Recent Publications

Retrospective on the Design and Implementation of the Milestone-Based Fusion Development Program of the U.S. Department of Energy

Scott C. Hsu, Samuel E. Wurzel, Narayan S. Subramanian

This paper provides a detailed account of the origins, objectives, design, and implementation of the Milestone-Based Fusion Development Program, a public-private-partnership (PPP) program launched by the U.S. Department of Energy's Office of Science in September 2022. The purpose of this program is multi-faceted, with policy, scientific and technological (S&T), and commercialization objectives. Tactically, the program supports privately funded fusion companies in closing S&T gaps toward delivering preliminary engineering designs of their demonstration fusion plants (aka "fusion pilot plants"). The program is a key element of a shift in U.S. fusion strategy, initiated in 2022, to accelerate fusion commercialization by leveraging PPPs. The design of the Milestone Program was underpinned by its authorizing legislation and the U.S. National Academies report Bringing Fusion to the U.S. Grid (2021), and drew inspiration from other PPP programs discussed in this paper. Finally, the paper provides the authors' perspectives and reflections on the strengths/weaknesses of the program as implemented, implementation barriers, and lessons learned, with the intent to inform future PPP programs in fusion and other energy/technology disciplines.

Systems analysis of reactor-scale stellarators with optimised plasma–coil spacing

Jedrzej Walkowiak, Felix Warmer, Sehyun Kwak, Andrea Pavone

This study evaluates the feasibility of a stellarator power plant using a new Stable Quasi-Isodynamic Designs (SQuID) configuration within the PROCESS systems code. Our results indicate that for a stellarator constructed with high-temperature superconducting (HTS) technology, a neutron wall load is a primary restriction for size reduction. With an optimistic assumption of 1.5 MW m−2 neutron wall load limit, a major radius of 16.5 m is achievable for 1GW of plant net electric power. We achieve the reduction in size by changing the coil radius in relation to major radius. It is shown that right preselection of the minimal plasma-coil distance at the stage of coil set optimization allows to find optimal solution in machine optimization. Analysis of the proposed coil set suggests that both HTS and low-temperature superconducting (LTS) technologies are viable magnet options. The PROCESS cost model shows that HTS becomes economically advantageous when its material cost is less than five times that of LTS, assuming comparable manufacturing complexity and risk.

Observations for a Fusion Tritium Economy

Mohamad Abdallah, Bjorn Cole, Daniel Clark, Jonas Kessing, Felipe Novais, Jonathan Naish, Paul Humrickhouse

Adaptation of Nuclear Fission Cost Estimation Tools for Fusion Energy Systems

Matthew J. Nyberg, Virginia Lilly, Jia Zhou, Nicolas Stauff, Craig M. Jacobson, Ben A. Lindley

Special Issue Featuring Papers from the Innovation Network for Fusion Energy (INFUSE)

Arnold Lumsdaine, Ales Necas

Compact Experimental Negative TriAngUlarity Reactor (CENTAUR): A design study for a compact, affordable breakeven tokamak

The CENTAUR Collaboration, Samuel W. Freiberger, Evan Bursch, Javier Chiriboga, Hiro J. Farre-Kaga, Eliot Felske, Sophia Guizzo, John Labbate, Shreyas Seethalla, Frederick Sheehan, et al.

This work presents the compact experimental negative triangularity reactor (CENTAUR), a low overnight cost, high-field tokamak, breakeven reactor design, achieving a predicted total fusion power of 40MW and scientific energy gain of 1.3. Ballooning stability calculations confirm that the device's pedestal is within the first stability regime, which is consistent with the expected ELM-free operation associated with negative triangularity (NT) plasmas. The geometry of the NT divertor allows for high fraction of radiated power (13.5$\%$) between the separatrix and plasma facing components. Heat transport modeling based on simulations of the edge region show heat loads into plasma facing components well below material limits. The magnet system employs rare-earth barium copper oxide (REBCO) high-temperature superconductors in 18 toroidal field coils, an hourglass-shaped central solenoid, and six poloidal field coils to support high-field ($B_0=10.9$ T) plasma confinement, shaping, and current drive. Neutronics analysis shows that a 12 cm $B_4C$ shield keeps superconducting magnet heating below the 33~K quench limit during 10 s, 40 MW DT pulses. With this shielding, the modeled fluence indicates HTS components can survive more than ten times the 3000-pulse design lifetime. Iteration of economic analysis in tandem with the technical design process allows CENTAUR to achieve its overnight cost goal of $\$$2B determined using a custom costing model that predicts a total overnight cost of $1.6$B$\pm0.2$B.

