Progress in Coil and Blanket Engineering

Wishing a restful and reflective Memorial Day to our U.S. readers.

This week, we’re highlighting two papers that may have flown under the radar but mark real progress in fusion engineering.

1. Coils That Can Survive Real-World Stress: SIMSOPT + ReBCO

ReBCO (rare-earth barium copper oxide) is a next-generation superconducting material that enables compact, high-field magnetic coils. It’s essential to many advanced fusion concepts, from Commonwealth Fusion’s ARC to compact stellarators.

But there’s a challenge: ReBCO is brittle. Its ceramic structure can’t tolerate much strain, especially when bent into the complex 3D geometries required for stellarator magnets. Exceed the strain limit, and superconductivity collapses.

Addressing this constraint, a recent paper in the Journal of Plasma Physics introduces a major advancement in stellarator design. Researchers have integrated mechanical strain penalties into the SIMSOPT coil optimization framework. So, instead of optimizing solely for magnetic field quality (like quasisymmetry), SIMSOPT now also factors in binormal curvature and torsion—key geometric contributors to mechanical strain.

When applied to several real-world test cases, including:

• A compact stellarator (EPOS)
  

• An upgraded university-scale experiment (CSX)
  

• And a conceptual reactor-scale coil pack

…the approach successfully maintained magnetic performance while reducing peak strain on ReBCO tape below critical thresholds.

The result is a magnet geometry that not only works on paper, but also survives manufacturing and operation. It’s a meaningful step toward stellarator designs that can leverage HTS materials while staying within critical mechanical limits.

2. Fueling the Reaction: Microfluidic Li₂TiO₃ Manufacturing

Meanwhile, within the reactor blanket, another materials breakthrough is unfolding.

Most D-T fusion concepts rely on breeding tritium within the reactor blanket using lithium-containing ceramics that capture neutrons produced by the fusion reaction. When a neutron strikes a lithium-6 nucleus, it triggers a nuclear reaction that produces a tritium atom and an alpha particle—effectively converting neutron flux into new fuel.

This integrated tritium breeding is essential because tritium is rare, radioactive, and decays quickly. There are no large-scale natural reserves, and external production is limited.

Li₂TiO₃ (lithium titanate) is a favored solid breeder: it’s thermally stable, chemically inert, and capable of efficient tritium release under typical operating conditions. The challenge has been how to manufacture it into strong, uniform pebbles at scale.

A new article in the Journal of Fusion Energy presents a novel method using droplet microfluidics and UV curing:

• A Li₂TiO₃ slurry is mixed with a UV-curable binder.

• It flows through a microfluidic chip that dispenses droplets of precisely controlled size.

• UV light then instantly “freezes” each droplet midstream, preserving perfect sphericity.

• These “green” spheres are sintered at high temperature to densify the ceramic.

The resulting pebbles are:

• Monodisperse, with sub-3% variation in diameter (0.5–1.5 mm)

• Nearly perfectly spherical, with excellent packing behavior

• Mechanically strong, handling >25–90 N crush loads

• Dense, reaching up to 97% of theoretical ceramic density

The results address key engineering concerns: irregular pebbles can compact unevenly, fracture under load, or block coolant flow, disrupting tritium breeding and heat extraction. These new pebbles offer predictable behavior under reactor conditions.

Crucially, the process is scalable. The microfluidics process runs continuously and UV curing solidifies each pebble almost instantly, avoiding the slower chemical hardening steps used in traditional methods. The process produces highly uniform pebbles, reducing the need for secondary processing and offering an accelerated path to scaled production.

Key Takeaway

Fusion won’t arrive all at once. It will be built, layer by layer, through materials and engineering breakthroughs like these. Strain-tolerant ReBCO coils and more efficient Li₂TiO₃ pebble manufacturing may not grab headlines, but they’re exactly the kind of progress that will enable commercial fusion.