General Fusion's approach is based on the Linus concept developed by the United States Naval Research Laboratory (NRL) beginning in 1972. Researchers at NRL suggested an approach that retains many of the advantages of liner compression to achieve small-scale, high-energy-density fusion. According to Laberge, Linus could not properly time the compression using the technology of the era. Faster computers provide the required timing. However, this claim is not borne out by the literature as various Linus devices with no timing constraints, including systems using single pistons, were built during the experimental runs during the 1970s and demonstrated fully reversible compression strokes.
General Fusion's magnetized target fusion system uses a ~3 meter sphere filled with liquid metal. The liquid is spun, creating a vertical cavity in the centre of the sphere. This vortex flow is established and maintained by an external pumping system; liquid flows into the sphere through tangentially directed ports at the equator and exits radially through ports near the poles of the sphere.
A plasma injector is attached to the top of the sphere, from which a pulse of magnetically confined deuterium-tritium plasma fuel is injected into the center of the vortex. A few milligrams of gas are used per pulse. The gas is ionized by a bank of capacitors to form a spherical tokamak plasma (self-confined magnetized plasma rings) composed of the deuterium–tritium fuel.
The outside of the sphere is covered with steam pistons, which push the liquid metal and collapse the vortex, thereby compressing the plasma. The compression increases the density and temperature of the plasma to the range where the fuel atoms fuse, releasing energy in the form of fast neutrons and alpha particles.This energy heats the liquid metal, which is then pumped through a heat exchanger to generate electricity via a steam turbine. The plasma forming and compressing process repeats and the liquid metal is continuously pumped through the system. Some of the steam is recycled to power the pistons.
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In addition to its role in compressing the plasma, the liquid metal liner shields the power plant structure from neutrons released by the deuterium-tritium fusion reaction, overcoming the problem of structural damage to plasma-facing materials. The lithium in the mixture breeds tritium.
Lawson Machine 26 (LM26)
In August 2023, General Fusion announced it intends to build a new fusion demonstration machine named Lawson Machine 26 (LM26) to achieve important technical milestones using magnetized target fusion. LM26 aims to achieve fusion conditions of over 100 million degrees Celsius by 2025 and progress towards scientific breakeven equivalent by 2026.
LM26 will use a Marshall gun to inject a deuterium plasma into a target chamber. The target chamber's outer wall is a solid lithium liner contained within a cylindrical composite vacuum vessel. Toroidal coils mounted on the outside of the cylindrical vessel are pulsed and push on the liner to initiate compression. As the liner collapses, the plasma is compressed to higher density and temperature.
In January 2024, the company reported it had achieved symmetrical compression of a solid lithium ring within a few weeks of announcing LM26 and had built and began operating a compression test bed for LM26 named Prototype 0.
Fusion Demonstration Program
The Fusion Demonstration Program is a 70% scale prototype which was being built in Oxfordshire, UK with a reported cost of US$400 million. It had been announced that the core technology had been proven out and was ready to be put together and that the plant was to commence operations in 2027. However the plant was put on hold in 2023 when the company announced that it would instead build a different machine in Canada aimed at demonstrating breakeven by 2026.
The plant had several key differences from the commercial power plant concept:
70% scale.
1 pulse per day repetition rate vs 1 pulse per second for a power plant.
Among other things this increases the time available to re-establish the high vacuum conditions required for plasma formation by a factor of 86400, avoiding a significant engineering obstacle that will need to be solved for any future commercial application to be viable.
Drive gas system using helium rather than hydraulic rams.
A compression system using liquid lithium rather than lead-lithium.
Ideally plasma facing materials should be composed of light elements. Plasma contamination by heavier elements, such as lead, significantly increase plasma power loss due to Bremsstrahlung radiation. The choice of lithium rather than lead-lithium therefore significantly reduces plasma power losses making the demonstration program much more viable than it otherwise would be. However, this comes at the expense of having to solve materials compatibility issues with lithium rather than lead-lithium as will be necessary for any future power plant.
Conceptual design
In General Fusion's most recent conceptual design, the MTF power plant proposed by General Fusion would produce about 300 MWe from two 150 MW machines running in tandem. The net thermal efficiency of the conceptual power plant is approximately 17%.
Research collaborations
Canadian Nuclear Laboratories (CNL): In November 2022, General Fusion and CNL signed an MOU to collaborate on projects in key areas, including feasibility studies, regulatory framework, power plant siting and deployment, infrastructure design, and testing and operations support. In April 2024, the partners launched a new project to examine and propose the most efficient and cost-effective designs to integrate the fusion machine, balance of plant, and power conversion systems in a MTF commercial power plant.
