US Researchers Design Compact Fusion Power Plant
The Compact Advanced Tokamak (CAT) concept, developed by DIII-D, represents a compact, economical solution for fusion energy leveraging the latest plasma physics simulation codes and advanced technologies such as high-temperature superconductors. Here, visualized is the larger ARIES-AT concept on which it is based. Courtesy General Atomics; tokamak graphic modified from F. Najmabadi et al., Fus. Eng. Des. 80, 3 (2006).

US Researchers Design Compact Fusion Power Plant

New concept delivers continuous electricity with an approach that reduces cost and risk

San Diego, March 29, 2021 – Fusion energy is heating up. In the past few months, both the U.S. Department of Energy’s (DOE) Fusion Energy Sciences Advisory Committee (FESAC) and the National Academies of Sciences, Engineering, and Medicine (NASEM) released reports calling for aggressive development of fusion energy in the U.S.

Now, scientists at the DIII-D National Fusion Facility have released a new design for a compact fusion reactor that can generate electricity and help define the technology necessary for commercial fusion power. The approach is based on the “Advanced Tokamak” concept pioneered by the DIII-D program, which enables a higher-performance, self-sustaining configuration that holds energy more efficiently than in typical pulsed configurations, allowing it to be built at a reduced scale and cost.

The comprehensive final report released by FESAC in late February lays out a strategic plan for fusion energy in the U.S. over the next decade. The NASEM report calls for bold action to place fusion power on the grid in the 2035–2040 time frame. A key recommendation of both reports is developing the science and engineering basis for a low-capital-cost fusion pilot plant that will lay the groundwork for commercial fusion reactors.

A fusion power plant uses magnetic fields to hold a ball of current-carrying hot gas, called a plasma, to make a miniature sun that generates energy through nuclear fusion. The plasma is confined in a powerful vacuum chamber known as a tokamak.

“The key to our approach is to raise the pressure inside the tokamak,” said project lead Dr. Richard Buttery. “This makes more fusion occur, allowing us to reduce the current, which in turn makes the plasma easier to sustain and more stable. Our simulations show that by carefully shaping the plasma and moving the current toward its edge, we can suppress turbulent heat losses and support higher pressures at lower currents, to reach a state where the plasma sustains itself. This enables a device that can simply be turned on, generating electricity continuously in a steady state.”

The Compact Advanced Tokamak (CAT) concept, described in an article published in the journal Nuclear Fusion, arose from first-of-a-kind reactor simulations that leverage the latest physics understanding of these plasmas to raise performance. The approach combines state-of-the-art theory developed at GA with leading-edge computing by Oak Ridge National Laboratory scientists using the Cori supercomputer at the National Energy Research Scientific Computing Center (NERSC), and is based on development and testing of the underlying physics concepts on DIII-D.

As the CAT drives most of its own current during operation, this reduces the need for expensive current-drive systems that consume generated power and reduce the plant’s efficiency. The increased performance and energy containment of the CAT approach enables it to operate at lower plasma current than pulsed concepts. This, and continuous steady-state operation, reduce stress on the device and lower risks to machine integrity, making for a more robust, compact design with lower heat loads.

“On the way to a fusion power plant, there are still a variety of design options to be considered,” said Professor Hartmut Zohm, a leading scientist on fusion energy development with the Max-Planck-Institute of Plasma Physics in Germany, who was not involved in the design. “The one presented here is an aggressive, optimistic approach, building on the work done at the DIII-D tokamak over the last two decades, and I think it adds an interesting perspective on the problem.”

As a national strategy for fusion energy takes shape in the United States, this new design helps identify the technologies needed, and alleviates critical design challenges. The DIII-D facility, where Buttery serves as director, lies at the heart of this research. DIII-D is the largest magnetic fusion research facility in the U.S. and is operated by General Atomics (GA) as a national user facility for DOE’s Office of Science. DIII-D is pioneering development of advanced current-drive and plasma-shaping techniques to find the path to high fusion performance. Work is now progressing to resolve control and heat management in steady-state plasmas. Meanwhile, technology programs are ramping up across the United States to develop the reactor materials, magnets, and other advanced techniques required for deployment of the first fusion pilot plant. (See Fusion Energy 101 explainer below for more detail on how fusion works.) 

“These are exciting times for fusion energy,” Buttery said. “The United States now has a vision for a fusion pilot plant with design commencing soon. We have a good understanding of the work needed to get us there and many amazing tools we can deploy in this quest to bring limitless carbon-free energy to the planet.”

 About General Atomics: Since the dawn of the atomic age, General Atomics innovations have advanced the state of the art across the full spectrum of science and technology – from nuclear energy and defense to medicine and high-performance computing. Behind a talented global team of scientists, engineers, and professionals, GA’s unique experience and capabilities continue to deliver safe, sustainable, economical, and innovative solutions to meet growing global demands.

About the DIII-D National Fusion Facility. DIII-D is the largest magnetic fusion research facility in the U.S. and has been the site of numerous pioneering contributions to the development of fusion energy science. DIII-D continues the drive toward practical fusion energy with critical research conducted in collaboration with more than 600 scientists representing over 100 institutions worldwide. For more information, visit

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Zabrina Johal



Fusion Energy 101

  • Nuclear fusion occurs when light elements such as hydrogen are brought together at extremely high temperatures and pressures, causing the nuclei to fuse into heavier elements such as helium. This process powers stars like our sun and releases vast amounts of energy.
  • Fusion differs from nuclear fission, where heavy elements are split into lighter elements, releasing energy. Fission is the process used in existing commercial nuclear power plants.
  • Fusion power plants will be fueled by a mixture of hydrogen isotopes: deuterium (the nucleus comprises a proton and a neutron) and tritium (the nucleus comprises a proton and two neutrons).
  • Deuterium can be extracted from seawater and tritium can be created from small amounts of lithium in the reactor, making fusion a nearly limitless, carbon-free source of energy that leaves no long-lived radioactive waste.
  • One way to achieve fusion on earth is in a tokamak (a doughnut-shaped metal vacuum chamber) surrounded by extremely powerful magnets that create strong magnetic fields.
  • Creating fusion in a tokamak requires that the fuel be converted into a plasma by heating it to over 100 million degrees.
  • Plasma is the “fourth state of matter” in which electrons are stripped from the nuclei of their atoms. This creates an electric charge that allows the plasma to be confined by the magnetic fields within the tokamak without touching the inside walls.
  • Plasma is the most common state of matter in the universe. It can be seen all around us in places such as the stars, lightning, and fluorescent light bulbs.

Tokamaks are inherently safe – any loss of control causes the plasma to touch the inside wall, immediately cooling it and stopping the fusion reaction.

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