Alternatives

Alternative Fusion Concepts

Due to the large scale of the more traditional fusion development lines - conventional tokamaks, stellarators and laser fusion - the progress is necessarily slow due to the high costs of each step. Recently this has led to development of some more speculative smaller concept lines which can be more rapidly improved upon, with a view to reaching commercialisation earlier. Industry has also become involved in these initiatives and partnerships with scientific laboratories, which not only injects funds into the development but also ensures the commercialisation goal remains paramount. In some cases this has led to the revival of concepts that were previously investigated in the earlier days of fusion development, and which were abandoned in favour of pursuing the good confinement seen in the tokamak. These alternative concepts have been reported recently by Sharon Ann Holgate [22] and her list has been kindly augmented for us by Luigi Di Pace. We have also made use of studies by the Fusion Industry Association in 2022 [52], 2023 [75] and 2024 [79]. Only those development lines with concept-critical hardware experiments currently operational or under construction/upgrade are included below.

Spherical Tokamaks, Compact Tokamaks, Spheromaks

	Tokamak Energy (Oxford, UK). They are currently operating a copper (i.e. resistive) coiled spherical tokamak ST-40 which has already reached a plasma temperature of 100M°C and record fusion triple product, and demonstrated divertor plasma operation. Collaborative upgrade underway in 2025 with additional funding from US DOE and UK DESNZ. A successor ST-X which uses high temperature superconductor coils, easing the cryogenic requirements and creating higher field than "conventional" superconductors, improving plasma confinement, is in final design and testing/start of construction. This is due to operate in 2030.
	Commonwealth Fusion Systems (Devens, Mass., USA). A spin-off of Massachusetts Institute of Technology Plasma Science and Fusion Center, built on research and development on the Alcator C-mod tokamak, the SPARC tokamak is designed to achieve Q>2. SPARC uses high field superconducting coils which were successfully demonstrated in 2021, and construction is now underway. Operation is expected in 2026. SPARC is due to be followed by ARC, the first commercial power plant, for which a global siting search is now underway.
	General Fusion (Richmond, Canada). Magnetised target fusion using mechanically driven liquid metal liner. A spherical tokamak plasma is fired into a liquid lithium vortex which is then mechanically compressed tenfold, heating the plasma to fusion conditions. The vortex then rebounds and the cavity is reset. LM26, under construction, designed to achieve 100M°C in 2025 and scientific breakeven in 2026. Near-commercial demonstration plant planned to be built in Culham, UK from 2026.
	ENN Energy Research Institute (Langfang, China). Spherical tokamak EXL-50 started operation in 2018. Emphasis on exploiting p-¹¹B reactions.
	Startorus Fusion (Xi'an, China). Spherical Tokamak. Jointly built and operated with Tsinghua University. First plasma 2023. 0.5MA 1T plasma achieved 17M°C ion temperature in 2024. Preparing validation device CTRFR-1.

Field-Reversed Configuration

	Princeton Fusion Systems (Princeton, USA). They aim to develop a "back-of-a-truck" reactor that would be compact and mobile. It would generate 1 MW using D+³He but avoiding neutron-generating side reactions by rapid exhaust. Based on a field-reversed plasma configuration using an RF-driven rotating magnetic field (RMF) system to drive plasma current, heat the plasma, and stably confine it. It would produce electricity using helium/xenon cooling and direct conversion of x-rays and synchrotron radiation. Current experiments in PFRC-2 run for 0.3s duration using hydrogen. The next step, PFRC-3, will be to improve the RMF effect at higher field, also in hydrogen. A reactor prototype PFRC-4 would then be built to operate with D+³He and test the exhaust system.
	TAE Technologies (Foothill Ranch, CA., USA). The aim is to exploit the p+¹¹B reaction. The concept uses an "advanced beam-driven field-reversed configuration" [23]. This is a compact toroid, which is then hit by externally accelerated fuel ions to heat the plasma or fuel it. Temperatures of 3000M°C must be attained [69] for multiple milliseconds for the reaction to be effective. The current machine "Norman" has operated so far at 50M°C. The following machine "Copernicus", under construction, is intended to operate by 2025 and reach 100M°C.
	Helion Energy (Everett, WA., USA). Two field-reversed configuration plasmas are fired together and magnetically compressed. The aim is to use D+³He fuel and direct conversion to generate electricity. The ³He will be made in a closed cycle particle accelerator process using deuterium. The current prototype "Polaris" achieved 150M°C using DT fuel in February 2026, and is intended to demonstrate direct electricity production with D+³He fuel.