Princeton Plasma Physics Laboratory (PPPL): General Fusion partners with PPPL through the U.S. Department of Energy Innovation Network for Fusion Energy (INFUSE) program. In March 2024, the company presented a plasma stability analysis completed with PPPL at the program's annual workshop. The project applied advanced computational stability analyses to model equilibrium states of plasma, providing insights important for the company's MTF machine.
Oak Ridge National Laboratory (ORNL): General Fusion partners with ORNL through the U.S. Department of Energy Innovation Network for Fusion Energy (INFUSE) program. The company has announced two projects with ORNL to provide modelling and study plasma diagnostics for a commercial MTF machine.
Savannah River National Laboratory (SRNL): General Fusion partners with SRNL through the U.S. Department of Energy Innovation Network for Fusion Energy (INFUSE) program. SRNL is completing research modelling the tritium fuel cycle and the total inventory of tritium required for a MTF commercial power plant.
TRIUMF: In March 2024, General Fusion and TRIUMF announced they are developing an ultra-fast neutron spectrometer with new funding from Canada's NSERC program. The neutron spectrometer system is a flagship project under the collaborative agreement signed by TRIUMF and General Fusion in 2023. Simon Fraser University and Université de Sherbrooke are also collaborating on the project.
University of Lisbon: In December 2023, General Fusion and the University of Lisbon's Instituto Superior Técnico (IST) announced a collaboration agreement, through the university's Instituto de Plasmas e Fusão Nuclear (IPFN) research unit, to develop a key diagnostic for the company's Magnetized Target Fusion technology. The reflectometer diagnostic will provide data about plasma density in the company's plasma injector.
Kyoto Fusioneering: In October 2023, General Fusion and Kyoto Fusioneering announced a collaborative agreement. The companies will collaborate to advance critical systems for MTF commercialization, including the tritium fuel cycle, liquid metal balance of plant, and power conversion cycle.
Microsoft: In May 2017 General Fusion and Microsoft announced a collaboration to develop a data science platform based on Microsoft's Azure cloud computing system. A second phase of the project was to apply machine learning to the data, with the goal of discovering insights into the behavior of high temperature plasmas. The new computational program would enable General Fusion to mine over 100 terabytes of data from the records of over 150,000 experiments. It was to use this data to optimize the designs of their fusion system's plasma injector, piston array, and fuel chamber. During this collaboration, the Microsoft Develop Experience Team was to contribute their experience and resources in machine learning, data management, and cloud computing.
Los Alamos National Laboratory (LANL): General Fusion entered a cooperative research and development agreement (CRADA) with the U.S. Department of Energy's LANL for magnetized target fusion research.
McGill University: In 2017, McGill and General Fusion acquired an Engage Grant from the Natural Sciences and Engineering Research Council of Canada to study General Fusion's technology. Specifically, the project was to use McGill's diagnostic abilities to develop techniques to understand the behavior of the liquid metal wall during plasma compression and how it might affect the plasma.
Princeton Plasma Physics Laboratory: In 2016 the two created an magnetohydrodynamics (MHD) simulation of compression during MTF experiments
Queen Mary University of London: In 2015 General Fusion funded a research study on high fidelity simulations of non-linear sound propagation in multiphase media of nuclear fusion reactor pursued using QMUL CLithium and Y codes.
Hatch Ltd: General Fusion and Hatch joined in 2015 to create a fusion energy demonstration system. The project aimed to build and demonstrate, at power plant scale, the primary subsystems and physics underpinning General Fusion's technology, including their proprietary Magnetized Target Fusion (MTF) technology. Simulation models will be used to verify that this fusion energy system is commercially and technically viable at scale.
Culham Centre for Fusion Energy: In June 2021, General Fusion announced it would accept the UK government's offer to host the world's first substantial public-private partnership fusion demonstration plant, at Culham. The plant will be built from 2022 to 2025 and is intended to lead the way for commercial pilot plants in the late 2020s or early 2030s. The plant will be 70% of full scale and is expected to attain a stable plasma of 150 million degrees using deuterium fuel. In October 2022 the UKAEA and General Fusion elaborated on the nature of their partnership, stating that it will "harness UKAEA's extensive neutron modelling software and expertise to simulate the neutron flux distribution from General Fusion's operational large-scale plasma injector", including by building a new, larger Thomson scattering system for General Fusion's demonstration machine.
