils on the outside of the device. The magnetic field coils produce a three-dimensional, steady magnetic field in the plasma. This means the plasma is not subject to the same kind of disruptions found in plasmas produced in tokamaks. Some researchers say this advantage makes stellarators a promising technology for developing fusion energy as a source of electric energy. 

A long-term partnership

Under the agreement, American scientists will help commission W7-X, and conduct research using the device, analyze data, present papers at conferences and oversee graduate students in their scientific investigations. The U.S. participants, including PPPL, will provide equipment to allow scientists to analyze the properties of the plasma. Participants also will contribute data to the W7-X database and provide any necessary expertise to advance science. 

PPPL designed and delivered five massive trim coils for the W7-X that will fine-tune the shape of the plasma in experiments aimed at studying the conditions necessary to produce fusion energy. Now PPPL physicists are working on diagnostics and simulation tools to prepare for research on the machine. The U.S. contributions to the project, though small in dollar value compared to the overall cost of the facility, form the basis for a real partnership in which the U.S. scientists be part of the W7‑X team and have a voice in the research planning.

“The real payback will be in the form of science,” Neilson said. “We’re in this to have the opportunity to do research on this facility in collaboration with the IPP and its other partners. What’s in it for us is the science that we’ll get out of it and make available to ourselves and the world.”

Managing the U.S. program  

As the program technical coordinator for the U.S., Neilson will be in charge of managing the U.S. program at W7-X and “proposing and recommending research objectives,” according to the agreement. Neilson said his primary responsibility would be to make it easier for U.S. researchers to take long-time assignments at the facility. He had to arrange numerous details for his own trip. He learned, for example, that long-term visitors like him, who are being paid by institutions at home, do not have to pay German taxes as one document stated. Neilson has already put together a FAQ sheet for researchers with advice on how to handle some of these arrangements.

Since 2010, the DOE has provided over $12M in funding to PPPL, ORNL, and LANL for this collaboration, and has agreed to a budget of $2.5 million to fund the collaboration in the next fiscal year. The project will cost more than $1.4 billion to build.

Neilson’s wife Linda traveled with Neilson to Germany. She recently retired from her job as an office manager at Applied Educational Research, where she worked for 24 years. Their children are grown.

Gates taking the reins

Gates took over the position at the end of June and Neilson arrived in Germany on July 16. Neilson said he wouldn’t be able to take on such an assignment without someone like Gates to take the reins. “I could not have even considered it if there were not a capable leader like David Gates to take over in my absence,” he said. “Under Dave’s leadership, I know the department will be in good hands.”

As temporary head of Advanced Projects, Gates will take on numerous administrative tasks during Neilson’s absence. “There’s a fair number of departmental responsibilities,” he said. 

Gates said one major difference for him is that he’ll no longer be able to walk down the hall to talk to Neilson about their research projects or anything else that comes up.  

“Hutch always encouraged me to have an impact on the program’s direction,” Gates said. “The difference is I used to go talk to Hutch about these things and now I won’t be able to do that.”

Gates and Neilson have led efforts to build a new stellarator program through international collaborations. In addition to W7-X, they have also worked on the Large Helical Device (LHD) project in Japan.

Tools for W 7-X

Gates, along with Novimir Pablant and Sam Lazerson, has been working on tools that will be used after the W7-X begins operation. Pablant has been  conducting research using diagnostic tools that include an X-ray imaging crystal spectrometer. Lazerson and Gates have been calculating whether the field coils built by PPPL affect the magnetic configuration as researchers predicted. These calculations will help determine how the coils can control the plasma performance.

Gates will continue his research while he assumes new responsibilities. He is in charge of the control system development on the NSTX-U, which is expected to begin operating early next year These systems coordinate computer software programs developed through collaboration with General Atomics. The tools employ real-time data to generate the commands that control power supplies, neutral beams, high-frequency waves, and gas input of the plasma during experiments.

Gates plans to continue collaborating with Luis Delgado-Aparicio investigating a physical phenomenon limiting fusion reactions. They found that magnetic islands, small bubble-like regions that appear in the hot charged gases formed during magnetic fusion experiments can cool the plasma and cause a “density limit” that can prevent fusion reactors from producing as much power as possible. The American Physical Society cited this type of research when it named Gates an APS fellow last fall, an honor given to only one half of one percent of all APS members each year.

Gates also plans to work with other researchers at PPPL to analyze data from NSTX recording the process by which neutral beam energy in NSTX heats plasma.  He and other researchers want to understand how efficient this mechanism is. The data will be used to test the theory and model the effects of Alfvén waves produced during neutral beam injection.

Gates will no longer be able to stroll down the hall to chat with Neilson to share ideas. But he is sure he will remain in touch with him via telephone, email or video chat. “We’ll still talk about that stuff,” Gates said. “And I don’t imagine the relationship will change because we’re all fairly collaborative.”

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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