Dense Plasma Focus

LPPFusion (Middlesex, NJ., USA). Uses filament and kink instabilities to create dense reacting plasmoid. High temperatures (2500 M°C so far) achieved on FF-1 mean that p+¹¹B can be exploited. Currently upgraded to FF-2B device with tungsten and beryllium electrodes. Ensuring a sharp current initiation appears critical. Began experimenting with p-¹¹B fuel in 2023.

Magnetic Mirror

	Novatron Fusion Group AB (Stockholm, Sweden). Stable magnetic mirror with easy fuelling and continuous operation at high "beta". Test rig for Novatron 1 completed and commissioned, and first plasma achieved in 2024, with completion and full operation of Novatron 1 expected in 2025.
	Realta Fusion (Madison, WI., USA). Magnetic mirror created between two high temperature superconducting magnets provided by Commonwealth Fusion Systems. WHAM experiment achieved peak field of 17T and first plasma in July 2024. Forerunner of demonstration reactor (ANVIL) projected to operate before 2030. Joint venture with University of Madison-Wisconsin.
	Terra Fusion (College Park, MD, USA). Magnetic mirror spinning at supersonic speed providing enhanced stability and confinement. Centrifugal Mirror Fusion Experiment (CFMX) at University of Maryland, in operation since 2022, in 2024 achieved stable discharges for 10s, limited only by uncooled components. Terra Fusion has been set up to build the next generation machine commercially.

Levitron

OpenStar (Wellington, New Zealand). Levitated dipole. Achieved first plasma in November 2024, reaching 0.3M° for 20s. Continued experimentation towards better performance. Next-step design under development.

Z-Pinch

	MagLIF (Sandia, NM., USA). Magneto-inertial fusion. Z-pinch. A cylindrical fuel capsule has an intense current (20MA) passed along its length while it is being compressed by an intense magnetic field (16T) after preheating by a 1.2kJ laser. Power is provided by the Z-machine. This results in a (currently) deuterium ion temperature of 30M°C at a fuel density of 10¹⁹m^-3. A more powerful Z-machine would gain the order of magnitude necessary to reach breakeven.
	MIFTI (Tustin, CA., USA). Staged multi-layer Z-pinch magneto-inertial combination tested using ZEBRA device at University of Nevada Reno. Achieved neutron yield of 2 x 10¹¹ on 3 MA "Double Eagle" machine in 2024.
	ZAP Energy (Everett, WA., USA). Z-Pinch with sheared-flow stabilisation. Latest device (Century) integrates three major technologies required for a reactor: repetitive pulsed power, liquid metal walls, and electrode damage mitigation. In 2024 more than 1000 plasma 100kA pulses were carried out in under 3 hours under vacuum in a chamber protected by flowing liquid bismuth.
	fuse (Palo Alto, CA., USA, Napierville, Canada). Building on and extending Sandia's MAGLIF experimental approach, using impedance-matched Marx generators for pulsed power. Testing and constructing 1 TW TITAN generator in 2023, with a view to constructing 15 TW Z-Star prototype in 2025. Licensed by Canadian Nuclear safety Commission for production of up to 10¹³ neutrons per annum.

Inertial

First Light Fusion (Kidlington, UK). Projectile-based inertial fusion. A high speed disc is fired at a carefully designed target which amplifies the impact shock and focusses the shockwave uniformly onto the fuel capsule inside the target. Ultimately fusion neutrons would impact a flowing liquid lithium waterfall cylindrically surrounding the target. The flowing lithium is then used as a heat exchange medium and tritium generator. Experiments are currently focussed on projectile and target development. Target impact speeds of 20km/s have been achieved.

Biconic Cusp

Lockheed Martin Aeronautics (Bethesda, MD, USA). Biconic cusp with double superconducting magnetic mirrors at each end forming diamagnetic cusps to restrict losses [31]. The aim is to produce a small-scale reactor suitable for the back of a large truck or to fit inside a submarine. Radiofrequency heating in T4 experiment replaced by beams in T4B experiment. Only cold plasmas (200k°C, 10¹⁶m^-3) produced so far. T5 experiment announced in 2019 but no details available.

Horne Technologies (Longmont, CO., USA). Superconducting biconic cusp configuration [24]. A proof of principle was built and operated in 2017 producing a 10 minute plasma. A second generation device is now operating.

Electrostatic

Avalanche Energy (Seattle, WA, USA). "Orbitron". High energy ions orbit around a negatively charged cathode, with high energy electrons confined by a weak magnetic field providing a "crossed field" electrostatic confinement. Modular design (5-15 kW_e). Likely most suited to p-¹¹B fuel. Reached an operating voltage of 200 kV with "Marty" device in 2023.