Physicist Stefano Munaretto of the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) has received leadership roles in two DOE three-year awards. Both are designed to improve the models used to design and evaluate the performance of spherical tokamaks, compact fusion facilities that are being explored as possible designs for future fusion power plants. The researchers hope to develop models that could be applied to other compact tokamaks with high magnetic fields and to a variety of fusion facilities.

Fusion, the power that drives the sun and stars, combines light elements in the form of plasma - the hot, charged state of matter composed of free electrons and atomic nuclei - that generates massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a virtually inexhaustible supply of power to generate electricity.

Simulate critical heat flow
The first award funds efforts by both PPPL and the DOE's Oak Ridge National Laboratory (ORNL) to develop software tools to allow scientists to simulate the critical flow of heat from fusion plasma. Munaretto will head this effort, to be conducted using engineering design and plasma scenario details from the high-field SPARC tokamak being developed by Commonwealth Fusion Systems (CFS) in collaboration with the Massachusetts Institute of Technology (MIT).

The funding aims to increase the accuracy of plasma simulations and help scientists tailor the operations of differently shaped tokamaks to be as efficient as possible. "In compact spherical tokamaks like PPPL's National Spherical Torus Experiment-Upgrade (NSTX-U), which are shaped like cored apples, we are trying to make a plasma as powerful as those in larger, more conventional tokamaks, which look more like donuts," Munaretto said.

"The spherical space is more compact. So what we're going to do with this grant is develop some tools that allow rapid evaluation of features of typical irregular, or 3D, magnetic fields and how they affect the heat flux. This speed could allow the software to suggest changes that help machine operations and aid engineers when designing new tokamaks and components."

This project is expected to build on the original development of the HEAT code completed by the DOE's Oak Ridge National Laboratory (ORNL) and the University of Tennessee-Knoxville for NSTX-U. Key contributors to HEAT, now CFS employees working on SPARC, will contribute to the PPPL/ORNL team.

Plasma does not behave uniformly when spiraling throughout a tokamak because the magnetic fields that shape and confine the plasma are not the same in all locations. Some of the irregularities occur because of slight imprecisions in the machine's construction. Others are caused by scientists who apply magnetic fields to just one area of the plasma to prevent eruptions known as edge-localized modes (ELMs) from damaging the machine.

"This project represents a significant new collaboration between PPPL and CFS," said Rajesh Maingi, head of Tokamak Experimental Science at PPPL. "The resulting codes will be applicable not only to NSTX-U but also to spherical tokamak pilot plant and reactor designs."

Principal investigator
The second award involves PPPL and General Atomics, which operates the DIII-D tokamak in San Diego for the DOE. Munaretto is the principal investigator for the PPPL side of the research, which calls for experiments on the United Kingdom's Mega-Amp Spherical Tokamak-Upgrade (MAST-U).

These experiments will focus on accurately measuring how magnetic fields affect the plasma. "This research matters because it pertains to both spherical tokamaks and ITER," Munaretto said. "We will be using 3D fields with different shapes to see how each one affects the plasma. Some shapes might suppress ELMs better and could therefore help tokamaks operate more efficiently."

"While the first award is for developing tools for future fusion machines, the second involves running experiments to observe how 3D fields affect plasma," Munaretto said.

Adds Maingi: "It is a remarkable achievement for any scientist to win two awards from a single funding opportunity announcement, and especially an early career scientist who recently joined a new institution. PPPL is very fortunate that Stefano joined the NSTX-U team!"

For Munaretto, "This is a new adventure. It's exciting and I'm looking forward to it."

The three-year PPPL awards total $1.5 million for the SPARC research and $195,000 for the MAST-U experiments.

Related Links
Princeton Plasma Physics Laboratory
Powering The World in the 21st Century at Energy-Daily.com

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