Commonwealth Fusion Systems and Tokamak Energy: DOE’s tokamak fusion pilot picks

The two tokamak developers are the final pair of Milestone awardees to be featured by Nuclear Newswire. We previously evaluated Realta Fusion and Zap Energy (“innovative concepts”), Focused Energy and Xcimer Energy (inertial fusion), and Princeton Stellarators and Type One Energy (stellarators), to explore what each pair has in common and how their separate technologies distinguish them from each other and from other fusion developers.

Both CFS and Tokamak Energy offer engineering solutions to the fusion plasma confinement challenge by applying recent advances in high-temperature superconducting (HTS) magnets to decades of international tokamak research.

Donuts and apples: CFS claims that out of eight Milestone awardees, they are “the only one pursuing the conventional tokamak approach to commercial fusion.” That’s because Tokamak Energy is working on a spherical tokamak, shaped more like a cored apple than a conventional tokamak donut.

Both companies’ designs would rely on HTS magnets manufactured from REBCO (rare earth barium copper oxide), and both are currently constructing demo-scale machines to prove their magnet tech, with plans for pilot plants to follow.

In the rapidly expanding field of fusion developers, both are also among the more established players—CFS was spun out of the Massachusetts Institute of Technology in 2018, and Tokamak Energy is nominally the elder statesman in the group of eight. Based near Oxford, U.K., it was spun out from the U.K. Atomic Energy Authority’s Culham Centre for Fusion Energy in 2009. (Its U.S. subsidiary, Tokamak Energy Inc., is newer, however—it was incorporated in West Virginia in 2021. Mark Koepke, a professor of physics at West Virginia University and former chair of the Fusion Energy Sciences Advisory Committee, is listed as the principal investigator for Tokamak Energy Inc.’s Milestone award.)

Both companies have received multiple INFUSE (Innovation Network for Fusion Energy) awards since that program was established in 2019 by the DOE’s Office of Fusion Energy Sciences to support national laboratory and university work with private fusion companies. Eighteen of 74 INFUSE awards have gone to CFS (more than any other company), while seven have gone to Tokamak Energy (once its U.S. subsidiary made it eligible). Tokamak Energy is not alone in having reached “across the pond” for research and development assistance: CFS and the UKAEA signed a five-year collaboration agreement in 2022.

Tokamak Energy is not the only firm with foreign control to have been named a Milestone awardee—in this it joins inertial fusion developer Focused Energy, a German American company headquartered in Darmstadt, Germany, with some staff in Austin, Texas.

Still image from a CFS SPARC animation. (Image: CFS)

CFS’s pulsed power: Originally headquartered in Cambridge, Mass., CFS now hails from Devens, Mass., about one hour northwest of Boston, where it is building a new facility and putting to use the more than $2 billion in funding the company has attracted since its founding.

CFS is working on a pulsed magnetic confinement fusion concept, according to ARPA-E, having received nearly $1.4 million in 2020 for an ARPA-E BETHE project to develop a “Pulsed High Temperature Superconducting Central Solenoid.” That project is scheduled to conclude this August.

According to the ARPA-E summary of that work, “The tokamak is the most scientifically mature fusion energy concept, which confines hot plasma in the shape of a torus (similar to a donut). This plasma is controlled in part by a central solenoid electromagnet. Using [HTS] and an innovative design, [CFS] and its partners aim to build a central solenoid capable of quickly changing (‘fast ramping’) its current and magnetic field, while also being robust enough to survive many thousands of cycles. This new HTS magnet will enable a new mode of tokamak operation, in which power output is repetitively pulsed. By comparison, traditional, steady-state tokamaks require expensive and complex external current-drive systems, and aggressive plasma physics with substantial scientific risk. The pulsed-tokamak power-plant pathway has the potential to reduce costs, speed timelines, and revolutionize the future of fusion power.”

CFS has established milestones for the first 18 months of the program that focus on SPARC, its “commercially relevant net energy fusion device.” The company expects the machine to achieve net energy (Q>1) and to demonstrate the technologies and provide data required for the CFS’s power plant design, called ARC. In 2020, CFS publicly released a comprehensive summary of the physics basis for SPARC in the Journal of Plasma Physics.

“CFS is honored to be selected for the DOE’s milestone-based fusion development program,” said Bob Mumgaard, CFS cofounder and chief executive officer in a May 31 press release. “This program is part of the bold commitment from the Biden-Harris administration to bring clean fusion energy to the grid within the next decade. It leverages the strengths of the private and public sectors and encourages collaboration to accelerate progress. Participating companies only get paid if they deliver results and the public program verifies the science is sound, sending a powerful signal for fundamental progress in this important endeavor.”

A rendering of Tokamak Energy’s ST-40 device. (Image: Tokamak Energy)

Tokamak Energy goes spherical: Tokamak Energy claims to be “the only private company with more than 10 years’ experience of designing, building, and operating tokamaks,” and points to “strong links with U.S. national laboratories, including Oak Ridge, Princeton Plasma Physics Laboratory and Los Alamos, as well as the University of Illinois.”

The company’s website explains how one of its founders, Alan Sykes, theorized in the 1980s that modifying the shape of the tokamak could impact performance. “By moving from a doughnut-shaped plasma to a cored apple–shaped plasma, the plasma is contained more efficiently,” the company said. “Combining the increased efficiency of the spherical tokamak with the improved magnetic confinement made possible by high-field HTS magnet technology provides the most viable route to cost-effective fusion energy in compact machines.”

In 2022, Tokamak Energy announced it had reached a plasma ion temperature of 100 million degrees Celsius in its ST40 tokamak. The next step is to complete construction of the ST80-HTS at the UKAEA’s Culham campus, designed to demonstrate the use of HTS magnets and reach longer pulse durations needed for sustained high power output. Next, Tokamak Energy expects to build a fusion pilot plant, ST-E1, which it believes will demonstrate “the capability to deliver electricity into the grid in the early 2030s, producing up to 200 MW of net electrical power.”

In a May 31 press release, Tokamak Energy managing director Warrick Matthews said, “We are delighted to be selected by the U.S. DOE for its Milestone-Based Fusion Development Program. It’s a fantastic endorsement of the strength of our team, technology, and path to commercial fusion energy, combining the spherical tokamak with high-temperature superconducting magnets. We look forward to working with the DOE on the next steps toward delivering clean, secure, affordable fusion power to the world, addressing the twin challenges of energy security and climate change.”

There’s more: Newswire has more coverage of the DOE’s picks for the milestone fusion program. Look for separate articles on the companies using “innovative” confinement concepts (Realta Fusion and Zap Energy), inertial confinement (Focused Energy and Xcimer Energy), and magnetic confinement stellarators (Princeton Stellarators and Type One Energy).