PPPL and ITER: Lab teams support the world’s largest fusion experiment with leading-edge ideas and design
The U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) is a key contributor to ITER, a huge international fusion facility under construction in Cadarache, France. ITER is designed to demonstrate the scientific and technological feasibility of fusion power by the late 2020s.
PPPL provides hardware, fabrication and research and development for ITER under contract to US ITER, a DOE Office of Science project managed by Oak Ridge National Laboratory. The United States participates in ITER together with China, the European Union, India, Japan, South Korea and Russia. “It is very exciting to work on such a challenging global science project with the potential for so great a global payoff,” said PPPL physicist Dave Johnson, who heads the development of diagnostic tools for US ITER.
The PPPL tools will provide essential data during experiments on the donut-shaped, 10-story tall ITER fusion facility, or tokamak. PPPL also is procuring the bulk of the electrical network that will deliver steady-state, or constant, power across the sprawling 445-acre ITER site. PPPL contracts for these and other hardware components of the $17 billion-plus machine could total about $180 million, some $90 million of which will flow to subcontractors.
PPPL is conducting experimental and theoretical research relevant to ITER as well. For example, experiments planned for the National Spherical Torus Experiment (NSTX), PPPL’s major fusion facility, could contribute to understanding how plasma will behave and perform in ITER. The NSTX is currently undergoing an upgrade that is doubling the strength of both its electric current and magnetic fields.
“The US ITER project office at Oak Ridge is pleased to have PPPL as a partner laboratory,” said US ITER Project Manager Ned Sauthoff. “Not only for the PPPL staff's expertise in fusion engineering, and in design and operation of nuclear fusion facilities, but also for its wealth of experience in plasma science and tokamaks.”
Here’s a look at PPPL’s role in ITER:
Diagnostics. The Laboratory manages the design and production of seven diagnostic systems for ITER. These crucial instruments will help gauge the performance of the superhot, electrically charged plasma gas that will fuel fusion reactions inside the ITER tokamak. The systems include a novel, space-saving design for a device called a reflectometer that will measure the density of the plasma. Developed by scientists at Oak Ridge and the University of California at Los Angeles, the device employs a single antenna system in place of the bulkier dual-antenna system that is the current industry standard. “This should give us far more room to fit everything in,” Johnson said.
The diagnostic systems will peer into the plasma through shielded enclosures called port plugs that PPPL is designing under an agreement with the ITER Organization, which coordinates the overall international project. These 45-ton, minivan-sized plugs will be set into the tokamak’s interior walls and must withstand the electromagnetic forces inside the facility and exposure to the energetic neutrons, or subatomic particles, that come from fusion reactions.
PPPL’s solution is a modular design that fits the tightly packed diagnostic instruments into port plugs that consist of vertical drawers. This arrangement will provide clear views of the plasma while minimizing the penetration of neutrons into the port plugs. “You want high diagnostic access to the plasma together with low exposure to the neutrons,” said PPPL engineer Russ Feder, who leads the PPPL port plug design effort. “That’s the challenge.”
The innovative PPPL design will serve as the model for 18 diagnostic port plugs inside the ITER tokamak. Included in the modular design are stainless steel components called diagnostic first walls that will directly face the plasma. These components, which PPPL engineer Doug Loesser is designing, will dissipate heat and provide openings up to the size of basketball hoops for diagnostic viewing. Loesser also contributes to the port plug design.
PPPL’s final task with respect to the diagnostics will be to assemble and test four port plugs fully equipped with instruments. Testing will be done in a large vacuum tank that produces hydraulic pressure and temperature similar to the conditions the port plugs will encounter in the ITER machine. Research teams in Russia are building this port plug test facility and are slated to deliver it to PPPL by early 2017.
Steady-state electrical network. PPPL is now purchasing $30 million of transformers and other electrical equipment for the network that will deliver all steady-state AC power to the ITER site. The current will run heating and cooling systems, among other functions, and light ITER buildings. Experiments on the huge tokamak itself will draw electricity from a separate system that supplies power in pulses.
Leading the procurement effort is PPPL engineer Charles Neumeyer, who also heads an international group of experts that is charged with reviewing the pulsed power systems. Working with Neumeyer is a seven-member team at PPPL whose members are drafting specifications for 16 different groups of electrical items for the steady-state system. With so much to buy, “the team is working really hard to keep up,” Neumeyer said.
In-vessel coils. The superhot plasma in tokamaks can send out flares called edge localized modes (ELMs) that can erode the vessel’s plasma-facing surfaces. At PPPL, a team headed by engineer Mike Kalish is designing magnetic coils to suppress flares inside the ITER tokamak. The team’s tasks also include designing a separate set of coils to enhance the vertical stability of the plasma.
Both types of in-vessel coils must contend with neutron bombardments that could quickly wear out conventional materials. “New technology had to be developed,” Kalish said. His team’s solution: Magnets fabricated from conductors composed of a stainless steel jacket that wraps around a copper tube. The jacket and copper tube are separated by magnesium oxide insulating material. The project calls for 27 such coils for ELM suppression and two to help stabilize the plasma.
The key to PPPL’s solution was the heat- and radiation-resistant magnesium oxide, a mineral that insulates coils in harsh environments such as high-energy physics experiments. The final design phase is being done in collaboration with China’s Academy of Science Institute of Plasma Physics (ASIPP), which is building a prototype of the PPPL design.
Research in support of ITER. Experiments on the revamped NSTX will support ITER in many ways. These include studies of the cause of plasma disruptions that can thwart fusion reactions by allowing the plasma to flash apart. Such research could help developers of ITER create tools to mitigate the disruptions. “If you want to design new tools, you have to understand the physics, and our experiments can help with that,” said Masayuki Ono, project director of the NSTX.
PPPL also conducts purely theoretical studies on ITER’s behalf. PPPL physicist Stephen Jardin is developing a computer model to simulate the impact of large-scale disruptions inside the ITER tokamak. The study, which Jardin is conducting under a three-year contract with the ITER Organization, will be used to show that the tokamak can withstand the force that a worst-case major disruption would produce.
PPPL participates in international forums for ITER as well. PPPL scientists serve on panels of a group called the International Tokamak Physics Activity (ITPA) that brings together researchers from all the ITER partners. The panels plan experiments on topics, such as how to control ELMs, that members can conduct on their own fusion facilities and then compare results. “Research done in that way equals more than the sum of its parts,” said PPPL physicist J. R. “Randy” Wilson, who heads international collaborations at the Laboratory and serves on the ITPA coordinating committee. “You get more understanding that way.”