Behind the Physics of the Infinity Two Pilot Plant

The team at Type One Energy recently released a baseline physics design for Infinity Two, a high-field stellarator pilot plant aiming to generate 800 MW of fusion power by the mid-2030s.

The plant is based on a quasi-isodynamic stellarator design, leveraging REBCO-based HTS magnets to reach a ~9 T average magnetic field. This is ~2-3× higher than typical stellarators and comparable to Commonwealth Fusion Systems’ upcoming SPARC tokamak. 

These high fields enable a compact device (~12.5m major radius) that can operate at high pressure and density while keeping plasma beta well within stability margins.

Infinity Two’s baseline parameters are ambitious:

• 800 MW of fusion power, with ~350 MWe net electrical output.

• Fusion gain (Q) ≈ 40, well into “burning plasma” territory.

• Plasma density ~2×10²⁰ m⁻³ at 9 T field, with core temperatures on the order of 10 keV.

• Tritium Breeding Ratio (TBR) ~1.3, using a helium-cooled pebble-bed (HCPB) blanket.

• Alpha energy confinement >98%, minimizing wall losses and preserving self-heating.

It’s worth noting that despite promising simulations, no stellarator has ever operated at this scale or with a self-heated burning plasma.

The heart of Infinity Two is its modular non-planar coil set, made from high-temperature superconductors (HTS) operating at ~20 K. While HTS technology is maturing (e.g., SPARC’s 20 T test coil), implementing it in the complex 3D geometry required by stellarators is enormously difficult. These coils must not only survive extreme Lorentz forces, but also maintain shape tolerances to within millimeters: any deviation can degrade the carefully optimized magnetic field.

This is likely the single greatest engineering challenge of the project.  While Type One has shown progress in modifying MIT’s VIPER HTS cable technology for curved geometries, moving from lab-scale prototypes to a full power plant comes with significant scaling risks.

Coil fabrication and tolerances aren’t the only challenges. There are still open questions around:

• Blanket & Shielding Geometry: The reactor layout must accommodate not only the coils and plasma, but also a tritium breeding blanket, neutron shielding, and remote maintenance systems. Ensuring a sufficient tritium breeding ratio while keeping the coils protected and serviceable will require some complex engineering.
  

• Power Exhaust: Even at “modest” 800 MW scale, the continuous operation will impose high heat fluxes on divertor components. Tungsten, beryllium, or advanced carbon composites may be required, and each approach comes with trade-offs.
  

• HTS Radiation Tolerance: While the blanket would shield most neutron flux, the cumulative damage to HTS materials over time is poorly understood. Ensuring multi-year coil lifetimes will require continued materials R&D.

In short, Infinity Two offers a compelling vision: a steady-state fusion reactor capable of net power production with a modular, maintainable architecture. But that vision hinges on whether supporting technologies (coil manufacturing, shielding, heat exhaust, etc.) can scale effectively. It’s an open question, and one we’ll be watching closely.