The U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) is partnering with private industry on groundbreaking fusion research aimed at achieving commercial fusion energy. This work, powered by a public-private DOE grant program, supports efforts to develop high-performance fusion-grade plasmas. In one such project, PPPL is partnering with MIT’s Plasma Science and Fusion Center (PSFC) and Commonwealth Fusion Systems, a start-up born out of MIT developing a tokamak fusion device called “SPARC”.
The aim of the project is to predict the leakage of fast “alpha” particles produced during the fusion reactions in SPARC, given the size and possible misalignment of the superconducting magnets that trap the plasma. These particles can create a largely self-heating or “burning plasma” that fuels fusion reactions. The development of burning plasma is an important scientific goal for fusion energy research. However, alpha particle leakage can slow or stop fusion energy production and damage the interior of the SPARC facility.
New superconducting magnets
Key features of the SPARC machine include its compact size and the powerful magnetic fields made possible by the ability of new superconducting magnets to operate at higher fields and voltages than existing superconducting magnets. These properties will allow the design and construction of smaller and less expensive fusion facilities, as described in recent publications from the SPARC team – assuming that the fast alpha particles generated by fusion reactions can be held long enough to keep the plasma warm .
“Our research indicates that this is possible,” said PPPL physicist Gerrit Kramer, who is participating in the project through the DOE Innovation Network for Fusion Energy (INFUSE) program. The two-year-old program, of which PPPL physicist Ahmed Diallo serves as Deputy Director, aims to accelerate the development of fusion energy in the private sector through partnerships with national laboratories.
Well locked up
“We found that the alpha particles are indeed well contained in the SPARC design,” said Kramer, co-author of a paper in the Journal of Plasma Physics that reports the findings. He worked closely with lead author Steven Scott, a Commonwealth Fusion Systems consultant and former physicist at PPPL.
Kramer used the SPIRAL computer code developed at PPPL to verify the particle containment. “The code, which simulates the wavy pattern, or ripples, in a magnetic field that allows the escape of fast particles, showed good confinement and lack of damage to the SPARC walls,” said Kramer. In addition, he added, “the SPIRAL code matched well with the ASCOT code from Finland. Although the two codes are completely different, the results were similar.”
The findings made Scott happy. “It is gratifying to see the computational validation of our understanding of ripple induced losses,” he said, “as I studied the issue experimentally for my thesis in the early 1980s.”
Fusion reactions combine light elements in the form of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei, or ions, that make up 99 percent of the visible universe – to generate enormous amounts of energy. Scientists around the world are trying to bring about fusion as a virtually limitless energy source for generating electricity.
Main guidance
Kramer and colleagues noted that misalignment of the SPARC magnets will increase the ripple-induced losses of fusion particles, leading to more power hitting the walls. Their calculations should provide the SPARC engineering team with important guidance on how well the magnets should be aligned to avoid excessive power loss and wall damage. Well-aligned magnets will allow for the first time research into plasma self-heating and the development of improved plasma control techniques in future fusion power plants.