Commonwealth Fusion Systems (CFS), a spin-off from MIT’s Plasma Science and Fusion Center (PSFC), successfully tested a large-scale high-temperature superconducting (HTS) magnet, achieving a peak magnetic field strength of 20 tesla. The demonstration, which took place at CFS’s Cambridge, Massachusetts facility, validated the core technology behind the company's compact fusion energy strategy. The D-shaped magnet, weighing 10 tons and standing 10 feet tall, is a full-scale prototype for the 18 toroidal field magnets that will be used in the SPARC experiment. This test represents a pivotal de-risking event for the high-field approach to magnetic confinement fusion. Source: Technologyreview

The magnet's performance relies on HTS tapes made from rare-earth barium copper oxide (REBCO), which can conduct electricity with zero resistance at higher temperatures and generate stronger magnetic fields than the low-temperature superconductors used in projects like ITER. Fusion power density in a tokamak scales with the magnetic field to the fourth power (B⁴), meaning a twofold increase in field strength yields a sixteenfold increase in power from the same plasma volume. The CFS magnet required only 30 watts of cooling power to maintain its superconducting state while carrying 265,000 amps of current, demonstrating a significant advantage in operational efficiency over traditional superconducting magnet systems. Source: Technologyreview

[Source: Technologyreview](https://www.technologyreview.com/2022/02/23/1045122/fusion-power-mit-startup-commonwealth/)

This successful test is the foundational technology for the SPARC device, a compact, high-field tokamak currently under construction. The goal of SPARC is to be the first magnetic confinement experiment to achieve a net energy gain from fusion, defined as a plasma energy gain factor (Q_plasma) greater than one. The project specifically targets a Q value greater than two, which would produce at least twice as much thermal energy from fusion reactions as is required to heat the plasma. Data from the magnet test provides the final engineering validation needed to proceed with the manufacturing of the full set of SPARC's toroidal field magnets. Source: Technologyreview

The achievement provides strong support for the thesis that private-sector development can accelerate fusion timelines. By leveraging HTS magnets, the planned ARC (Affordable, Robust, Compact) power plant, the successor to SPARC, is projected to be significantly smaller than other proposed reactors. According to designs, ARC could produce the same power output as ITER in a device roughly 10 times smaller by volume. This reduction in size and complexity directly impacts construction costs and timelines, positioning the high-field tokamak as a potentially faster and more commercially viable path to grid-scale fusion energy. This milestone validates a key component of the private fusion industry's strategy. Source: Technologyreview