Selling a dream? Fusion experts’ perspectives on the challenges of fusion deployment: Evidence from conference workshops

Piotr Stankiewicz, Gaston Meskens, Christian Oltra, Vanja Čok, Alessio Giacometti, Chiara Bustreo

An Integrated AHP-SWOT Analysis on the Strategic Transition of Traditional Oil and Gas Companies to Fusion Energy in China

Chao Guo, Ya Yuan, Yongxin Zheng, Bo Wang, Xingang Li

Criteria for the economic viability of fusion power plants

D. G. Whyte, A. Lo, R. Bielajew, M. Hancock, R. Moeykens, G. Shaw

Maintenance strategy, structural design, and site layout of the ST-E1 fusion power plant

J. Willis, K. Chandrasekhar, P. Cheema, J. England, V. Godhani, E. Guise, S.M. Levine, R. Pocock, A. Scott, A. Shone, et al.

An effective fusion reactor maintenance scheme enables safe operations and short downtimes. This in turn leads to high availability, which is critical to the commercial viability of a power-producing plant. In tokamak-based fusion power plants, the chosen maintenance approach has a significant impact on the spatial design of the tokamak, as well as the surrounding infrastructure, and therefore needs to be considered from the outset. Tokamak Energy has developed a pre-concept design of a fusion power plant, ST-E1. This work describes the major drivers and constraints that have been considered, presents the tokamak architecture and chosen maintenance regime, and discusses how this enables the plant’s two-phased approach to demonstrating commercial operations. It also shows the implications for the design of other systems areas, in particular the machine structural arrangement and bioshield and hot cell layout. The reactor core segmentation and removal scheme replaces entire toroidal segments radially through a large vacuum port, along a single axis only. The result is a change-tolerant machine and plant layout that can accommodate the evolving designs of the tokamak.

Tokamak Energy’s pre-concept design for a fusion power plant: an overview of ST-E1

J. Willis, S.A.M. McNamara, E.N.J. Maartensson, J. Astbury, E. Yildirim, N. Hinton, C.L. Wilson, X. Zhang, J.W. Berkery, L. Baylor, et al.

Climate change and rapidly rising energy demand, driven in part by artificial intelligence and data-centre growth, create an urgent need for stable, low-carbon, and abundant power. Fusion is a promising long-term solution, yet its commercialisation faces a fundamental paradox in today’s investment environment: pilot plants are essential to de-risk physics, engineering, and operations, but their limited lifetime energy output and high upfront costs make them difficult to finance. This paper presents Tokamak Energy’s response: ST-E1, a pre-concept design for a low-aspect-ratio tokamak power plant engineered specifically to overcome this challenge. ST-E1 is designed from the outset for phased operation—pilot and commercial phases, with an upgrade phase in between—with emphasis on commercial viability, maintainability, nuclear engineering, modularity, and upgradability. A key design principle is the deliberate separation of long-lived assets, such as the magnet cage and vacuum vessel, from replaceable in-vessel systems. This provides an attractive and credible investment approach to generate operational data and de-risk key technologies while preserving most capital-intensive assets for later commercial phases. The architecture supports continuous optimisation toward high net electric power (targeting 800–1000 MW net electric), a normalised capital expenditure of $ 12–14k/kW of net electric power, and high availability (targeting > 80 % ). A tokamak core with a 5 m major radius, aspect ratio of 2.3, and on-plasma axis toroidal field of 5.25 T was selected to meet these objectives. This paper summarises the ST-E1 design philosophy, principal features, and development methodology. It introduces a Focus Collection of 11 papers detailing the pre-concept design of the entire tokamak and corresponding plant.

Design scoping and systems modelling of ST-E1 using the PyTok power plant simulation code

C.L. Wilson, J. Astbury, M.J. Ginsberg, N. Hinton, E.N.J. Maartensson, S.A.M. McNamara, J. Willis, E. Yildirim

To support the pre-concept design of Tokamak Energy’s (TEs) ST-E1 fusion power plant, we developed a new systems code, PyTok. PyTok codifies plasma physics and engineering constraints within a pure Python, object-oriented framework designed for rapid design iteration and exploration of the power-plant parameter space. The code base and its human- and machine-readable data structures enable coupling to external physics codes and data-analysis tools. Informed by TEs design philosophy and techno-economic analyses, the code was used to identify an initial reference design point for ST-E1. A commercially competitive fusion power plant is achievable with a tokamak power core of major radius 5.0 m, aspect ratio 1.9 ⩽ A ⩽ 2.3 and toroidal field 3.25 ⩽ B T ⩽ 5.25 T. The selected design point serves both as a pilot plant and as a commercially competitive reactor using the same permanent power core hardware, enabled by an in-vessel component upgrade phase. The commercial phase targets steady-state operation and a normalised capital expenditure of $12 000–15 000 per kW e , corresponding to a fusion power of 2.0–2.5 GW and a net electric power of 800–1000 MW.

A Method of (in)validating the Projected Levelized Cost of Electricity of Fusion Power

Adam Jackson