Chapter 2
From the dominant tokamak design to innovative alternatives, exploring the diverse approaches to achieving controlled fusion on Earth.
The tokamak, a Russian acronym meaning "toroidal chamber with magnetic coils," has been the dominant approach to magnetic confinement fusion for over 50 years. Its design uses powerful magnetic fields to confine plasma in a donut-shaped (toroidal) chamber, keeping the 100-million-degree plasma away from the reactor walls.
The key insight of the tokamak is combining two magnetic field components: a strong toroidal field created by external coils wrapped around the torus, and a poloidal field created by a current flowing through the plasma itself. These fields twist together to form helical field lines that provide stable confinement.
The world's largest fusion experiment, a collaboration of 35 nations. ITER aims to demonstrate Q=10 sustained operation, producing 500 MW of fusion power from 50 MW of heating.
Korea's "artificial sun" holds the world record for sustained high-temperature plasma: 48 seconds at 100 million °C in 2024. KSTAR is a testbed for ITER technologies.
The Joint European Torus held the fusion power record (16 MW) for 25 years. JET pioneered D-T operations and trained a generation of fusion scientists.
The Experimental Advanced Superconducting Tokamak achieved 1,056 seconds of plasma operation in 2023, demonstrating long-pulse capability.
Stellarators create the helical magnetic field entirely with external coils, eliminating the need for plasma current. This makes them inherently steady-state capable, but the complex 3D coil geometry is challenging to design and build.
The world's largest stellarator, W7-X demonstrated that advanced optimization can achieve tokamak-like confinement in a steady-state-capable device.
Rather than confining plasma with magnets, inertial confinement uses powerful lasers to compress and heat a tiny fuel pellet so rapidly that fusion occurs before the plasma can expand. In December 2022, NIF achieved scientific breakeven with Q > 1.
NIF's 192 laser beams deliver 2 megajoules to a BB-sized target. In December 2022, NIF achieved fusion ignition with 3.15 MJ output from 2.05 MJ input.
A new generation of private companies is pursuing faster, cheaper paths to fusion, often using innovative approaches enabled by advances in superconducting magnets, computing, and materials.
| Company | Approach | Funding | Target |
|---|---|---|---|
| Commonwealth Fusion Systems | Compact tokamak (SPARC) | $2B+ | Q>2 by 2025 |
| TAE Technologies | Field-reversed configuration | $1.2B | P-B11 fusion |
| Helion Energy | Pulsed FRC | $600M | Electricity by 2024 |
| General Fusion | Magnetized target | $400M | Pilot plant 2025 |
| Tokamak Energy | Spherical tokamak | $250M | 100M°C achieved |
| Zap Energy | Sheared-flow Z-pinch | $200M | Compact device |
Traditional fusion magnets use low-temperature superconductors (LTS) that must be cooled to 4 Kelvin (-269°C). The recent development of high-temperature superconductor (HTS) tape, particularly REBCO (Rare Earth Barium Copper Oxide), enables much stronger magnetic fields in smaller packages.
Higher magnetic field strength (B) improves fusion performance dramatically because the fusion power density scales as B⁴. A doubling of magnetic field from 5T to 10T increases power density by 16×, enabling much more compact reactors.